FXUS64 KJAN 262036
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
236 PM CST SAT DEC 26 2009
.SHORT TERM...(TONIGHT THROUGH MONDAY NIGHT)...THE ARKLAMISS WILL BE
UNDER THE INFLUENCE OF AN WEST/EAST ELONGATED RIDGE OF HIGH PRESSURE
TONIGHT SQUEEZED BETWEEN DEEP LOW PRESSURE TO OUR NORTH AND A
DEVELOPING AREA OF LOW PRESSURE OVER THE WESTERN GULF OF MEXICO. A
FEW GUSTS ACROSS FAR NORTHERN ZONES MAY LINGER INTO THE EARLY
EVENING HOURS AS THE SFC PRESSURE GRADIENT CONTINUES TO WEAKEN IN
THIS AREA. SHORT RANGE GUIDANCE IS IN DISAGREEMENT AS TO THE IMPACT
LOW PRESSURE OVER THE GULF WILL HAVE ON SOUTHERN ZONES AS IT
INTERACTS WITH AN UPPER LEVEL S/WV ROUNDING THE BASE OF THE PARENT
UPPER LOW OVER THE WESTERN GREAT LAKES REGION. THE ECMWF IS RATHER
ROBUST WITH THE NORTHERN EXTENT OF MEASURABLE PRECIP AS IT SHOWS
MUCH BROADER LIFT AHEAD OF THE S/WV REACHING SOUTHERN ZONES BY 12Z
SUNDAY WHILE GFS/NAM KEEP LIFT FARTHER NORTH UNTIL LATE
MORNING/EARLY AFTERNOON. WENT WITH MAV GUIDANCE KEEPING POPS ON THE
LOW END THROUGH THE MORNING HOURS AS NO SIG PRECIP IS EXPECTED EITHER
WAY CONSIDERING THE DRY LOW LEVELS IN PLACE...HOWEVER DID MENTION A
SLIGHT CHANCE OF SPRINKLES SOUTH OF HBG.
SFC HIGH PRESSURE WILL THEN TAKE STRONG HOLD OF THE REGION TOMORROW
AFTERNOON WITH THE UPPER LEVELS VEERING TO A DRY NORTHWESTERLY FLOW.
ONLY AREA OF UNCERTAINTY SUNDAY NIGHT INTO MONDAY IS THE SOUTHERN
EXTENT OF LOW CLOUDS WRAPPING AROUND THE DEPARTING LOW PRESSURE OVER
THE GREAT LAKES. FOR NOW THINK THAT AT LEAST PARTLY CLOUDY SKIES WILL
MOVE ACROSS NORTHERN ZONES LATE TOMORROW AFTERNOON AND LINGER THROUGH
MONDAY MORNING. THIS MAY HINDER LOW TEMPS FROM REALLY DROPPING IN
THESE AREAS ALTHOUGH STILL EXPECTING LOWS IN THE UPPER 20S AREAWIDE.
MONDAYS HIGH TEMPS WILL BE IMPACTED BY THE EXTENT OF CLOUD COVER
THAT LINGERS INTO THE DAYTIME HOURS. DO THINK THE GFS IS A BIT LIGHT
ON THE CLOUD COVER...AS WELL AS WITH THE STRENGTH OF THE COLD AIR
MOVING INTO THE REGION AND CUT GFS MOS HIGHS MONDAY TOWARD THE COOLER
NAM GUIDANCE. DRY CONDITIONS CAN CERTAINLY BE EXPECTED. IN FACT
COLD/DRY CONDITIONS CAN BE EXPECTED THROUGH TUESDAY MORNING AS HIGH
PRESSURE MAINTAINS ITS HOLD ON THE ARKLAMISS.
MAV TEMPS GENERALLY ACCEPTED EXCEPT FOR MONDAYS HIGHS WHERE THEY
WERE DECREASED. IN THE LONGER RANGE...POPS FOR TUESDAY NIGHT WERE
BROUGHT IN LINE WITH THE 00Z GFS GUIDANCE BASED ON CONSISTENT TIMING
BETWEEN THE GFS/12Z AND ECMWF/12Z BRINGING PRECIP INTO WESTERN ZONES
AT THIS TIME. //BK/CME//
&&
.PREVIOUS LONG TERM...MONDAY THROUGH FRIDAY.
