FXUS64 KJAN 021146 AAA
AFDJAN
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
546 AM CST WED DEC 2 2009
.AVIATION...MESSY CONDITIONS ACROSS THE ARKLAMISS THIS EARLY MORNING
AND THIS SHOULD CONTINUE THROUGH MUCH OF THE TAF CYCLE. RAIN IS
AFFECTING MANY SITES IN THE REGION THOUGH IS MOSTLY LIGHT IN NATURE.
EXPECT WIDESPREAD IFR TO LIFR CONDITIONS TO CONTINUE FOR THE NEXT
FEW HOURS. AS A LOW PRESSURE SYSTEM CONTINUES TO MOVE OFF TO THE
EAST AND NORTHEAST...LIGHT RAIN AND DRIZZLE WILL CONTINUE THROUGH
MUCH OF THE DAY INTO THE EARLY PORTIONS OF THE EVENING. THE PRECIP
SHOULD BEGIN TO TAPER OFF FROM SOUTHWEST TO NORTHEAST LATE THIS
AFTERNOON INTO EARLY EVENING AS THE LAGGING UPPER TROUGH MOVES OVER
THE REGION...BEFORE ENDING BY 06Z. CLOUDS WILL CONTINUE TO BE BKN TO
OVC AND GENERALLY LESS THAN 2000-2500 FT FOR MUCH OF THE TAF PERIOD
BUT SOME IMPROVEMENT TO MVFR CATS WILL BE POSSIBLE BY 19-24Z. WINDS
WILL BE OUT OF THE SOUTH...THEN SHIFT OUT OF THE WEST THIS AFTERNOON
BEFORE BECOMING NORTHERLY LATE TONIGHT AND DEFINITELY BY 04-06Z.
WIND SPEEDS WILL GENERALLY BE 10-12KTS WITH SOME HIGHER GUSTS UP TO
AROUND 18KTS AT TIMES. A STEADILY IMPROVING SCENARIO SHOULD FOLLOW
WITH VFR RETURNING AS WE HEAD INTO THURSDAY MORNING. /28/
&&
.PREV DISCUSSION... /ISSUED 437 AM CST WED DEC 2 2009/
SHORT TERM...TODAY THROUGH THURSDAY NIGHT...LOCAL AREA RADARS
SHOWING PRECIPITATION ACROSS MUCH OF THE DEEP SOUTH THIS EARLY
MORNING. MOST OF THE RAIN IS LIGHT TO MODERATE INTENSITY ACROSS MUCH
OF THE ARKLAMISS. HOWEVER...SOME HEAVIER BANDS ARE LOCATED FROM SOUTHEAST
MS(JUST TO THE SOUTH OF MY SOUTHERN BORDER)...TO THE GULF
COAST...AND OUT ACROSS THE WATERS OF THE GULF OF MEXICO. THIS IS
WHERE THE THUNDERSTORMS ARE LOCATED MOVING INTO THE GULF COAST OF
ALABAMA AND WHERE A TORNADO WATCH HAS BEEN POSTED. FURTHER
NORTH...VERY LITTLE IN THE WAY OF THUNDER HAS MADE IT INTO MY
CWA...WITH A COUPLE OF STRIKES NOTED ACROSS SOUTHERN CLARKE COUNTY
AND THAT IS ABOUT IT. ALL OF THIS ACTIVITY IS DUE TO THE SFC LOW
THAT HAS BEEN ADVERTISED NOW FOR THE PAST FEW DAYS. THIS LOW IS
MAKING ITS WAY ALONG THE SOUTHERN LOUISIANA COAST.
