FXUS64 KJAN 262034
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
230 PM CST THU NOV 26 2008
.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)...THE PRIMARY WEATHER
CONCERN FOR THIS PERIOD WILL BE FOR THE LATE SEASON FREEZE ISSUE FOR
THE LOW TEMPERATURES FOR FRIDAY MORNING. ALSO TO DETERMINE WHETHER
THE FREEZE WARNING NEEDS TO BE EXPANDED IN AREA.
LATEST SATELLITE SHOWS A SHARP COOL TROF EXTENDING FROM THE GREAT
LAKES TO THE LOWER MISSISSIPPI VALLEY. THIS WAS PROVIDING A DIRECT
ROUTE OF COOL AIR FROM CANADA. SURFACE HIGH PRESSURE(1029MB) WAS
CENTERED OVER THE SOUTHERN PLAINS. TEMPS ACROSS THE REGION WERE IN
THE UPPER 50S TO LOWER 60S. THE PRESSURE GRADIENT ACROSS THE REGION
WAS PROVIDING SOME GOOD COLD ADVECTION GUSTY WINDS ACROSS THE
REGION...ESPECIALLY ON AREA LAKES. GUSTY WINDS WERE PROBABLY
APPROACHING 25 MPH ON AREA LAKES.
HIGH PRESSURE WILL CONTINUE TO BUILD ACROSS THE REGION FROM THE WEST.
IN THE WAKE OF THE COLD FRONT THAT PASSED THROUGH THE REGION
OVERNIGHT INTO EARLY THIS MORNING. DRY NORTHWESTERLY FLOW ALOFT WILL
KEEP CLEAR SKIES IN THE FORECAST FOR TONIGHT...AND CONTINUE INTO THE
START OF THE WEEKEND.
FRIDAY LOOKS TO BE THE COLDEST MORNING FOR THIS FALL SEASON ACROSS THE
ARKLAMISS. MAV...NAM AND MOS GUIDANCE HAVE CONTINUED TO TREND TOO WARM
WITH LOWS...ESPECIALLY EAST OF INTERSTATE 55. SO WENT WITH CURRENT
TEMPERATURE FORECAST...EXCEPT EXTENDED FREEZING TEMPS INTO LEFLORE
COUNTY. SO WITH CLEAR SKIES...LIGHT WINDS...GOOD RADIATIONAL COOLING
AND DRY SOIL DECIDED TO KEEP THE CURRENT FREEZE WARNING IN EFFECT
WITH THE ADDITION OF LEFLORE COUNTY. EXPECT LOW TEMPS NEAR 30 FOR
MOST AREAS EAST OF I-55 ALTHOUGH THE FARTHER WE GET INTO SOUTHERN MS
THE TOUGHER IT WILL BE TO GET TO 30. TEMPS CLOSER TO 31 OR 32 ARE
EXPECTED IN THESE AREAS. A TRICKY FORECAST ENSUES WEST OF I-55.
TEMPS GENERALLY EXPECTED TO APPROACH 32 EXCEPT NEAR AND SOUTH OF
NATCHEZ...AS WELL AS IN THE DELTA NORTH OF VICKSBURG WHERE LOW TEMPS
AT OR ABOVE 33 ARE EXPECTED. SO IT SHOULD BE EASIER TO MEET THE FREEZE
WARNING CRITERIA EAST OF INTERSTATE 55 AND NORTH OF HATTIESBURG.
MEETING THE DURATION OF THE FREEZE WARNING MAY BE A PROBLEM IN THE SOUTH
FOR TONIGHT...BUT FEEL THAT WITH FAVORABLE CONDITIONS WILL GO AHEAD
AND GO FOR IT.
THE REST OF FRIDAY WILL BE NICE ONCE AGAIN WITH CLEAR SKIES AND HIGH
TEMPS JUST BELOW SEASONAL NORMS. SATURDAY MORNING WILL BE WARMER
THAN FRIDAY AS RETURN FLOW GRADUALLY SETS UP ACROSS THE CWA. NEAR
FREEZING TEMPS WILL STILL BE POSSIBLE ACROSS FAR EASTERN
ZONES...GENERALLY WENT WITH CURRENT FORECAST AS MAV GUIDANCE WAS A LITTLE
WARM.
