041
FXUS64 KJAN 091704
AFDJAN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
1055 AM CST TUE FEB 9 2010
UPDATE
WATER VAPOR IMAGERY/RUC ANALYSIS SHOWS THE CLOSED OVER
CENTRAL MISSOURI WITH A POTENT SHORTWAVE ROUNDING ITS BASE OVER
EASTERN MISSISSIPPI. THIS SHORTWAVE HAS HELPED MOVE THE
PRECIPITATION FARTHER EAST A LITTLE FASTER THAN EXPECTED THIS
MORNING AND BRING ABOUT CLEARING SKIES FROM THE WEST A LITTLE
FASTER. TEMPERATURES HAVE BEEN SLOWER TO COOL OVER OUR AREA THOUGH
AS THE STRONGEST CAA LOOKS TO BE GETTING A LATER START. HIGHS HAVE
ALREADY BEEN REACHED TODAY AND WILL COOL THROUGH THE AFTERNOON
ALTHOUGH AT A SLOWER RATE CONSIDERING A LITTLE MORE INSOLATION THAN
EXPECTED. HAVE UPDATED FCST TO ACCOUNT FOR LESS CLOUD COVER...END
MENTION OF PRECIPITATION AND SLOW COOLING OF TEMPERATURES THROUGH
THE DAY. GUSTY NW WINDS WERE BEING OBSERVED AND SHOULD INCREASE TO
LAKE WIND CRITERIA NEXT HOUR. GREATER MIXING OVER AREA LAKES WILL
RESULT IN LOCALLY HIGHER WINDS THERE SO WL MAINTAIN A WIND ADVISORY
THERE THIS AFTERNOON. UPDATES HAVE BEEN POSTED. /22/
AVIATION
LATEST SATELLITE IMAGERY SHOWS THE CLEARING LINE FROM
SOUTHEAST ARKANSAS TO NORTHWEST LOUISIANA...TRACKING EAST TOWARD THE
REGION. MVFR CEILINGS WAS NOTED ACROSS THE REGION WITH CEILINGS OF
1200-2000 FEET. EXPECT THOSE CEILINGS TO PERSIST UNTIL THE CLOUDS
BREAK UP FROM THE WEST FOR THIS AFTERNOON. BY THIS AFTERNOON...SKIES
WILL HAVE BEGUN CLEARING FROM NORTHWEST TO SOUTHEAST...WITH VFR
CONDITIONS EXPECTED AREAWIDE BY 10/0000 UTC. A FEW LOW-LEVEL CLOUDS
WILL DRIFT SOUTHEASTWARD ACROSS THE REGION TONIGHT. GUSTY NORTHWEST
WINDS ARE EXPECTED TO IMPACT THE REGION TODAY...WITH SPEEDS OF 15 TO
20 KT AND GUSTS BETWEEN 23 AND 28 KT. NORTHWEST WINDS WILL DIMINISH
TO 7 TO 13 KT AFTER 10/0000 AND CONTINUE INTO WEDNESDAY MORNING. /17/
PREV DISCUSSION
/ISSUED 616 AM CST TUE FEB 9 2010/
.ACCUMULATING SNOW EXPECTED THURSDAY NIGHT INTO FRIDAY
DISCUSSION...TODAY THROUGH WEDNESDAY NIGHT...THE DEEP-LAYER VORTEX
DROPPING SOUTHEASTWARD FROM THE UPPER MIDWEST HAS PHASED WITH A
FAST-MOVING SOUTHERN STREAM SHORTWAVE TROUGH...WITH ENHANCED
DEEP-LAYER ASCENT HAVING NOW PUSHED EAST OF THE FORECAST AREA. THE
INITIAL SURFACE COLD FRONT ASSOCIATED WITH THE SOUTHERN STREAM
DISTURBANCE HAS ACCELERATED EAST OF THE CWA BY THE MESOSCALE
CIRCULATION ASSOCIATED WITH THE LINEAR...ELEVATED CONVECTIVE BAND
THAT MOVED ACROSS THE CWA LAST NIGHT. IN THE WAKE OF THIS
FRONT...TEMPERATURES HAVE BEEN GRADUALLY FALLING THROUGH THE
40S...AND 30S ACROSS THE DELTA REGION. THE MODIFIED ARCTIC COLD FRONT
ASSOCIATED WITH THE AFOREMENTIONED VORTEX IS SURGING SOUTHEASTWARD
THIS MORNING AS APPARENT BY A FINE LINE BEING TRACKED ON KDGX RADAR.
