FXUS64 KJAN 041037
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
437 AM CST FRI DEC 4 2009
...EARLY SEASON SNOW EXPECTED ACROSS SOUTH TONIGHT...
.SHORT TERM...THE HOPE IN ARRIVING TONIGHT WAS FOR SOME CONSISTENCY
IN THE FORECAST GUID WHICH WOULD ALLOW FOR A SMOOTH TRANSITION INTO
THIS EVENT. I SHOULD HAVE KNOW THAT IS NEVER THE CASE AND BASICALLY
THAT IS HOW THINGS ARE NOW. THE FOCUS OF THIS FORECAST REMAINS ON
THE POTENTIAL SNOW EVENT TONIGHT. A LOT MORE QUESTION MARKS HAVE
RETURNED AS THE TREND WITH ALL OF THE GUID WAS TO BACK OFF ON SNOW
AMOUNTS THUS BACKING OFF ON THE POTENTIAL FOR SNOW AT ALL FOR A GOOD
PORTION OF THE CWA.
THE OVERALL PATTERN IS BASICALLY THE SAME WITH WHAT HAS BEEN
DISCUSSED IN PREV FORECASTS. WE HAVE STRONG SFC HIGH PRESSURE TO OUR
NW WHICH IS ALLOWING FOR STEADILY BUILDING 1022-1025MB PRESSURE INTO
THE REGION. THE AIR ASSOCIATED WITH THIS AIRMASS IS QUITE COLD WITH
MANY TEENS AND SOME SINGLE DIGITS OVER THE PLAINS NEAR THE CORE OF
THIS AIRMASS. TEMPS ACROSS OUR AREA THIS MORNING HAVE NOT ACHIEVED
POTENTIAL LOWS THANKS TO SOME PESKY LOW CLOUDS AND A NICE VAIL OF
HIGH CLOUDS ALONG WITH SOME LIGHT NORTHERLY WINDS. THE DRIVING
FEATURE FOR THIS SYSTEM IS THE STRONG S/W DROPPING TROUGH THE BASE
OF THE LONG WAVE TROUGH WHICH WILL SEEN SOLID HEIGHT FALLS OUR WAY.
THERE WILL BE A SFC LOW TAKE SHAPE ACROSS THE N GULF WHICH WILL
DEEPEN AND TRACK NE THROUGH THE N GULF AS THE S/W PASSES THROUGH THE
AREA. AS THESE FEATURES COMBINE...WE WILL SEE SOME LIGHT PRECIP
BREAK OUT AS STRONG ASCENT UTILIZES THE AVAILABLE MOISTURE. THE
LATEST GUID IS A BIT FASTER WITH THE BEST LIFT WHICH IS PRIMARILY
FOCUSED BETWEEN 00Z AND 08Z. THIS SHOULD RESULT IN THE PRIMARY TIME
FOR ANY SNOW TO BE BETWEEN 7PM AND 2AM TONIGHT. ONE REASON GUID HAS
BACKED OFF ON THE AMOUNTS IS DUE TO THE GULF LOW BEING A BIT FURTHER
S/SE. ALSO...I THINK THE MODELS HAVE PICKED UP ON THE FACT THAT
THERE WILL REMAIN SOME DRIER AIR AT AND BELOW 850MB WHICH WILL HELP
TO EVAP A LOT OF THE FALLING PRECIP/SNOW. ALSO...THE PRIMARY LIFT
WITH THIS SYSTEM WILL BE AT OR ABV 600MB...SOMEWHAT REMOVED FROM THE
HIGHEST MOISTURE CONTENT. THE LIFT WILL BE IN A FAVORED DENDRITIC
GROWTH AREA FOR EFFICIENT SNOW PRODUCTION...BUT THE FALLING SNOW
WILL FIGHT THE BATTLE IN THE LOWER PART OF THE ATMS AND
ULTIMATELY...ACCUMULATIONS AND SNOWFALL RATES WILL SUFFER. THIS IS
ALL SUPPORTED THE LATEST GUID WHICH HAS DRAMATICALLY BACKED OFF ON
PROBABILITIES OF SEEING >1 IN AND EVEN BACKED OFF ON SEEING
MEASURABLE SNOW.
