FXUS64 KJAN 120256 AAB
AFDJAN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
855 PM CST FRI DEC 11 2009

.UPDATE...LATEST SATELLITE IMAGERY SHOWS THAT MOISTURE TRANSPORT IS
NOT COMING AS FAST AS EXPECTED FOR THIS EVENING...BUT IT DOES SHOW
SOME ENHANCEMENT OVER THE REGION DURING THE PAST HOUR.  AREA RADARS 
SHOWS SOME MOSTLY LIGHT RAIN TRYING TO MAKE ITS WAY INTO THE REGION 
FROM THE SOUTHWEST. 00Z SOUNDING WAS STILL PRETTY DRY WITH 
PRECIPITABLE WATER OF AROUND .70 INCH. THE LATEST MODELS AND 
RUC...SHOWS THAT THE RAINS WILL MOVE ACROSS MAINLY THE SOUTH HALF OF 
THE REGION AFTER MIDNIGHT.  VAPOR IMAGERY SHOWS SOME ASCENT 
APPROACHING THE REGION FROM SOUTH TEXAS WHERE SOME CONVECTION IS 
TAKING PLACE. EXPECT IT TO REACH THE REGION AFTER MIDNIGHT
...WHICH WILL HELP TO PUSH THE RAINS OVER THE REGION. SO HAVE DELAYED 
THE ONSET OF THE RAINS DURING THE NIGHT. AS FAR AS TEMPS ARE 
CONCERN. THE CLOUD COVER HAS SLOWED DOWN THE FALLING TEMPS ACROSS 
THE REGION. SO HAVE FOLLOWED THE SLOWER DESCENT OF THE 18Z MOS 
GUIDANCE...BUT LEFT CURRENT OVERNIGHT LOWS IN PLACE. STILL HAVE THE 
MOISTURE TRANSPORT ABOVE THE LAYER OF COOL AIR ABOVE THE SURFACE. SO 
STILL EXPECT A SLIGHT WINTRY MIX ACROSS THE NORTH AFTER 
MIDNIGHT...BUT DO NOT EXPECT ANY ACCUMULATION OR TRAVEL ISSUES. THE 
REST OF FORECAST LOOKS TO BE ON TRACK./17/

./PREVIOUS DISCUSSION...405 PM CST FRI DEC 11 2009

.DISCUSSION...

A SUPPRESSED STORM TRACK ALONG THE GULF COAST WILL CONTINUE TO 
MAINTAIN AN ACTIVE/WET WEATHER OVER THE ARKLAMISS FOR THIS WEEKEND 
INTO EARLY NEXT WEEK...BUT EXPECT A QUICK TRANSITION TO A MUCH DRIER 
AND CONTINUED CHILLY WEATHER PATTERN FOR LATE NEXT WEEK AS AN UPPER 
LEVEL RIDGE BUILDS OVER THE WRN CONUS WHILE A TROUGH DEVELOPS IN THE 
EAST. THERE WILL BE TWO STORM SYSTEMS TO FOCUS ON IN THE NEXT 
SEVERAL DAYS...INCLUDING ONE THIS WEEKEND AND ANOTHER FOR MON- 
TUES...BOTH OF WHICH COULD BRING HEAVY RAIN AND RAISE CONCERNS FOR 
FLOODING. 

TONIGHT THROUGH SUNDAY NIGHT...A MID LEVEL SHORTWAVE TROUGH 
APPROACHING IN THE SRN STREAM HAS INCITED WEAK SOUTHERLY FLOW AND 
WARM ADVECTION ABOVE THE SHALLOW COLD AIRMASS CURRENTLY IN PLACE. 
THERE HAS BEEN ENOUGH ISENTROPIC UPGLIDE TO GENERATE VERY LIGHT 
PRECIPITATION WITH A COUPLE OF SLEET REPORTS RECEIVED EARLIER FROM 
JONES COUNTY...BUT BY FAR...THE BETTER SYNOPTIC SCALE FORCING IS 
EXPECTED TO DEVELOP TONIGHT INTO EARLY SATURDAY AS ISENTROPIC 
UPGLIDE AND MOISTURE TRANSPORT INCREASE DRAMATICALLY IN RESPONSE TO 
THE BUCKLING UPPER LEVEL JET. 

