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Drought Continues in the Northeast, Is Relief in Sight?

A persistent pattern over the last several months has left much of Northeast in a drought. According to the most recent update from the National Drought Monitor, portions of Western New York and also Central New England are experiencing severe drought.

Update from August 2 on drought conditions across the Northeast, Image provided by NOAA.

Heavy showers and thunderstorms have been common across the Mid-Atlantic states recently, eliminating any drought concerns, but the bulk of the rainfall has remained well south or well north of areas that need it the most.

Map shopwing percent of normal rainfall from May 1 through July 31 across the Northeast. Image provided by the Northeast Regional Climate Center — Map showing percent of normal rainfall from May 1 through July 31 across the Northeast. Image provided by the Northeast Regional Climate Center

According to data from the Northeast Regional Climate Center, the period between Marc 1 and August 2 is the driest on record for several locations across New York and New England, including cities such as Lawrence, MA, and Elmira and Batavia, NY. Other locations, such as Hartford, CT and Hingham, MA, are in the Top 5 driest March 1-August 2 on record. Many rivers and streams across the region are at near record low levels. Water restrictions and/or bans are in effect for hundreds of cities and towns across the region.

A cold front will cross the region on Saturday, producing scattered showers and thunderstorms. While some of these storms could be locally heavy, most places will receive just light rainfall, which will barely put a dent in the drought. The bigger concern on Saturday is for severe weather across the Northeast. While the timing of the front won’t be optimal for a severe weather outbreak, conditions will be favorable for some strong to severe thunderstorms, especially across Southern New England and southeastern New York during the afternoon hours. Some storms may produce strong winds along with hail and brief downpours.

GFS model forecast for rainfall through Saturday night. Image provided by WeatherBell.

Once the front moves through, high pressure builds back in with sunshine and dry conditions for the first half of the upcoming week. Another front will move through on Wednesday with a chance for some additional showers and thunderstorms before stalling out across the region. Exactly where that front stalls out will be critical, as waves of low pressure are expected to ride along it, bringing chances for some much-needed rainfall. If the front stalls along the southern New England coast, then some significant rainfall could fall across much of New York and Southern New England. If the front stalls out across the Mid-Atlantic states, then the heaviest rain would be focused there, and not where it is needed most. The forecast models are split on where the front will stall out, so it’s too early to get a good idea of which idea might be correct. However, if history is any indication, then expect the front to stall out to the south. Droughts feed on themselves, which leads to an old forecasting rule of thumb – “When in drought, leave it out”.

Satellite loop showing a disturbance in the Gulf of Mexico. Loop provided by NOAA. — Satellite loop showing Tropical Storm Early moving into eastern Mexico and a disturbance in the northeastern Gulf of Mexico. Loop provided by NOAA.

Normally, when the Northeast experiences a drought in the summer, it ends with heavy rainfall from a tropical system, or the remains of a tropical system that made landfall elsewhere. Tropical Storm Earl is moving into eastern Mexico this evening, but it is not expected to have any impacts on the US. However, there is a cluster of thunderstorms in the northeastern Gulf of Mexico that needs to be watched. While development of a tropical cyclone is not expected over the next few days, the system could slowly organize. The main impact from this system will be heavy rainfall across the Gulf Coast, especially in portions of Florida and southern Georgia. Some models are showing the potential for 5-10 inches of rain over the next few days. This will almost certainly lead to flooding in parts of the region.

GFS model forecast for rainfall across the Gulf Coast through Tuesday. Image provided by WeatherBell.

The ideal situation would be for some of this moisture to be drawn northward and ride along the front into the Northeast, finally bringing significant rainfall to the area. While this is a possibility, it does not seem like a likely scenario at this point. In fact, some of the models show the moisture remaining in place across the Northern Gulf of Mexico right through the week, with heavy rain and thunderstorms continuing across the region.

When in Drought, Leave it Out

“When in Drought, Leave it Out”

We don’t know who first coined that phrase, but like most meteorological rules of thumb, it tends to hold true most of the time. Currently in New England, especially Southern New England, a drought currently grips the region.

Latest update from the U.S. Drought Monitor.

A persistent pattern has led to warm and dry conditions across the Northeast for the past several months. While scattered showers and thunderstorms have produced locally heavy rainfall in some areas recently, widespread rainfall has been lacking. Many cold fronts have come across the region with little rainfall and coastal storms are rare in the summer to begin with. Even waves of low pressure passing south of New England along stalled out cold fronts have been too far south to produce much rain across out area.

