March: Warm Days To End The Month With Isolated Showers

[srainhoutx]

The 12Z GFS has slowed the progression of the frontal boundary/trough next Tuesday into Wednesday much as the over night ensembles suggested. If the Operational GFS is correct, very heavy rains with multiple days of severe storms would impact the Lone Star State and points N into OK and the Central Plains. The Western trough should be very slow to eject E with such a strong upper ridge in place near the Ohio Valley and a deep cut off low develops over Texas at the base of the trough suggesting our wet pattern will only increase as we head into the late weekend time frame into the beginning of the work week.

[srainhoutx]

Messy complex pattern shaping up...

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
317 PM EDT THU MAR 15 2012

VALID 12Z SUN MAR 18 2012 - 12Z THU MAR 22 2012

...EXCESSIVE RAINFALL POSSIBLE OVER THE SOUTHERN PLAINS...

THE VERY STRONG AND SLIGHTLY LONGITUDINAL-ORIENTED UPPER JET
CURRENTLY CROSSING THE PACIFIC IS EXPECTED TO CULMINATE IN A FULL
LATITUDE UPPER TROUGH OVER THE WEST COAST AT THE BEGINNING OF THE
MEDIUM RANGE PERIOD DAY 3/SUN...WITH THE POTENTIAL FOR A CUTOFF
LOW OVER THE SOUTHWEST. MEANWHILE...ANOMALOUSLY HIGH HEIGHTS WITH
ABOVE NORMAL TEMPERATURES IS EXPECTED ACROSS THE EAST.

THE SOLUTION SPREAD APPEARS NEAR AVERAGE ON DAY 3...BUT QUICKLY
INCREASES BEGINNING DAY 5/TUE DUE TO DIFFERING SPEEDS AND
TRAJECTORIES FOR THE POTENTIAL CUTOFF LOW OVER THE SOUTHWEST.
NEARLY ALL OF THE DETERMINISTIC SOLUTIONS FROM THE 00-06Z
CYCLES...INCLUDING THE GFS/ECMWF/CANADIAN...EJECT THE LOW BETWEEN
THE PLAINS AND THE MISSISSIPPI RIVER BY DAY 7/THU...WHILE ALL THE
GLOBAL ENSEMBLE MEANS ARE AS MUCH AS 1 TO 2 DAYS SLOWER AND
FARTHER WEST. 12Z GUIDANCE...INCLUDING THE
GFS/CANADIAN/UKMET/ECMWF...HAVE ALSO SHIFTED FARTHER WEST AND IN
ACCORDANCE WITH THE ENSEMBLE MEANS...LENDING SLIGHTLY GREATER
CONFIDENCE TOWARD A SLOWER EJECTION. WAVE PACKET ENERGY
ACCOMPANYING THE UPPER TROUGH IS ALSO PROJECTED TO BE QUITE
HIGH...SUPPORTING THE NOTION THAT WHILE THE UNCERTAINTY REMAINS
QUITE HIGH BEYOND DAY 5...THAT A SLOWER/MORE AMPLIFIED SOLUTION
PERHAPS EVEN MORE SO THAN DEPICTED BY CURRENT GUIDANCE...IS THE
PREFERRED APPROACH AT THIS TIME. THUS...THE PREFERENCE IS TO LEAN
TOWARD THE SLOW SIDE OF THE GUIDANCE...WHICH INCLUDES THE
GFS/ECMWF ENSEMBLE MEANS...AND TO A LESSER BUT SUPPORTING
EXTENT...THE 12Z GFS/ECMWF/CANADIAN.

