FXUS64 KJAN 250152 AAA
AFDJAN
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
752 PM CST THU DEC 24 2009
.UPDATE...
DESPITE LARGE AMOUNT OF MID/UPPER-LEVEL DRYING...PARTICULARLY STRONG
850-700 MB FRONTOGENESIS DRIVEN BY DEEPENING LOW PRESSURE NORTHWEST
OF THE REGION IS FORCING BANDS OF LOW-TOPPED SHOWERS TO DEVELOP
ACROSS CENTRAL MISSISSIPPI...WHERE THE FORECAST HAS BEEN UPDATED TO
RAISE POPS TO THE LIKELY CATEGORY. ADDITIONALLY...THE LARGE AREA OF
SHOWERS OVER THE EASTERN CWA CONTINUES PUSHING EASTWARD AND POPS HAVE
BEEN REDUCED TO LIKELY WEST OF THE AREA. /COHEN/
&&
.PREV DISCUSSION... /ISSUED 724 PM CST THU DEC 24 2009/
PREVIOUS UPDATE...
A COMPLEX LOW PRESSURE SYSTEM CONTINUES TO IMPACT THE SOUTH CENTRAL
AND SOUTHEASTERN CONUS. SURFACE LOW PRESSURE OVER WESTERN ARKANSAS IS
ASSOCIATED WITH AN OCCLUDED FRONT THAT TRAILS SOUTHEASTWARD ACROSS
THE EASTERN CWA. NEAR THIS FRONT...STRONG DEEP-LAYER ASCENT CONTINUES
SUPPORTING NUMEROUS SHOWERS OVER THE EASTERN AND NORTHERN CWA...WHERE
POPS WERE INCREASED FOR THIS EVENING. BEHIND THE OCCLUDED
FRONT...WINDS SHIFT TO THE SOUTH TO SOUTHWEST AT 15 TO 25...WITH
SPEEDS OF 20 TO 30 MPH ACROSS THE MISSISSIPPI DELTA. THESE WINDS ARE
BEING DRIVEN BY THE STRONG PRESSURE GRADIENT IN THE SOUTHERN
SEMICIRCLE OF THE BROAD SURFACE CIRCULATION. THE ASSOCIATED MID/UPPER-
LEVEL CIRCULATION CENTER IS OVER SOUTHERN ARKANSAS...WITH RECENT
WATER VAPOR IMAGERY INDICATING A PRONOUNCED MID/UPPER-LEVEL DRY SLOT
BETWEEN THE CIRCULATION CENTER AND THE BELT OF MOIST AND DIFFLUENT
SOUTHWESTERLY FLOW ALOFT PARTLY RESPONSIBLE FOR SEVERE WEATHER ACROSS
THE ARKLAMISS EARLIER TODAY. THIS DRY SLOT IS CURRENTLY ENTERING
WESTERN PORTIONS OF THE CWA...REDUCING PRECIP CHANCES TEMPORARILY.
POPS ACROSS THE SOUTHWESTERN TWO-THIRDS OF THE FORECAST AREA WERE
DROPPED TO THE SLIGHT CHANCE TO CHANCE CATEGORY BASED ON THESE
TRENDS. HOWEVER...LOW-LEVEL CLOUDS AND PERHAPS A FEW LOW-TOPPED
SHOWERS WILL PERSIST AS MOISTURE TRAPPED BENEATH A LOW-LEVEL
INVERSION WILL CONTINUE WRAPPING AROUND THE CYCLONE INTO THE REGION.
ADDITIONAL LOW/MID-LEVEL MOISTURE IN THE WESTERN SEMICIRCLE OF THE
CIRCULATION IS EXPECTED TO MOVE ACROSS CENTRAL AND NORTHERN PORTIONS
OF THE CWA TONIGHT...RESULTING IN A SLIGHT CHANCE FOR FLURRIES/SPRINKLES
ACROSS THESE AREAS AFTER MIDNIGHT. SOUNDINGS SHOW MOSTLY SUB-FREEZING
TEMPERATURE PROFILES THROUGHOUT THE ATMOSPHERIC COLUMN BY LATE
TONIGHT...WITH A COMBINATION OF CRYSTAL GROWTH AND SUPERCOOLED LIQUID
WATER BEING SUPPORTED BY MINIMUM WET-BULB TEMPERATURES WITHIN THE
LOW-LEVEL COLD LAYER BELOW H85 AROUND -7C. THIS PRECIPITATION WILL BE
FURTHER SUPPORTED BY A SECONDARY/REINFORCING SURFACE COLD FRONT
PROGGED TO MOVE ACROSS THE REGION LATER TONIGHT. AS THIS FRONT MOVES
ACROSS THE REGION...WINDS WILL CONTINUE TO ATTAIN MORE OF A WESTERLY
COMPONENT. LOW TEMPERATURES TONIGHT WERE ADJUSTED DOWNWARD ACROSS
MOST AREAS BY A COUPLE DEGREES BASED ON LATEST GUIDANCE...AND GIVEN
THE SOURCE REGION OF THE APPROACHING COLD AIRMASS MARKED BY
SUBFREEZING OBSERVED TEMPS UPSTREAM.
