961
FXUS64 KJAN 210229
AFDJAN
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
825 PM CST FRI NOV 20 2009
UPDATE
LATEST SATELLITE IMAGERY SHOWED A SHORT WAVE OVER THE SOUTHERN
PLAINS WITH AN ASSOCIATED SURFACE WAVE OVER THE NORTHWEST GULF OF
MEXICO. THE ARKLAMISS WAS WELL NORTH IN THE COOLER AND STABLE
AIRMASS. AREA RADARS WERE PICKING UP SOME PATCHY VERY LIGHT RAIN
TO THE WEST AND SOUTH OF THE REGION. STILL EXPECT SOME VERY LIGHT
RAIN TO IMPACT THE REGION LATER TONIGHT FROM THE SOUTH. THIS WILL
NOT BE A SHOWERY TYPE SYSTEM FOR THIS REGION IN THIS COOL STABLE
AIRMASS. SO FOLLOWING RADAR TRENDS OF DEVELOPMENT. HAVE PUSHED BACK THE
FIRST WAVE OF VERY LIGHT RAIN IN THE SOUTH UNTIL NEAR MIDNIGHT...THEN PUT
PULLED BACK RAIN CHANCES FOR THE REST OF THE NIGHT. GOING FROM A SLIGHT
CHANCE ALONG AND NORTH OF INTERSTATE 20 TO CHANCE POPS SOUTH. ALSO DELAYED
HIGH POPS UNTIL THE LATER HALF OF SATURDAY MORNING FOR THE REGION.
CURRENT LOWS IN THE 40S LOOKS TO BE ON TRACK. WILL KEEP THE BEST
CHANCE POPS ACROSS THE SOUTH HALF WHERE THE LIGHT RAIN WILL
ORIGINATE FROM./17/
PREV DISCUSSION
352 PM CST FRI NOV 20 2009
SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT
PRIMARY CONCERN THIS
PERIOD REVOLVES AROUND WIND SPEEDS AND PRECIP ACCUMULATIONS THROUGH
SUNDAY AFTERNOON.
THIN UPPER LEVEL CLOUD COVER IS ON THE INCREASE THIS AFTERNOON AHEAD
OF A S/WV TROUGH CROSSING THE RIO GRANDE VALLEY. THIS S/WV WILL
DEEPEN AN AREA OF SFC LOW PRESSURE LOCATED OVER THE WESTERN GULF OF
MEXICO AS IT ADVANCES EAST THROUGH THE NIGHT TONIGHT. AS A
RESULT...PRECIP CHANCES WILL INCREASE FROM THE SW OVERNIGHT AS THE
SFC LOW TRANSLATES TOWARD THE LA COAST. SOME DIFFERENCES EMERGE
AMONG THE NWP GUIDANCE AT THIS POINT CALLING THE EVENTUAL
PROGRESSION OF THIS SYSTEM INTO QUESTION. THE GFS REMAINS ON THE
FAST EDGE OF THE ENVELOPE THROUGH THE WEEKEND AND MAINTAINS A WEAKER
MORE PERSISTENT SFC LOW RIGHT ALONG THE COAST. THE ECMWF DEVELOPS A
MUCH DEEPER SURFACE LOW WITH SOME UNUSUAL BULLS EYES IN THE PRECIP
FIELDS LIKELY ASSOCIATED WITH GRID SCALE FEEDBACK PROBLEMS. SREF
CAME IN MORE WITH THE GFS IN TERMS OF SURFACE LOW TRACK ALTHOUGH WAS
NOT AS FAST PUSHING THE LOW INTO THE AL COAST. FOR THIS
PACKAGE...LEANED MORE ON THE SREF IN TERMS OF OVERALL SPEED OF THE
SYSTEM WITH A GFS/ECMWF/SREF BLEND FOR THE TRACK. THIS DID MEAN SOME
DIVERGENCE FROM THE 12Z MAV GUIDANCE POPS...PRIMARILY ON SATURDAY
AFTERNOON/NIGHT WHERE ALL AREAS GOT BUMPED ABOVE GUIDANCE. GFS
REALLY KEEPS THE RAIN ISOLATED SE OF THE NATCHEZ TRACE. THIS IS NOT
SUPPORTED BY THE ECMWF OR SREF WHICH BOTH SHOW MEASURABLE RAINFALL
ACROSS THE AREA DURING THESE TIMES. DO FEEL THE HEAVIEST RAINFALL
WILL BE SE OF THE TRACE...BUT NOT LIMITED TO THIS AREA.