THE LARGEST IMPACT OF THIS PREFERENCE IS THE POTENTIAL FOR A
NARROW CORRIDOR OF EXCESSIVE RAINFALL TO FORM AHEAD OF THE PLAINS
DRYLINE/FRONTAL SYSTEM...INCLUDING TEXAS AND OKLAHOMA. ADJUSTING
FOR NORMALLY LOW BIASES OF MULTI-DAY ENSEMBLE MEAN QPF...THE
POTENTIAL EXISTS FOR BASIN-WIDE AMOUNTS OF 3 TO 6 INCHES OVER A
MULTI-DAY PERIOD...WITH LOCALIZED AMOUNTS OF 5 TO 10 INCHES
POSSIBLE. OTHERWISE...THE MOST NOTICEABLE IMPACTS OF THE EXPECTED
LONGWAVE PATTERN IS ABNORMALLY COOL TEMPERATURES CONTINUING ACROSS
PARTS OF THE WEST AT LEAST THROUGH DAY 5...AND ABNORMALLY WARM
TEMPERATURES CONTINUING BENEATH THE UPPER RIDGE ACROSS MUCH OF THE
EAST.

[srainhoutx]

Forecaster Roth will perk some ears with his early morning HPC medium Range discussions. The over night guidance has trended a touch slower in the progression of the upper trough/Pacific frontal boundary and the severe potential has increased greatly for a large swath of the Lone Star State that is knocking on the door of SE TX by day 4, Monday the 19th. The 00Z Euro was completely dismissed as too progressive while the UKMet and Canadian were slower. The 06Z GFS has also slowed the progression of the boundary and the dry line activity will be near SE TX for a longer period of time. Worrisome to even see the mention of April 27, 2011 in any set up and especially from the HPC...


PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
438 AM EDT FRI MAR 16 2012

VALID 12Z TUE MAR 20 2012 - 12Z FRI MAR 23 2012

...HEAVY RAINFALL/SEVERE WEATHER POSSIBLE OVER THE PLAINS EARLY
NEXT WEEK...

WHILE A POSITIVE 500 HPA HEIGHT ANOMALY REORIENTS/SHIFTS ACROSS
THE CENTRAL PACIFIC...TROUGHING REMAINS PREFERRED NEAR THE WEST
COAST WITH RIDGING PREFERRED DOWNSTREAM ACROSS THE UPPER MIDWEST
AND EAST. ENERGY DIGGING TOWARDS THE BASE OF THE WESTERN TROUGH
IS EXPECTED TO CLOSE OFF AND TRACK FROM THE SOUTHWEST/PLAINS
TOWARDS THE GREAT LAKES...WHICH IS A PATTERN SEEN OVER THE PAST
MONTH.

THE 00Z ECMWF WAS A QUICK OUTLIER WITH A SHORTWAVE MOVING TOWARDS
THE WESTERN US/CANADIAN BORDER...WHICH CAUSED IT TO MOVE THE DEEP
CYCLONE ACROSS THE PLAINS QUICKER THAN THE REMAINDER OF THE
GUIDANCE. THE 00Z CANADIAN/00Z UKMET/00Z GFS WERE CLOSE TO THE
00Z GEFS/12Z ECMWF ENSEMBLE MEANS SLOWER PROGRESSION...AND WITH
PROGRESSIVE RIDGING EXPECTED TO MOVE OVER THE TOP OF THE CLOSED
CYCLONE...A SLOWER MOTION IS MORE LIKELY TO VERIFY. TAKING
CANADIAN PRESSURE BIASES INTO ACCOUNT...USED A 00Z UKMET/00Z GFS
COMPROMISE THROUGH WEDNESDAY BEFORE SWITCHING TO A 00Z GFS/12Z
ECMWF ENSEMBLE MEAN COMPROMISE THEREAFTER WHICH LED TO SOME
SLOWING FROM CONTINUITY.

