FXUS64 KJAN 280325 AAA
AFDJAN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
925 PM CST FRI NOV 27 2009

.UPDATE...
MINOR CHANGES WERE MADE WITH THE TEMPERATURE AND SKY COVERAGE 
FORECASTS FOR TONIGHT.

MID-EVENING SURFACE ANALYSIS PLACES A 1023 MB SURFACE HIGH OVER THE 
NORTH CENTRAL GULF...WITH AN ASSOCIATED RIDGE AXIS EXTENDING 
NORTHEASTWARD OVER EASTERN MISSISSIPPI AND WESTERN ALABAMA. WEST OF 
THIS AXIS...WEAK SOUTHERLY RETURN FLOW WAS GRADUALLY ADVECTING 
SLIGHTLY HIGHER BOUNDARY LAYER MOISTURE NORTHWARD ACROSS NORTHEAST 
LOUISIANA AND SOUTHEAST ARKANSAS. SURFACE DEWPOINTS ACROSS THIS AREA
ARE AROUND 40...WITH DEWPOINTS IN THE MID AND UPPER 30S FURTHER TO
THE EAST NEAR THE RIDGE AXIS. FOR TONIGHT...TEMPERATURES WILL COOL
INTO THE LOWER 30S ACROSS EASTERN AREAS...ESPECIALLY AS DEWPOINTS
DROP IN RESPONSE TO FROST FORMATION. LATEST INFRARED SATELLITE
IMAGERY DEPICTS MID/HIGH-LEVEL CLOUDS STREAMING NORTHWARD IN
ASSOCIATION WITH A SHARP UPPER-LEVEL SHEAR AXIS. THESE CLOUDS WILL
PROVIDE SOME MITIGATING FACTOR FOR HOW MUCH TEMPERATURES FALL ACROSS
SOUTHERN AREAS. ALSO...HIGHER DEWPOINTS OVER WESTERN AREAS AND LACK
OF FROST FORMATION WILL KEEP TEMPERATURES FROM FALLING BELOW 40. THE
ONLY CHANGE MADE TO OVERNIGHT LOWS WAS TO DROP TEMPERATURES ACROSS
CENTRAL MISSISSIPPI BY A DEGREE OR TWO...WHERE ONSET OF THICKER
CLOUDS WILL BE DELAYED UNTIL AFTER DAWN. CORRESPONDINGLY...HOURLY
TEMPERATURES WERE ADJUSTED. THIS YIELDS OVERNIGHT LOWS RANGING FROM
THE LOWER 30S ACROSS EASTERN AREAS TO NEAR 40 IN THE WEST. SKY
COVERAGE WAS ALSO INCREASED ACROSS SOUTHERN AREAS THROUGH THE
NIGHT...AS THE SHEAR AXIS AND ASSOCIATED UPPER-LEVEL ASCENT AND
MOISTURE APPROACH. WITH THE INCREASED CLOUD COVERAGE AND ANTICIPATED
FALL IN BOUNDARY LAYER DEWPOINTS...FOG FORMATION IS UNLIKELY... WITH
THE POTENTIAL RESTRICTED TO SOUTHEAST MISSISSIPPI NEAR HATTIESBURG.
/COHEN/

&&

.PREV DISCUSSION... /ISSUED 249 PM CST FRI NOV 27 2009/ 

SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)...
THE PRIMARY WEATHER CONCERN WILL BE OUR CHANCE OF SHOWERS WITH A 
COLD FRONT FOR THE SUNDAY-SUNDAY NIGHT TIME RANGE. ALSO IF ANY 
INSTABILITY WILL BE WITH THIS SYSTEM.

LATEST SATELLITE IMAGERY SHOWS AN UPPER RIDGE BUILDING TOWARD THE 
REGION FROM THE SOUTHERN PLAINS AS WE REMAIN UNDER DRY NORTHWEST 
FLOW ALOFT. A BLANKET OF MID TO MOSTLY HIGH CLOUDS WAS ASSOCIATED 
WITH THE UPPER RIDGE. SOME OF THOSE HIGH CLOUDS WERE BEGINNING TO 
ENTER THE SOUTHERN PORTION OF THE REGION. 

