Severe weather shifts east into the River Valleys

An upper low currently crossing eastern Kansas is forecast to accelerate eastward across Missouri and into the Midwest by tonight.  This system, along with a shortwave trough moving into the Gulf of Mexico will quickly shift a cold front across the southeast.  This front is expected to be span from the Ohio Valley down to the Florida panhandle by Friday morning.

Current Conditions

 

Currently, the last of the Tornado Watches has expired.   Strong to severe thunderstorms continue to shift east through Louisiana and Mississippi with a few strong storms up in Illinois.  The storms in Illinois should weaken this morning,  but the southern storms across the gulf states will remain locally severe.

Cloud cover from the current storms will help limit some of the day time heating this afternoon.  The Storm prediction center had a moderate risk area in the forecast yesterday.   This has been downgraded to enhanced this morning.  Do not be surprised if a smaller area of moderate risk re-appears this afternoon as the location of the most destabilization becomes obvious.   The entire area should see at least some instability along and ahead of the cold front, which should be along the Mississippi River by Midday. This front will shift east and provide the mechanism by which storms will form.

Severe Risk

New storm development is expected my early to mid afternoon.  Rotation should be limited with height, but speed shear should generate enough rotation to make tornadoes a risk for a large area as rotating supercells and small bow echoes become possible, particularly over the lower Ohio Valley.

Expect hail and strong winds to remain a risk from this afternoon into the overnight hours near the Appalachians.  The risk will shift even further east into the D.C. area by Friday.  The system should be much weaker with a lower risk for severe weather at that time.  The northeast will even be experiencing snow Friday into the weekend.

Category 4 Severe Risk Today

The spring severe weather season is not any breaks. The Southern Plains are under the gun again for severe thunderstorms this afternoon and evening. The Storm Prediction Center upgraded the thunderstorm outlook, which includes a moderate risk for southwestern Oklahoma and northwestern Texas. There is an enhanced risk surrounding this moderate risk, which includes the OKC Metro and locations just west of the DFW Metroplex.


Today’s Severe Thunderstorm Outlook (SPC)

A moderate risk is considered a category 4 risk on a scale of 1-5 (with five being the most significant). By SPC definition, a category 4 risk means this area has a likely chance of widespread severe weather with several tornadoes and/or numerous severe thunderstorms.

Severe Thunderstorm Risk Categories (SPC)

Taking a look at the latest observations across the Southern Plains, currently a surface low is located across southeastern New Mexico/far western Texas, with a warm front extending across southern portions of northern Texas. To the south of this warm front, rich moisture has returned and is advecting northward. Dewpoints are currently in the mid 60s-close to 70 south of the warm front. This front will continue its northward progress and likely lie across the Red River Valley this afternoon.

The position of the warm front is important in today’s severe potential because the warm front can serve as a boundary for enhanced tornado risks where enhanced Storm Relative Helicity value swill exists. The SRH in the vicinity of the warm front should exceed 100-250m^2/s^2. Recent literature shows SRH values, which is basically a measure of potential rotation, larger than 100m^2/s^2 increases the tornado threat. The warm front should be near the Red River during the early afternoon, once some daytime heating has occurred, so this area may see a couple supercells develop across north Texas/southern Oklahoma during the afternoon hours.

The current satellite imagery indicates skies are obscured in many areas, but sunshine should partially ensue. This coupled with the low-level moisture, will allow CAPE values (ML) to exceed 2000-3000 J/kg. This means there will be adequate “food” for the storms.

2m Dewpoint HRRR Forecast This Afternoon (Pivotal Weather)

Mixed Layer CAPE HRRR Forecast This Afternoon (Pivotal Weather)

A storm or two could erupt along the warm front (north Texas/southern Oklahoma) around 4:00PM or later today, and thunderstorms also develop along the dryline around 4:00PM in western Texas. With time, as the storm system traverses eastward, the discrete mode of thunderstorms should transition into a linear mode. A large squall line should impact much of Oklahoma and Texas overnight. The main threats during the late evening and overnight will transition from tornadoes and very large hail, to damaging winds, hail, and isolated flash flooding. It should be noted, the severe threat (primarily damaging winds and hail) will continue well into the overnight hours.