FOR SATURDAY AND SATURDAY NIGHT...THE UPPER FLOW WILL HAVE DEVELOPED
INTO A FLAT UPPER RIDGE PATTERN. SOUTHWEST FLOW ALOFT WILL BEGIN TO
RETURN SOME MID TO UPPER LEVEL MOISTURE ACROSS THE REGION IN THE FORM
OF MID TO UPPER LEVEL CLOUDS. WITH RETURN FLOW COMING BACK TO THE REGION
TEMPS WILL RISE TO A LITTLE ABOVE NORMAL WITH HIGHS IN THE MID TO
UPPER 60S. LOWS FOR SATURDAY NIGHT WILL RISE TO ABOVE NORMAL WITH LOWS
IN THE LOWER 40S TO AROUND 50. ON BOTH PERIODS WENT CLOSE TO MAV
GUIDANCE./17/
/.PREVIOUS DISCUSSION...
LONG TERM...SUNDAY THRU WEDNESDAY...GFS AND ECMWF TEND TO AGREE
EARLY IN THE PERIOD WITH A SPLIT FLOW REGIME TAKING SHAPE ACROSS THE
CONUS. SIGNIFICANT MID LEVEL PIECE OF ENERGY BREAKS OFF IN TROF
MOVING THRU THE WESTERN STATES AND DEEPENS INTO A CUT OFF LOW OVER
NRN MEXICO WHILE NRN STREAM TROF PULLS AWAY ACROSS THE NRN TIER OF
STATES. THIS NRN STREAM TROF WILL ALLOW A RATHER SHALLOW SURFACE
FRONT TO SLIDE THRU THE AREA SUNDAY NIGHT AND MONDAY. STRONG WARM
ADVECTION SETS UP IN ADVANCE AND WITH THE PASSAGE OF THE FRONT
MAINLY BELOW 600 MB. INSTABILITY LOOKS VERY LIMITED (MUCAPES BLO 300
J/KG)...BUT WITH STRENGTH OF THE FORCING BELIEVE SOME THUNDER WILL
BE SEEN.
ISENTROPIC LIFT LOOKS TO WANE MONDAY NIGHT AS S/W RIDGING
TEMPORARILY BUILD INTO THE AREA. MODELS DIVERGE FROM HERE ON HOW SRN
STREAM SYSTEM PROGRESSES THRU THE AREA. ECMWF AS WELL AS MAJORITY OF
GFS ENSEMBLE MEMBERS HAVE THE MID LEVEL CUT OFF LOW OPEN UP AND
BEGIN PHASING WITH SECONDARY MID LEVEL WAVE DIVING RAPIDLY SOUTH OUT
OF CANADA...WHILE THE OPERATIONAL GFS STILL WANTS TO MAINTAIN THE
LOW AS CUT OFF. ACTUALLY...LOOKING AT THE NEW 06Z RUN...THE
OPERATIONAL GFS IS BEGINNING TO COME INTO MORE ALIGNMENT WITH THE
REST OF THE ENSEMBLE AND ECMWF. REGARDLESS OF THE EXACT SCENARIO OF
THE LIFTING OUT LOW...DEEP ISENTROPIC LIFT WILL GET UNDERWAY ONCE
AGAIN TUESDAY AS THE LOW/OPEN TROF MOVE ACROSS THE AREA. GFS MODEL
SOUNDINGS SHOWING SOME POSSIBILITY OF SOME CONVECTIVE SNOW SHOWERS
OVER THE NRN CWA WEDNESDAY AS THE COLD CORE MOVES THRU. WONT MENTION
IN THE FORECAST YET...BUT WILL HAVE TO WATCH FUTURE MODEL RUNS FOR
CONSISTENCY./GRG/
&&
.AVIATION...VFR CONDITIONS WILL CONTINUE THROUGH THE PERIOD AS HIGH
PRESSURE CENTERED OVER TEXAS CONTINUES TO MOVE TO THE EAST TOWARDS
THE ARKLAMISS. THE WINDS WILL QUICKLY DIMINISH AFTER SUNSET THIS
EVENING WITH LIGHT AND VARIABLE WINDS OVERNIGHT. COLD TEMPS CAN BE
EXPECTED TOMORROW MORNING...WITH FREEZING CONDITIONS OVER MUCH OF
THE AREA. /15/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 31 61 37 67 / 0 0 0 6
MERIDIAN 30 60 32 66 / 0 0 0 6
VICKSBURG 31 62 39 69 / 0 0 0 6
HATTIESBURG 31 62 35 66 / 0 0 0 4
NATCHEZ 33 61 40 66 / 0 0 3 7
GREENVILLE 33 60 41 67 / 0 0 0 6
GREENWOOD 31 60 38 66 / 0 0 0 5
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...FREEZE WARNING FROM 4 AM TO 8 AM CST FRIDAY FOR MSZ025>033-
036>040-042>059-061>066-072>074.
LA...FREEZE WARNING FROM 4 AM TO 8 AM CST FRIDAY FOR LAZ007>009-015-
016-023-025.
AR...NONE.
&&
$$
