FXUS64 KJAN 060353 AAA
AFDJAN
AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE JACKSON MS
950 PM CST SAT DEC 5 2009
.DISCUSSION...
UPDATE: TEMPERATURES HAVE FALLEN TO WITHIN A FEW DEGREES OF
FORECASTED LOWS THIS EVENING IN SOME CASES...BUT AN ABUNDANCE OF
THIN CIRRUS MOVING ACROSS THE ARKLAMISS IS KEEPING TEMPERATURES FROM
REALLY PLUMMETING. HAVE ONLY LOWERED FORECAST OVERNIGHT LOWS 1-2
DEGREES ACROSS THE AREA DUE TO THE POSSIBILITY THAT CIRRUS WILL
THICKEN MORE AND NOT ALLOW MUCH MORE NOCTURNAL COOLING. ALL ELSE IS
ON TRACK...THE UPDATED AVIATION DISCUSSION IS BELOW. /EC/
PREVIOUS DISCUSSION...
THE SNOWY COLD START TO THIS WEEKEND APPEARS GIVE WAY TO AN
INCREASINGLY WETTER PATTERN AS WE START THE WEEK AHEAD. A LARGE MEAN
TROUGH AXIS DIGGING IN THE WRN CONUS ALREADY TAPPING INTO
SUBTROPICAL MOISTURE REGION OFF BAJA AND THROWING PLENTY OF HIGH
LEVEL CLOUDS INTO THE SRN PLAINS. A VERY PERSISTENT ISENTROPIC
REGIME SETTING UP FROM SUNDAY THROUGH TUESDAY WITH SEVERAL WAVES OF
RAINFALL RACING THROUGH THE REGION.
SHORT TERM...FIRST WE DEAL WITH A VERY COLD NIGHT AHEAD AS A SURFACE
HIGH(1024MB) PRESSURE AXIS FROM THE OH VALLEY TO THE TX COAST
PRODUCES THE COLDEST TEMPS WE'VE SEEN SINCE THE MIDDLE OF FEBRUARY.
A FEW RECORD LOWS WILL PROBABLY BE SET(I.E. HBG 28F) HOWEVER MANY
LOCATIONS WOULD NEED TO DROP BELOW 20F TO SET NEW LOWS FOR 12/6
SUNDAY MORNING. WINDS ALOFT WILL BE BACKING TO THE SOUTHWEST AHEAD OF
THE DEEPENING WRN TROUGH SO HIGH LEVEL CLOUDS LIKELY ARRIVING IN NERN
LA AND SERN AR SHORTLY AFTER MIDNIGHT AND THEN INTO WRN HALF OF MS
BEFORE DAYBREAK. EXPECT LITTLE IMPACT ON THE RADIATIONAL COOLING LOWS
EXCEPT POSSIBLY W OF THE MS RIVER.
CLOUDS GRADUALLY THICKEN AND THEN LOWER DURING THE DAY SUNDAY FROM W
TO E AND THESE WILL IMPACT HIGHS SUNDAY WITH MOST LOCATIONS STAYING
IN THE LOWER 50S. UPGLIDE WILL INCREASE BY SUNDAY EVENING AS A
SURFACE LOW IS EXPECTED TO MOVE FROM THE SOUTHERN PLAINS TO THE MID
MISSISSIPPI RIVER VALLEY BY MONDAY MORNING. WAA RAINS BREAK OUT AHEAD
OF THIS SYSTEM AS A TRAILING COLD FRONT EDGES INTO OUR NWRN ZONES
EARLY ON MONDAY. THE CURRENT DRY AIRMASS(0.2 INCH PWATS) WILL STILL
BE RATHER DRY EARLY SUNDAY BUT RAPID MOISTENING WITH PWATS RISING TO
0.75 TO 1 INCH OVER THE SWRN HALF OF OUR CWFA BY EVENING. LIGHT RAINS
MAY BEGIN REACHING THE GROUND OVER OUR WRN ZONES BY THAT TIME AND
SPREAD EWD SUNDAY NIGHT TO THE ENTIRE AREA AS PWATS EDGE ABOVE 1
INCH. A LOW LEVEL SLY JET AXIS DEVELOPS LATE SUNDAY NIGHT ALONG THE
MS RIVER AND MOVES ACROSS THE CWFA MONDAY MORNING WITH 850MB
TRANSPORT YIELDING SOME K INDEXES OF 30-33 FOR OUR SRN HALF. HAVE
DECIDED TO INCLUDE A MENTION OF TSRA IN THESE AREAS. HAVE LEANED ON
THE ENSEMBLE MEANS FOR TEMPS DURING THE FIRST SEVERAL DAYS OF THE
WEEK DUE TO UNCERTAINTIES IN CLOUDS/RAINFALL.