HRRR Forecast Radar This Afternoon (Pivotal Weather)

HRRR Forecast Radar Overnight (Pivotal Weather)

Again, all modes of severe weather are possible this afternoon. This includes very large hail, tornadoes, and wind. Initially, between 4:00PM and 8:00PM, very large hail (tennis ball to baseball size) and tornadoes are most likely for southwestern Oklahoma and northwestern Texas–and whatever storm develops across the Red River Valley. Then, the threat should transition to an isolated tornado and hail threat with more on an emphasis on wind damage due to the evolution of a squall line.

SPC Tornado Probability Map

SPC Hail Probability Map

SPC Wind Probability Map

This forecast is not intended to create hype or worry you. I am simply implying the severe threat is real today if all the parameters come together as the short-range numerical guidance is indicating. Do not panic, just have a plan in place. Tune in to your local television station so you’re notified of warnings, call your elderly neighbors to make sure they have a plan, and know where you will shelter in case a warning is issued for you area. This is nothing unusual for this time of the year in the Southern Plains.

Severe weather risk continues for the next few days

After yesterday’s severe weather across parts of Oklahoma and Texas, storms have spread to the east.  Severe Thunderstorm watches are in effect across several states from now until tonight.

Severe Risk

A trough across Missouri this morning moved eastward to the middle Ohio River Valley and will arrive by late tonight. A belt of 40-50 kt west-southwesterly mid level winds will continue to overspread an increasingly moist warm sector. A cold front has moved across the Ozarks and Ark-La-Tex region and continues east through Kentucky and Tennessee down to the Gulf Coast.  Organized convection across far northeast Arkansas far southeast Missouri from late this morning has spread east-northeastward and increased in coverage and intensity into Tennessee and Kentucky. This activity will pose a damaging wind and severe hail risk, although a tornado cannot be ruled out.

Farther south, more discrete storms have developed within the warm sector this afternoon across additional portions of Tennessee, northern Mississippi and northwest Alabama.  A supercell-favorable wind profile and steep mid-level lapse rates will support large hail potential. A few tornadoes also appear possible,  particularly into early evening across middle portions of Tennessee and northern Mississippi and northwest Alabama.   In this corridor, a modest westerly component of the mid-level winds  and modestly strong low-level shear coincide.

Severe

Tornado Risk

Hail Risk

Wind Risk

Current Watches

A Convective line stretching from near Huntingburg Indiana southward across central Kentucky and middle Tennessee and into northwest Alabama is expected to continue moving eastward over the next few hours. The downstream airmass is generally cooler and has less overall instability. However, the line is well-organized and the bulk shear
is expected to remain relatively constant for the next several hours. Near-severe gusts have been measured at several sites as the line moved through. The ongoing severe threat will persist for the next few hours.  A threat is possible downstream in eastern Kentucky, Tennessee and far northwest Georgia and a watch has been issued for this region.  Additionally, the cluster of storms ahead of the line in eastern Kentucky pose an isolated hail and damaging wind threat.

Current warnings

 

 

Robert Millette

 

Spring Tornadoes Possible Today

The Storm Prediction Center upgraded the thunderstorm outlook this morning and there’s now a moderate risk from the Oklahoma City Metro down into northern Texas (this includes much of Texoma). This needs to be taken seriously since several major metro areas are included within the risk areas; more than 28 million people have the chance to see severe thunderstorms today.

Today’s Severe Thunderstorm Outlook (SPC)

Zoomed-In Severe Thunderstorm Outlook (KXII)

A moderate risk is considered a category 4 risk on a scale of 1-5 (with five being the most significant). By SPC definition, a category 4 risk means this area has a likely chance of widespread severe weather with several tornadoes and/or numerous severe thunderstorms.

Severe Thunderstorm Risk Categories (SPC)

Taking a look at the soundings across central and southern Texas, deep and rich moisture has returned to the region and is rapidly being transported northward into northern Texas and Oklahoma. The quality of moisture was questioned initially, but current observations show moisture should not be an issue. The latest short-range numerical guidance shows surface dewpoints in the 60s across the Southern Plains just ahead of the dryline. The current visible satellite imagery indicates sunshine, coupled with the eventual low-level moisture, will allow CAPE values (ML) to exceed 1000-2000 J/kg. This means there will be adequate “food” for the storms.