FOR TONIGHT THROUGH SATURDAY NIGHT...SURFACE HIGH PRESSURE WILL MOVE 
EAST OF THE REGION DURING THE PERIOD AS MID TO HIGH LEVEL CLOUDS MOVE 
ACROSS THE REGION. NORTHWESTERLY FLOW ALOFT WILL GRADUALLY BECOME 
WESTERLY AND EVENTUALLY SOUTHWESTERLY BY SATURDAY AS A WEAK SOUTHERN 
STREAM S/WV CROSSES THE GULF COAST. THIS WILL HELP TO KEEP THE MID 
TO HIGH LEVEL CLOUDS AROUND. LOOKING AT TEMPS FOR THE DRY PERIOD. 
FOR TONIGHT WENT WITH MOS GUIDANCE WHICH BRINGS ONE MORE ROUND OF 
FREEZING TEMPS FOR THE EASTERN COUNTIES. EVEN WITH THE HIGH CLOUDS 
AROUND BELIEVE THAT IT SHOULD BE ABLE TO REACH IT WITH THE DRY 
DEWPOINTS AROUND. FOR SATURDAY WITH RETURN FLOW AROUND AND 850 TEMPS 
PUSHING TOWARD 10C...READINGS SHOULD REBOUND INTO THE LOWER TO UPPER 
60S. THIS IS SUPPORTED BY AFTERNOON READINGS IN THE MID TO UPPER 60S 
ACROSS THE ARKLATEX REGION...WHICH WILL COME TO OUR REGION ON 
SATURDAY. WENT CLOSE TO MAV GUIDANCE. FOR SATURDAY NIGHT EXPECT 
CLOUDS TO GRADUALLY INCREASE IN COVERAGE AHEAD OF THE APPROACHING 
SYSTEM COMING FROM THE PLAINS. WE SHOULD BE ABLE TO REACH THE UPPER 
30S IN THE EAST WITH 40S ELSEWHERE. WENT CLOSE TO THE COOLER MOS 
GUIDANCE.

FOR SUNDAY INTO SUNDAY NIGHT. THE SREF...EUROPEAN...NAM...GFS AND UKMET
HAVE SLOWED THE RAIN TIMING WITH THE SUNDAY NIGHT-MONDAY FRONTAL 
SYSTEM AND ASSOCIATED SHORT WAVE. MODELS STILL SHOW THAT THE INSTABILITY
WITH THIS SYSTEM WILL BE QUITE WEAK. IN THE ISENTROPIC DEPARTMENT
THERE WILL BE SOME PRETTY GOOD ISENTROPIC LIFT...SOME ISENTROPIC NET 
OMEGA...SOME GOOD GENERAL INCREASING GENERAL OMEGA AHEAD AND BEHIND THE 
FRONT. PRECIPITABLE WATER WILL INCREASE TO AROUND 1.5 INCHES.  THIS 
SHOULD PROVIDE SOME PRETTY GOOD RAIN COVERAGE FOR SUNDAY NIGHT. MOS 
POPS LOOKED A LITTLE HIGH FOR SUNDAY...SO CUT BACK ON POPS FOR 
SUNDAY. WENT CLOSE TO MOS HIGH POPS FOR SUNDAY NIGHT. AS FAR AS 
TEMPS ARE CONCERN 850 TEMPS WILL BE IN THE 9-11C RANGE. SO TEMPS 
WILL BE IN MIDDLE 60S TO LOWER 70S. WENT CLOSE TO MAV GUIDANCE. FOR 
SUNDAY NIGHT TEMPS WILL CONTINUE TO MODERATE WITH LOWS FROM THE 
LOWER TO MIDDLE 50S. WENT CLOSE TO MAV GUIDANCE AS THE GMOS GUIDANCE 
LOOKED TOO COOL./17/ 

/PREVIOUS DISCUSSION...LONG TERM...MONDAY THRU THURSDAY...THE 
FORECAST PROBLEM DURING THIS PERIOD IS THE EVOLUTION OF MID LEVEL 
CUTOFF LOW OVER THE NRN BAJA OF CA AT 12Z SUNDAY AND THE 
DISASSOCIATED MID LEVEL TROF PULLING AWAY OVER THE NRN PLAINS. 