THIS FRONT WILL BE FOLLOWED BY A FASTER DROP IN TEMPERATURES ALONG
WITH AN ABRUPT INCREASE IN NORTHWESTERLY WINDS. HIGH TEMPERATURES
TODAY WILL BE REACHED EARLY THIS MORNING BEFORE FALLING THROUGH THE
DAY...WITH AFTERNOON TEMPERATURES DROPPING INTO THE UPPER 20S AND
LOWER 30S NORTH OF INTERSTATE 20...AND THE LOWER AND MID 30S TO THE
SOUTH. TEMPERATURES ARE NOT EXPECTED TO WARM MUCH TODAY WITH AN
OVERCAST DECK OF LOW-LEVEL CLOUDS AND PERSISTENT COLD ADVECTION.
THE STRONG PRESSURE GRADIENT IN THE WAKE OF THE FRONT WILL
SUPPORT NORTHWEST WINDS OF 15 TO 25 MPH WITH GUSTS TO 30 MPH ACROSS
THE REGION...EXCEPT NORTHWEST WINDS OF 20 TO 30 MPH AND GUSTS TO 40
MPH ON THE LARGER LAKES. TIME-HEIGHT ANALYSES CONTINUE TO INDICATE
THE POTENTIAL FOR THE POST-FRONTAL MIXED LAYER BELOW THE 960 MB
LEVEL TO INTERSECT WIND SPEEDS OF 20-25 KT. THESE WINDS WILL
EFFICIENTLY BE MIXED TO THE LAKE SURFACES DUE TO LOCALIZED
INSTABILITY ENHANCEMENTS CAUSED BY THE COLD AIR OVERLAYING
RELATIVELY WARMER WATERS. THE STRONGEST WINDS WILL BE FOUND OVER THE
LARGER LAKES...WHERE A WIND ADVISORY IS IN EFFECT FOR TODAY.
ELSEWHERE...A LAKE WIND ADVISORY REMAINS IN EFFECT FOR THE SMALLER
LAKES. THE PRESSURE GRADIENT IS FORECAST TO SLACKEN THIS EVENING...
WHEN WINDS WILL BE SUBSIDING. THE WINDS TODAY WILL RESULT IN WIND
CHILL READINGS IN THE TEENS AND 20S.
LOW-LEVEL MOISTURE BENEATH 900 MB IN THE WAKE OF THE FRONT WILL
CONTINUE TO FILTER INTO THE REGION TODAY. AS THE COLDER AIR WEDGES
SOUTHEASTWARD INTO THE REGION TODAY...ISENTROPIC SURFACES BELOW THE
900 MB LEVEL WILL ASCEND AND SUPPORT AN OVERCAST DECK OF
STRATIFORM CLOUDS. ALSO...NWP MODEL GUIDANCE IS INDICATING THAT THE
ISENTROPIC ASCENT WILL BE SUFFICIENT TO SQUEEZE OUT PATCHY
PRECIPITATION ACROSS THE CWA. FORECAST SOUNDINGS INDICATE WET-BULB
ZERO HEIGHTS FALLING BELOW 1500 FT AND TEMPS AROUND 925 MB FALLING
TO BELOW -5C BEFORE THE LOW-LEVEL MOISTURE MOVES AWAY FROM THE
REGION. FORECAST SOUNDINGS AND SREF OUTPUT INDICATE THE POTENTIAL
FOR FLURRIES...DRIZZLE...AND POSSIBLY LIGHT SLEET TO OCCUR ACROSS
MUCH OF THE REGION NORTHWEST OF THE INTERSTATE 59 CORRIDOR THIS
MORNING. SURFACE TEMPERATURES WILL NOT LIKELY HAVE FALLEN BELOW
FREEZING FOR AN APPRECIABLE AMOUNT OF TIME WHILE DRIZZLE IS ONGOING
FOR FREEZING DRIZZLE TO BE A CONCERN...CONSISTENT WITH NEAR-ZERO
SREF PROBS FOR FREEZING RAIN. THUS...FREEZING RAIN/DRIZZLE IS BEING
LEFT OUT OF THE FORECAST. NO ACCUMULATIONS OF WINTRY PRECIPITATION
ARE EXPECTED TODAY...AND POPS HAVE BEEN KEPT AT OR BELOW 20 PERCENT
TODAY.