THE MAIN IMPACTS FROM THIS SYSTEM ARE EXPECTED TO BE SEVERE
WEATHER AND HEAVY RAINFALL /ON THE ORDER OF 3-5 INCHES WITH LOCAL
AMOUNTS NEAR 10 INCHES/ ACROSS PORTIONS OF THE SOUTHERN AND
CENTRAL PLAINS EARLY NEXT WEEK. THE SYNOPTIC PATTERN EXPECTED ON
MARCH 19 RESEMBLES THAT OF APRIL 27 2011 SHIFTED SEVERAL HUNDRED
MILES WESTWARD. SEE STORM PREDICTION CENTER OUTLOOKS FOR MORE
INFORMATION ON THE SEVERE WEATHER THREAT FROM THIS SYSTEM...AND
QPF PRODUCTS ISSUED BY OUR CENTER CONCERNING THE LATEST ON
PROJECTED RAINFALL AMOUNTS.



DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0347 AM CDT FRI MAR 16 2012

VALID 191200Z - 241200Z

...DISCUSSION...
MEDIUM-RANGE MODELS IN FAIRLY GOOD GENERAL AGREEMENT THROUGH DAY 4
/MON 3-19/...BUT BEGIN TO DIVERGE DAY 5 /TUE 3-20/ AS THE GFS CLOSES
OFF A LOW IN THE BASE OF THE SLOWLY ADVANCING LARGE SCALE
TROUGH...WHILE THE ECMWF KEEPS THE SYSTEM OPEN.

THE ECMWF EVENTUALLY DEVELOPS A LOW DAY 6...BUT IS MUCH MORE
PROGRESSIVE WITH THE LOW AS COMPARED TO THE GFS -- WHICH KEEPS THIS
FEATURE INVOF OK FOR ROUGHLY 48 HOURS. WHILE A VARYING DEGREE OF
SEVERE POTENTIAL WOULD EXIST DAY 5 -- AND PERHAPS BEYOND -- IN
EITHER MODEL SOLUTION...DUE TO THESE DIFFERENCES WILL REFRAIN FROM
HIGHLIGHTING ANY THREAT AREAS BEYOND DAY 4.

THE PRIMARY SEVERE THREAT DAY 4 IS EXPECTED TO RESIDE OVER ROUGHLY
THE ERN HALF OF THE SRN PLAINS...AS THE INITIAL COLD FRONT ADVANCES
WITH TIME. WHILE SOME THREAT WILL LIKELY EXTEND MUCH FARTHER NWD
AHEAD OF THE FRONT...PERSISTENT CONVECTION MAKING VERY SLOW EWD
PROGRESS DUE TO VERY STRONG MERIDIONAL FLOW ALOFT SHOULD LIMIT
INSTABILITY WITH NWD EXTENT.

FARTHER S HOWEVER...A MORE SWLY BELT OF FLOW ALOFT -- AND THUS MORE
FAVORABLE DIRECTIONAL SHEAR WITH HEIGHT -- IS PROGGED. AS THE FRONT
ADVANCES ACROSS TX/OK INTO A DESTABILIZING AFTERNOON
AIRMASS...SEVERE STORM DEVELOPMENT APPEARS LIKELY. WITH THREATS FOR
HAIL...DAMAGING WINDS...AND POSSIBLY TORNADOES APPARENT ATTM...WILL
MAINTAIN THE ONGOING SEVERE THREAT AREA ACROSS PARTS OF THE SRN
PLAINS REGION -- WHERE THE MOST WIDESPREAD/SUBSTANTIAL THREAT
APPEARS TO EXIST.

[srainhoutx]

The 12Z GFS is suggesting a line of severe slow moving storms developing on Tuesday across portions of SE TX. It is interesting to note that a wave of low pressure develops along the Middle TX coastal region and heads NNE along that slow moving frontal boundary as suggested by the GFS.

24 Hour Precip Totals...

Precip Totals 120 Hours...

[Ptarmigan]

Areas around Big Bend got some rain last night. Up to 1 inch, which is a lot for that area. A good start.

[srainhoutx]

HPC Final Update for today suggests the boundary/upper trough will swing by late Tuesday into early Wednesday of next week. It still appears via guidance that a fairly significant squall line will slide through during the afternoon/evening hours on Tuesday and with ample daytime heating, the severe potential does look noteworthy besides the very heavy rainfall expected.