THROUGH THE MORNING...THE SFC LOW SHOULD MOVE ONTO LAND AROUND OR
JUST TO THE SOUTH OF THE I-59 CORRIDOR. AS THIS DOES...THE UPPER LOW
THAT WAS SPINNING ACROSS NORTH CENTRAL TEXAS THIS MORNING WILL
CONTINUE TO MOVE EAST AS WELL. AS IT DOES...IT SHOULD BECOME MORE OF
AN OPEN TROUGH AND MERGE WITH THE LARGER STREAM TROUGH. WITH THE SFC
LOW TRACKING NORTHEAST ACROSS THE EASTERN PORTIONS OF THE CWA INTO
AL/TN...MOISTURE WRAPPING AROUND IT WILL COMBINE WITH THE PASSING
UPPER LOW/TROUGH AND ALLOW FOR A LITTLE MORE LIGHT RAIN/DRIZZLE
ESPECIALLY FOR LOCATIONS ACROSS THE NORTH THIS AFTERNOON. AREAS ACROSS THE
SOUTH SHOULD BEGIN TO TAPER OFF THIS MORNING AND BE LEFT WITH ONLY
SLIGHT CHANCES OF LIGHT RAIN/DRIZZLE FOR THE REST OF THE
MORNING/EARLY AFTERNOON. WITH THE SFC LOW PASSING...WINDS COULD BE
GUSTY AT TIMES BUT SHOULD REMAIN BELOW CRITIERIA FOR ANY ADVISORY.
LIGHT RAIN/DRIZZLE SHOULD BE GONE BY LATE THIS AFTERNOON/EARLY
EVENING. COOLER AND DRIER AIR WILL BEGIN TO MOVE IN ALONG WITH A
SMALL DECREASE IN CLOUD COVER. MODELS CONTINUE TO INDICATE LOW LEVEL
MOISTURE LINGERING AND THIS WILL RESULT IN A LACK OF CLEARING FOR
WEDNESDAY NIGHT THROUGH THURSDAY. TEMPERATURES WILL REMAIN BELOW
NORMAL TODAY WITH HIGHS LOOKING TO TOP OUT IN THE UPPER 40S NORTH TO
UPPER 50S SOUTH. LOWS WILL RANGE IN THE MID TO UPPER 30S AREAWIDE.
DRY WEATHER RETURNS TO THE ARKLAMISS ALONG WITH COOLER THAN NORMAL
TEMPERATURES FOR THURSDAY. A COLD CANADIAN HIGH PRESSURE WILL DROP OUT OF
THE PLAINS AND FILTER ACROSS OUR REGION. TEMPERATURES ON THURS. WILL
ONLY GET INTO THE UPPER 40S TO MID 50S. IN ADDITION...A LARGE SCALE
TROUGH OVER THE CENTRAL CONUS WILL BRING COLDER TEMPS FOR THURSDAY
NIGHT. 850MB ZERO DEGREE ISOTHERMS ARE SHOWN ACROSS THE NATCHEZ
TRACE CORRIDOR WITH THE PLACEMENT AT 925MB BEING AROUND THE HIGHWAY
84 CORRIDOR. GIVEN SOME LINGERING CLOUDS AND LIGHT WINDS....WE WOULD
NOT GET AS COLD AS WE POSSIBLY COULD...BUT TEMPS WILL GET CHILLY FRI
MORNING AND RANGE FROM THE LOWER 30S NORTH TO THE MID 30S SOUTH.
GUI POPS CAME IN FINE WITH THE HIGHER POPS ACROSS THE NORTH FOR
TODAY. THESE SHOULD OCCUR EARLY IN THE PERIOD AND TAPER OFF FOR THE
AFTERNOON AS THE SFC LOW PULLS OUT AND THE UPPER TROUGH MOVES
THROUGH. TEMPS WERE GENERALLY ON THE WARMER SIDE OF THE MEANS AND
WERE CUT IN A FEW PLACES....AND ESPECIALLY LOWS FOR THURS NIGHT AS
CAA SHOULD BE IN FULL FORCE BY THEN(WITH A LITTLE LESS CLOUD COVER).