2m Dewpoint HRRR Forecast This Afternoon (Pivotal Weather)

Mixed Layer CAPE HRRR Forecast This Afternoon (Pivotal Weather)

Thunderstorms should erupt along the dryline around 4:00PM to 5:00PM once surface heating and the arrival of lift aloft erode the cap. The dryline at this time will be about 50 miles west of I-35, so this is the best location for initial thunderstorm development. Once storms initiate, they should move off towards the east-northeast. Looking at the forecast 500mb maps, they indicate storms will develop and remain discrete towards I-35–likely exhibiting supercell characteristics due to southwesterlies of 50-60kts from Oklahoma City down towards Dallas. The Storm Relative Helicity in this area should exceed 100-250m^2/s^2, which indicates if a tornado develops it has the chance to become strong within the first couple of hours of storm initiation from OKC down to Denton. Recent literature shows SRH values, which is basically a measure of potential rotation, larger than 100m^2/s^2 increases the tornado threat.

HRRR Forecast Radar This Afternoon (Pivotal Weather)

HRRR Forecast 500mb Wind This Afternoon (Pivotal Weather)

HRRR Forecast 0-1km SRH This Afternoon (Pivotal Weather)

All modes of severe weather are possible this afternoon. This includes very large hail, tornadoes, and wind. Initially, between 4:00PM and 8:00PM, very large hail (tennis ball to baseball size) and tornadoes are most likely for the I-35 corridor. Then, from about 8:00PM to Midnight, the threat should transition to an isolated tornado and hail threat with more on an emphasis on wind damage for the Red River Valley.

SPC Tornado Probability Map (Pivotal Weather)

SPC Hail Probability Map (Pivotal Weather)

SPC Wind Probability Map (Pivotal Weather)

This forecast is not intended to create hype or worry you. I am simply implying the severe threat is real today if all the parameters come together as the short-range numerical guidance is indicating. Do not panic, just have a plan in place. Tune in to your local television station so you’re notified of warnings, call your elderly neighbors to make sure they have a plan, and know where you will shelter in case a warning is issued for you area. This is nothing unusual for this time of the year in the Southern Plains.

Possible Tropical Development in the Atlantic

Tropical systems are not what we typical look to talk about in forecasts for this time of year, but a low pressure system north of Puerto Rico and the Dominican Republic could become our first tropical system of the year over the coming days. This system would be the first March Tropical system since 1908 and would be named Arlene should this develop.  There is currently no risk to the Southeast United States.

Current Tropical Conditions

Currently, this system is not overly strong, but is generating a large area of Gale force winds over the open ocean waters and has an area of tropical thunderstorms associated with it.  Those areas of strong winds and heavy storms are not currently near the center of the system as we normally see with Tropical Cyclones. Sub-Tropical Systems, or systems that have mainly Tropical characteristics but maintain some non tropical characteristics, can have the worst conditions away from the center.  Sub-Tropical status is what we will be watching for over the next week as this system moves slowly toward Bermuda.

Sea Surface Temperatures

The map above is the current Sea Surface Temperatures for the Atlantic.  Water temperatures are averaging 80 degrees near the islands and remain in the lower 70s southeast of Bermuda.  While these temperatures only slightly above average for this time of year for the Caribbean and Atlantic waters, water temperatures near the coast of the Southeastern United States are running 5 or more degrees above average.

Model Analysis

For the ongoing forecast, model data suggests this system will slowly move north toward Bermuda over the next couple days.  This should leave the system in fairly good conditions to slowly develop, and data suggests that is what will occur when the wind shear in the area drops.  the shear will pick up again towards the middle of  next week so the timeframe for development could be short.

Tropical

This is the expected location for the system by Monday morning.   Those in the Eastern Caribbean should anticipated occasionally gusty winds and scattered downpours.  Rough seas can be expected north of the big islands up towards Bermuda West to the Eastern Bahamas.

