Significant Severe Outbreak Monday

[jeffl]

Parameters coming together for an extensive and long tracked severe weather outbreak Monday from E TX and OK into the Mid MS valley and deep south.

***Long tracked violent supercells with large and very damaging tornadoes are possible over NE TX, NW LA, AR, and SE OK within SPC moderate risk area***

Next shortwave over the central Rockies will move ESE into W TX early Monday with surface low pressure forming over SW OK and moving E into NE OK by late evening. Rich Gulf moisture will surge northward on increasing low level S flow as surface pressures fall over C TX and C OK early Monday. 140kt jet core will arc in under the surface low over OK by early afternoon with surface winds backing to the ESE and SE over N LA and NE TX. Impressive 0-1km shear of 35kts and strongly veering hodographs support intense supercells with all severe modes expected. Greatest risk will be along and ahead of the surface dry line from E OK into E C TX where a few violent tornadoes will be possible. Storms will form into an intense squall line and march E overnight across AR, LA, MS, MO, TN, KY. Supercells forming ahead of the main line will have an increased tornado potential after dark.

Review tornado safety rules and have NOAA weather radio batteries fully charged. Pay close attention to approaching weather and act quickly if a warning is issued for your location.

[ticka1]

Does this include us here in the Houston area Jeff?

[jeffl]

I think the main threat will be N of I-10 and more likely over E and NE TX.

[jeffl]

Potential for significant severe weather outbreak Monday.

Long lived supercells with very large hail, high end wind events (80mph +), and very destructive tornadoes are possible over SE TX, E TX into OK, LA, and AR.

Discussion:

Latest forecast models now have the upper level trough moving further south than expected earlier today. Surface low pressure will develop over southern OK this evening and move very slowly ENE into W AR by late Monday. Surface dry line over C TX will sharpen and begin to move east early Monday. An impressive 55-60kt low level jet will be screaming N from the Gulf of Mexico providing rapid moistening over the area. 140kt jet max rounds the base of the trough and slams into SE TX during peak heating and in a favorable position with the dry line. This puts SE TX in the left front quad of the upper level jet couplet with increasing upper level divergence.

Thermodynamic profile:

Air mass will become very unstable by early afternoon as Gulf moisture (mid 60 degree dewpoints) is brought northward into the developing cyclone over OK. ETA forecast soundings for IAH show SBCAPE values of 2500-3500 J/kg and LI's of -4 to -8, along with very steep lapse rates. Capping is noted on both the LCH and CRP soundings, but can be broken with temps. of 75-78 degrees. We should reach these values by early to mid afternoon and release the tremendous build up of surface based energy.

Wind Profiles:

Low level SE winds will increase tonight to 15-20mph. At 850mb winds will be S at 50-60mph and at 600mb winds will veer WSW at over 140mph. Low level shear of 35-45kts between the surface and 1 km along with strongly veering profiles and curved hodographs support violent updraft rotation. Surface based updrafts will feed off high instability and evolve into mesocyclones due to strong low and mid level shear. Given the degree of shear a few violent tornado events will be possible especially north of a line from College Station to Conroe to Liberty. Updraft velocities on the order of 150-200mph will result in cloud tops approaching 65000 to 70000 feet.

Supercells should initiate along the C TX dry line by mid afternoon and go quickly severe. All severe modes will be possible. Supercells will likely develop into an intense squall line and sweep across the area between 300pm and 800pm Monday evening. Discrete cells ahead of the main line will have a high tornado threat.

SPC currently has a large part of SE TX outlooked with a moderate risk. Small scale changes in the track of the potent upper low and or thermodynamic profile may result in a lesser or greater threat.

[ticka1]

Jeff I will be at work tomorrow - I work close to IAH airport right off the Beltway. I don't have interent access except for my cellphone. If you can please post here - I have Coriolis's number so he can relay any serious weather situation to me.

Looks like you might have a busy busy day tomorrow. Can we say welcome to spring!

[Bozo]

Jeff, Ticka and I are going to ATTEMPT to chase tomorrow. Can you and/or Jim nowcast for us?

Ticka, I'm checking all my other chase sites to see what they're saying.

[jeffl]

I can nowcast for you.

I think you have my work and cell numbers.