/28/
LONG TERM...WHAT I HAD FEARED LAST NIGHT IS BECOMING MORE OF A
POSSIBILITY AS THE OUTLYING MODEL...WHICH WAS DEVELOPING SNOW ACROSS
THE AREA...IS NOT THE OUTLIER ANYMORE. THE GFS...IS NOW LEADING THE
WAY AND HAS STRONG SUPPORT FROM THE SREF AND MOST OF ITS ENSEMBLE
MEMBERS AND SOME SUPPORT FROM THE NAM AND EURO. 8 OF 12 ENSEMBLE
MEMBERS GENERATE MEASURABLE SNOW FRI NIGHT ACROSS THE CWA AND SNOW
PROBABILITIES FROM THE SREF ARE RANGING FROM 40-60%. SUCH SUPPORT
HAS TO BE TAKEN SERIOUSLY AND THE RESULT WILL BE SIGNIFICANT CHANGES
FOR THE FRI NIGHT FORECAST WRT POPS AND PRECIP TYPE BECOMING AT
LEAST LIGHT SNOW.
ONE MAY BE ASKING...WHAT HAS CHANGED TO NOW INCLUDE THIS INTO THE
FORECAST? MAINLY DEEPER MOISTURE AND STRONGER SUPPORT FROM MORE
MODELS. FORECAST LEADING INTO FRI/FRI NIGHT HAS GENERALLY ALWAYS
PORTRAYED SOME SORT OF S/W MOVING THROUGH THE BASE OF THE LONG WAY
TROUGH. HOWEVER...THE TREND LAST NIGHT WAS FOR THE S/W TO BE
STRONGER. WITH THAT...THE LARGE MAJORITY OF THE MODEL GUID WAS
GENERALLY DRY AND ONLY HAD CLOUDS WITH THAT TROUGH PASSAGE. THE GFS
WAS REALLY THE ONLY MODEL SHOWING SNOW ALONG WITH A COUPLE OF ITS
ENSEMBLE MEMBERS. SINCE LAST NIGHT...MUCH MORE SUPPORT HAS COME IN
FROM VARIOUS GUID AND BASICALLY THERE HAS BEEN A 180 SWITCH AND NOT
THE OUTLYING SOLUTION IS THE DRIER VERSION.
AS FOR SOME OF THE DETAILS...THE S/W IN QUESTION WILL BE RATHER
POTENT AND PROVIDE STRONG ASCENT ACROSS THE REGION ALONG WITH
HELPING TO DEVELOP A SFC LOW ACROSS THE N GULF. IT WILL BE THIS SFC
LOW DEVELOPMENT THAT WILL GIVE THE S/W THE MOISTURE TAP TO DEVELOP
PRECIP ABOVE THE COLD AIRMASS. I WILL SAY...THAT UNCERTAINTY IS
STILL FAIRLY HIGH IN THIS SOLUTION AS IT IS SOME 60-72 HRS OUT AND
ANYTIME WE ARE DEALING WITH WINTRY PRECIP IN OUR AREA...THINGS OFTEN
CHANGE. THE GENERAL SETUP FOR THIS WINTRY POTENTIAL FRI NIGHT IS
QUITE FAVORABLE AS WE WILL SEE CAA ONGOING FRI INTO FRI NIGHT WITH
SFC PRESSURES RISING AS HIGH PRESSURE BUILDS IN FROM THE N. THE
COMBINATION OF THE DEVELOPING GULF LOW IS ALSO SUPPORTIVE B/C IT
PROVIDES MOISTURE. THE FLY IN THE OINTMENT IS WILL THE COLDER AIR
MOVING SOUTHWARD BE TOO DRY AND EVAPORATE ALL OF THE FALLING PRECIP.