Rainfall since the start of April has been well below normal across the Northeast. Image provided by the Northeast Regional Climate Center.

The dryness has been most noticeable since the beginning of June. Since June 1, Boston’s Logan Airport has recorded just 1.99″ of rain. This is the driest June/July on record in the city. The current record is 2.03″ from 1949. If Boston does not receive more than 0.04″ before Sunday night, a new record will be set (more on that later). In Worcester, the 3.18″ during the same timeframe is the 4th lowest total on record. In Lowell, 3.12″ of rain has been reported since June 1. This is the 8th lowest total on record.

Is there any relief on the way? A cold front will move across the region late Thursday and early Friday, then stall out south of New England. A wave of low pressure will ride along the wave, passing south of us on Friday. This wave will produce locally heavy rain and thunderstorms across the Ohio and Tennessee Valleys on Thursday, before it heads for the Mid-Atlantic states Thursday night. The question then is, how far north does the low and its associated rain shield get. This is the same situation we often see in the winter when trying to determine if a storm will miss us completely, bury us with heavy snow, or come too close and give us rain instead of snow. Thankfully, we don’t have to worry about snow for another 3-4 months at least.

Right now, there are several different solutions among the models, which have a rather large impact on the forecast.

GFS model forecast for total rainfall through Saturday night. Image provided by WeatherBell.

GEM model forecast for total rainfall through Saturday night. Image provided by WeatherBell.

NAM model forecast for total rainfall through Saturday night. Image provided by WeatherBell.

For the past few months, as we’ve mentioned previously, most of these storms have passed too far south to have much of an impact on us. For this reason, we’re inclined to lean that way with the forecast for Friday as well. Droughts feed on themselves, which is how the expression at the top of the page came into existence. When the ground is dry, there is even less moisture available for approaching systems. When there’s less moisture available, less rain falls. When less rain falls, the drought gets worse. So how do you break a drought? When you have one in the summer, usually, the answer is with a tropical system. Either a tropical storm/hurricane comes up the coast and slams into New England dumping copious amounts of rain on us, or one hits farther down the coast (North Carolina or the Gulf) and weakens inland and the remains of it move this way with heavy rainfall. The Summer of 1955 was hot and dry like this one has been. Then, in the span of a week in August, two Tropical Storms (Connie and Diane) brought record rainfall to the region, with widespread flooding. Of course, that’s not the preferred scenario. A more gradual transition to a wetter pattern is the best case scenario, but that isn’t how is usually works.

Speaking of the tropics, things may be starting to heat up. Since a record-setting June, there hasn’t been any activity at all in the Atlantic in July, but that could be changing. A tropical wave moved off the coast of Africa on Tuesday, producing plenty of shower and thunderstorm activity. Although some of that activity diminished today, conditions are still favorable for some development over the next few days. The odds of the system becoming a tropical depression are still fairly low, and the odds of it impacting any land, let alone New England are still fairly remote.

Model forecasts for the track of a tropical disturbance in the Eastern Atlantic. Image provided by the University of Wisconsin.

Model forecasts for the intensity of a tropical disturbance in the Eastern Atlantic. Image provided by the University of Wisconsin.

Now that we’re approaching the beginning of August, these waves should start to move off the coast of Africa every few days. At least a few of these will eventually become tropical systems as we approach the peak of hurricane season, which is late August into late September. Another area to watch is down near the Bahamas. Sometimes tropical systems form in this region, and they can quickly strengthen and head up the coast within a couple of days, which is exactly what Hurricane Bob did in August of 1991.

Intense Heat Across the Plains Will Spread into the Southwest

A ridge of high pressure over the Plains states will slowly shift westward over the next few days, with intense heat across the Plains heading for the Desert Southwest.

High temperatures soared well into the 90s across the Southern Plains on Wednesday, but when the humidity was factored in, the heat index exceeded 100-110 degrees in parts of the nation’s midsection. Only a few showers and thunderstorms provided scattered relief to the region. On Thursday, with similar conditions expected across much of the Southern Plains and parts of the Mississippi Valley, heat advisories have been posted for much of the region. High temperatures will be well into the 90s once again with some triple digit readings expected. When the humidity is factored in, heat index values will be in the 100-115 degree range across the region.