THE PRIMARY WEATHER CONCERN WILL BE TO ASSESS THE COLD AIR
ASSOCIATED WITH THE MID WEEK GULF SYSTEM. TO SEE HOW FAST OR SLOW
THE MODELS ARE GOING WITH THIS SYSTEM AND SEE IF WE CAN KEEP IT A
COLD RAIN AS WELL AS ALSO TO ASSESS TEMPS AND POPS FOR THE LONG TERM.
LOOKING AT THE GFS ENSEMBLES...CANADIAN...EUROPEAN...SREF AND UKMET.
ALL MODELS ARE IN GENERAL AGREEMENT ABOUT THE GENERAL UPPER PATTERN
WITH THE SHORT WAVE TROUGH COMING FROM THE PLAINS...WHICH WILL HELP
TO SET UP THE GULF SYSTEM FOR THE MIDDLE OF NEXT WEEK. AS WE GET INTO
THE MIDDLE OF THE WEEK THE MORE CONSISTENT EUROPEAN SLOWS THE SYSTEM
DOWN FOR TUESDAY THROUGH THURSDAY NIGHT...WHILE THE GFS AND CANADIAN WAS
FASTER WITH IT. SO HAVE ADJUSTED GRIDS FOR THE SLOWER EUROPEAN
SOLUTION. MOST OF THE ENSEMBLES ALONG WITH THE GFS AND EUROPEAN
AGREE ON THE PASSAGE OF A SHORT WAVE FOR FRIDAY. THE EUROPEAN MODEL
WAS A LITTLE SLOWER WITH MUCH MORE AMPLITUDE WITH THE UPPER TROUGH
ALONG WITH A 533 CLOSED LOW PUSHING INTO THE TENNESSEE VALLEY BY
EARLY SATURDAY. THE GFS HAD A 528 CLOSED LOW OVER THE GREAT LAKES AT
THIS TIME...WHILE MOST OF THE ENSEMBLES HAD A CLOSED LOW IN CANADA
WITH A FEW OVER THE GREAT LAKES. WITH THIS SYSTEM IT LOOKS TO BE
PRETTY DRY. EITHER WAY IT LOOKS TO BE A COOL PATTERN FOR THE LONG
TERM.
TAKING IT DAY BY DAY...
FOR MONDAY INTO TUESDAY...THE MODELS AND ENSEMBLES SHOWS A 1030-35 MB HIGH
PUSHING ACROSS THE SOUTHERN PLAINS. THE SURFACE HIGH WILL PUSH
NORTHEAST INTO THE NORTHERN MISSISSIPPI VALLEY ON TUESDAY. THE UPPER
RIDGING WILL BUILD ACROSS THE REGION EARLY IN THE WEEK. THERE WAS MORE
AMPLITUDE WITH THE EUROPEAN MODEL THEN WITH THE GFS AND ENSEMBLES
WITH THE APPROACH OF THE SHORT WAVE TROUGH.
FOR TUESDAY NIGHT INTO THURSDAY NIGHT...MODELS SHOWS THAT STRONG
ISENTROPIC UPGLIDE WILL DEVELOP ACROSS THE REGION AS SURFACE LOW
PRESSURE DEVELOPS IN THE NORTHWEST GULF. ALONG WITH THIS WE WILL GET
SOME STRONG ASCENT ALONG WITH STRONG Q DIVERGENCE. PRECIPITABLE WATER
WILL BE AROUND 1.2 INCHES. HPC SHOWS PRECIP OF ONE HALF TO AROUND
ONE INCH ACROSS MOST OF THE REGION. AS FAR AS INSTABILITY IS CONCERN
ELEVATED INSTABILITY WILL BE QUITE WEAK...SO WILL KEEP IT NONCONVECTIVE
RAIN. WE WILL HAVE A LAYER OF COLD AIR IN THE LOW LEVELS WITH THIS
SYSTEM. RIGHT NOW AS FAR AS PRECIPITATION IS CONCERN MODEL SOUNDINGS
SHOW THAT IT WILL BE A COLD RAIN WITH LOW LEVEL TEMPS AT 4-5C IN THE
CENTRAL AND SOUTH AND AROUND 3C IN THE NORTH. WET BUILD ZERO WILL BE
ABOVE 5KFT. FREEZING DEWPOINTS WILL STAY NORTH OF THE REGION DURING
THIS PERIOD...EXCEPT AT THE START OF THE PERIOD BEFORE THE RAIN
HITS. AS NOTED ABOVE HAVE FOLLOWED THE SLOWER ECMWF SOLUTION.