Feel free to call. If you do not have my numbers send me an e-mail

[Bozo]

Gracias Jeff.
Latest from NWS this morning (yes I'm actually awake at this time!):
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX
330 AM CST MON MAR 21 2005

...SIGNIFICANT SEVERE WEATHER THREAT TODAY AND THIS
EVENING ACROSS THE NORTHERN HALF OF SE TX...

.DISCUSSION...
LOW CLOUDS ARE EXPANDING OVER THE AREA EARLY THIS MORNING.
DW PTS STILL IN THE MID 50S ACROSS THE CENTRAL AND NORTHERN ZONES
WITH LOW 60S ALONG THE COAST. MOISTURE GRADIENT ACROSS THE
CENTRAL ZONES IS INDICATIVE OF WHAT IS LEFT OF THE WEAK COOL
FRONT THAT ACCELERATED SOUTHWARD LAST NIGHT WITH OUR ROUND OF
CONVECTION. EXPECT THE WARM AND MOIST AIRMASS SOUTH OF THE CWA
TO SPREAD NORTHWARD THIS MORNING ACROSS SE TX AS LOW PRESSURE
DEEPENS ACROSS THE SOUTHERN PLAINS.

THE MAIN FORECAST ISSUE IS THE POTENTIAL SVR WX EVENT TODAY AND
THIS EVENING. NO SIGNIFICANT CHGS TO THE PREVIOUS THINKING
CONCERNING THIS EVENT. WOULD LIKE TO SEE THE ETA AND GFS IN A
LITTLE BETTER AGREEMENT CONCERNING PRECIP PATTERN. HAVE DECIDED
TO TREND THE LATEST FORECAST TOWARD THE GFS. IT APPEARS TO HAVE
A BETTER HANDLE ON CURRENT PRECIP TRENDS. ETA IS TOO AGGRESSIVE
DEVELOPING PRECIP OVER NORTHERN PORTIONS OF SE TX TONIGHT.
FOLLOWING THE GFS IDEA...EXPECT CONVECTION TO BEGIN DEVELOPING
LATER THIS MORNING OVER THE NW ZONES OF SE TX. BEST CHC FOR
THE CENTRAL AND COAST WILL BE IN THE AFTERNOON AND EVENING HOURS.
THERE IS SOME CAPPING TO OVERCOME...BUT IT IS NOT EXPECTED TO BE A
PROBLEM WITH HEATING AND LIFT FROM THE APPROACHING UPPER
LEVEL JET CORE AND MID-LEVEL LOW WHICH WILL AMPLIFY NORTH OF THE
REGION AND SAG SE DURING THE EVENING HOURS. DRY LINE/WEAK COOL
FRONT WILL MOVE ACROSS TONIGHT FROM WEST TO EAST. THIS IS SLIGHTLY
SLOWER THAN THE PREVIOUS FORECAST...SO HAVE RAISED THE EVE POPS A
LITTLE. NOT SURE HOW MUCH CONVECTION WILL BE ON THE BOUNDARY
ITSELF...AS BEST LIFT APPEARS TO BE A LITTLE AHEAD OF THE
BOUNDARY. COULD END UP SEEING A COUPLE OF ROUNDS OF TSTMS...
ESPECIALLY ACROSS THE NORTHERN ZONES. DEGREE OF INSTABILITY AND
LOW-LEVEL SHEAR WILL BE SUFFICIENT FOR SUPERCELLS...ESPECIALLY
ALONG AND NORTH OF I-10. WILL MENTION THE SVR THREAT AREAWIDE
TODAY AND THIS EVENING AND HIGHLIGHT THE NORTHERN HALF AS HAVING
THE HIGHEST THREAT. BASED ON HELICITY VALUES OVER 200 AND CAPES
EXPECTED TO BE CLOSE TO 2K...TORNADOES AND HAIL ARE THE PRIMARY
THREATS. SHOULD CONVECTION BECOME ORGANIZED...DAMAGING
WINDS ARE ALSO A THREAT DUE TO STRONG MID-LEVEL WINDS AND DRY
LAYER ALOFT.

[ticka1]

Looking at the radar this morning - looks like the storms are already starting to develop to our north around Waco. Looks like they are moving in the general direction of SE Texas.

[Bozo]

Ticka, I'm hoping that's round 1 of 2. If there IS no round 2, bustola city. Got to have more heating to really get something firing. I'll be watching until 11:00 or so (while I'm finally doing my english paper due tomorrow!). :rolleyes3

Hey Jeff, if you read this, got some ideas for a good position for us?