SOME EVAPORATIVE COOLING IN THE COLD DRY AIR COULD ALLOW THE INITIAL 
ONSET OF PRECIPITATION TO BE IN THE FORM OF VERY LIGHT 
SLEET/FREEZING RAIN ACROSS NORTH CENTRAL MS LATE TONIGHT AND EARLY 
SATURDAY MORNING. GIVEN THAT THE COLD AIRMASS IS RETREATING...ANY 
LIGHT FREEZING RAIN WILL BE VERY BRIEF WITH NO MORE THAN TRACE 
AMOUNTS EXPECTED AS WARM RAIN PROCESSES BRING SURFACE TEMPERATURES 
QUICKLY ABOVE FREEZING. TRAVEL ISSUES ARE NOT EXPECTED.

PRECIPITABLE WATER WILL INCREASE TO > 1.5 INCHES...AND WITH GFS 
SHOWALTER INDICES ~ -3 INDICATIVE OF SUBSTANTIAL CONVECTIVE 
INSTABILITY...WE COULD SEE SOME HEFTY RAINFALL TOTALS PERHAPS 
REACHING THE TWO TO THREE INCH RANGE BY THE TIME RAIN DIMINISHES 
LATE SAT NIGHT. ALSO...THE POTENTIAL FOR SMALL HAIL WILL EXIST IN 
TSTMS SOUTH OF THE HWY 84 CORRIDOR. THE MODELS HAVE TRENDED STRONGER 
WITH THE WARM ADVECTION AND FRONTOGENETIC FORCING OVER NORTHERN 
PORTIONS OF THE FORECAST AREA...AND THE LATEST GUIDANCE QPF HAS 
DEFINITELY TRENDED FARTHER NORTH. THE LATEST SREF IS NOW HITTING THE 
I-20 CORRIDOR WITH THE GREATEST POTENTIAL FOR EXCEEDING TWO INCHES 
WHILE THE GFS ENSEMBLE MEAN IS NOW HITTING NORTH CENTRAL MS WITH THE 
GREATEST RAINFALL. THERE ARE STILL QUESTIONS REGARDING THE INFLUENCE 
OF CONVECTIVE DEVELOPMENT ALONG THE COAST AND HOW MUCH MOISTURE MAY 
BE INTERCEPTED THERE...BUT FEEL CONFIDENT ENOUGH TO EXTEND THE RISK 
FOR HEAVY RAINFALL NORTH ACROSS THE ENTIRE AREA. THIS RAISES THE 
CONCERN FOR FLOODING AS RIVERS/STREAMS ARE HIGH IN NRN BASINS AND A 
HYDROLOGIC OUTLOOK IS BEING ISSUED TO EXPRESS THIS CONCERN.

ANOTHER QUESTION CONCERNS HOW QUICKLY THE RAIN/TSTMS WILL END 
SATURDAY NIGHT. WHILE THE GREATER LARGE SCALE FORCING WILL BE 
SHIFTING EAST...A WEAK MOISTURE CONVERGENCE AXIS WILL REMAIN AND 
THERE SHOULD BE ENOUGH FORCING FOR AT LEAST LIGHT/MDT SHOWER 
ACTIVITY MUCH OF THE NIGHT...ESPECIALLY OVER CNTRL/ERN MS. EXPECT A 
DRYING TREND FOR SUNDAY WITH MUCH WARMER TEMPS AS WEAK AND MILD HIGH 
PRESSURE MOVES OVER THE AREA. 

LONG TERM...MONDAY THROUGH THURSDAY...DRIER WEATHER WILL CONTINUE 
INTO EARLY MONDAY...BUT ANOTHER SHORTWAVE IS EXPECTED TO RETURN 
INCREASING ISENTROPIC UPGLIDE RAINS BY MONDAY AFTERNOON. THE WARMEST 
TEMPS FOR NEXT WEEK SHOULD ALSO ARRIVE MONDAY WITH 850MB TEMPS OF 
13-14C AND HIGH TEMPS FROM U60S N TO M70S FAR S.

