349 
FXUS64 KFWD 081341 AAC
AFDFWD

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE FORT WORTH TX
741 AM CST THU MAR 8 2012

.UPDATE...
WINDS BEHIND THE FRONT ARE A BIT STRONGER THAN PREVIOUSLY THOUGHT.
BUMPED UP THE FORECASTED WINDS AND ISSUED A WIND ADVISORY TO
ACCOUNT FOR THESE HIGH WINDS EXPECTED IN THE NORTHWESTERN ZONES
TODAY. LATEST OB AT WICHITA FALLS HAD SUSTAINED WINDS NEAR 30 MPH
WITH GUST UP TO 50 MPH. 

85/NH

&&

.AVIATION...

FOR THE 12Z TAFS...MVFR CEILINGS...THE PASSAGE OF A COLD FRONT AND
PRECIPITATION CHANCES ARE THE PRIMARY FORECAST CONCERNS THRU THE
VALID FORECAST PERIOD.

CONCERNING THE COLD FRONT...BUMPED UP THE TIMING OF THE FRONT
THROUGH METROPLEX AREA TAF SITES TO 16 TO 17 Z BASED ON LINEAR
EXTRAPOLATION OF FRONTAL SPEED OVER THE LAST 2 HOURS. WILL
CONTINUE TO MONITOR AND AMEND THE TAFS AS NECESSARY AS THE FRONT
MOVES INTO NORTH TEXAS THIS MORNING.  

PRECIPITATION CHANCES...OUR BEST PRECIPITATION CHANCES ARE
EXPECTED TO LIE ALONG AND NORTH OF THE COLD FRONT...SO THE TIMING
OF THE COLD FRONT IS CRUCIAL TO DETERMINE WHEN THUNDERSTORMS WILL
AFFECT AREA TAF SITES TODAY. AT THIS TIME BECAUSE MOST
THUNDERSTORM ACTIVITY IS EXPECTED TO HOLD NORTH OF THE COLD
FRONT...CONVECTION IS EXPECTED TO REMAIN MOSTLY ELEVATED AS STORMS
AFFECT AREA TAF SITES. WITH THIS IN MIND THINK THAT THE POTENTIAL
FOR SEVERE/DAMAGING WINDS IS REDUCED...HOWEVER THE USUAL CAVEATS
APPLY...IF A STORM IS DIRECTLY OVER AN AIRPORT STRONG VARIABLE
WINDS ARE POSSIBLE.

CEILINGS...MVFR CIGS WILL LIKELY PERSIST THROUGH THE VALID
FORECAST PERIOD. CIGS ARE MOST LIKELY TO FALL TO THE 2 KFT LEVEL
OR BELOW DURING PERIODS OF HEAVIER OR PERSISTENT PRECIPITATION.
TRIED TO KEEP THE TAFS SIMPLE AT THIS TIME AND DIDNT BRING CIGS
DOWN BELOW THE 2 KFT LEVEL UNTIL COLDER AIR FILTERS INTO THE
REGION A FEW HOURS BEHIND THE INITIAL WIND SHIFT LINE ASSOCIATED
WITH THE FRONT. OPTED TO ADVERTISE PERIODS OF SIGNIFICANT WIND
SHIFT AND PERIODS OF PERSISTENT RAINFALL WITH CHANGE GROUPS.

CAVANAUGH 


&&



.PREV DISCUSSION... /ISSUED 416 AM CST THU MAR 8 2012/
00Z UPPER AIR ANALYSIS INDICATED A CLOSED LOW CENTERED NEAR THE 4
CORNERS REGION. HEIGHT FALLS TO THE EAST OF THIS SYSTEM ARE
RELATIVELY NON-EXISTENT WITH THE ONLY HEIGHT FALLS ALMOST DUE
SOUTH OF THE LOW. THIS WOULD INDICATE THAT THE LOW WILL DRIFT
SOUTH OVER THE NEXT 12-18 HOURS. MODELS SEEM TO BE HANDLING THIS
WELL...MOVING IT SLOWLY TO THE SOUTH AND EAST AND THEN STALLING THE
LOW OVER NEW MEXICO THROUGH SATURDAY. ANOTHER DISTURBANCE IN THE
MAIN FLOW IS MOVING THROUGH THE NORTHERN PLAINS THIS MORNING AND
IS CAUSING A STRONG COLD FRONT TO PUSH SOUTH. LATEST SURFACE
ANALYSIS SHOWS THIS FRONT HAS PUSHED SOUTH OF OKLAHOMA CITY AND
EXTENDS SOUTHWEST INTO CHILDRESS TO NEAR LUBBOCK. THE TIMING IS A
BIT FASTER THAN THE MODELS HAVE INDICATED AND GIVEN PRESSURE RISES
BEHIND THE FRONT ARE APPROACHING 5MB/3HR...THINK THIS FASTER
SOUTHERN PUSH WILL CONTINUE. THEREFORE...SPED UP THE TIMING OF THE
WIND SHIFT IN THE FORECAST BY SEVERAL HOURS. THE EXACT TIMING OF
THE FROPA WILL HAVE A DIRECT EFFECT ON HIGH TEMPERATURES TODAY.
MANY LOCATIONS...ESPECIALLY NORTH OF INTERSTATE 20 WILL SEE THEIR
HIGHS IN THE MORNING HOURS...RIGHT BEFORE THE FROPA. TEMPERATURES
ARE EXPECTED TO FALL 15-20 DEGREES BEHIND THE FRONT...AND SLOWLY
CONTINUE TO FALL DURING THE REMAINDER OF THE DAY.

