FXUS64 KJAN 102154 CCA
AFDJAN
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE JACKSON MS
345 PM CST THU DEC 10 2009
.DISCUSSION...
THE POWERFUL POLAR VORTEX OVER THE NERN CONUS WILL HELP KEEP AN
ACTIVE SOUTHERN STREAM SUPPRESSED SOUTHWARD ACROSS THE GULF COAST
REGION. THIS WILL MAINTAIN AN ACTIVE AND MOSTLY CHILLY WEATHER
PATTERN FOR THE ARKLAMISS. THERE WILL BE TWO STORM SYSTEMS TO FOCUS
ON IN THE NEXT SEVERAL DAYS...INCLUDING ONE THIS WEEKEND WHICH COULD
BRING LOCALLY HEAVY RAINFALL...AND ANOTHER EARLY NEXT WEEK THAT
COULD RESULT IN HEAVIER RAINFALL AND POSSIBLY A FEW STRONG TO SEVERE
THUNDERSTORMS OVER SOUTHERN PORTIONS OF THE AREA.
TONIGHT THROUGH FRIDAY NIGHT...FORECAST MODELS ARE IN GOOD AGREEMENT
THAT STRONG CONFLUENT FLOW ALOFT OVER ERN CONUS WILL HELP MAINTAIN
COLD HIGH PRESSURE OVER THE GULF STATES THROUGH FRIDAY...AND THAT A
SHORTWAVE TROUGH APPROACHING IN THE SRN STREAM WILL INCITE SOUTHERLY
FLOW AND WARM ADVECTION ABOVE THE COASTAL FRONT. PRECIPITABLE WATER
AIRMASS > 1 INCH WILL BE DRAWN NORTH TO ABOUT THE HWY 84 CORRIDOR BY
LATE FRIDAY AFTN. THE RESULTING ISENTROPIC LIFT WILL INITIALLY BE
WEAK LEADING TO A MID CLOUD DECK AND PERHAPS VERY LIGHT
PRECIPITATION BY FRIDAY MORNING OVER SRN PORTIONS OF THE AREA...BUT
GIVEN THE LARGE POTENTIAL FOR EVAPORATIVE COOLING AND VERY CHILLY
AIR IN PLACE...EXPECT THAT LIGHT SLEET WOULD BE PROBABLE AS WELL.
THE VERY LIGHT RA/IP MIX WOULD GRADUALLY SHIFT NORTH INTO NRN
PORTIONS OF THE AREA BY FRIDAY EVNG. EXPECT ANY SLEET FRI/FRI EVNG
TO BE BRIEF AS LATENT HEATING FROM CONDENSATION AND CONTINUED WARM
ADVECTION QUICKLY OVERWHELM THE RETREATING COLD HIGH PRESSURE.
FURTHERMORE...SFC TEMPERATURES ARE EXPECTED TO REMAIN ABOVE FREEZING
AND WE DO NOT EXPECT ANY TRAVEL PROBLEMS ASSOC WITH WINTRY PRECIP
SHOULD IT OCCUR.
SATURDAY THROUGH SATURDAY NIGHT...STRONGER ISENTROPIC LIFT WILL
DEVELOP EARLY SATURDAY MORNING AS SOUTHERLY FLOW INCREASES ABOVE
THE STRONG FRONTAL INVERSION AHEAD OF THE APPROACHING SHORTWAVE
TROUGH. WITH PRECIPITABLE WATER APPROACHING 1.5 INCHES ALONG THE HWY
84 CORRIDOR...EXPECT THAT MDT-HVY PERIODS OF RAIN WILL BE
LIKELY...ESPECIALLY SOUTH OF THE I-20 CORRIDOR WHERE THE 15Z SREF
SHOWS 50-75% 24 HR PROBABILITIES FOR EXCEEDING ONE INCH OF RAINFALL.
