SE TX/SW LA weather: Much cooler and WET after Tuesday

[Ptarmigan]

They look less impressive on radar. They were quite a storm 30 minutes ago.

[Ed Mahmoud]

Does 0Z GFS suggest wintry precip for DFW area Monday?


0Z Canadian seems to suggest close, but no cigar, as only light precip remaining when cold air arrives.



DGEX says no, and raw GFS numbers from my AccuWx PPV site says DFW area stays above freezing, so it looks like the kids have school next Monday, but I will keep a close watch.


0Z GFS also implies almost all precipitation is post-frontal, reducing the risk for severe weather in SE Texas, despite SPC having HOU area in a Day 4 and Day 5 outlook area.

[jasons2k]

0Z GFS also implies almost all precipitation is post-frontal, reducing the risk for severe weather in SE Texas, despite SPC having HOU area in a Day 4 and Day 5 outlook area.

Keep in mind that the GFS precip maps are for the 6 hours prior to the map times.

On another board, Wxman57 (who often posts in our tropical forums) has corrected some of the 'usual suspects' who imply there is a risk for frozen precip. based on the GFS output. Wxman has said, basically, that all the GFS is showing is a squall line pushing through that accompanies the front and there is no precip falling in the cold air behind the front.

[jasons2k]

From Jeff Lindner:

Cool and dry air mass this morning will begin to undergo moistening today ahead of next major storm system expected on Monday.

Upper air flow will transition over the next 24 hours to a moist SW flow aloft. At the surface low pressure will develop over W TX today allowing southerly winds to return. In fact S winds have already returned to most regions this morning and NW Gulf buoys shows winds already in the 10-20mph range. Once the sun is up for a few hours 20-30mph winds at 2000-3000ft will begin to mix to the surface…so a windy day is in store. Southerly flow will pull Gulf moisture inland with dewpoints on the rise from the current low to mid 30’s toward the lower 60’s on Friday. With the increase in moisture, clouds will increase especially after sunset tonight and hang tough on Friday in moist warm air adevtion regime.

SW flow aloft will allow weak disturbances to cross the region Friday through Sunday. A weak front will stall across C and E TX late Friday and provide a focus for a few showers. Will cover the Friday late afternoon to midday Saturday with 20-30% for light showers and then go with 10% until Sunday evening.

Attention quickly turns westward where upper air amplification will allow a digging trough down the US west coast into N Mexico late Saturday into Sunday. Progressive upper air flow means this trough moves into TX late Sunday and Monday. As upper trough approaches a good polar intrusion empties out of Canada and surges down the plains. Expect surface low pressure to develop Sunday afternoon over SW TX where dryline feature may setup. 100-120kt jet noses across S TX into SW LA during this time period with strong low level jet pumping deep moisture into the region. Per sounder satellites there is at least 1.5 in PWS over the Bay of Campeche that could advect northward into the area by late Sunday.

Given shear profiles and convective parameters expect healthy thunderstorm development as upper trough/cold front moves across the state early Monday into the day on Monday. See no reason to argue against severe except the fact that the event is still in the Day 4-5 time period and this is usually early to get specific with severe threats. Models are in very good agreement on squall line formation and show good wind energy with this system so very close watch should be applied over the next 2-3 days.

Strong polar front blasts through next Monday with GFS showing 925mb winds howling at nearly 50kts Monday afternoon. Expect some pretty good surface winds easily above 25mph. May be at or above gale force over the waters where GFS is showing 925mb winds of 60kts. For now will go with 20-30kts with gust up to 40kts Monday afternoon in post frontal cold air advection pattern. Upstream air mass will be cold and we may have to entertain the idea of freezing temps. Wednesday morning as this will be the day 2 post front and that is typically the coldest although models are showing next system rapidly approaching late Wednesday and this may shift winds around to the south before sunrise stopping the temp fall.

[Ed Mahmoud]

0Z GFS also implies almost all precipitation is post-frontal, reducing the risk for severe weather in SE Texas, despite SPC having HOU area in a Day 4 and Day 5 outlook area.

Keep in mind that the GFS precip maps are for the 6 hours prior to the map times.