By Tuesday, models bring the system to the southeast of Bermuda as it continues to develop.  Bermuda should see rain Monday night into Tuesday and should expect heavy surf and high ways as the system passes.

By Wednesday and Thursday, the system should continue to be strengthening as it moves well out into the Atlantic.  There will be no further development in the tropics after this at this time.  Firsthand Weather will continue to monitor for any further developments in the region.

 

Robert Millette

Active Severe Weather Period for Southern Plains And South

The first week of spring is coming in strong! Severe thunderstorms impacted much of the Tennessee Valley and Southeast today. More severe thunderstorm events are possible by the end of the week through the weekend for the Southern Plains and parts of the South.

Thursday Evening And Friday (Southern Plains)
By late Thursday, an upper-level trough will approach the Southern Plains. In response to the approaching trough, deep moisture will move into Texas and Oklahoma, and a dryline will begin to develop and sharpen across western Texas/Oklahoma. Thunderstorms should develop along the dryline and move towards the I-35 corridor overnight on Thursday. The storms should be pretty numerous overnight on Thursday into Friday morning due to no temperature inversion. This may actually influence Friday’s thunderstorms (more on that in a moment).

As the trough moves across the Southern Plains on Friday, the dryline will move towards the I-35 corridor or just east. Thunderstorms will likely redevelop along this boundary Friday afternoon, but the storms from Friday morning may limit instability. If storms are not as numerous Friday morning, or move out earlier than expected, then a higher severe threat would evolve–this will have to be monitored as we get closer to the event. Damaging winds and large hail appear to be the main threats at this point. The Storm Prediction Center does have a slight risk area for this time frame.

SPC’s 15% Contour Area (Friday Afternoon/Overnight)

Friday Night And Saturday (South/Southeast)
The storms that develop along the dryline Friday afternoon in northeast Texas/eastern Oklahoma will move towards the Arklatex–likely posing an enhanced damaging wind threat Friday night. It is possible this thunderstorm complex may survive into early Saturday morning and impact southern Arkansas, Louisiana, and western Mississippi.

Once the storms move out of the area, rich moisture should remain in place during the day on Saturday for the South. This coupled with deep shear and cold temperatures aloft should allow for severe thunderstorms to redevelop across Louisiana, Mississippi, and possible western Alabama. The Storm Prediction Center does have a slight risk area for this time frame.

SPC’s 15% Contour Area (Saturday)

Sunday (Southern Plains)
By Sunday, the Southern Plains may be at risk again to see severe thunderstorms. To me, this setup looks very impressive! Moisture should hang around the area through the weekend, which sets the stage for convection as another upper-level trough approaches the area. This trough will not be as impressive as the one on Friday, but the deep layer shear is impressive. Moisture will be much deeper, too, which should lead to a great amount of instability–energy (food) for the storms. Numerical guidance shows winds veering. Sunday has the best chance to see tornadic activity in my opinion if the moisture indeed is not scoured out with Friday’s system. The Storm Prediction Center does not have a slight risk area for this time frame, but this will likely change soon.

It should be noted, this is several days out, so a lot may change. Please keep checking back for updates.

Southeast Severe Storms

This is a brief post, but I want to mention the chance of severe thunderstorms this afternoon into the evening hours across the Southeast. A complex of thunderstorms is beginning to intensify across northwestern Tennessee at this hour. This complex should continue to strengthen as it propagates towards the southeast.

3KM NAM Simulated Radar (Tuesday Evening)

This will place northeastern Alabama, central and eastern Tennessee, and northern Georgia in a favorable location to see damaging winds and large hail later today as the atmosphere continues to become more unstable with afternoon heating. The Storm Prediction Center has an enhanced risk of severe thunderstorms for the aforementioned areas this afternoon/evening.

Thunderstorm Outlook (Tuesday Afternoon/Evening)

Severe Storms Late This Week

Tomorrow (Monday, March 20th) is the first day of spring and it won’t take too long for spring-time thunderstorms to occur. A strong storm system will approach the Southern Plains late in the day on Thursday into Friday, which should aid in severe thunderstorms by Friday–and potentially overnight on Thursday.