FINAL ISSUANCE:

MODEL TRENDS WITH THE UPPER LOW EJECTING OUT OF THE SOUTHWEST FROM
THE 12Z CYCLE ARE FASTER BY A MUCH AS 12 TO 24 HRS...DUE IN LARGE
PART TO LESS AMPLIFICATION OF A REINFORCING SHORTWAVE TROUGH
AFFECTING THE WEST COAST. MODEL SPREAD STILL REMAINS QUITE LARGE
HOWEVER...
WITH THE 12Z ECMWF FASTEST...12Z GFS SLOWER...AND 12Z GEFS MEAN
THE SLOWEST BUT IS IN PHASE WITH THE 00Z GFS. THUS...FINAL
PREFERENCES HAVE SHIFTED EASTWARD ABOUT MIDWAY BETWEEN EARLIER
PREFERENCES AND A CONSENSUS INVOLVING THE SLOWER HALF TO ONE THIRD
OF THE 12Z CYCLE. THIS ADJUSTMENT INCORPORATES THE LATEST MODEL
TRENDS WHILE RESPECTING CONTINUITY DURING A HIGHLY UNCERTAIN
PORTION OF THE MEDIUM RANGE PERIOD. THE LARGEST SENSIBLE WEATHER
IMPACTS WILL LIKELY RESULT FROM THE PROGRESSION OF THE CLOSED
LOW...WITH BASIN-AVERAGE RAINFALL AMOUNTS OF 3-6 INCHES OVER PARTS
OF THE SOUTHERN PLAINS...WITH LOCAL AMOUNTS NEAR 10 INCHES
POSSIBLE.

[srainhoutx]

Code: Select all

BULLETIN - IMMEDIATE BROADCAST REQUESTED
   SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 78
   NWS STORM PREDICTION CENTER NORMAN OK
   315 PM CDT FRI MAR 16 2012
   
   SEVERE THUNDERSTORM WATCH 78 IS IN EFFECT UNTIL 900 PM CDT
   FOR THE FOLLOWING LOCATIONS
   
   TXC003-033-043-081-103-105-115-135-151-165-173-227-235-317-329-
   335-353-371-383-389-415-431-443-461-475-495-170200-
   /O.NEW.KWNS.SV.A.0078.120316T2015Z-120317T0200Z/
   
   TX 
   .    TEXAS COUNTIES INCLUDED ARE
   
   ANDREWS              BORDEN              BREWSTER            
   COKE                 CRANE               CROCKETT            
   DAWSON               ECTOR               FISHER              
   GAINES               GLASSCOCK           HOWARD              
   IRION                MARTIN              MIDLAND             
   MITCHELL             NOLAN               PECOS               
   REAGAN               REEVES              SCURRY              
   STERLING             TERRELL             UPTON               
   WARD                 WINKLER             
   
   
   ATTN...WFO...MAF...SJT...

[srainhoutx]

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0211 AM CDT SAT MAR 17 2012

VALID 191200Z - 201200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MN VICINITY SSWWD INTO
THE LOWER RIO GRANDE VALLEY...

...SYNOPSIS...
HIGHLY-AMPLIFIED FLOW FIELD ALOFT IS FORECAST THIS PERIOD...AS A
LARGE/FAIRLY SHORT WAVELENGTH TROUGH CONTINUES A SLOW EWD SHIFT
TOWARD THE CENTRAL U.S. WHILE A STRONG/LARGE-SCALE RIDGE PREVAILS
ACROSS THE ENTIRE ERN CONUS.

AT THE SURFACE...HIGH PRESSURE IS FORECAST ACROSS BOTH THE WRN AND
ERN THIRDS OF THE COUNTRY...WHILE THE CENTRAL U.S. EXPERIENCES THE
EFFECTS OF A SLOWLY ADVANCING COLD FRONT. THIS FRONT WILL FOCUS THE
PRIMARY AREA OF STRONG/POTENTIALLY SEVERE CONVECTION THIS PERIOD.