SO WHAT I EXPECT IS FOR THE BEST POTENTIAL FOR MEASURABLE SNOW TO BE
FOR AREAS S OF I-20. INITIALLY LIGHT RAIN WILL FALL THEN QUICKLY MIX
WITH LIGHT SNOW AND THEN TURN TO ALL LIGHT SNOW. THERE COULD BE A
BRIEF PERIOD OF MOD SNOW FOR THAT S 1/3 AS THE SYSTEM PROGRESSES
E-WARD. AREAS ALONG AND JUST N OF I-20 WILL ONLY SEE A LIGHT DUSTING
AT BEST AND LOCATIONS THROUGH THE HWY 82 CORRIDOR WILL LIKELY JUST
SEE FLURRIES AND POSSIBLY NOTHING AT ALL. WITH THAT...I HAVE MADE
THE PREV WATCH AREA A WINTER WX ADV FOR SNOW. SNOW TOTALS WILL BE
LIGHT AND AROUND 1 IN AT BEST. LIGHT ACCUM ON GRASSY/ELEVATED SFC'S
WILL BE THE MAIN ISSUE WITH SOME ELEVATED RDS POSSIBLY SEEING SOME
SLUSHY CONDITIONS. THE SNOW LOOKS TO BE OUT OF THE AREA FASTER WITH
PRECIP ENDING BY 3-4 AM.
NOW FOR SPECIFICS ON THE MAIN FORECAST ELEMENTS. TEMPS TODAY HAVE
TRENDED COOLER WITH THE LATEST GUID AND THAT MAKES SENSE. I ACTUALLY
LOWERED HIGHS TEMPS EVEN MORE FOR SOME OF THE CWA. THERE WILL BE A
CONTINUOUS VAIL OF MID CLOUDS FOR THE FIRST 1/2 OF TODAY WHICH WILL
THICKEN QUICKLY DURING THE AFTERNOON WITH A GOOD DEAL OF VIRGA
FALLING AND HELPING TO COOL THE COLUMN RATHER QUICKLY. I THINK THIS
WILL SERVE TO KEEP TEMPS DOWN CLOSER TO ENSEMBLE VALUES. GUID HAS A
GOOD HANDLE ON TEMPS TONIGHT AND I HAVE FOLLOWED. FOR SAT...FULL
SUNSHINE WILL EXIST AND THAT WILL ALLOW FOR A WARMUP. HOWEVER...CAA
WILL STILL BE OCCURRING...ALBEIT WEAK WHICH WILL LEAD TO CONTINUED
COOL CONDITIONS. I FOLLOWED THE COOLER NAM/ENSEMBLE MOS WHICH WAS A
BIT WARMER THAN PREV FORECAST HIGHS. I HAD TO WARM THOSE FROM
EARLIER THOUGHTS AS WE WILL NOT BE EXPECTING SNOW COVER TO LINGER
MUCH IF AT ALL INTO SAT MORNING. FOR SAT NIGHT...CONDITIONS WILL BE
COLD BUT LIKELY NOT REACH FULL POTENTIAL DUE TO INCREASING CIRRUS
LATE IN THE NIGHT. HOWEVER...I DID LEAN TO COOLER READINGS BASED OFF
THE NAM/ENSEMBLE MOS.
AS FOR POPS TODAY/TONIGHT. GUID HAS COME IN MUCH LOWER THAN PREV
RUNS FOR TONIGHT. AND I BASICALLY FOLLOWED SUIT. THE EXCEPTION BEING
THE S 1/3 WHERE I LEFT THE 80-100% GOING. FOR LATE AFTERNOON
TODAY...I FOLLOWED THE GUID VALUES IN THE W/SW DUE TO THE POSSIBLE
EARLY ONSET. NO PRECIP CHANCES EXPECTED SAT OR SAT NIGHT. /CME/
.LONG TERM...SUNDAY THROUGH NEXT FRIDAY...MODELS CONTINUE TO
INDICATE A RATHER ACTIVE PATTERN ACROSS THE LOWER MISSISSIPPI RIVER
VALLEY THROUGH THE FORECAST PERIOD. TEMPERATURES WILL WARM SLIGHTLY
ON SUNDAY WHILE BOTH CLOUDS AND RAIN CHANCES INCREASE THROUGH THE
AFTERNOON AND OVERNIGHT HOURS AHEAD OF A WEAK COLD FRONT. THIS
FRONT IS PROGGED TO MOVE INTO AND THROUGH THE FORECAST AREA MONDAY
MORNING...AND EVENTUALLY STALL ACROSS THE NORTHERN GULF OF MEXICO
MONDAY AFTERNOON...ALLOWING THE CWA TO BRIEFLY DRY OUT.