ALTHOUGH SUBTLE DIFFERENCES DO EXIST...GFS...GFS ENSEMBLE AND ECMWF
ARE ALL IN REASONABLE GOOD AGREEMENT DURING THIS TIME PERIOD.
DISASSOCIATED MID LEVEL TROF PULLING AWAY FROM THE CUTOFF LOW WILL
CONTINUE TO TRANSITION EAST...DEEPENING AS IT DOES SO. THIS FEATURE
WILL DRAG A FRONT INTO THE AREA BY SUNDAY NIGHT/MONDAY. UNTIL IT DOES
SO...PERSISTENT SWLY FLOW WILL SLOWLY MOISTEN THE ATMOSPHERE IN
STEADILY INCREASING DEEP LAYER WARM AIR ADVECTION. BEST ISENTROPIC
LIFT LOOKS TO GET GOING JUST ALONG AND BEHIND THE FRONT AS IT ENTERS
THE AREA MOVING INTO MONDAY MORNING. WHILE OVERALL OMEGA INCREASES
DURING THIS TIME FRAME...MAGNITUDES AND LACK OF INSTABILITY SUGGEST
ADIABATIC MOTIONS WILL DOMINATE WITH A LACK OF DEEP CONVECTION. HAVE
REMOVED THUNDER WORDING PREVIOUSLY IN THE FORECAST.

PRECIP WANES DURING LATE MONDAY NIGHT/TUESDAY MORNING AS FRONT 
STALLS ALONG THE COAST...WINDS VEER AND ISENTROPIC LIFT SHUTS DOWN. 
THIS IS SHORT-LIVED...HOWEVER AS BACKING WINDS DURING THE AFTERNOON 
ALLOW BOUNDARY TO LIFT RAPIDLY BACK NORTH IN RESPONSE TO THE 
APPROACHING COLD CORE LOW MOVING OUT OF TX BY THIS TIME. A SURFACE 
LOW LOOKS TO DEVELOP OVER THE NRN GULF IN INCREASING WAR 
ADVECTION/ISENTROPIC LIFT WHICH WILL GIVE THE AREA ANOTHER SHOT AS 
SOME SHOWERY ACTIVITY TUESDAY NIGHT ESPECIALLY SOUTH. SHOWERS WILL 
ONCE AGAIN BE POSSIBLE WEDNESDAY AS THE COLD CORE LOW ACTUALLY MOVES 
ACROSS THE CWA. /GRG/ 

&&

.AVIATION...
VFR CONDITIONS ARE EXPECTED THROUGH SATURDAY NIGHT...AS SURFACE HIGH 
PRESSURE DRIFTS EASTWARD ACROSS THE REGION. MID/HIGH-LEVEL CLOUDS 
WILL STREAM NORTHWARD IN ASSOCIATION WITH AN UPPER LEVEL DISTURBANCE 
PASSING NORTH ACROSS THE AREA. PATCHY FOG COULD FORM ACROSS 
SOUTHEAST MISSISSIPPI LATE TONIGHT AND EARLY SATURDAY 
MORNING...RESULTING IN MVFR VISIBILITIES. KHBG HAS THE GREATEST 
CHANCE OF EXPERIENCING THESE CONDITIONS FROM 28/1000 UNTIL 28/1300 
UTC. OTHERWISE...LIGHT WINDS TONIGHT WILL BECOME SOUTHERLY AT 4 TO 9 
KT ON SATURDAY AS SURFACE HIGH PRESSURE MOVES EASTWARD. LOOKING 
FURTHER AHEAD...A COLD FRONT WILL MOVE SOUTHWARD ACROSS THE 
ARKLAMISS FOR SUNDAY NIGHT AND MONDAY...AND NUMEROUS SHOWERS ARE EXPECTED
TO ACCOMPANY THE FRONT. THE FRONT WILL BE FOLLOWED BY AN INCREASE IN
NORTHERLY WINDS. /COHEN/

&&

.PRELIMINARY POINT TEMPS/POPS...
JACKSON       36  65  44  70 /   0   0   3  14 
MERIDIAN      31  66  38  70 /   0   0   0  13 
VICKSBURG     40  66  45  71 /   0   1   8  16 
HATTIESBURG   33  67  44  71 /   0   0   0  12 
NATCHEZ       41  66  46  71 /   0   2   8  15 
GREENVILLE    41  64  45  66 /   0   2   6  24 
GREENWOOD     38  66  42  67 /   0   0   3  20 

&&

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

$$

COHEN/17/GRG