...ERN HALF OF THE PLAINS AND INTO THE MID MO VALLEY/OZARKS...
COMPLEX/CHALLENGING WEATHER SCENARIO IS UNFOLDING THIS PERIOD...AS
CONTINUED/SLOW EWD ADVANCE OF THE LARGE STORM SYSTEM INTO THE PLAINS
IS EXPECTED. ONGOING SHOWERS AND STORMS -- AND POSSIBLY SOME SEVERE
POTENTIAL -- ARE EXPECTED AT THE START OF THE PERIOD...WHICH --
ALONG WITH ASSOCIATED CLOUD COVER AND GENERAL SLOW MOVEMENT OF THE
PRECIPITATION -- WILL LIKELY HINDER DESTABILIZATION POTENTIAL ACROSS
A LARGE PORTION OF THE POTENTIAL THREAT AREA.

ATTM...IT APPEARS THAT A BROAD ZONE OF RISK FOR SEVERE STORMS WILL
EXIST AHEAD OF THE COLD FRONT AS IT ADVANCES ACROSS THE
PLAINS...WITH AT LEAST SOME THREAT EXTENDING FROM NRN MN SWD TO THE
LOWER RIO GRANDE VALLEY. THOUGH INSTABILITY SHOULD REMAIN FAIRLY
LIMITED ACROSS MUCH OF THE AREA FROM ERN OK NWD...FAVORABLE SHEAR
AND FAIRLY STRONG LOW-LEVEL FORCING SHOULD SUPPORT VIGOROUS STORMS
CAPABLE OF PRODUCING LOCALLY DAMAGING WINDS AND HAIL.

THE GREATEST THREAT ATTM APPEARS TO EXIST FROM ERN OK AND PERHAPS
WRN AR SSWWD ACROSS PARTS OF CENTRAL AND ERN TX -- ROUGHLY ALONG THE
I-35 CORRIDOR. HERE...GREATER DESTABILIZATION POTENTIAL IS EVIDENT
ALONG THE SERN FRINGE OF ONGOING STORMS. THIS COMBINED WITH
SLIGHTLY MORE SWLY COMPONENT TO THE FLOW ALOFT YIELDING A MORE
FAVORABLE WIND PROFILE SUGGESTS A FOCUSED AREA OF GREATER SEVERE
POTENTIAL -- REFLECTED IN THE OUTLOOK GRAPHIC.

MODELS ARE FAIRLY CONSISTENT IN DEVELOPING A MORE LINEAR/SLOW-MOVING
BAND OF CONVECTION FROM SWRN MO/ERN OK/WRN AR SWWD TO THE LOWER RIO
GRANDE VALLEY THROUGH THE EVENING AND INTO THE OVERNIGHT HOURS ALONG
THE ADVANCING FRONT. ALONG WITH ONGOING SEVERE RISK...POTENTIAL FOR
LOCALLY VERY HEAVY RAINFALL ALSO APPEARS TO EXIST.

..GOSS.. 03/17/2012

[srainhoutx]

A worrisome pattern is developing regarding severe weather potential for Central and Eastern TX Monday afternoon into Tuesday. Some of the shorter range meso guidance suggests a significant severe weather episode may develop near the I-35 Corridor and points E. We’ll need to monitor the situation fairly closely and I would not be surprise to see a possible Moderate Risk introduced by the SPC sometime tomorrow or Monday for a rather large chunk of real estate for the Eastern Half of the Lone Star State. Stay Tuned!

[Portastorm]

In its afternoon area forecast discussion (AFD), NWSFO Austin/San Antonio believes the squall line will move through the I-35 corridor in its forecast area between 2-8 am Tuesday. I don't know why, but it always seems like we (Austin) get our worst storms during the late night/early morning hours.

[weatherguy425]

I'll be on my way back to Lubbock tomorrow, potentially driving into one of the best severe weather set ups northwest Texas has seen in a couple of years...I'll keep y'all posted as best as I can.