On another board, Wxman57 (who often posts in our tropical forums) has corrected some of the 'usual suspects' who imply there is a risk for frozen precip. based on the GFS output. Wxman has said, basically, that all the GFS is showing is a squall line pushing through that accompanies the front and there is no precip falling in the cold air behind the front.

I'm no dummy, but when the leading edge of the GFS 6 hour precip is along, or even a bit behind, the position of the front, it implies all/most precip is post frontal.


That six hour thing is how people get in trouble/over-enthusiastic about frozen precip, because the 540 dm thickness line and 850 mb freezing line are at that hour, while precip is an accumulated amount over six hours.

[Ed Mahmoud]

If you look at the images above, both show the front and the leading edge of the six hour precip almost co-located. Suggesting the cap doesn't break, storms form right on the front, and are probably immediately undercut. The 'big time' severe storms usually form ahead of the front, although, of course, a well organized squall line right on the front can produce some vigorous wind gusts.

[Ed Mahmoud]

Do you remember what happened a couple of weekends ago on what was supposedly (and all the model soundings were showing it) the mother of all severe weather outbreaks in Southeast Texas. The cap never broke, all the storms that did form developed right on the front, immediately moved North of the front and became elevated, and might have even accelerated the front by cold downburst. Yes, it was a squall line, with a few severe reports, but it was nothing to write home about. Look where the windshift is, and then note the leading edge of the 6 hour precip is actually behind it. If the 12Z GFS is right, storms will not form in the warm sector except right on the front.






Of course, if all the models showed a near perfect setup for tornadoes two weeks ago and were wrong, maybe they'll be wrong this time.



Even with instaneous 540 dm line and 850 mb freezing line, 12Z GFS still forecasting winter joy for Tupelo and vicinity.

[southerngale]

Special Weather Statement

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE LAKE CHARLES LA
825 AM CST SUN MAR 2 2008

LAZ027>033-041>045-051>055-TXZ180>182-201-215-216-022100-
VERNON-RAPIDES-AVOYELLES-BEAUREGARD-ALLEN-EVANGELINE-ST. LANDRY-
CALCASIEU-JEFFERSON DAVIS-ACADIA-LAFAYETTE-UPPER ST. MARTIN-
CAMERON-VERMILION-IBERIA-ST. MARY-LOWER ST. MARTIN-TYLER-JASPER-
NEWTON-HARDIN-JEFFERSON-ORANGE-
INCLUDING THE CITIES OF...LEESVILLE...ALEXANDRIA...MARKSVILLE...
DERIDDER...OAKDALE...VILLE PLATTE...OPELOUSAS...LAKE CHARLES...
JENNINGS...CROWLEY...LAFAYETTE...ST. MARTINVILLE...CAMERON...
ABBEVILLE...NEW IBERIA...MORGAN CITY...WOODVILLE...JASPER...
NEWTON...LUMBERTON...BEAUMONT/PORT ARTHUR...ORANGE
825 AM CST SUN MAR 2 2008

...MODERATE RISK FOR SEVERE THUNDERSTORMS ON MONDAY...

THE STORM PREDICTION CENTER IN NORMAN OKLAHOMA HAS INDICATED THERE
IS A MODERATE RISK FOR SEVERE THUNDERSTORMS ON MONDAY ACROSS MOST
OF LOUISIANA...WITH A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER
SOUTHEAST TEXAS.

A POWERFUL UPPER LEVEL STORM SYSTEM WILL MOVE INTO THE LOWER
MISSISSIPPI VALLEY ON MONDAY. AT THE SAME TIME...A STRONG COLD
FRONT WILL PUSH INTO SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA
DURING THE AFTERNOON...AND REACH SOUTH-CENTRAL LOUISIANA BY
MONDAY EVENING.

CONDITIONS APPEAR QUITE FAVORABLE FOR THE DEVELOPMENT OF SEVERE
THUNDERSTORMS ALONG AND AHEAD OF THE COLD FRONT. DAMAGING
WINDS...LARGE HAIL...ISOLATED TORNADOES...HEAVY RAINFALL...AND
LOCALIZED FLOODING WILL ALL BE POSSIBLE WITH THIS STORM SYSTEM.