Forecast for heat index values for Thursday afternoon. Image provided by WeatherBell

While the nation’s midsection has been enduring the heat, a trough of low pressure has been keeping the West cool for the past few days. Temperatures have been as much as 10 to 20 degrees below normal, especially across the Pacific Northwest. Across the higher elevations of the Cascades, several inches of snow has been reported.

Forecast for 500mb heighs for Sunday June 19. Image provided by Pivotal Weather. — Forecast for 500mb heights for Sunday June 19. Image provided by Pivotal Weather.

While the Northwest will remain cool into the weekend, much warmer weather will move into the Southwest as a ridge of high pressure builds westward. By Saturday, temperatures will be 10-20 degrees above normal in the Desert Southwest. For a place that is “normally” hot, anomalies that big can break records. In Phoenix, high temperatures could approach 120 degrees on Sunday. The record high for that day is 115, set in 1968.

High temperature forecast for Sunday June 19. Image provided by WeatherBell. — High temperature forecast from the GFS model for Saturday June 18. Image provided by WeatherBell.

High temperature forecast from the GFS model for Sunday June 19. Image provided by WeatherBell.

Excessive heat watches have been posted for much of the Southwest from Saturday through Tuesday. The hottest days look to be Sunday and Monday, when high temperatures will likely exceed 110 degrees in Las Vegas, and could approach 120 degrees in Phoenix and Yuma. In Death Valley, California, high temperatures on Sunday and Monday could approach 125 degrees.

Even at night, there will be little relief, as low temperatures may only drop into the 80s to lower 90s across the area. In Death Valley, temperatures may only drop below 100 degrees for a couple of hours.

While temperatures may drop a few degrees later in the week, the ridge of high pressure is expected to remain in place across the Southwest right through the end of the month, keep temperatures above to well above normal.

Heavy Rain in the Plains and Mississippi Valley Tuesday

After Sunday’s cold front ushers in cooler and drier air for Monday in the Northern Plains, a warm front will push north Tuesday. This warm front is attached to a low pressure system that will be moving northeast through the Rockies and into the Northern Plains. Areas in between the northward moving warm front and the southeastward moving cold front could see some strong to severe thunderstorms on Tuesday. This would mainly occur in the eastern Central Plains and portions of the Middle Mississippi Valley where convective energy, CAPE, and turning of the winds, shear, overlap to be able to support these storms.

Cooler and drier air (green colors) moving into the Northern Plains behind a cold front. Courtesy of College of Dupage.

A warm front nestled between North and South Dakota. Courtesy of College of DuPage.

Showalter Index showing possible instability in the Northern Plains, but higher values occur in the Eastern Central Plains and Middle Mississippi Valley. — Showalter Index showing possible instability with negative values in the Northern Plains, but even lower negative values occur in the Eastern Central Plains and Middle Mississippi Valley. Courtesy of AccuWeather.

Severe weather categorical outlook for Tuesday showing the highest probability of severe weather in the Central Plains and Middle Mississippi Valley. Courtesy of the Storm Prediction Center.

Farther north along the warm front in the Northern Plains, factors like limited sun exposure, saturated atmospheric columns and a lack of a shear/CAPE overlap may preclude strong to severe thunderstorms all together. There is some question as to how far north the warm front will be able to push into North Dakota so if it is able to push farther north and allow more sun, some strong to possibly severe thunderstorms may occur. At the very least, some thunderstorms may be embedded in what does appear to be a heavy rain event as a result of a vigorous upper level disturbance that appears to go negatively tilted in the upper levels of the atmosphere. This negative tilt allows for a strong draw of moisture into the system as a result of a strong low level jet stream. At the same time, very moist low levels and total column precipitable water values between 1.5 and 2 inches get wrapped around the northeastward moving low pressure system bringing the potential for a heavy rain event into the Northern Plains. Furthermore, large scale lift as a result of a collocated upper level jet stream will help to support the event. All told, 1 to 2.5 inches of precipitation in 24 hours from morning Tuesday to morning Wednesday seems reasonable for this event, but could be higher in any embedded thunderstorm.

The vigorous possibly negatively tilted energy moving into the Central and Northern Plains. Courtesy of College of DuPage

Strong low level jet in the Northern Plains along with the Central Plains and Middle Mississippi Valley helping fuel heavy rain and strong to severe thunderstorms respectively. Courtesy of College of DuPage.