[srainhoutx]

I smell a special sounding from CLL coming with this situation. Worrisome is the slowing of the progression of the dry line Monday evening into Tuesday for Central/SE TX. The stage is being set for training cells and a flood potential increasing along and E of the I-35 Corridor and N of I-10, IMO. 30% hatched does raise an eyebrow as well. Should we see the 12Z guidance increase the profiles a touch stronger, the the SPC might raise the threat level a bit with areas from Austin to Waco and back down to near Tomball being the 'favored' areas to to watch. 2-4 inches of rain with higher isolated totals of 6+ inches may not be out of the question. We will see.

[Andrew]

I smell a special sounding from CLL coming with this situation. Worrisome is the slowing of the progression of the dry line Monday evening into Tuesday for Central/SE TX. The stage is being set for training cells and a flood potential increasing along and E of the I-35 Corridor and N of I-10, IMO. 30% hatched does raise an eyebrow as well. Should we see the 12Z guidance increase the profiles a touch stronger, the the SPC might raise the threat level a bit with areas from Austin to Waco and back down to near Tomball being the 'favored' areas to to watch. 2-4 inches of rain with higher isolated totals of 6+ inches may not be out of the question. We will see.

Look like things will be interesting for me in college station. Looking at the 00z suite compared to the 12z suite and the gfs, euro and CMC all cut off the trough a lot more and some of them even create a cut off low. They also seem to bring the energy farther south which is going to bring rain totals higher farther south. This is a very nice setup overall and I think we are going to see some pretty nasty weather.

[Andrew]

Day 2 SPC Outlook:

SPC AC 180600

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT SUN MAR 18 2012

VALID 191200Z - 201200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE MID MO VALLEY AREA
SWD/SSWWD TO THE LOWER RIO GRANDE VALLEY...

...SYNOPSIS...
HIGHLY AMPLIFIED UPPER FLOW FIELD TO CONTINUE ACROSS THE U.S. THIS
PERIOD...AS A VERY LARGE TROUGH MOVES SLOWLY OUT OF THE ROCKIES
TOWARD THE GREAT PLAINS. MEANWHILE...A CORRESPONDING DOWNSTREAM
RIDGE WILL AFFECT BASICALLY THE ENTIRE ERN U.S. E OF THE MS VALLEY.

AT THE SURFACE...HIGH PRESSURE WILL PREVAIL OVER THE ERN AND WRN
PORTIONS OF COUNTRY...WHILE A N-S COLD FRONT ASSOCIATED WITH THE
ADVANCING TROUGH CROSSES THE PLAINS STATES THROUGH THE PERIOD. THIS
FRONT WILL BE THE FOCUS FOR A N-S ZONE OF STORMS EXTENDING FROM THE
CANADIAN TO THE MEXICAN BORDER.

...MID MO VALLEY SSWWD TO THE LOWER RIO GRANDE VALLEY...
SHOWERS AND STORMS -- AND POSSIBLY ONGOING SEVERE POTENTIAL --
SHOULD EXTEND ACROSS PARTS OF KS/OK/TX AT THE START OF THE
PERIOD...WITH WEAKER CONVECTION EXTENDING NNEWD INTO THE MID MO
VALLEY REGION. THE ONGOING PRECIPITATION AND CLOUD COVER -- BEING
CARRIED CONTINUALLY NNEWD BY THE STRONG SLY/MERIDIONAL FLOW ALOFT --
SHOULD HINDER DESTABILIZATION POTENTIAL...AND THUS LIKEWISE LIMIT
ASSOCIATED SEVERE WEATHER POTENTIAL N OF THE SRN PLAINS WHERE LOWER
PROBABILITY THREAT FOR HAIL/WIND IS EXPECTED.