ON MONDAY...THE FRONTAL SYSTEM SLOWS IT/S SEWD PROGRESS AND BECOMES
DIFFUSE MONDAY EVENING AS A FAST-MOVING MID LEVEL RIDGE ALOFT GIVES A
BREAK IN THE RAINFALL FOR ONLY 6-8 HOURS. A RAPID TURN AROUND IN WAA
AFTER MIDNIGHT MONDAY BRINGS RAINS BACK IN FROM THE S QUICKLY BY
TUESDAY MORNING WITH APPARENT WARM FRONTOGENESIS ALONG THE GULF
COAST. THE BIG QUESTION WILL THEN BE HOW THIS FRONT RESPONDS IN A
CONTINUING RAIN SHIELD INLAND OVER THE GULF STATES. QPF BY THIS TIME
SHOULD AVERAGE JUST ONE HALF TO ONE INCH ACROSS OUR CWFA AHEAD OF THE
MORE POTENT STORM SETTING UP LATER TUESDAY. /40/ WILL DEFER TO THE
PREVIOUS DISCUSSION ON THIS SYSTEM FOR NOW:
GOOD RAIN CHANCES REMAIN IN PLACE ACROSS THE FORECAST AREA ON
TUESDAY AS A FAST MOVING UPPER LEVEL TROUGH SWINGS EAST ACROSS THE
CENTRAL PLAINS AND INTO THE MID MISSISSIPPI RIVER VALLEY. THIS WILL
CAUSE A SURFACE LOW TO DEVELOP AND LIFT NORTHEAST ACROSS THE
SOUTHERN PLAINS...WHILE DRAGGING A STRONG COLD FRONT TOWARDS THE
LOWER MISSISSIPPI RIVER VALLEY. AS THE BEFORE MENTION WARM FRONT
LIFTS NORTHWARD IN RESPONSE TO THE APPROACHING SYSTEM...MOISTURE IS
EXPECTED TO SURGE NORTHWARD INTO THE FORECAST AREA AHEAD OF THE COLD
FRONT THAT'S EXPECTED TO TRAVERSE THE ARKLAMISS REGION TUESDAY NIGHT
INTO WEDNESDAY MORNING.
THIS REMAINS SOME FOUR DAYS OUT...AND OTHER THAN SOME MINOR
PLACEMENT ISSUES...MODELS REMAIN IN DECENT AGREEMENT WITH THEIR
HANDLING OF THIS SYSTEM. SEVERAL PARAMETERS WITHIN THE MODELS
CONTINUE TO INDICATE THAT THERE IS THE POTENTIAL FOR SOME STRONG TO
SEVERE THUNDERSTORMS OVER PORTIONS OF THE CWA TUESDAY AFTERNOON INTO
TUESDAY NIGHT AS THE SYSTEM APPROACHES AND MOVES THROUGH THE AREA.
THIS WILL OBVIOUSLY CONTINUE TO BE MONITORED OVER THE NEXT SEVERAL
DAYS IN ORDER TO GET A BETTER IDEA OF WHERE THE BEST POTENTIAL FOR
ANY SEVERE WEATHER IS AS WELL AS OTHER SPECIFICS.
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 EARLY FRIDAY.
I DID LOWER LOW TEMPERATURES QUITE A BIT COMPARED TO WHAT GUIDANCE
WAS SUGGESTING FOR THURSDAY MORNING. GUIDANCE SHOWS LOWS IN THE MID
TO UPPER 30S ACROSS MUCH OF THE AREA DURING THIS TIME. HOWEVER...
LOCAL CLIMATOLOGY SUGGESTS COLDER TEMPERATURES THAN THIS WITH THE
ADVERTISED AIRMASS THAT'LL BE OVER THE REGION AT THE TIME. WITH
LIGHT TO CALM WINDS EXPECTED AS HIGH PRESSURE SITS NEAR THE FORECAST
AREA...COUPLED WITH CLEAR SKIES...TEMPERATURES SHOULD HAVE NO
PROBLEM RANGING FROM THE LOWER 30S TO THE MID 30S WEDNESDAY NIGHT
INTO THURSDAY MORNING.
SUBTLE AMOUNTS OF MOISTURE WILL RETURN TO THE REGION FRIDAY
AFTERNOON INTO SATURDAY AS HIGH PRESSURE SHIFTS EAST OF THE LOWER
MISSISSIPPI RIVER VALLEY. RAIN CHANCES WILL YET AGAIN INCREASE
ACROSS THE ARKLAMISS REGION DURING THIS TIME AS ANOTHER UPPER LEVEL
DISTURBANCE SWINGS EAST INTO THE MID MISSISSIPPI RIVER VALLEY...
FORCING A WEAK COLD FRONT INTO AND THROUGH THE CWA FRIDAY NIGHT INTO
SATURDAY. /19/
&&
.AVIATION...VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD UNDER
HIGH PRESSURE. SKIES WILL REMAIN CLEAR TONIGHT AND THE WINDS
WILL BE LIGHT AND VARIABLE OVERNIGHT BECOMING SOUTHEAST BY SUNDAY
MORNING. A MID LEVEL CLOUD DECK AROUND 15 KFT SHOULD MOVE IN SUNDAY
AFTERNOON AS WARM ADVECTION INCREASES ALOFT.
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