MONITOR NOAA WEATHER RADIO OR YOUR LOCAL MEDIA FOR THE LATEST
UPDATES ON THIS POTENTIAL SEVERE WEATHER SITUATION.

[MississippiHurricane]

Special weather statement for Jackson Ms forecast area:

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE JACKSON MS
1111 AM CST SUN MAR 2 2008

...SEVERE WEATHER OUTBREAK EXPECTED MONDAY AFTERNOON INTO MONDAY
NIGHT...

SIGNIFICANT SEVERE WEATHER WITH WIDESPREAD DAMAGING WINDS...
TORNADOES...AND LARGE HAIL WILL BE POSSIBLE MONDAY AFTERNOON INTO
MONDAY NIGHT.

AS A LARGE AND POWERFUL STORM SYSTEM APPROACHES THE AREA...AN
UNSTABLE AND MOIST AIRMASS WILL BEGIN SURGING NORTH FROM THE GULF OF
MEXICO EARLY MONDAY. AHEAD OF THE STRONG COLD FRONT...THIS MOISTURE
WILL COMBINE WITH VERY STRONG WIND SHEAR TO BRING THE POTENTIAL FOR A
MAJOR SEVERE WEATHER EVENT.

SEVERE THUNDERSTORMS COULD DEVELOP AS EARLY AS MIDDAY MONDAY WEST OF
THE MISSISSIPPI RIVER...BUT THE GREATEST POTENTIAL FOR SEVERE STORMS
WILL EXIST FROM MID AFTERNOON THROUGH EVENING...AS SCATTERED SEVERE
THUNDERSTORMS DEVELOP ALONG AND AHEAD OF THE COLD FRONT AND FORM INTO
A SQUALL LINE.

ACTIVITY OCCURRING WEST OF THE INTERSTATE 55 CORRIDOR MONDAY
AFTERNOON INTO EARLY MONDAY EVENING WILL HAVE THE GREATEST CHANCE OF
PRODUCING TORNADOES...WHILE ACTIVITY MONDAY EVENING ALONG AND EAST OF
INTERSTATE 55 CORRIDOR WILL HAVE THE HIGHEST CHANCE OF PRODUCING
WIDESPREAD DAMAGING WINDS. PLEASE CONTINUE TO MONITOR LATER FORECASTS
CONCERNING THIS POTENTIAL SEVERE WEATHER OUTBREAK.


And THEN a chance of snow Tuesday here!

[JenBayles]

Public Severe Weather Outlook
ZCZC SPCPWOSPC ALL
WOUS40 KWNS 030941
ARZ000-LAZ000-MSZ000-031745-

PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0341 AM CST MON MAR 03 2008

...A SEVERE THUNDERSTORM OUTBREAK IS EXPECTED OVER PARTS OF THE
LOWER MISSISSIPPI VALLEY THIS AFTERNOON AND TONIGHT...

THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE
DEVELOPMENT OF WIDESPREAD DAMAGING WINDS AND A FEW STRONG TORNADOES
OVER PARTS OF THE LOWER MISSISSIPPI VALLEY THIS AFTERNOON AND
TONIGHT.

THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE

SOUTHEASTERN ARKANSAS
LOUISIANA
MISSISSIPPI

THERE IS ALSO A RISK OF OTHER SEVERE THUNDERSTORMS ACROSS TEXAS
EASTWARD INTO ALABAMA...MIDDLE TENNESSE AND SOUTHERN KENTUCKY.

A POWERFUL UPPER LEVEL LOW...LOCATED IN WESTERN TEXAS THIS MORNING
...IS FORECAST TO LIFT NORTHEASTWARD INTO NORTHERN ARKANSAS TONIGHT.
THIS SYSTEM WILL AID IN PUSHING A COLD FRONT EWD ACROSS THE LOWER MS
VALLEY REGION LATER TODAY AND TONIGHT.