THE FOCUS FOR GREATER SEVERE POTENTIAL REMAINS FROM ROUGHLY ERN
KS/MO SWD -- PARTICULARLY INTO SERN OK/WRN MO AND SWD ACROSS E TX ON
THE SERN FRINGE OF ONGOING STORMS. AS AFTERNOON DESTABILIZATION
PUSHES MIXED-LAYER CAPE INTO THE 1000 TO 2000 J/KG RANGE ACROSS THIS
REGION...STORMS WILL INTENSIFY/REDEVELOP ACROSS THIS AREA THROUGH
PEAK HEATING.

AS STRONG /60 TO 70 KT/ SWLY FLOW AT MID LEVELS OVERSPREADS THE
MOIST/UNSTABLE BOUNDARY LAYER FEATURING SSELY PRE-FRONTAL
WINDS...DEVELOPING STORMS WITHIN THE FAVORABLY SHEARED ENVIRONMENT
WILL QUICKLY BECOME SEVERE/SUPERCELLULAR...WITH VERY LARGE HAIL AND
LOCALLY DAMAGING WINDS POSSIBLE. A COUPLE OF TORNADOES MAY ALSO
OCCUR -- GIVEN AMPLE LOW-LEVEL SHEAR AND THE MOIST BOUNDARY LAYER
FORECAST IN THIS REGION. OVERNIGHT...INCREASINGLY LINEAR
ORGANIZATION OF THE CONVECTION IS EXPECTED ALONG THE SLOWLY
ADVANCING FRONT. WHILE SEVERE THREAT CONTINUES INTO THE OVERNIGHT
HOURS...THREAT FOR HEAVY RAIN SHOULD ALSO INCREASE GIVEN OVERALL
SLOW MOVEMENT OF THE CONVECTIVE BAND AND POTENTIAL FOR TRAINING
CONVECTION.

..GOSS.. 03/18/2012

DAY 3:

SPC AC 180729

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0229 AM CDT SUN MAR 18 2012

VALID 201200Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM PORTIONS OF AR SWD INTO
COASTAL SERN TX/SRN LA...

...SYNOPSIS...
AS THE LARGE UPPER TROUGH MOVING OUT OF THE ROCKIES CONTINUES A SLOW
ADVANCE THIS PERIOD...EVOLUTION OF THE SYSTEM INTO A CLOSED LOW IS
FORECAST...WITH THE LOW EXPECTED TO RESIDE OVER ERN PORTIONS OF THE
SRN PLAINS BY THE END OF THE PERIOD. ELSEWHERE...RIDGING IS
FORECAST TO PREVAIL OVER BOTH THE ERN U.S. AND ALSO THE
SOUTHWEST...TO THE S OF FAST WSWLY FLOW EXPECTED OVER THE NWRN
CORNER OF THE CONUS.

AT THE SURFACE...SLOW EWD ADVANCE OF THE FRONT ASSOCIATED WITH THE
UPPER TROUGH WILL CONTINUE THROUGH THE FIRST HALF OF THE
PERIOD...BUT EVENTUAL UPPER LOW DEVELOPMENT OVER TX/OK MAY DRIVE
FRONTAL CYCLOGENESIS INVOF OK. DEPENDING UPON THE STRENGTH OF THIS
LOW DEVELOPMENT...SOME WWD RETREAT OF THE FRONT IN A WARM-FRONTAL
FASHION MAY OCCUR N OF THE LOW...WHILE SLOW EWD ADVANCE OF A COLD
FRONT TOWARD THE LOWER MS VALLEY WOULD CONTINUE S OF THIS FEATURE.

