In an effort to help make this weekend’s severe weather threat easier to understand I’m going to style this post much like some of our winter storm posts this past winter. Hopefully this will curb some confusion and help get valid information out in an easy to understand manner.
It is important to understand the main focus point for thunderstorm development on Saturday and Sunday will be along and ahead of the dryline. Locations west of the dryline will be dry with no severe weather threat but very high fire danger with gusty west/southwest winds. The western edge of the severe weather risk this weekend will be on the leading edge of the dryline so if you’re wondering where it will be located each day simply look at the western edge of the severe weather risk zone.
For severe weather outlook we use those issued by the Storm Prediction Center. These outlooks were issued this morning and the new outlooks won’t be issued until Friday morning so be sure to check back on Friday for the new outlook and forecast.
Saturday Afternoon into Saturday Night
An Enhanced Risk of Severe Weather has been issued for Northwest Texas, western North Texas, and West-Central Texas. A few towns include Sonora, San Angelo, Brownwood, Abilene, Seymour, Vernon, Wichita Falls, and Bowie. This zone is where confidence is highest that a couple to multiple supercells will develop just east of the dryline.
The “Standard” Possible Risk zone of Severe Weather surrounds the enhanced risk zone includes the extreme eastern Texas Panhandle into the Texas Hill Country and the western half of North Texas. A few towns include Wheeler, Shamrock, Childress, Snyder, Del Rio, Junction, Stephenville, Decatur, and Gainesville. The western edge of this risk zone marks where the dryline is expected to be located based on the outlook this morning. The eastern edge of the risk marks where thunderstorms should be weakening as they move east during the nighttime hours on Saturday.
The strongest supercells could produce destructive hail up to the size of baseballs and damaging winds up to 70 MPH. A tornado threat may develop after 8 PM. Storms that are able to form into clusters during the evening hours could produce ping-pong ball size hail and damaging winds over 75 MPH.
On Saturday the main severe weather threat will develop during the late afternoon hours perhaps as late as the early evening. This event has the possibility of continuing well into the evening hours. Like Wednesday the main thunderstorm mode will be supercellular in nature. Supercells by definition are rotating thunderstorms that are almost always severe. Instability values and wind shear aloft will support long-lived supercells so some storms may last several hours with a threat of very large hail up to the size of baseballs and damaging wind gusts over 60 MPH. Low level wind shear will dramatically increase after sunset and based on current data it appears some storms will likely persist well past sunset. The result is that a tornado threat could develop with the strongest supercells that maintain themselves after sunset. This is preliminary based off current weather model data so you can except refinements on Friday as we narrow down the most likely area to receive severe weather. We should get a much better idea of everything as new weather model data arrives this evening and we continue into Friday.
Here is the text from the Storm Prediction Center’s outlook for Saturday.
DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0212 AM CDT THU APR 24 2014
VALID 261200Z – 271200Z
…THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL AND SOUTHERN
SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG A
DRYLINE ACROSS PORTIONS OF KANSAS…OKLAHOMA…AND PARTS OF WEST
TEXAS. VERY LARGE HAIL…AND POSSIBLY TORNADOES…CAN BE EXPECTED.
..CENTRAL AND SOUTHERN PLAINS
STRONG MID-LEVEL SPEED MAX IS FORECAST TO ROUND THE BASE OF A
PROGRESSIVE TROUGH ALONG THE SWRN U.S./MEXICAN BORDER EARLY SATURDAY
BEFORE SHIFTING INTO NM BY 27/00Z. THIS FEATURE WILL THEN EJECT
INTO THE CNTRL HIGH PLAINS OF WESTERN KS OVERNIGHT…INCREASING TO
80KT+ AT 500MB. INTENSE 12-HR MID-LEVEL HEIGHT FALLS…APPROACHING
200M…WILL DEVELOP ACROSS THE HIGH PLAINS CENTERED ON SERN CO.
AS UPPER TROUGH SHIFTS INTO THE SRN ROCKIES…SFC LOW WILL DEEPEN
OVER ERN CO AND A WELL-DEFINED LEE TROUGH WILL EXTEND SWD INTO NRN
MEXICO. INTENSE HEATING IS EXPECTED ALONG THIS TROUGH DURING THE
DAY AND A DRYLINE SHOULD MIX INTO THE ERN TX PANHANDLE BY 21Z.
WHILE WARM SECTOR BOUNDARY LAYER MOISTURE IS EXPECTED TO GRADUALLY
INCREASE ACROSS THE SRN/CNTRL PLAINS OVER THE NEXT FEW DAYS IT
APPEARS DRYLINE CONVECTION MAY INITIALLY INGEST 50S SFC DEW POINTS
AS TEMPERATURES RISE THROUGH THE 80S…TO PERHAPS NEAR 90F FARTHER
SOUTH ACROSS THE EDWARDS PLATEAU. CONVECTIVE TEMPERATURES SHOULD BE
BREACHED BY 21Z AND SCT SUPERCELLS ARE EXPECTED TO DEVELOP ALONG THE
BOUNDARY. THIS ACTIVITY WILL INITIALLY BE DRIVEN BY DIABATIC
HEATING AS LARGE-SCALE FORCING ASSOCIATED WITH APPROACHING SPEED MAX
WILL LAG THIS CORRIDOR OF INITIATION UNTIL WELL AFTER DARK. DELAYED
LARGE-SCALE SUPPORT MAY LIMIT THE NUMBER OF STORMS THAT ULTIMATELY
EVOLVE ALONG THE DRYLINE.
CONVECTION THAT DEVELOPS DURING THE LATE AFTERNOON WILL DO SO ALONG
A NARROW CORRIDOR OF 3000 J/KG SBCAPE AND SHOULD MATURE INTO THE
EARLY EVENING HOURS AS VERTICAL SHEAR INCREASES FROM THE WEST.