THIS SYSTEM WILL STILL BEAR WATCHING AS TO HOW COLD THE AIR WILL BE
ACROSS THE REGION WHEN THIS SYSTEM DEVELOPS. SO WITH THIS IN MIND
WILL KEEP IT ALL RAIN AT THIS TIME. THE RAINS ACCORDING TO THE ECMWF
WILL MOVE OUT OF THE REGION ON THURSDAY EVENING.
FOR FRIDAY...ON FRIDAY MORNING HIGH PRESSURE WILL MOVE INTO THE
REGION FROM THE WEST AS A SHORT WAVE PUSHES TOWARD THE REGION FROM
THE NORTHWEST. THIS SHORT WAVE WILL BRING SOME VERY LIGHT SPRINKLES
ACROSS THE REGION DURING FRIDAY AFTERNOON AND EVENING...WHICH MAY
BECOME A FEW FLURRIES EARLY SATURDAY. THINK THAT IT WILL BE TOO
LIGHT TO MENTION IN THE GRIDS. PRECIPITABLE WATER WILL BE AROUND ONE
HALF INCH.
AS FAR AS TEMPS ARE CONCERN...WE WILL GO THROUGH A COOL PERIOD WITH BELOW
NORMAL HIGHS AND AROUND NORMAL LOWS. FOR MONDAY HIGHS WILL BE MIDDLE
40S NORTH TO LOWER 50S SOUTH WENT CLOSE TO MAV GUIDANCE. FOR MONDAY
NIGHT LOWS WILL BE IN THE MID TO UPPER 20S...WENT CLOSE TO A BLEND OF
MOS GUIDANCE AND ENSEMBLE GUIDANCE. FOR THE RAINY PERIOD OF TUESDAY
THROUGH THURSDAY NIGHT KEPT NIGHTLY LOWS ABOVE FREEZING IN THE MIDDLE
30S...WHICH IS A LITTLE ABOVE MAV...ENSEMBLES AND MOS GUIDANCE.
HIGHS ON TUESDAY AND WEDNESDAY WILL BE IN THE 40S AND 50S. WENT
CLOSE TO A BLEND MOS GUIDANCE AND ENSEMBLE GUIDANCE. FOR FRIDAY
HIGHS ON FRIDAY WILL BE IN THE 40S...WENT CLOSE TO MAV GUIDANCE. FOR
FRIDAY NIGHT LOWS WILL BE IN THE MID TO UPPER 20S...WENT CLOSE TO
MOS GUIDANCE.
AS FAR AS POPS ARE CONCERN WENT CLOSE TO FOLLOWING THE EUROPEAN
MODEL WITH THE SLOWER SOLUTION OF THE MID WEEK SYSTEM. SO KEPT
HIGHER POPS FOR THE WEDNESDAY INTO THURSDAY. /17/
&&
.AVIATION...VFR CONDITIONS WILL PREVAIL THROUGH THE NEXT TAF PERIOD
WITH JUST SOME CIRRUS STREAMING ACROSS THE AREA. THERE DOES LOOK TO
BE A WINDOW OF TIME (04-10Z) WHERE A MID LEVEL DECK (~10 KFT) WILL
SPREAD ACROSS THE S PORTION OF THE CWA. OTHER THAN THAT...SFC WINDS
LOOK TO BE GENERALLY LIGHT AND OUT OF THE WEST. /CME/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 31 51 28 45 / 3 4 0 0
MERIDIAN 29 53 25 45 / 3 5 1 0
VICKSBURG 32 50 29 45 / 3 3 0 0
HATTIESBURG 34 52 28 49 / 13 13 1 0
NATCHEZ 32 50 27 46 / 4 4 0 0
GREENVILLE 30 47 29 44 / 3 2 0 0
GREENWOOD 30 47 27 45 / 3 3 0 0
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
BK/CME
