FXUS64 KJAN 021641
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
1020 AM CST WED DEC 2 2009
.UPDATE...MOST OF THE SIGNIFICANT PRECIPITATION HAS MOVED EAST OF
THE CWA WITH ONLY PATCHY LIGHT DRIZZLE REMAINING BUT LIGHT RAIN WILL
MOVE BACK OVER THE NORTHERN HALF OF THE CWA THIS AFTERNOON. HAVE
DECREASED POPS THIS MORNING AND ACROSS THE CENTRAL PORTIONS
REMAINDER OF THE DAY. SURFACE ANALYSIS PLACES THE LOW OVER NORTHERN
MISSISSIPPI WITH THE COLD FRONT BOWING EAST INTO ALABAMA. THIS LOW
WILL CONTINUE MOVING NORTH NORTHEAST ACROSS TENNESSEE THIS AFTERNOON
WHILE THE CLOSED UPPER LEVEL LOW SEEN ON SATELLITE/RUC ANALYSIS OVER
THE ARKLATEX MOVES NORTHEAST ACROSS DELTA REGION. THIS UPPER LEVEL
LOW WILL BRING A CHANCE OF LIGHT RAIN THIS AFTERNOON TO OUR NORTHERN
HALF ALONG WITH ENHANCING COOL GUSTY WEST WINDS ACROSS OUR AREA. AS
THE SFC LOW MOVES NORTH THE PRESSURE GRADIENT WILL INCREASE OVER OUR
CWA AND RESULT IN GUSTY WINDS. THE BOUNDARY MARKING THIS REINFORCING
SHOT OF COOL AIR WAS NOTED NEAR INTERSTATE 55. THE COLD AIR
ADVECTION WILL BE STRONGEST THIS AFTERNOON OVER THE LAKES AND THE
GUSTY WINDS WILL ONLY MEET LOCAL LAKE WIND ADVISORY CRITERIA THERE.
HAVE ISSUED A LIMITED LAKE WIND ADVISORY FOR THIS AFTERNOON FOR THE
AREA LAKES. TEMPERATURES IN THE EAST WERE RUNNING A LITTLE WARMER
THAN EXPECTED BUT AS THE COOLER AIR MOVES IN THIS AFTERNOON
TEMPERATURES WILL DROP SLIGHTLY OR REMAIN NEARLY STEADY. HAVE
DECREASED AFTERNOON HIGHS A COUPLE OF DEGREES IN THE WEST. UPDATES
HAVE BEEN POSTED. /22/
&&
.AVIATION...SURFACE LOW PRESSURE OVER CENTRAL MISSISSIPPI WILL
QUICKLY MOVE NORTHEASTWARD THROUGH THURSDAY...AS AN UPPER LEVEL LOW
ALSO MOVES NORTHEASTWARD ACROSS THE REGION. MOISTURE WRAPPING AROUND
THESE FEATURES WILL RESULT IN AN OVERCAST DECK OF LOW CLOUDS
TODAY...WITH MVFR CEILINGS ACROSS MUCH OF THE REGION. AREAS OF LIGHT
RAIN OR DRIZZLE WITH IFR CEILINGS/VISIBILITIES WILL AFFECT NORTHERN
PORTIONS OF CENTRAL MISSISSIPPI THROUGH THIS AFTERNOON. A FEW BREAKS
IN THE CLOUDS WILL BE FOUND IMMEDIATELY BEHIND A FRONT PIVOTING
AROUND THE LOW ACROSS CENTRAL AND EASTERN MISSISSIPPI THIS
AFTERNOON. WINDS WILL BECOME SOUTHWEST TO WEST AT 12 TO 17 KT WITH
GUSTS BETWEEN 18 AND 23 KT BEHIND THE FRONT...WITH THE STRONGEST
WINDS EXPECTED AROUND KHBG...KMEI...KGTR...AND KJAN. FOR
TONIGHT...MVFR TO OCCASIONALLY IFR CEILINGS WILL CONTINUE...WITH
DRIZZLE ALONG AND NORTH OF INTERSTATE 20 RESULTING IN MVFR
VISIBILITIES. BY THIS EVENING AND CONTINUING INTO THURSDAY...WINDS
WILL SUBSIDE TO THE 3 TO 6 KT RANGE WHILE BECOMING NORTHWESTERLY. BY
THURSDAY MORNING...THE DRIZZLE IS EXPECTED TO HAVE ENDED...WITH VFR
VISIBILITIES ANTICIPATED AREAWIDE. HOWEVER...MVFR CEILINGS ARE
EXPECTED TO PERSIST FOR MUCH OF THURSDAY. /COHEN/
&&
.PREVIOUS 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 CRITERIA 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/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 55 38 50 32 / 22 11 0 10
MERIDIAN 58 38 53 32 / 23 11 0 10
VICKSBURG 52 38 51 34 / 29 11 0 10
HATTIESBURG 58 40 54 35 / 19 8 0 10
NATCHEZ 54 37 50 33 / 20 9 0 10
GREENVILLE 50 36 48 30 / 52 15 0 10
GREENWOOD 53 37 50 31 / 53 18 0 10
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...LAKE WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR MSZ026-030-
031-043-049-052.
LA...LAKE WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR LAZ009.
AR...LAKE WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR ARZ075.
&&
$$
22/COHEN/28/CME