Forecast rainfall totaling 1 to 3 inches. Possibly higher in any thunderstorms from Tuesday morning to Wednesday morning. — Forecast rainfall totaling 1 to 2.5 inches. Possibly higher in any thunderstorms from Tuesday morning to Wednesday morning. Courtesy of the Weather Prediction Center of NWS.

It is also interesting to note that the ECMWF model contains around an inch less of precipitation than the GFS model, with the NAM model being closer to the mean of the two models despite the ECMWF model reaching the above parameters. With this in mind, it appears any flooding risk would be low, but could still occur if the higher end of the precipitation range is realized.

The low pressure system is forecast to move away from the Northern Plains allowing for drier air to come in for Wednesday and Thursday. However, clouds are forecast to return as another low pressure system ejects off the Rockies for Friday allowing for some more rain.

The Heat is On Across the Plains

A large ridge of high pressure will shift from the West coast into the Nation’s midsection over the next few days, bringing with it some of the hottest weather so far this year to the Plains states.

Temperature anomalies for the past 30 days across the nation. Image provided by WeatherBell.

A persistent ridge of high pressure has been anchored across the West for the past few weeks, keeping temperatures well above normal for much of May and early June. Numerous records were set across the region, even in normally hot locations like the Desert Southwest, where temperatures exceeded 110 degrees several times. In Death Valley, California, which is frequently the nation’s hotspot, the first 8 days of June have averaged 10.6 degrees above normal, with high temperatures exceeding 115 degrees each day.

While the West has been baking, temperatures across the Plains states have been 1 to 3 degrees below normal for the past month. That is about to change as the ridge slides eastward. By the end of the week and the weekend, the ridge will be centered across the Plains and doesn’t look to move that much right through next week.

Map showing heights at the 500mb level across the United states on Friday June 8. Image provided by Pivotal Weather. — Map showing heights at the 500mb level across the United states on Sunday June 12. Image provided by Pivotal Weather.

Map showing heights at the 500mb level across the United states on Friday June 15. Image provided by Pivotal Weather. — Map showing heights at the 500mb level across the United states on Friday June 17. Image provided by Pivotal Weather.

With the ridge of high pressure in place, temperatures will soar well into the 90s across the Plains states and adjacent portions of the Mississippi Valley for much of the remainder of the week, with some triple-digit heat possible across parts of the Dakotas, especially Friday and Saturday.

High temperature forecast based off of the GFS model for Friday June 10. Image provided by WeatherBell — High temperature forecast based off of the GFS model for Saturday June 11. Image provided by WeatherBell

Some relief will settle into the Northern Plains in the form of a cold front early next week, but the heat will continue from the Southern Plains and Texas eastward into the Southeast. Across these areas, humidity levels will be higher, with dewpoints rising into the 60s and 70s. The result will be heat index values well over 100 degrees across parts of these areas.

The ridge will also act to suppress thunderstorm activity across the Plains states for much of the remainder of the week. Cluster of thunderstorms may develop across the Northern Rockies and ride over the Ridge and into the Great Lakes and eventually the Northeast later in the week. One of these clusters could produce some severe weather across the Eastern Great Lakes and Mid-Atlantic states on Saturday.

Tropical Depression Two Develops – Threat to the Carolinas?

The second tropical depression of the 2016 Hurricane Season has developed in the Western Atlantic Ocean.

As of 8pm EDT Friday, Tropical Depression Two was centered approximately 400 miles southeast of Charleston, South Carolina, and was moving towards the west-northwest at 13 mph. Maximum sustained winds are near 35 mph, and additional strengthening is expected.

Infrared satellite loop of Tropical Depression Two. Loop provided by NOAA.

The storm is expected to continue on a general west-northwest track into Saturday, with some modest strengthening possible. If the system attains maximum sustained winds of 39 mph or more, it would be named Tropical Storm Bonnie. This may occur on Saturday. However, many of the forecast models are indicating that the system may not strengthen much over the next few days, due to a combination of, wind shear aloft, and sea surface temperatures that are only marginally warm enough to sustain a tropical cyclone. Most of these models do show a track towards South Carolina over the next 24-48 hours.