As the upper-level trough moves into the Southern Plains late Thursday into Friday, a dryline should sharpen across western Texas/Oklaoma and move towards the I-35 corridor overnight on Thursday into Friday. Thunderstorms could develop along this dryline overnight on Thursday despite the unfavorable timing. If storms manage to develop late Thursday night or Friday morning, they would likely face meager instability. Despite the meager instability, due to the other parameters, it’s possible a couple storms could produce hail.

By Friday afternoon, the latest numerical guidance shows the upper-level trough moving overhead and the dryline moving to–or east–of I-35.

GFS 2-m Dewpoint Map (Friday Afternoon)

GFS 500 mb Vorticity Map (Friday Afternoon)

At this point, a second round of thunderstorms (with a greater chance of reaching severe levels) could develop across eastern Oklahoma, northeastern Texas, western Arkansas, and northwestern Louisiana. It’s still too early to determine the storm modes and evolution, but looking at shear values, it appears isolated thunderstorms along the dryline in eastern Oklahoma/northeastern Texas would evolve into an eastward moving complex of storms that would eventually impact parts of Arkansas and Louisiana. Initial storms potentially could produce all modes of severe weather with the threat of damaging winds increasing as the storm move east and evolve into a complex. The consistent support of the numerical guidance has allowed the Storm Prediction Center to allow for a 15% severe thunderstorm area in this region.

SPC’s 15% Contour Area (Friday Afternoon)

It should be noted, if the system slows down or speeds up, there may be an increased chance of severe thunderstorms and the SPC’s 15% area may at that point be adjusted to encompass different areas. Please keep checking back for updates.

Preliminary Nor’easter Impact Map

Northeast
A significant nor’easter will take shape across the Mid-Atlantic and New England from late Monday night through early Wednesday morning. It’s likely that travel will be disrupted from Washington D.C. to Boston, and rural areas may see a loss of electricity. This is the vicinity that may see severe impacts from this winter storm; including several inches of snow (more than a foot from just north of Washington D.C. up through much of Maine), frigid temperatures, and wind gusts exceeding 50 mph.

Northern Plains and Mid-West
The Northern Plains and Mid-West will also see snowfall tonight into Monday–parts of the Northern Plains are receiving snowfall at this hour. Travel impacts are likely in this region, and Chicago will likely see several inches of snowfall, which will end the ‘snow-drought’ the city has recently been plagued by.

Southeast
It should also be noted, another round of precipitation will impact parts of the Southeast late Monday into Tuesday. It is possible, with surface temperatures just marginal enough for a wintry-mix, parts of northeastern Georgia (in the highest terrain) may see snow mix in with the rain overnight on Monday. Significant accumulations are not expected.

Tomorrow, we will release a detailed discussion outlining the technical details and potential accumulations for the nor’easter. Here is a preliminary nor’easter impact map, as well as impact map for the system impacting the Mid-West, for early this upcoming work week.

Southeast Snow?

Snow is already falling in parts of Arkansas and Tennessee this early afternoon, and the snow should eventually shift further south throughout the evening into Sunday as precipitation increases across the Southeast. This increase in precipitation chances across the region is in response to a shortwave moving out of Texas and one moving out of the Plains. These two features will phase together and cause an enhanced area of lift across the region.

With surface temperatures in the 30s and 40s, surface dewpoints in the teens and 20s, and cold air aloft, it is likely that far northern parts of Alabama, Georgia, and Upsate South Carolina will see snow mix in with the rain at some point late today or Sunday morning. Confidence is relatively high with this scenario. When it comes to accumulations, that’s when the confidence level drops. Right now, it doesn’t appear much accumulations will occur outside of Tennessee, the highest terrain of Georgia, and the mountainous regions of North Carolina. It should be noted, the dynamics with this system are pretty strong, so there is the potential for a small enhanced zone that sets up somewhere in the region. This could cause a quick inch or two of accumulations if it evolves, but again, this type of feature is too hard to forecast where it may setup. At this point, the best chance of accumulations will be on the roof of your car/homes and possibly on bridges/overpasses.

This pink region outlines which areas have the best chance of seeing snow mix in with the rain. This is not an accumulation map.