00Z FWD RAOB CONTINUED TO SHOW A STOUT CAP IN PLACE...BUT THIS EML
HAS LIFTED A BIT FROM YESTERDAYS 12Z SOUNDING. THIS CAP WILL PLAY
A KEY ROLE ON WHEN THUNDERSTORMS WILL DEVELOP TODAY. THINK THE CAP
SHOULD HOLD THINGS MOSTLY STABLE UNTIL THE FRONTAL BOUNDARY
PROVIDES ENOUGH LOCALIZED FORCING TO LIFT/BREAK THE CAP. THE 00Z
NAM SEEMED TO HAVE PROBLEMS WITH ITS CONVECTIVE SCHEME AS IT
QUICKLY ERODED THE CAP BETWEEN 15Z AND 18Z ACROSS THE CWA. BECAUSE
OF THIS THE MODEL WAS OUTPUTTING WIDESPREAD QPF IN THE WARM
SECTOR SOUTH OF THE APPROACHING FRONTAL BOUNDARY. THIS DIDNT SEEM
LIKELY...AND STUCK CLOSER TO THE GFS AND THE SUITE OF HIGH
RESOLUTION MODELS /WRF...HRRR...RUC/ THAT ARE MORE EQUIPPED WITH
CONVECTIVE MODELING.

SHOWERS AND ISOLATED THUNDERSTORMS ARE ONGOING ACROSS OKLAHOMA AND
THE EASTERN TEXAS PANHANDLE. THIS CONVECTION IS FORMING JUST
BEHIND THE FRONTAL BOUNDARY...AS WARM MOIST AIR IS LIFTED OVER
THE FRONT. AS THE FRONTAL BOUNDARY PROPAGATES SOUTH...IT INCREASES
THE SLOPE OF THE ISENTROPIC SURFACES. AS THE WARM MOIST AIR
ASCENDS UP THE SURFACE...THE CAP LIFTS/BREAKS AND PRECIP IS
ALLOWED TO FORM. GIVEN THAT THE LATEST MESOANALYSIS ACROSS NORTH
TEXAS STILL SHOW CIN VALUES BETWEEN 200-500 J/KG...THINK THIS
SCENARIO OF PRECIP FORMING JUST BEHIND THE FRONTAL BOUNDARY WILL
LIKELY CONTINUE THROUGH THE DAY. THE MAIN UPPER LOW REMAINS WELL
TO OUR WEST...AND COOLING OF THE EML IS NOT EXPECTED FROM DEEP
SYNOPTIC LIFT. LOW LEVEL LAPSE RATES ARE RATHER POOR...AROUND 5
C/KM...BUT ONCE THE UPDRAFTS BECOME ESTABLISHED IN THE MID-LEVELS
WHERE LAPSE RATES WILL BE NEAR 8 C/KM...THEN THE UPDRAFTS WILL
STRENGTHEN AND BE ABLE TO BE INFLUENCED BY DEEP LAYER SHEAR THAT
IS IN PLACE. A FEW UPDRAFTS COULD ROTATE WHICH WOULD ENHANCE THE
OVERALL SEVERE HAIL POTENTIAL. THINK THE WIND/TORNADO THREAT WILL
REMAIN LOW...BUT IF ANY STORMS DO DEVELOP AHEAD OF THE FRONT...WE
COULD SEE AN ISOLATED EVENT. HOWEVER...STORM MOTION TODAY WILL BE
TO THE NORTHEAST AT 35 TO 40 MPH...AND ANY DISCRETE STORM WOULD
QUICKLY BECOME UNDERCUT BY THE SOUTHWARD MOVING FRONT.