Model forecasts for the strength of Tropical Depression Two. Image provided by tropicaltidbits.com

Model forecasts for the track of Tropical Depression Two. Image provided by tropicaltidbits.com

A tropical storm warning has been posted for most of the South Carolina coastline, from the Savannah River to Little River Inlet. Showers and thunderstorms should begin to move into the region later on Saturday, with some locally heavy rainfall totals expected. Wind gusts to tropical storm force will likely be confined to the immediate coast.

As the storm nears the coastline it will start to slow down as the upper-level steering currents start to weaken. A turn towards the north is possible, but if the turn occurs too early, it would prevent the storm from making landfall in South Carolina, but would make a landfall in southeastern North Carolina a bit more likely. Residents along the coast from Georgia to North Carolina should keep an eye on the storm’s progress, as it will likely have a significant impact on the holiday weekend forecast.

The storm will also have an indirect impact on the weekend forecast for much of the remainder of the East Coast. As the upper-level flow becomes south-to-north along the East Coast, it will take moisture from the storm and send it northward, ahead of a cold front. This will result in periods of heavy rain for the Mid-Atlantic states later on Sunday, and the Northeast on Monday. Rainfall totals of 1-2 inches or more are expected, and while it will ruin plans for barbecues and beach days, the region has not received much rain this Spring, so any moisture that does fall is needed.

Rainfall forecast from the GFS model for the weekend. Image provided by Pivotal Weather — Rainfall forecast from the GFS model for Sunday and Monday Image provided by Pivotal Weather

The 2016 Hurricane Season got off to an extraordinarily early start when Hurricane Alex formed back in January. Alex became the first January tropical system in the Atlantic when it acquired subtropical characteristics south of the Azores on January 13. It became a full-fledged hurricane on January 14, the first January hurricane in the Atlantic since Alice in 1955. Alex crossed the Azores on January 15, before weakening to a tropical storm and then becoming extratropical later that day as it headed out in the open Atlantic.

Hurricane Season in the Atlantic Starts on June 1

June is a little more than a week away, and while that marks the start of meteorological summer, it also marks the start of Hurricane season in the Atlantic Basin (North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico).

Hurricane season in the Atlantic runs from June 1 through November 30, but it got off to an extraordinarily early start in 2016 when Hurricane Alex formed back in January. Alex became the first January tropical system in the Atlantic when it acquired subtropical characteristics south of the Azores on January 13. It became a full-fledged hurricane on January 14, the first January hurricane in the Atlantic since Alice in 1955. Alex crossed the Azores as a strong tropical storm on January 15, and eventually head out in the open Atlantic transitioning to an extratropical cyclone on January 17. The next storm that forms will be given the name Bonnie.

Name list and pronunciation for the 2016 Atlantic Hurricane Season

Is the early start a harbinger for an active hurricane season? Not necessarily. What will be more of a factor is the developing La Nina in the Pacific Ocean. In an El Nino, such as the one we had in 2015, the subtropical jet stream is stronger, which inhibits storm development as the jet stream effectively cuts the tops off of storms before they can develop. In a La Nina, the subtropical jet is weaker, allowing easterly winds to dominate, which allows the storms to develop.

Map showing all tropical systems across the Atlantic Basin from the 2015 Hurricane Season. Image provided by the National Hurricane Center.

The presence of El Nino or La Nina is just one of many factors that go into whether a hurricane season is active or quiet, but most predictions are for activity to be more common than in 2015 and above normal. In a normal season, the Atlantic Basin sees 12 named storms, of which 6 become hurricanes and 3 become major hurricanes (Category 3 or higher on the Saffir-Simpson Scale). While there are plenty of hurricane forecasts out there, these were pioneered by Dr. William Gray, who recently passed away after over 50 years in the field. His research team at Colorado State University continues his work, and for this season is calling for 14 named storms, of which 8 could become hurricane, and 3 major hurricanes.

An active season doesn’t guarantee that a storm will make landfall in the United States though. In 2010, there were 19 named storms, 12 hurricanes, and 5 major hurricanes. Only 1 storm, Tropical Storm Bonnie, made landfall in the United States. On the flip side, 1992 was a quiet season, with just 7 named storms, 4 hurricanes, and 1 major hurricane, with the first named storm not forming until August 16. Of course, that first storm was Andrew, which slammed into South Florida on August 24 as a Category 5 hurricane, one of just 3 Category 5 storms to ever make landfall in the United States.