STRONG TO SEVERE STORMS ARE ALREADY ONGOING ACROSS PORTIONS OF
TEXAS...AND THE STORMS SHOULD BECOME MORE WIDESPREAD LATER TODAY AS
THEY SPREAD EASTWARD. THE STORMS WILL ALSO INTENSIFY AS A MID LEVEL
JET MAX...WITH WIND SPEEDS OVER 100 MPH...OVERSPREADS THE REGION.
THIS WILL RESULT IN AN ENVIRONMENT FAVORABLE FOR A FAST MOVING
SQUALL LINE TO DEVELOP AND PRODUCE WIDESPREAD WIND
DAMAGE...ESPECIALLY ACROSS SOUTHEASTERN ARKANSAS AND LOUISIANA THIS
AFTERNOON...AND MISSISSIPPI TONIGHT. ACROSS THIS SAME AREA...THE
POWERFUL JET MAX AND OTHER ENVIRONMENTAL CONDITIONS WILL BE
FAVORABLE FOR SUPERCELLS AHEAD OF THE SQUALL LINE...WITH THE
POTENTIAL FOR STRONG TORNADOES.

WIND DAMAGE IS ALSO EXPECTED WITH THE FAST MOVING LINE TONIGHT AS IT
MOVES ACROSS TENNESSEE...ALABAMA AND POSSIBLY SOUTHERN KENTUCKY.

THOSE IN THE THREATENED AREA ARE URGED TO REVIEW SEVERE WEATHER
SAFETY RULES AND TO LISTEN TO RADIO...TELEVISION...AND NOAA WEATHER
RADIO FOR POSSIBLE WATCHES...WARNINGS...AND STATEMENTS LATER TODAY.

..IMY.. 03/03/2008

[Extremeweatherguy]

For an idea of how strong this front is, consider the following...

-Killeen, TX fell from 70F at 4am to 46F at 5am. That is a 26-degree temperature drop in 1 hour or less!!!

-Waco, TX fell from 69F at 4am to 47F at 5am. That is a 24-degree temperature drop in 1 hour or less!!!

So buckle up! It is more likely than not that we will experience similar temperature drops here as well. Definitely going to be an interesting morning/afternoon..

[JenBayles]

GAG! And I was just getting used to Spring temps. Usually the last, awful gasp of winter in Houston coincides with all the trail riders rolling in to Houston for the rodeo. For once they got some great riding weather, but the Weather Gods must apparently make up for the mistake. Drat!

[Extremeweatherguy]

SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 90
NWS STORM PREDICTION CENTER NORMAN OK
650 AM CST MON MAR 3 2008

SEVERE THUNDERSTORM WATCH 90 IS IN EFFECT UNTIL 100 PM CST
FOR THE FOLLOWING LOCATIONS

TXC005-015-037-039-041-051-063-067-071-073-089-149-157-167-183-
185-199-201-203-225-241-285-287-291-313-315-339-343-347-351-365-
373-387-401-403-405-407-419-423-449-455-457-459-471-473-477-481-
499-031900-
/O.NEW.KWNS.SV.A.0090.080303T1250Z-080303T1900Z/

TX
. TEXAS COUNTIES INCLUDED ARE

ANGELINA AUSTIN BOWIE
BRAZORIA BRAZOS BURLESON
CAMP CASS CHAMBERS
CHEROKEE COLORADO FAYETTE
FORT BEND GALVESTON GREGG
GRIMES HARDIN HARRIS
HARRISON HOUSTON JASPER
LAVACA LEE LIBERTY
MADISON MARION MONTGOMERY
MORRIS NACOGDOCHES NEWTON
PANOLA POLK RED RIVER
RUSK SABINE SAN AUGUSTINE
SAN JACINTO SHELBY SMITH
TITUS TRINITY TYLER
UPSHUR WALKER WALLER
WASHINGTON WHARTON WOOD
$$

[jasons2k]

Latest from Jeff Lindner.

Severe weather outbreak likely today including damaging long tracked tornadoes across the mid south.

Powerful storm system over the southern plains this morning with squall line ongoing over C TX and newly issued weather watch box for our region. Will tackle severe potential first and then the temperature and high wind issues this afternoon and tonight.