FOR TONIGHT...SKIES WILL BEGIN CLEARING AS SURFACE HIGH PRESSURE
OVER THE PLAINS BUILDS EASTWARD INTO THE FORECAST AREA. LOW TEMPS
TONIGHT WILL FALL INTO THE MID 20S. WHILE NORTHWEST WINDS WILL BE
DECREASING...THEY WILL STILL REMAIN IN THE 10 TO 15 MPH RANGE...
RESULTING IN WIND CHILL READINGS IN THE TEENS. SUFFICIENT MIXING
FROM THESE WINDS WILL KEEP THE REGION FROM EXPERIENCING OPTIMAL
RADIATIONAL COOLING CONDITIONS AND EVEN COLDER TEMPERATURES TONIGHT.
THEN FOR WEDNESDAY AND WEDNESDAY NIGHT...CONFLUENT NORTHWESTERLY
FLOW ALOFT WILL SUPPORT EASTWARD PROGRESSION OF THE AFOREMENTIONED
SURFACE HIGH. DRY CONDITIONS ARE EXPECTED FOR THIS PERIOD AS THE
ASSOCIATED RIDGE AXIS PASSES OVER THE REGION. HOWEVER...TEMPERATURES
WILL REMAIN 10 TO 15 DEGREES BELOW SEASONAL AVERAGES...WITH HIGHS IN
THE 40S AND LOWER 50S AND LOWS IN THE MID AND UPPER 20S. THESE TEMPS
ARE NEAR TO A FEW DEGREES BELOW MAV GUIDANCE GIVEN THE LINGERING
MODIFIED ARCTIC AIR OVER THE REGION. CLOUDS WILL BE INCREASING AHEAD
OF THE NEXT STORM SYSTEM FOR WEDNESDAY NIGHT. THE CLOUDS WILL KEEP
TEMPS FROM FALLING EVEN MORE THAN THOSE CURRENTLY ANTICIPATED.
/COHEN/
THURSDAY THROUGH NEXT TUESDAY...
THE FOCUS OF THIS FORECAST IS ON THE POTENTIAL HEAVY SNOW EVENT FOR
THU NIGHT INTO THE FIRST HALF OF FRI. ASIDE FROM THAT...TEMPS WILL BE
THE OTHER FOCUS.
FOR THU...WE WILL SEE A NICE CANADIAN SFC HIGH CENTERED OVER THE
MIDWEST WHICH WILL KEEP THE COOL CONDITIONS GOING OVER OUR REGION AS
WEAK CAA CONTINUES. ATOP THIS AIRMASS WAA WILL BE WELL UNDERWAY AND
WE WILL SEE A THICKENING/LOWERING MID LEVEL CLOUD DECK TAKE SHAPE.
THIS WILL MAKE THE TEMP FORECAST TRICKY AND READINGS WILL LIKELY BE
RATHER COOL WITH THE ENTIRE AREA ONLY REACHING 40-45 DEGREES. I ALSO
EXPECT SOME VIRGA ALOFT TO OCCUR AND THIS TYPICALLY HELPS TO KEEP
TEMPS FROM RISING TOO MUCH. I CAN SEE THE AREA BARELY REACHING
40...BUT I WILL STAY CONSERVATIVE AND USE A BLEND OF THE COLDER
ENSEMBLE MEAN AND OPS GFS MOS. BY THE SECOND HALF OF THE
AFTERNOON...SOME LIGHT PRECIP SHOULD BE ABLE TO REACH THE
GROUND...ESPECIALLY OVER THE W/SW CWA. THE THERMAL PROFILE SUGGESTS
A MIX OF -RA AND -PL (SLEET) FOR THE SW/S HALF. THE FURTHER N...WHAT
EVER REACHES THE GROUND COULD JUST BE ALL -SN WITH TEMPS FALLING TO
35-37 DEGREES.