The peak of the season usually occurs from mid-August through late September, but an early start isn’t unusual. On average, the first name storm of the season occurs on July 9, with the first hurricane forming around August 10. In 2015, there were two tropical storms during May and June (Ana and Bill), while 2012 saw 4 named systems (Alberto, Beryl, Chris, and Debby) with 1 hurricane (Chris) forming before the end of June.

Severe Weather Outbreak Across the Southern Plains on Tuesday

While the attention has been on heavy rain and flooding across portions of southern and eastern Texas recently, areas to the north of there will be in the spotlight early next week.

Severe Weather Outlook for Tuesday from the Storm Prediction Center

All of the ingredients appear to be coming together for a severe weather outbreak from Kansas into northern Texas on Tuesday. Low pressure, both at the surface and aloft will move out of the Rockies and across the Central Plains on Tuesday. Ahead of the storm, warm, moist air will flow northward from the Gulf of Mexico into Texas and the Southern Plains. A cold front trailing the system will provide the lift needed to initiate thunderstorm development during the afternoon hours across the region.

Forecasted CAPE (Convectice Available Potential Energy) for Tuesday evening. Image courtest of WeatherBell. — Expected CAPE (Convective Available Potential Energy) for Tuesday evening. Image courtesy of WeatherBell.

As the storms move into south-central Kansas, central Oklahoma, and north-central Texas, they will encounter a very unstable airmass. The above map shows the forecast of Convective Available Potential Energy (CAPE) across the Southern Plains for Tuesday evening. CAPE is a measure of instability through the depth of the atmosphere, and is related to updraft strength in thunderstorms and is measured in Joules of energy per kilogram of air. A CAPE value of 1000 or less is considered “weak” instability, a value of 1000-2500 is “moderate” instability, a value of 2500-4000 is “strong” instability, and over 4000 is “extreme” instability. Areas shaded in purple on the map have values over 4000 Joules/kg, with some of the lighter purple shading in excess of 4500 Joules/kg. With this much instability in place, it won’t take much for storms to quickly become severe, with strong winds, large hail, torrential downpours, and tornadoes all possible.

Late April and early May are a time when severe outbreaks can be common across the Central and Southern Plains. If this outbreak does pan out, it will fall on the 25th anniversary of another outbreak across parts of the same area. On April 26, 1991, a total of 54 tornadoes were observed from Iowa and eastern Nebraska into portions of Missouri, Kansas, Oklahoma, and northeastern Texas, resulting in 21 deaths.

Plot of all 55 tornadoes that were reported on April 26, 1991 across the Central and Southern Plains. Image courtesy of the Storm Prediction Center — Plot of all 54 tornadoes that were reported on April 26, 1991 across the Central and Southern Plains. Image courtesy of the Storm Prediction Center

There was one F5 tornado reported that day – the one that moved across portions of Wichita, Kansas, including McConnell Air Force Base, before devastating the town of Andover, Kansas.

Residents of this region should pay attention to the forecast over the next few days and keep an eye to the sky if they have outdoor plans for Tuesday.

Flooding Possible in the Southern Plains

Heavy rain will move across the Southern and Central Plains through Monday night as a result of an upper level low pressure system west of the region. What is a dry line and pre frontal trough of instability Saturday into the overnight hours will turn into a cold front early Sunday. This will provide a center for showers and thunderstorms with the threat of heavy rain as warm/moist flow comes in from the south. Parameters for this event indicate heavy rain with precipitable waters (a measure of the amount of moisture in a column of the atmosphere that could fall as rain) above normal by 2 to 3 standard deviations and low level jet stream winds reaching 1 to 2 standard deviations above normal from the south indicating strong inflow of warm/moist air. This is also collocated with a strong area of large scale ascent indicated by upper level divergence of winds that also translate east through the time period.

Departures from normal of Precipitable Water forecast by the NAEFS ensemble system for Sunday morning.

2 week departure from normal of precipitation over the Southern and Central Plains. Notice the higher amounts in Texas and Oklahoma.

Placement of midlevel theta-e (a measure of warmth and moisture) and midlevel vertical velocity indicate the placement of heavy rain will move from a line between western Nebraska to western Texas later Saturday to a line between eastern Nebraska and eastern Texas by daybreak Monday along the aforementioned eventual cold front. Many times, overnight convection and thunderstorms die off as instability fades, but a self-sustaining area of heavy rainfall (called a mesoscale convective system, MCS) results. A similar process looks to form an MCS at the southern end of the cold front in southwestern/south-central Texas. This will move east slowly toward southeastern Texas by daybreak Tuesday.