Severe:

Severe Thunderstorm Watch has been issued until 100pm for a large portion of SE TX. Per radar trends squall line has weakened within the last 3 hours…but should begin to intensify over the next few hours as air mass over SE TX becomes unstable and capping weakens. Powerful cold front noted by 20-30 degree temp falls slicing into C TX will plow across the region this morning as surface low pressure develops along the boundary and moves ENE across the N 1/3rd of SE TX. Per HGX 88D winds at 850mb are howling at 50-60kts in the low level jet with a 500mb 110kt jet max approaching from the WSW in the base of the upper level trough. Squall line has shown numerous bowing segments this morning with surface wind damage resulting around the Waco/Temple area….including at 59mph wind gust at KXXV-TV in Waco. As downstream air mass over SE TX warms and cap weakens expect squall line to intensify with bowing segments producing winds damage across the region. Cap should be maintained enough to keep pre-frontal convection limited and hence the threat for warm sector supercell/tornado formation appears low over SE TX…but grows greatly over areas just to our east where significant tornadoes appear likely this afternoon and this evening. This could be a substantial tornado outbreak over LA and MS this afternoon. Will go with squall line reaching CLL within the next 1-2 hours and then metro areas 1100am-200pm and off the coast 100pm-400pm.

Temperatures:

Cold front is clearly noted in surface obs with at least a 20 degree drop and in some places nearly a 30 degree temp. fall in an hour or less. Georgetown is 50 while Austin is 72. Front will cross the region quickly late this morning and early this afternoon with temps. falling into the 50’s within the first few minutes after frontal passage and then continue on downward into the 40’s by early evening. Given upstream temps. in the low 40’s over the Dallas area and continued cold air advection overnight expect lows Tuesday to bottom out in the mid 30’s central to low 30’s north.

Winds:

Very tight pressure gradient remains this morning after howling winds the past 24 hours. Frequent gusts at or above wind advisory criteria Sunday PM with winds coming down slightly overnight and this morning. Pressure gradient will tighten greatly after frontal passage and expect very strong offshore flow this afternoon and evening. Will go sustained speeds of 20-30mph all areas with frequent gust over 30mph. Winds this morning over the Rio Grande plains and Hill Country behind the front have been gusting well over 40mph. May need gale warnings coastal waters and bays and will likely need wind advisories all areas after noon today.

Aviation/Marine:

Poor weather day for both aspects. Strong low level shear continues at all terminals this morning with surface flow around 15-20kts and 850mb flow around 50-60kts. Cross winds are strong out of the south with low cloud deck based around 1000-2000ft. Expect squall line with strong to severe winds and potential for microburst/downburst especially at metro area airports late this morning. Post frontal winds shift to NW and increase into the 20-30mph range at the surface.

Numerous marine advisories are up and small craft should remain in port given expect dangerous boating conditions that will develop this afternoon post frontal passage. S winds 20-30mph this morning shifting to NW and increasing 25-35mph with gust to 40mph this afternoon. Seas building 9-12 feet. Will see high winds across all inland area lakes with greatest winds likely over Conroe and Somerville.

Extended:

Much calmer period on Tuesday as polar high moves eastward allowing weak onshore flow to return ahead of next system due in on Thursday. Much colder air mass poised over NW Canada to sink southward and arrive early Thursday with overrunning clouds and a few showers. Models are not in full agreement yet on W Gulf of Mexico surface low and track and continue to differ on rain chances and temps. Wed-Fri. Could be fairly cool around here during this period and temps. may flirt with freezing come Friday and Saturday mornings.

[jasons2k]

MESOSCALE DISCUSSION 0330
NWS STORM PREDICTION CENTER NORMAN OK
1018 AM CST MON MAR 03 2008

AREAS AFFECTED...EAST TX...WRN LA...SRN AR

CONCERNING...SEVERE THUNDERSTORM WATCH 90...

VALID 031618Z - 031745Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 90
CONTINUES.