SUPERCELLS WITH VERY LARGE HAIL…GREATER THAN 2 INCHES…ARE
EXPECTED. AS TSTMS SHIFT EAST AND BOUNDARY LAYER COOLS SLIGHTLY
THERE MAY BE A PROPENSITY FOR CLOUD BASES TO LOWER AND TAKE
ADVANTAGE OF LOWER 60S SFC DEW POINTS. AS A RESULT…TORNADO THREAT
SHOULD INCREASE DURING THE EARLY EVENING HOURS BEFORE ACTIVITY
DECOUPLES FROM THE BOUNDARY LAYER.
WITH LARGE SCALE FORCING EXPECTED TO EJECT INTO THE PLAINS OVERNIGHT
THERE MAY BE CONVECTIVE REDEVELOPMENT ALONG THE DRYLINE AS IT BEGINS
TO SURGE ACROSS SWRN KS/WRN OK/NWRN TX.
SEVERE PROBABILITIES MAY BE INCREASED ACROSS THIS REGION IF
MID-LEVEL SPEED MAX/FORCING OVERSPREADS THE DRYLINE AT A MORE
FAVORABLE TIME DIURNALLY.
Late Sunday Morning through Sunday Night
Severe Weather is Expected on Sunday along and ahead of a dryline across North Texas, Central Texas, Northeast Texas, and East Texas. A few towns include Gainesville, the entire D/FW Metroplex, Waco, Fort Hood, Temple, College Station, Tyler, Paris, Texarkana, Shreveport, and Lufkin.
The western edge of this risk will depend on where the dryline sets up shop by early afternoon Sunday. The position of the dryline is low-confidence on Sunday right now due to considerable model spread thus this forecast will be adjusted as we get closer to Sunday.
The strongest supercells could produce destructive hail up to the size of tennis-balls and damaging winds up to 70 MPH. A tornado threat is possible but still uncertain due to the time-range. Storms that are able to form into clusters during the evening hours could produce ping-pong ball size hail and damaging winds over 75 MPH.
The storm system responsible for the severe weather threat on Saturday will intensify on Sunday as it begins to push east. The dryline will be near I-35 by the early afternoon hours with moist, unstable air to the east of the dryline. Dry air and gusty winds will create high fire danger to the west of the dryline. There is about a 100 mile difference between various weather models. The dryline’s location will play a critical role on Sunday as it will determine who ends up in the risk zone and who ends up with a fairly nice afternoon. If the dryline ends up east of the D/FW Metroplex by early afternoon than outdoor events should be good to go. If the dryline sets up shop west of D/FW than the threat of severe weather will include the I-35 corridor. This is a low-confidence forecast and adjustments are expected as we continue into Friday and Saturday so please check back.
Overall Sunday has the potential to be a very busy severe weather day as upper level forcing erodes the cap and causes numerous thunderstorms to develop. With strong instability and wind shear in place severe weather is expected. As we get closer to Sunday and we narrow down the specifics we can refine the severe weather outlook, timing, and threats.
There have been conflicting forecasts from various media agencies for this weekend. Some have taken it upon themselves to use analogs of past events or errous graphics to highlight the threat for a major tornado outbreak this weekend. The pattern setting up is supportive of a classic severe weather event across the Southern Plains and Southeast United States. However, there is so much more that comes into play when forecasting severe weather. Specifically when forecasting high-end, significant severe weather. Timing has to be just right to support major severe weather verses a hail/wind event. Saturday will likely be active in terms of severe weather, but a few days ago it looked like it could be a major tornado outbreak. Because the storm system responsible for all this mess is now expected to move a few hours slower the main ingredients for widespread outbreak of tornadoes won’t arrive in time before the atmosphere begins stabilizing Saturday night. Sunday has the potential to be a widespread severe weather event with many reports of hail and strong winds, but we’re four days out with considerable model variability. One model says severe storms could form 20-25 miles west of I-35 while another has severe weather staying 100 miles east of I-35 on Sunday.
The storm system hasn’t even moved on-shore into the Western United States from the Pacific Ocean yet and won’t fully do so until tomorrow morning. That means we have been using computer model estimation up until this point to try and figure out what’s going to happen this weekend. Now that the storm is beginning to move onshore we can use weather balloons to figure out exactly how strong the system is over the western United States and thus weather models should really begin converging on a set solution or at least one or two main ideas of what might happen verses throwing out four or five different ideas. I doubt any one model has the scenario just right for Saturday or Sunday at this point. If I haven’t said it enough yet in this article let me say it again: The forecast for Saturday and Sunday will change. The threat of severe weather could lower to the point of a few hail storms on Saturday and Sunday or we could end up with tornadic supercells on Saturday and a widespread significant severe weather outbreak on Sunday. We’re sitting between those two ballparks right now waiting to see which camp wins out.
I understand everyone has a “I want to know now” mentality but the truth is I cannot tell you for sure what will happen right now. I’m giving you what forecasters believe could happen based on current weather model data. Changes are likely, for better or for worse I can’t say. Nevertheless it is always good to be prepared. Have a severe weather safety plan ready and practiced in case you need to use it this weekend or next year. If you’re going to be at an outdoor event this weekend in one of the threat zones than plan on keeping an eye to the sky.
Regardless of what I’ve written tonight know that there is no reason to be frightened of this weekend. This is Texas in April: We have severe weather every year and we’re in the middle of our spring severe weather season. Tornadoes, even large tornadoes, are tiny compared to the size of a county. The chance one hits you is low but that is no reason not to protect yourself.
DON’T BE SCARED – BE PREPARED!