Moderate to Severe drought conditions have formed in portions of the Central and Southern Plains.

Forecast precipitation over the Plains region. Notice the 4 to 8+ inches of rainfall forecast.

Flooding is very likely with this event especially in Oklahoma and Kansas where areas of Moderate to Severe drought conditions have developed. Remember that after a long dry spell and drought conditions, drier ground is harder to penetrate with water and so it remains standing on the surface allowing for flooding quickly. In addition, above normal rainfall has fallen over the past 2 weeks especially around Abilene and San Angelo, Texas and into Southwestern Oklahoma, which would allow for already swollen bodies of water to overflow quickly. In addition to the influence of the current ground conditions, the shear amount of moisture that is forecast to fall further exacerbates the flooding situation. 4 to 8 inches of rainfall is forecast to fall over portions of the Southern and Central Plains through Tuesday morning with the potential for higher amounts in thunderstorms. As a result, the National Weather Service has issued flash flood watches on a line from southwestern Nebraska to southwestern Texas ahead of the convection and heavy rain. This is very likely to translate east along with and ahead of the line of convection that is forecast to form.

Severe Weather Possible in the Plains This Week

The Storm Prediction Center has highlighted the Southern Plains with the potential for severe weather on Monday and Tuesday with Monday’s main hazard being marginally severe hail and Tuesday containing all of the main hazards including wind, hail and tornadoes.

Storm Prediction Center forecast of severe weather risk for Monday (left) and Tuesday (right). Hazards for Monday: marginally severe hail. Hazards for Tuesday: all hazard types including tornadoes are possible.

CIPS analogs based on the NAM (left) for Monday and GFS (right) for Tuesday. Notice that the analogs for Monday are contoured for 5 reports in an area and analogs for Tuesday are contoured for 1 report in an area.

This is a result of a strong low level jet flowing in from the Gulf of Mexico bringing in plenty of warm and moist air. Air with a dew point of 60F or greater moves into eastern Texas toward the end of the day Monday and dew points into the upper 50s exist in parts of the Central Plains. Plenty of turning in the wind, shear, exists in the atmosphere along with plenty of upward motion, CAPE. An area of very dry air exists in the mid levels of the atmosphere, which will act to inhibit weaker storm growth, but in areas where the upward motion is strong, the storms may have the chance to create hail, especially in any supercells that form. Analogs based on the Saturday night run of the short range forecast model, the NAM, have an area from the Panhandle of Texas into central Kansas where at least 5 previous severe weather reports occurred, which is close, but not the same as the SPC forecast severe weather risk, which has its severe area from southern Texas into south-central Kansas. Short range model simulations from the NAM as well as the NCAR ensemble forecast show convection firing in central Texas and eastern Oklahoma and moving into eastern Oklahoma and eastern Kansas as the day turns to night.

Height anomalies showing the general high and low pressure placements. Low anomalies (blue) indicate low pressure. — Height anomalies showing the general high and low pressure placements. Low anomalies (blue) indicate low pressure and vice versa. Via PivotalWeather.

For Tuesday, the strong energy that helped to force along the heavy flooding rain along the West Coast will move south into Mexico. This energy will help to drive more moisture and warm air into Southern Plains on Tuesday. Dew points will be into the 60s in eastern Texas and plenty of CAPE and shear will exist in that region. Plenty more energy around the region will help to spark more storms. With the copious amounts of CAPE and shear, all types of severe hazards will be in play including tornadoes. Towards the end of the day, when the sun’s heating turns off, storms tend to form into a convective line with strong winds or into a large complex with heavy rain and thunderstorms, called an MCS. The Storm Prediction Center hints that an MCS may form towards the end of the day in southern and Eastern Texas. Analogs based on the Saturday night run of the long range forecast, the GFS, have an area from central into northeast Texas where at least 1 previous severe weather report occurred. This is a smaller area of than the Monday setup, perhaps indicating a lesser event or because of the general bias of the shorter range NAM model to having more moisture to enhance storms. The SPC has a slight risk, which is the same severe risk category given for Monday covering eastern Texas and portions of the States bordering Texas. The SPC risk includes the analog risk area. Shorter range model projections have convection in Oklahoma and Missouri.

The severe weather risk continues into the middle and possibly the end of the work week in Southern United States.