A STRONGER SHORTWAVE IS EXPECTED TO CROSS THE SRN PLAINS MONDAY 
NIGHT EJECTING A MINOR IMPULSE TO 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 AFTERNOON 
THROUGH MONDAY NIGHT AND SCATTERED TSRA SHOULD BREAK OUT OVER MUCH 
OF OUR CWFA. INITIAL QPF SHOULD AVERAGE 1 TO 2 INCHES BUT COULD BE 
HIGHER AND WILL MENTION LOCALLY HEAVY RAINS. HAVE INCLUDED A 
FLOODING HAZARD IN THE GRIDS OUTLOOK WITH MORE IMPRESSIVE RUNOFF 
ISSUES POSSIBLE. PWATS RISE TO 1.6 INCHES MAINLY S OF I-20 WHERE 
MLCAPES BEING PROGGED TO REACH 600-1000 J/KG...SURFACE DEWPTS 
60-65F...SHOWALTER OF -2C AND 7-500MB LAPSE RATES NEAR 6C. THE RIGHT
ENTRANCE REGION OF A 130+KT 200MB JET CORE WILL ASSIST IN THE 
RAINFALL PRODUCTION AS VERTICAL WIND PROFILES ARE EXPECTED TO BE A 
BIT MORE UNIDIRECTIONAL. WILL NEED TO MONITOR THIS TIME FRAME FOR 
TRENDS IN THE MODEL INSTABILITY AND SHEAR FOR THE POTENTIAL OF 
STRONG/SVR TSRA.

THEN...GFS AND ECMWF SHOW A STRONG COLD FRONT DROPPING THROUGH OUR
REGION TUESDAY MORNING WITH COLDER AND DRIER WEATHER DOMINATING FROM 
TUESDAY NIGHT THROUGH THURSDAY. 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 ON WEDNESDAY AND INTO
THE MID SOUTH FOR THURSDAY MORNING.  HAVE LEANED TOWARD THE COLDER
ENSEMBLE MEMBERS IN THE WAKE OF THE FRONT BUT MAY HAVE TO ADJUST
THESE EVEN FURTHER DOWN IN FUTURE PACKAGES. OTHERWISE HAVE STAYED
CLOSE TO MEX MOS THROUGH THE LONGER TERM AS THEY ARE ACTUALLY NEAR
THE ENSEMBLE MEANS AND BELOW CLIMATOLOGY./40/

&&

.AVIATION...WIDESPREAD LIGHT RAIN IS EXPECTED TO ENTER INTO THE 
REGION FROM THE WEST AND SOUTHWEST AFTER MIDNIGHT...LIKELY REACHING 
KGTR/KGWO/KGLH BEFORE DAWN...WHERE THERE WILL BE A SLIGHT CHANCE FOR 
LIGHT SLEET AND LIGHT FREEZING RAIN TO INITIALLY MIX IN WITH THE 
PRECIPITATION BEFORE CHANGING OVER TO ALL RAIN. NO ICE ACCUMULATION 
IS EXPECTED...AND THE RISK FOR WINTRY PRECIPITATION IS TOO SMALL FOR 
MENTION IN THE TAFS AT THIS TIME.  MVFR CONDITIONS DUE TO REDUCED 
CEILINGS AND OCCASIONALLY REDUCED VISIBILITIES WILL ACCOMPANY THE 
RAIN TONIGHT...ESPECIALLY LATE. ON SATURDAY... WIDESPREAD RAIN WILL 
AFFECT THE ENTIRE AREA...WITH EMBEDDED THUNDERSTORMS POSSIBLE ALL 
DAY AND INTO THE EVENING. MVFR TO IFR CEILINGS/VISIBILITIES WILL 
ACCOMPANY THIS ACTIVITY. RAIN SHOULD TRY AND TAPER OFF FROM THE WEST 
LATE SATURDAY NIGHT...BUT MVFR TO IFR CONDITIONS WILL PROBABLY NOT 
BREAK UNTIL LATE MORNING ON SUNDAY AT THE EARLIEST. /17/

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&

$$