IN ADDITION...ELEVATED INSTABILITY WILL BECOME SUFFICIENT FOR
DEVELOPMENT OF DEEP CONVECTION AND THE POSSIBILITY OF THUNDER. RAIN
AND ANY CONVECTION WILL DIMINISH FROM WEST TO EAST LATE SAT-SAT
NIGHT AS THE MID LEVEL TROUGH PASSES BY. /EC/
LONG TERM...SUNDAY THROUGH WEDNESDAY...LONGWAVE TRENDS FAVOR A
CONTRACTION/WEAKENING OF THE POLAR VORTEX IN ERN NORTH AMERICA WHICH
RELAXES THE BROAD MEAN TROUGH AXIS IN THE ERN HALF OF THE CONUS AS WE
TRANSITION TO A FLATTER ZONAL FLOW PATTERN. THE GFS ENSEMBLE MEAN IS
A LITTLE QUICKER TO DRY US OUT SATURDAY NIGHT THAN EITHER THE OPS RUN
OR ECMWF WHICH KEEP SOME POPS THROUGH AT LEAST SUNDAY MORNING. WILL
HOLD ON TO SOME CHANCE OF LIGHT RAINS INCLUDING TSRA OVER SERN MS
SATURDAY NIGHT AND EARLY SUNDAY. DRIER WEATHER IS INDICATED FOR
SUNDAY NIGHT AND EARLY MONDAY BUT ANOTHER SHORTWAVE IS EXPECTED TO
RETURN ISENTROPIC RAINS BY MONDAY AFTERNOON. EXPECT THE WARMEST TEMPS
TO ARRIVE MONDAY WITH 850MB TEMPS OF 13-14C AND SURFACE HIGHS FROM
M60S TO L70S.
THEN...A STRONGER SHORTWAVE IS EXPECTED TO MOVE OVER THE SOUTHERN
PLAINS MONDAY NIGHT AND HELP DEVELOP A SURFACE LOW IN THE NWRN GULF
THAT IS PROGGED TO MOVE ALONG THE GULF COAST LATE MONDAY NIGHT/EARLY
TUESDAY. RAIN CHANCES WILL INCREASE MONDAY NIGHT AHEAD OF THE THIS
SYSTEM AND TSRA SHOULD BREAK OUT OVER AT LEAST SRN HALF OF OUR CWFA.
PWATS RISE TO 1.6 INCHES MAINLY S OF I-20 WHERE MLCAPES BEING PROGGED
TO REACH 500-600 J/KG...SURFACE DWPTS 60-65F AND 7-500MB LAPSE RATES
NEAR 6C. WIND SHEAR EXPECTED TO BE MORE MARGINAL AND WILL NEED TO
MONITOR THIS TIME FRAME FOR TRENDS IN THE MODEL INSTABILITY AND
SHEAR FOR THE POTENTIAL OF STRONG/SVR TSTMS. INITIAL QPF SHOULD
AVERAGE 1 TO 2 INCHES BUT COULD BE HIGHER IN SERN MS. THEN...GFS AND
ECMWF SHOW A STRONG COLD FRONT DROPPING INTO OUR REGION TUESDAY
MORNING WITH COLDER AND DRIER WEATHER DIVING IN TUESDAY NIGHT AND
WEDNESDAY. THE COLDER AIR MASS FROM THE CENTRAL PLAINS REMAINS QUITE
STOUT AS IT CROSSES OVER A LARGE SNOWPACK WITH A 1040MB HIGH CENTER
DROPPING DOWN THE MO VALLEY FOR WEDNESDAY. HAVE LEANED TOWARD THE
COLDER ENSEMBLE MEMBERS IN THE WAKE OF THE FRONT BUT OTHERWISE HAVE
STAYED CLOSE TO MEX MOS THROUGH THE LONG TERM./40/
&&
.AVIATION...
WIDESPREAD VFR CONDITIONS ARE EXPECTED THROUGH FRIDAY MORNING. A
SCATTERED TO BROKEN DECK OF HIGH-LEVEL CLOUDS WITH BASES BETWEEN 15
AND 25 KFT WILL AFFECT THE REGION (ESPECIALLY SOUTH OF I-20) FRIDAY.
NORTHERLY WINDS AT 8 TO 14 KT (AND OCCASIONALLY GUSTY) ARE EXPECTED
TODAY BEFORE BECOMING NORTHEASTERLY TONIGHT AND DECREASING TO 4 TO 8
KT. RAIN WILL BECOME WIDESPREAD FOR FRIDAY NIGHT INTO SATURDAY...
WITH MVFR CEILINGS/VISIBILITIES EXPECTED IN ADDITION TO A SLIGHT
CHANCE FOR THUNDERSTORMS ALONG AND SOUTH OF THE INTERSTATE 20
CORRIDOR. /BB/COHEN/
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
EC/BB/COHEN/40