THAT TYPICALLY HAPPENS. ADDITIONALLY...THE AIRMASS THAT WILL BE IN
PLACE WILL NOT BE VERY COLD AND HIGH TEMPS FRI SHOULD BE IN THE
MID/UPPER 40S. IF CLOUD COVER THICKENS FASTER AND VIRGA DEVELOPS
EARLIER THE EVAP COOLING PROCESS WILL KEEP TEMPS COOLER AND MORE
NEAR 40 DEGREES. WITH FREEZING CONDITIONS NOT ALREADY IN PLACE...WE
WILL NEED OTHER MEANS TO GENERATE SNOW. THAT DOES NOT LOOK TO BE A
PROBLEM AS DYNAMIC COOLING FROM THE STRONG S/W WILL PROVIDE THAT AS
STRONG ASCENT WILL GENERATE PRECIP ALOFT WHICH WILL EVAPORATE AND
COOL ANY LAYER THAT IS ABOVE FREEZING. ALSO...THIS ALL LOOKS TO COME
TOGETHER FRI NIGHT AND WILL BE AIDED BY DIURNAL COOLING WHICH WILL
MAKE IT EASIER TO DROP TEMPS TO CRITICAL LEVELS FOR PRECIP TO BECOME
LIGHT SNOW. IT APPEARS AS MOISTURE VALUES...VERTICAL MOTION AND
DURATION WILL ONLY SUPPORT LIGHT ACCUMULATIONS FROM 1/4 INCH TO
POSSIBLY 1 INCH. THIS WILL ALSO OCCUR WITH TEMPS 31-34
DEGREES...SIMILAR TO PREV SNOW EVENTS OVER THE PAST TWO WINTER
SEASONS. HOWEVER...THOSE EVENTS HAD MUCH HIGHER MOISTURE TO WORK
WITH WHICH RESULTED IN MORE ACCUMULATIONS OF WET SNOW. THIS LOOKS TO
BE MUCH LIGHTER AT THIS POINT. ANY ACCUMS SHOULD BE ON GRASSY SFC'S
OR ELEVATED SFC'S AND BE 1 INCH OR LESS.
IN THE WAKE OF THIS S/W FEATURE...SAT-SUN LOOK TO BE QUIET.
HOWEVER...THAT MAY NOT LAST TOO LONG AS THE PATTERN WILL BE MORE OF
FAST SW ALOFT WHICH OFTEN MAKES FOR QUICK TRANSITIONS AND A OVERALL
WETTER PATTERN. WHILE DETAILS WILL BE VERY TOUGH TO GET
DOWN...FOLLOWING THE GENERALITIES OF THE GUID SEEMS THE BEST WAY TO
GO FOR SUN NIGHT THROUGH WED. DECENT PRECIP CHANCES AND A WARMING
TREND LOOK TO BE IN STORE AND GUID VALUES WERE ACCEPTED.
AS FOR TEMPS/POPS AND WEATHER FOR FRI-SAT...I DID LOWER HIGHS ON FRI
DUE TO THE CLOUD COVER AND EVAP COOLING POTENTIAL. ENSEMBLE MOS
SUPPORTS THIS AS WELL. I DID LOWER POPS ON FRI AS I FEEL THE ON SET
OF ANY LIGHT PRECIP WILL BE LATE AND MAINLY IN THE FRI NIGHT PERIOD.
FOR FRI NIGHT...I LOWERED LOWS TO GET INTO THAT 31-34 RANGE WHICH
COVERS THE WET BULB EFFECT AND FOLLOWS THE ENSEMBLE MEAN WHICH HAS
BEEN LOWER THAN THE OPS GUID FOR THE PAST FEW RUNS. POPS WERE TOUGH
AS MY INTUITION WOULD BE TO LOWER POPS DUE TO THE UNCERTAINTY.
HOWEVER...ALL THE DATA I HAVE LOOKED SAYS TO JUST STAY WITH THE
LATEST GUID POPS AS MEASURING JUST A COUPLE HUNDREDTHS OF LIQUID
EQUIVALENT IS VERY POSSIBLE. FOR NOW...LIGHT SNOW WORDING FITS THE
SITUATION AS ANY SNOW ACCUM SHOULD BE AROUND 1 INCH OR LESS. /CME/
&&
.AVIATION...
WILL BE ISSUED SHORTLY.
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 52 38 50 32 / 42 11 0 10
MERIDIAN 57 38 53 32 / 44 11 0 10
VICKSBURG 53 38 51 34 / 43 11 0 10
HATTIESBURG 57 40 54 35 / 28 8 0 10
NATCHEZ 51 37 50 33 / 27 9 0 10
GREENVILLE 48 36 48 30 / 72 15 0 10
GREENWOOD 50 37 50 31 / 70 18 0 10
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
28/CME