[jeffl]

A good place would be up I-45 in Montgomery or Walker counties. A really better place would be up in Madison or Houston counties (chased up there before) away from the tall pines. The further north you get the more severe the weather.

Not up for a long drive head out 290 into Waller County away from the congested city.

[jeffl]

Significant Severe Weather Event today for SE TX

Dangerous thunderstorms capable for very large hail, damaging winds,
and long lived tornadoes are possible.

Discussion:

SPC has just issued the first of many watches today for C and N TX.
Thunderstorms are rapidly developing ahead of the surface dry line
over NC and C TX.

Gulf moisture is rapidly returning this morning with mid 60 degree
dewpoints over the coastal bend, this will spread rapidly inland over
the next few hours. CAPES of 2000 J/kg and Li's of -4 to -9 can be
expected by early afternoon over the region. A 140kt jet streak will
punch into the region by early afternoon with the jet couplet
splitting over SE TX. Severe Thunderstorms ongoing over C TX will
increase in coverage and intensity as they track E to ENE.

Wind profiles continue to support strong updraft rotation with 0-1km
shear on the order of 250 m^2/s^2. Veering profiles with height are
supporting curved hodographs indicating supercells potential.

Areas along and north of I-10 will be under the gun for all severe
modes including long tracked violent supercells. Updraft speeds will
support baseball size hail and damaging winds especially this
afternoon. The tornado threat will be greatest north of I-10 where
dynamics and shear are maximized.

This is a dangerous severe weather situation, heed NWS warnings with
rapid response.

If a tornado warning is issued for your area: Seek shelter on the
lowest floor of a sturdy structure away from windows. Cover your head
and body with blankets and pillows. If caught on the highway, get out
of your car and seek strong shelter. If there is no strong shelter lie
flat in a ditch or low spot, DO NOT shelter under underpasses.

NOTE: rapid scan visible imagery has been implemented over the TX
satellite sector to support Severe Weather Operations at SPC and local
NWS offices.

[jeffl]

Strong to Severe thunderstorms continue to development within an area
of enhanced convergance along the C TX dry line.

At 800am the dry line extended from W of Fort Worth to near Junction
and then to W of Del Rio. Numerous thunderstorms have develop over C
TX within deep WAA regime and forced ascent on the SE side of the
central plains surface low.

Visible images indicate low level stratus deck is breaking over the
coastal bend and SE TX allowing surface heating. CAPE values of 1500
J/kg are found east of I-35 over most of SE TX. Air mass is rapidly
becoming unstable with moisture advection and heating. with capping
starting to erode.

Southern tail end of the line over SC TX south of KAUS will probably
intensify over the next few hours as it encounters increasing
instability and low level inflow. Shear profiles remain favorbale for
tornadoes with 250 on the helicity scale and near 400 over N TX.

[stormy]

hope you both have fun chasing. Sure wish i could join you two. Maybe for Hurricane season.

[Bozo]

I'm talking to her about every hour. We're both crossing our fingers that this thing starts to kick before it gets too late. She can't get off work until 3:00 and I completely blew off class today to watch SPC and my email. We're so SILLY!!!

I do not relish the idea of chasing at night again. Stupid is okay once, but I hate to make a habit of it.

[jeffl]

Ticka, Bozo,

Call me ASAP.

Tornado Watch box expected shortly.

If you are going to chase head out I-10 or 290.

I am in contact with channel 11, and David wants to know where you are going.

713-684-4165

[jeffl]

ticka,

you and bozo may want to hold up for a few hours, and see what exactly is going to happen.

Most of the cells to the west have weakened and the cells to the north are elevated.

Cap appears to be holding strong over the region.

[swmochic]

Do you think it will make it to missouri????

[ticka1]

Jeff - thanks a million for the nowcast updates and talking to me over the phone. Work committments kept me from even attempting to go with Suzi.

Keep us updated on the severe weather situation tonight - I have my camcorder and camera ready for action here at the house.

Thanks,

[jeffl]

Finally the dry line has pushed into SE TX with severe thunderstorms moving off to the east. 12 hours under tornadoes watches with this system, yet only POSSIBLE touchdown was over NE TX in Lamar CO.

Had pea size hail at the house around KIAH around 300am and an impressive light show.

Better late than never I suppose.