THE SEVERE THREAT WILL CONTINUE ACROSS WW 90 WITH AN ISOLATED
TORNADO THREAT ALONG WITH A POTENTIAL FOR HAIL AND WIND DAMAGE. THE
SEVERE THREAT IS EXPECTED TO INCREASE OVER THE NEXT 1 TO 2 HOURS AND
PART OF WW 90 WILL NEED TO BE REPLACED WITH A TORNADO WATCH SOON.
LATEST SFC ANALYSIS SHOWS A COLD FRONT FROM NRN AR EXTENDING SSWWD
ACROSS EAST TX. A MOIST AXIS EXISTS AHEAD OF THE BOUNDARY WITH 60 TO
65 F DEWPOINTS. STRONG MOISTURE ADVECTION DUE TO A 50 KT LOW-LEVEL
JET AND SFC HEATING WILL INCREASE INSTABILITY MAKING THE POTENTIAL
FOR SEVERE CONVECTION GREATER THROUGH EARLY AFTERNOON. STRONG
LOW-LEVEL SHEAR PROFILES EVIDENT ON REGIONAL WSR-88D VWPS SHOULD BE
SUFFICIENT FOR A FEW TORNADOES. IN ADDITION...500 MB TEMPS OF -12 TO
-14C WILL BE CONDUCIVE FOR LARGE HAIL. THE STRONG LOW-LEVEL FLOW OF
40 TO 50 KT WILL ALSO BE FAVORABLE FOR WIND DAMAGE WITH BOWING
SEGMENTS IN THE LINE.

http://www.spc.noaa.gov/products/md/md0330.html

[JenBayles]

Only straight down light rain here under the Bear Creek Dome right now, but the temps? Whooo hooo! We are not amused....

[southerngale]

Tornado Watch

TORNADO WATCH OUTLINE UPDATE FOR WT 91
NWS STORM PREDICTION CENTER NORMAN OK
1035 AM CST MON MAR 3 2008

TORNADO WATCH 91 IS IN EFFECT UNTIL 600 PM CST FOR THE
FOLLOWING LOCATIONS

TXC199-241-245-351-361-403-405-419-457-040000-
/O.NEW.KWNS.TO.A.0091.080303T1635Z-080304T0000Z/

TX
. TEXAS COUNTIES INCLUDED ARE

HARDIN JASPER JEFFERSON
NEWTON ORANGE SABINE
SAN AUGUSTINE SHELBY TYLER

TORNADO WATCH OUTLINE UPDATE FOR WT 91...RESENT
NWS STORM PREDICTION CENTER NORMAN OK
1035 AM CST MON MAR 3 2008

TORNADO WATCH 91 IS IN EFFECT UNTIL 600 PM CST FOR THE
FOLLOWING LOCATIONS

LAC001-003-009-011-013-015-017-019-021-023-025-027-029-031-035-
039-041-043-049-053-055-059-061-065-067-069-073-079-081-083-085-
097-107-111-113-115-119-123-127-040000-
/O.NEW.KWNS.TO.A.0091.080303T1635Z-080304T0000Z/

LA
. LOUISIANA PARISHES INCLUDED ARE

ACADIA ALLEN AVOYELLES
BEAUREGARD BIENVILLE BOSSIER
CADDO CALCASIEU CALDWELL
CAMERON CATAHOULA CLAIBORNE
CONCORDIA DE SOTO EAST CARROLL
EVANGELINE FRANKLIN GRANT
JACKSON JEFFERSON DAVIS LAFAYETTE
LA SALLE LINCOLN MADISON
MOREHOUSE NATCHITOCHES OUACHITA
RAPIDES RED RIVER RICHLAND
SABINE ST. LANDRY TENSAS
UNION VERMILION VERNON
WEBSTER WEST CARROLL WINN
$$

[Ed Mahmoud]

Posted in severe thread....


DOUBLE POST ALERT!

Now, hail isn't really winter weather, but it is frozen. I can't order up a skew-T for HOU from the NIU site, as they are only available in 6 hour increments, and only from the 0Z and 12Z runs.

But, checking the AccuWx PPV map, our total-totals in HOU between 50 and 55, our surface based CAPE is right about 500 J/Kg, and the most unstable CAPE (from Utah U met dept site) is between 750 and 1000 J/Kg, and deep layer shear is about 60 knots.




So, if enough hail were to accumulate tomorrow evening, I might count it as a moral victory, and act like it was sleet, once the danger of lightning passed. Run around, and make hail balls or something.

[jasons2k]

Risk of severe weather today.

I have posted Jeff's full update in the WinterWx forum.

[jasons2k]

Convection starting to pop, especially to our SW.