THE MAIN EVENT/PRECIP WINDOW WILL BE THU NIGHT INTO THE FIRST HALF
OF FRI. THE LATEST MODEL DATA IS NOT IN THE BEST OF AGREEMENT...BUT
SOME SIMILARITIES EXIST AND HAVE BEEN CARRIED FROM THE PREV RUNS.
THE LATEST WITH THE GFS IS THAT IT IS MORE SUPPRESSED. THE SFC LOW
IS FURTHER SOUTH AND AS A RESULT...THE BEST ASCENT AND PRECIP
GENERATION REGION IS FURTHER S CLOSER TO I-10. IN TURN...THE OVERALL
ATMOSPHERE IS A TAD COLDER WHICH LEADS TO INCREASED CONFIDENCE THAT
PRECIP TYPE WILL BE ALL SNOW AFTER THE INITIAL LIGHT SLEET MIX. THE
EURO IS SIMILAR TO ITS PREV RUNS...A BIT WETTER...AND CLOSE TO THE
EARLIER GFS RUNS. IT TO IS A TAD COLDER AND PAINTS A SNOWIER
PICTURE. THE SREF AND GFS ENSEMBLE DATA IS MORE OF A BLEND OF THE
EURO/GFS AND IS THE WAY I WILL BE LEANING. THE SREF IS SLOWER AND IT
HAS MORE OF A NAM FLAVOR. I DON'T LIKE THE REAL SLOW SOLUTION AS
THOSE ARE OUTLIERS...SO A SLIGHTLY SPED UP SREF FITS GOOD WITH A
BLEND OF THE EURO/GFS. THE MAIN TIMEFRAME WILL WILL FOCUS MEASURING
SNOW AND ANY ACCUMULATING SNOW WILL BE BETWEEN 9 PM AND 10 AM...WITH
SOME STILL POSSIBLE A FEW HRS EITHER SIDE OF MY PREDICTED WINDOW.
AT THIS TIME...BASED OFF THE RECENT TRENDS FROM PREV RUNS AND PAST
EVENTS...THE MAIN AREAS THAT I EXPECT TO SEE MEASURABLE SNOW WILL BE
FOR LOCATIONS ALONG AND S OF I-20 WITH THE BEST POTENTIAL WITH IN
THE HWY 84 CORRIDOR. AMOUNTS BETWEEN 2-4 INCHES SEEMS STILL A GOOD
FIRST GUESS WITH SOME LOCATIONS SEEING A BIT MORE.
ADDITIONALLY...THE FURTHER N YOU GO...LIMITED MOISTURE AND BEING A
BIT REMOVED FROM THE BEST ASCENT SHOULD ONLY YIELD AN INCH OR SO.
NOW...THIS IS JUST MY BEST GUESS BASED OFF THE PREV MODEL RUNS AND
TRENDS FROM THE LATEST DATA. THERE STILL SEEMS TO BE DECENT SPREAD
IN THE MODEL GUID AND WITH THE TRACK OF THE GULF LOW STILL QUITE
UNCERTAIN...EXPECT THINGS TO CHANGE SOME WITH EACH MODEL RUN. LETS
HOPE THAT WITH THE FEATURE OF INTEREST JUST NOW COMING ONSHORE IN
CENTRAL CA...THAT THE MODELS WILL QUICKLY PICK UP ON A SOLUTION AND
CONVERGE TO SOMETHING IN THE NEXT 24-36HRS.
ANOTHER PRIMARY FORECAST ISSUE FOR FRI IS TEMPS. FOR SOME
REASON...GUID TEMPS ARE VERY WARM FOR HIGHS WITH VALUES RANGING FROM
THE LOWER/UPPER 40S. I WILL BE CUTTING THOSE SIGNIFICANTLY. WITH THE
COMBINATION OF SNOWY PRECIP FALLING/LINGERING INTO MIDDAY AND THEN
CLOUDS LASTING THROUGH THE DAY ALONG WITH AT LEAST SOME WEAK
CAA...TEMPS SHOULD ONLY REACH THE MID/UPPER 30S AT BEST.