...MID AND UPPER TX COAST EWD ACROSS SRN LA AND NWD INTO AR...
WIDESPREAD SHOWERS AND THUNDERSTORMS WILL BE ONGOING ALONG THE WRN
FRINGE OF THE OUTLOOK AREA AT THE START OF THE PERIOD...AHEAD OF THE
ADVANCING COLD FRONT. ONGOING SEVERE THREAT SHOULD RAMP UP THROUGH
THE AFTERNOON FROM ROUGHLY THE OZARKS SWD TO THE SERN TX/SRN LA GULF
COASTS...AS LIMITED HEATING OF THE VERY MOIST GULF AIRMASS RESULTS
IN AIRMASS DESTABILIZATION. ONCE AGAIN...THE NRN EXTENT OF THE
SEVERE THREAT SHOULD AGAIN BE LIMITED DUE TO WIDESPREAD
PRECIPITATION/CLOUD COVER AND THUS MODEST INSTABILITY.
HOWEVER...FARTHER S...SERN TX AND LA IN PARTICULAR MAY EXPERIENCE
MORE WIDESPREAD/HIGHER END SEVERE POTENTIAL -- INCLUDING THE
POSSIBILITY OF TORNADOES GIVEN THE VERY MOIST BOUNDARY LAYER AND
FAVORABLY STRONG LOW-LEVEL SHEAR. CONVECTION SHOULD SHIFT SLOWLY
ACROSS LA THROUGH THE SECOND HALF OF THE PERIOD...WITH SEVERE THREAT
LIKELY TO CONTINUE THROUGH THE OVERNIGHT HOURS.

..GOSS.. 03/18/2012

[srainhoutx]

NWS Austin/San Antonio issues Flash Flood Watch for Monday evening until Tuesday morning for areas E of a Rocksprings to Pearsall line including Kerrville and all the Hill Country Lakes region.

[srainhoutx]

The trend has been to slow things down by about 6-10 hours via the 00Z and 06Z suite of guidance regarding the eastward progression of the upper trough and deepening upper low. Guidance has suggested that a very deep closed core upper low will develop tomorrow into Tuesday across West Texas and the Panhandle and a dry line develops across the western region of the Lone Star State. The SPC, has Ed and Andrew have posted has a couple of large Slight Risk areas for tomorrow and Tuesday. Activity will begin to increase out west later today from the Texas Panhandle on N bound into Kansas and the Central Plains.

Tomorrow will be the time frame to watch closely. Activity should begin to develop along the dry line and some discrete super cells are not out of the questions for W Central TX and the Hill Country before the storms consolidate into a squall line or QLCS oriented from SW to NE and stalls as the upper trough axis creeps E during the late afternoon and over night hours of Monday. As the U/L deepens, a surface low appears to develop near Corpus and begin to trek along the frontal boundary lending to strong veering winds and rapid frontogenesis/cyclogenesis and rapidly falling pressures to the E in Central and E TX. A Pacific front will slowly begin to move E into our area as we head into Tuesday.

The severe parameters are most impressive and somewhat rare for our area and particularly in mid March. The squall line should begin to orient to a more S to N fashion with training cells developing and embedded super cells possible lending to a possible significant severe weather event for areas from Austin to near Waco and on SE to the Beaumont/Lake Charles area. We will see what the 12Z guidance offers, but again I would not be surprised to see a Moderate Risk introduced later today into tomorrow for some areas in the Eastern half of Texas. I urge folks to pay close attention to the weather the next day or two and let those know that may not be so weather wise.

[Katdaddy]

Good morning Srain. Impressive WV satellite image tells the story. This is a very large and dynamic system that will produce widespread severe weather. I too would not be surprised to see Moderate Risks for tomorrow and Tuesday. I will do my best to people I know informed on this significant weather event.

[txsnowmaker]

Hi all. I have family at the Lost Pines resort in Bastrop. They are making the trip back to Houston tomorrow with their two small kids and likely don't have a clue about the severe weather potential. Should they be okay if they are on the road and back in Houston by late afternoon, or should I alert them and advise them to consider leaving first thing Monday morning? Any thoughts would be most welcome.

[Ptarmigan]

This looks to be the biggest severe weather event so far for 2012 in Southeast Texas. This could challenge January 9, 2012 event. Bears watching.

[Andrew]

Sounds in college Station from the gfs would support moderate CAPE levels along with some very nice Helicity. Saturation across most levels looks pretty good also.