AT THIS POINT...HEAVY RAINFALL WARRANTING ANY FLOOD PRODUCTS IS NOT
NEEDED AS PW VALUES STRUGGLE TO CLIMB ABOVE 1.25 IN...EVEN ACROSS
SOUTHEASTERN AREAS. RAINFALL TOTALS ON THE ORDER OF 0.50 TO 1 INCH
ARE PROBABLE ACROSS THE CWA WITH THE HIGHEST AMOUNTS SE OF THE
TRACE. THAT BEING SAID...LOCALIZED AREAS RECEIVING A LITTLE OVER AN
INCH IS NOT OUT OF THE QUESTION. EASTERLY WINDS ARE STILL EXPECTED
TO INCREASE TOMORROW AFTERNOON AS THE SFC LOW NEARS. STRONGEST WINDS
WILL BE LIMITED TO AREAS S AND E...AND WILL GO AHEAD AND ISSUE A
LAKE WIND ADVISORY FOR THE ROSS BARNETT RES AND LAKE OKATIBBEE
STARTING LATE TOMORROW MORNING. THIS IS A MARGINAL EVENT CONSIDERING
THE SYNOPTIC SET-UP AND WILL BE WATCHED CLOSELY FOR POSSIBLE
TEMPORAL AND AREAL CHANGES AS THIS SYSTEM EVOLVES. IN ADDITION...
WENT AHEAD AND LEFT A SLIGHT CHANCE OF A THUNDERSTORM OR TWO
DEVELOPING ACROSS SERN AREAS TOMORROW AFTERNOON INTO THE EARLY
EVENING. GFS HINTS AT 100-200 J/KG OF MUCAPE SLIDING ACROSS THE AREA
AS THE LOW MAKES ITS CLOSEST POINT OF APPROACH AND COUPLED WITH DEEP
LAYER LIFT IN PLACE AHEAD OF THE UPPER LEVEL S/WV...FEEL THE CHANCES
ARE NON-ZERO.
PRECIP WILL CONTINUE INTO THE OVERNIGHT HOURS SAT NIGHT BEFORE
BEGINNING TO TAPER OFF FROM W TO E LATE SUN MORNING INTO THE
AFTERNOON AS THE BEST LIFT AND LOW LEVEL MOISTURE FEED MOVE INTO AL.
S/WV RIDGING AND SFC HIGH PRESSURE MOVE INTO THE ARKLAMISS LATE
SUNDAY AND SHOULD PROVIDE SOME CLOUD CLEARING AS A RESULT. WINDS
LOOK TO GO VERY LIGHT OR EVEN CALM MONDAY NIGHT...AND CONSIDERING
THE LACK OF A COOL/DRY PUSH AND RESIDUAL SFC MOISTURE FROM THE
RAINS, ADDED SOME PATCHY FOG FOR MONDAY MORNING.
MAV TEMPS LOOKED GOOD EXCEPT FOR SUN AFTERNOON HIGHS WHERE GFS
APPEARED TOO WARM CONSIDERING THE LINGERING RAIN AND CLOUD COVER.
WENT AHEAD AND LOWERED TEMPS A DEGREE OR TWO AREAWIDE AT THAT TIME.
/BK/
PREVIOUS LONG TERM...FOR MID- TO LATE-WEEK
A SERIES OF SHORTWAVE
TROUGHS AND ASSOCIATED SURFACE COLD FRONTS WILL DIVE SOUTHEASTWARD
ACROSS THE MIDWEST AND OHIO VALLEY REGIONS...CARVING OUT A MEAN
TROUGH OVER THE EASTERN CONUS. NWP MODEL GUIDANCE HAS COME INTO
BETTER AGREEMENT IN DROPPING ONE OF THESE COLD FRONTS SOUTHWARD
ACROSS THE REGION ON TUESDAY. THE FRONT WILL BECOME MORE SHALLOW AS
IT APPROACHES AND MOVES ACROSS THE ARKLAMISS AS THE ASSOCIATED UPPER
TROUGH AND STRONGER DEEP-LAYER SYNOPTIC-SCALE ASCENT REMAIN WELL
NORTH OF THE AREA. NEVERTHELESS... MOISTURE POOLING ALONG THE
BOUNDARY RESULTING IN PWATS NEAR ONE INCH WILL BE SUFFICIENT FOR
ISOLATED LIGHT SHOWERS ALONG OR JUST BEHIND THE SURFACE FRONT...ALONG
WITH AN INCREASE IN CLOUDS. POPS WERE LOWERED FROM MEX GUIDANCE TO
SLIGHT CHANCE FOR LATE MONDAY NIGHT OVER NORTHWESTERN AREAS...AS THE
OPERATIONAL GFS APPEARS TO MOVE THE FRONT TOO QUICKLY TO THE SOUTH
RELATIVE TO GFS ENSEMBLE MEMBERS AND ECMWF...AND WITH WEAK UPPER
SUPPORT OVER THE ARKLAMISS. BEHIND THE FRONT...WINDS WILL BECOME
NORTHERLY AND ADVECT COOLER AIR ACROSS THE REGION...WITH HIGH
PRESSURE BUILDING IN THE WAKE OF THE FRONT.