ON TUESDAY...RAIN CHANCES REMAIN FAIRLY HIGH ACROSS THE FORECAST
AREA AS THE ONCE STALLED FRONT BEGINS TO LIFT NORTHWARD. THIS IS
IN RESPONSE TO A FAST MOVING UPPER LEVEL LOW SWINGING EAST ACROSS
THE CENTRAL PLAINS INTO THE MID MISSISSIPPI RIVER VALLEY...AND THE
DEEPENING SURFACE LOW ASSOCIATED WITH IT DOING THE SAME. AS THE
WARM FRONT LIFTS NORTHWARD...MOISTURE WILL ALSO SURGE NORTHWARD INTO
THE FORECAST AHEAD OF A STRONG WESTWARD MOVING COLD FRONT THAT'S
EXPECTED TO TRAVERSE THE ARKLAMISS REGION LATE TUESDAY NIGHT INTO
WEDNESDAY MORNING.
ALTHOUGH THIS IS SOME FIVE DAYS OUT...MODELS ARE CURRENTLY IN DECENT
AGREEMENT WITH THIS SYSTEM. SEVERAL PARAMETERS WITHIN THE MODELS
HAVE ALSO BEEN INDICATING FOR A FEW RUNS NOW THAT THERE IS AT LEAST
SOME STRONG/SEVERE THUNDERSTORM POTENTIAL OVER PORTIONS OF THE CWA
TUESDAY AFTERNOON INTO TUESDAY NIGHT AS THE SYSTEM APPROACHES AND
MOVES THROUGH. BECAUSE OF THIS...I'LL INTRODUCE SUCH WORDING INTO
THE HWO FOR THIS TIME FRAME.
AS THE COLD FRONT EXITS THE FORECAST AREA WEDNESDAY MORNING...HIGH
PRESSURE WILL QUICKLY BUILD INTO THE LOWER MISSISSIPPI RIVER FROM
THE WEST THROUGH THE AFTERNOON AND OVERNIGHT HOURS. SKIES WILL
CLEAR THROUGH THE DAY WEDNESDAY AS A MUCH COOLER DRIER AIRMASS
ADVECTS INTO THE FORECAST AREA DURING THIS TIME. THESE CLEAR AND
COOLER CONDITIONS ARE EXPECTED TO REMAIN OVER THE REGION THURSDAY
INTO FRIDAY. /19/
&&
.AVIATION...FOR THE MOST PART...VFR CONDITIONS WILL PREVAIL FOR MOST
OF THE PERIOD. THERE WILL CONTINUE TO BE A BRIEF WINDOW WHERE SOME
MVFR CEILINGS LINGER IN THE SE PORTION AND CEILINGS JUST ABV 3 KFT IN
THE E THIS MORNING. THE FOCUS THEN SHIFTS TO THE LIGHT PRECIP AND
CHANGE TO MOSTLY -SN TONIGHT. FOR THE MOST PART...CEILINGS WILL BE
ABV 3 KFT BUT THERE COULD BE A TIME WHERE THAT LOWERS TO MVFR LEVELS
AROUND 06Z ACROSS THE S PORTIONS. CLEARING IS EXPECTED TO STEADILY
PUSH FROM W TO E AFTER 07-08Z WITH ALL OF THE REGION CLR BY 12-14Z.
/CME/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 46 29 48 27 / 16 51 0 0
MERIDIAN 47 28 48 24 / 7 51 4 0
VICKSBURG 45 29 48 27 / 27 42 0 0
HATTIESBURG 49 31 49 26 / 15 100 5 0
NATCHEZ 45 29 49 28 / 33 96 0 0
GREENVILLE 42 28 45 28 / 12 22 0 0
GREENWOOD 44 28 45 27 / 8 25 0 0
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 AM CST
SATURDAY FOR MSZ053>066-072>074.
LA...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 AM CST
SATURDAY FOR LAZ024-026.
AR...NONE.
&&
$$
CME/19/