SCATTERED RAIN SHOWERS OR THUNDERSTORMS WILL CONTINUE TONIGHT AND
INTO FRIDAY AS THE UPPER LOW REMAINS NEARLY STATIONARY OVER NEW
MEXICO. THIS ENABLES THE STRONG SOUTHERLY FLOW ALOFT TO CONTINUE 
RISING OVER THE FRONTAL LAYER...ALLOWING SCATTERED ACTIVITY TO
DEVELOP. MID-LEVEL LAPSE RATES TOMORROW WILL ONLY BE 6-6.5 C/KM
AND THE CHANCES FOR SEVERE HAIL WILL BE MUCH LOWER.

SATURDAY...THE UPPER LOW OVER NEW MEXICO WILL FINALLY BEGIN TO
EJECT TO THE NORTHEAST DURING THE DAY. CONFIDENCE CONTINUES TO
INCREASE ON THIS OUTCOME...AS SEVERAL OF THE COMPUTER MODELS NOW
SUPPORT THIS SOLUTION. AS THE LOW MOVES NORTHEAST...WIDESPREAD LIFT
WILL OVERSPREAD THE REGION ALLOWING NUMEROUS SHOWERS AND
THUNDERSTORMS TO DEVELOP. THE 850 FRONT IS EXPECTED TO SET UP
FROM NORTH TO SOUTH ACROSS OUR WESTERN ZONES BY SATURDAY AND THE
EXACT POSITIONING OF THE ELEVATED BOUNDARY WILL PLAY A KEY ROLE ON
THE POSITIONING OF HEAVY RAINFALL. TO THE EAST OF THE BOUNDARY...850
WINDS ARE EXPECTED TO BE FROM THE SOUTH AT 35-40 KNOTS. THIS WILL
ALLOW RICH GULF MOISTURE TO STREAM NORTH INTO THE REGION.
FORECASTED PW VALUES SATURDAY ARE IN THE 1.2-1.4 INCH RANGE WHICH
IS ABOUT 2 STANDARD DEVIATIONS ABOVE NORMAL. THE HIGHER VALUES
WILL BE LOCATED IN OUR EASTERN ZONES AND THIS IS WHERE THE
HEAVIEST PRECIP IS EXPECTED. FRONTOGENESIS WILL ALSO BE A SOURCE
OF MESOSCALE LIFT WHICH COULD ENHANCE PRECIP TOTALS ON THE WARM
SIDE OF THE 850 FRONT. CONFIDENCE IS INCREASING THAT AREAS TO THE
EAST OF INTERSTATE 35 CORRIDOR COULD RECEIVE IN EXCESS OF 3 TO 5
INCHES FOR THE ENTIRE EVENT BEGINNING TODAY...WITH MOST OF THESE
TOTALS FALLING ON SATURDAY. THE CANADIAN MODEL AND SOME SREF
MEMBERS HOLD ONTO THE UPPER LOW A BIT LONGER BEFORE EJECTING IT ON
SUNDAY...AND DIDNT WANT TO ISSUE A FLASH FLOOD WATCH FOR SATURDAY
UNTIL CONFIDENCE IS A BIT HIGHER. NEVERTHELESS...A SIGNIFICANT
RAIN EVENT IS BECOMING MORE APPARENT FOR THIS WEEKEND.

THINGS ARE EXPECTED TO DRY OUT BY MONDAY...AS SOUTHERLY WINDS
RETURN TO THE SURFACE...AND ANY REMAINING SHORTWAVES ARE WELL TO
OUR EAST. THE UPPER FLOW WILL BECOME MORE ZONAL FOR THE FIRST HALF
OF NEXT WEEK...AND WE SHOULD SEE A FEW DAYS OF DRY WEATHER. 

85/NH



&&


.PRELIMINARY POINT TEMPS/POPS...
DALLAS-FT. WORTH, TX  69  41  47  40  50 /  90  60  60  70  80 
WACO, TX              77  44  49  40  51 /  60  80  70  70  80 
PARIS, TX             68  42  53  43  52 / 100  90  50  70  90 
DENTON, TX            66  43  46  42  51 /  90  50  50  70  80 
MCKINNEY, TX          68  42  50  42  50 /  90  60  50  70  80 
DALLAS, TX            70  42  49  43  52 /  90  60  60  70  80 
TERRELL, TX           72  43  50  41  51 /  90  70  60  70  80 
CORSICANA, TX         75  45  50  42  49 /  70  80  70  70  80 
TEMPLE, TX            78  44  47  41  50 /  50  90  80  70  80 
MINERAL WELLS, TX     67  40  44  41  49 /  80  50  60  60  60 

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR TXZ091-092-100>103-
115>118-129>133-141.


&&

$$

69/85