FOR WEDNESDAY NIGHT OR THURSDAY...A REINFORCING COLD FRONT WILL
QUICKLY SURGE SOUTH ACROSS THE REGION...THOUGH DEEP-LAYER DRY AIR
WILL BE IN PLACE /PWATS OF ONLY 0.3 INCHES/ PRECLUDING PRECIP CHANCES
WITH THIS FRONT. THE ONLY IMPACTS TO SENSIBLE WEATHER WITH THE FRONT
WILL BE AN INCREASE IN NORTH WINDS ALONG WITH THE POTENTIAL FOR MUCH
COOLER CONDITIONS LATE IN THE WEEK. THE CORE OF THE COLD AIRMASS
WILL REMAIN NORTH OF THE CWA...THOUGH GFS AND ECMWF INDICATE 850-MB
TEMPS FALLING TO 3C ACROSS NORTHERN AREAS BEHIND THE FRONT...
POTENTIALLY SUPPORTING TEMPERATURES SEVERAL DEGREES BELOW SEASONAL
AVERAGES. HOWEVER...SIGNIFICANT DIFFERENCES BETWEEN GFS AND ECMWF IN
THE CHARACTERISTICS OF THE ASSOCIATED UPPER TROUGH SUGGEST LOW
CONFIDENCE IN THE TIMING OF THE CORRESPONDING SURFACE FRONT...AS
WELL AS HOW COLD TEMPERATURES GET. /COHEN/
AVIATION
A LOW PRESSURE SYSTEM APPROACHING FROM THE WEST KEPT
THE CIRRUS SHIELD OVER THE REGION FOR THIS EVENING. THIS CLOUD DECK
WILL GRADUALLY LOWER TONIGHT...BUT CEILINGS SHOULD REMAIN ABOVE 8000
FT THROUGH THE NIGHT GIVEN THE VERY DRY LOW LEVEL AIR IN PLACE. AS
RAIN DEVELOPS OVER THE AREA NORTH OF A WARM FRONT...CEILINGS AND
VISIBILITY WILL DETERIORATE...ESPECIALLY AT JAN/HBG/MEI WHERE IFR
CEILINGS MAY BECOME PREVALENT PRIOR TO NOON SATURDAY. ALL SITES
COULD EXPERIENCE MVFR/IFR RESTRICTIONS DUE TO LOWER CEILINGS AND
RAIN AS WE GO INTO SATURDAY AFTN/NIGHT. GREATER INSTABILITY IN THE
MEI/HBG AREA WILL SUPPORT A FEW TSTMS FROM SATURDAY AFTERNOON INTO
SATURDAY EVENING. /17/
PRELIMINARY POINT TEMPS/POPS
JACKSON 46 58 45 61 / 22 89 63 13
MERIDIAN 44 57 45 61 / 22 86 80 24
VICKSBURG 46 58 45 62 / 22 89 58 9
HATTIESBURG 48 58 49 63 / 49 90 56 12
NATCHEZ 47 57 44 63 / 47 90 45 5
GREENVILLE 46 60 44 63 / 18 80 69 13
GREENWOOD 45 60 45 62 / 13 83 80 19
JAN WATCHES/WARNINGS/ADVISORIES
MS...LAKE WIND ADVISORY FROM 9 AM SATURDAY TO MIDNIGHT CST SATURDAY
NIGHT FOR MSZ043-049-052.
LA...NONE.
AR...NONE.
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