IN THE WAKE OF THE THU/FRI SYSTEM...SFC HIGH PRESSURE LOOKS TO
SETTLE OVER THE REGION FOR SAT/SAT NIGHT. BY SUN...ALL GUID IS
INDICATING A POTENT UPPER LOW WILL DIVE SE OUT OF THE N PLAINS AND
HELP TO CARVE OUT A FAIRLY LARGE E CONUS TROUGH FOR EARLY WEAK. AS
THIS OCCURS...A SOLID COLD FRONT WILL CROSS THE REGION SOMETIME LATE
SUN INTO EARLY MON AND RE-ENFORCE THE COLD CONDITIONS AND BELOW
NORMAL PATTERN. AS FOR TEMPS SAT-TUE...GUID VALUES WERE GENERALLY
GOOD AND ACCEPTED. THE ONLY MAJOR ADJ WAS TO WARM SUN HIGHS AS THE
00Z GFS WAS TOO QUICK WITH THE FROPA AND GOING WITH A SLOWER/WARMER
SOLUTION FIT BEST. /CME/
AVIATION
A COLD FRONT HAS PUSHED EAST OF THE REGION THIS MORNING...WITH
WIDESPREAD RAIN HAVING EXITED THE AREA. AN OVERCAST DECK OF
LOW-LEVEL CLOUDS WILL IMPACT THE ENTIRE AREA THIS MORNING...WITH
CEILINGS IN THE MVFR AND IFR CATEGORIES....AND OCCASIONAL LIFR
CEILINGS EAST OF INTERSTATE 55. THERE WILL BE A SLIGHT CHANCE OF
DRIZZLE...FLURRIES...AND SLEET DURING THE MORNING HOURS ACROSS MUCH
OF THE AREA...THOUGH NO ACCUMULATIONS OF THIS PRECIPITATION ARE
EXPECTED. MVFR VISIBILITIES COULD ACCOMPANY THIS PRECIPITATION. THE
CHANCE FOR THE WINTRY PRECIPITATION TO IMPACT THE TAF SITES IS
TOO LOW FOR MENTION IN THE TAFS AT THIS TIME. CEILINGS ARE EXPECTED
TO BECOME MVFR AREAWIDE BY LATE MORNING INTO EARLY AFTERNOON. BY
LATE AFTERNOON...SKIES WILL HAVE BEGUN CLEARING FROM NORTHWEST TO
SOUTHEAST...WITH VFR CONDITIONS EXPECTED AREAWIDE BY 10/0000 UTC. A
FEW LOW-LEVEL CLOUDS WILL DRIFT SOUTHEASTWARD ACROSS THE REGION
TONIGHT. GUSTY NORTHWEST WINDS ARE EXPECTED TO IMPACT THE REGION
TODAY...WITH SPEEDS OF 15 TO 20 KT AND GUSTS BETWEEN 23 AND 28 KT.
NORTHWEST WINDS WILL DIMINISH TO 7 TO 13 KT AFTER 10/0000 AND
CONTINUE INTO WEDNESDAY MORNING. /COHEN/
PRELIMINARY POINT TEMPS/POPS
JACKSON 40 25 46 28 / 5 3 0 5
MERIDIAN 45 25 48 26 / 8 3 0 4
VICKSBURG 38 27 44 29 / 4 3 0 8
HATTIESBURG 47 27 52 29 / 8 3 3 9
NATCHEZ 41 26 46 28 / 4 3 1 11
GREENVILLE 35 26 41 27 / 4 3 0 4
GREENWOOD 35 24 43 26 / 4 3 0 3
JAN WATCHES/WARNINGS/ADVISORIES
MS...LAKE WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR MSZ018-019-
025>066-072>074.
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 LAZ007>009-
015-016-023>026.
WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR LAZ009.
AR...LAKE WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR ARZ074-075.
WIND ADVISORY UNTIL 6 PM CST THIS EVENING FOR ARZ075.
MME/CME/17
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