OTHERWISE...ALL TORNADO AND FLASH FLOOD WATCHES WERE ALLOWED TO
EXPIRE EARLIER. THE WIND ADVISORY FOR THE MISSISSIPPI DELTA AND THE
LAKE WIND ADVISORY FOR THE REMAINDER OF THE REGION REMAIN IN EFFECT.
/COHEN/
PREV DISCUSSION... /ISSUED 342 PM CST THU DEC 24 2009/
SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT...SQUALL LINE CURRENTLY
WORKING ITS WAY ACROSS THE EASTERN PORTIONS OF THE ARKLAMISS THIS
AFTERNOON AND SHOULD BE MOSTLY THROUGH THE AREA BY EARLY EVENING WITH
ONLY SOME POST FRONTAL SHOWERS REMAINING. THE GFS KEEPS SOME WRAP
AROUND MOISTURE ACROSS THE AREA TONIGHT WITH SOME LIGHT RAIN POSSIBLY
CHANGING OVER TO FLURRIES BEFORE ENDING IN THE EARLY MORNING...WITH
NO MEASURABLE ACCUMULATIONS EXPECTED. SANTA WILL BE ABLE TO MAKE
QUICK WORK ACROSS THE DELTA TONIGHT AS THE WINDS WILL CONTINUE TO BE
GUSTY WITH A STRONG SURFACE GRADIENT CONTINUING TONIGHT BEFORE
WEAKENING A BIT DURING THE EARLY MORNING. WILL ALSO LEAVE A LAKE WIND
ADVISORY IN AFFECT FOR THE REMAINDER OF THE AREA THROUGH FRIDAY
AFTERNOON. SKIES WILL BECOME PARTLY CLOUDY CHRISTMAS WITH VERY COOL
TEMPERATURES RANGING FROM NEAR 40 IN THE NORTH TO THE UPPER 40S IN
THE SOUTH.
TEMPERATURES WILL BE PRETTY COLD TOMORROW NIGHT WITH MOST AREAS
FALLING INTO THE UPPER 20S. THE MODELS DIVERGE A BIT ON SATURDAY
WITH THE GFS DEVELOPING A SHORT WAVE AND ASSOCIATED SURFACE LOW IN
THE GULF AND MOVE IT ACROSS THE NORTHERN GULF SATURDAY NIGHT INTO
SUNDAY MORNING. THE EURO DOES NOT DEVELOP THIS FEATURE AND BUILDS
STRONG HIGH PRESSURE RIDGING OVER THE AREA. WILL JUST BLEND THE MODELS
AND INTRODUCE JUST A SLIGHT CHANCE OF LIGHT RAIN IN THE SOUTH
SATURDAY NIGHT. STUCK PRETTY CLOSE TO GUIDANCE THROUGH THE PERIOD
WITH ONLY SOME MINOR CHANGES TO HIGHS ON SATURDAY AND TO POPS
SATURDAY NIGHT. WILL ATTACH THE APPLICABLE PREVIOUS LONG TERM
DISCUSSION BELOW./15/
PREVIOUS LONG TERM...SUNDAY INTO MONDAY THE LARGE UPPER VORTEX WILL
FINALLY LIFT OUT TO THE NORTHEAST BUT ANOTHER LARGE CLOSED LOW WILL
BE DROPPING SOUTH DOWN THE WESTERN CONUS. SHORTWAVE RIDGING SURFACE
AND ALOFT IS EXPECTED OVER OUR REGION MONDAY INTO TUESDAY. THIS
SHOULD BRING US SOME WARMER TEMPS TUESDAY ALTHOUGH THE SURFACE HIGH
WILL BE CENTERED NORTH OF OUR REGION KEEPING OUR REGION UNDER A DRY
NORTH FLOW. THE GFS AND ECMWF ARE IN A LITTLE BETTER AGREEMENT THIS
MORNING IN MOVING PRECIPITATION BACK INTO THE REGION LATE
TUESDAY...PROBLEM IS THAT COLD TEMPERATURES ARE EXPECTED IN OUR AREA
WITH THE PRECIPITATION. THE LARGE UPPER LOW THAT WAS DROPPING SOUTH
DOWN THE WESTERN CONUS MONDAY WILL OPEN UP AND SWING EAST THROUGH
MID WEEK. THE ECMWF IS STRONGER WITH THE SHORTWAVE TROUGH THAN THE
GFS BY TUESDAY NIGHT BUT LIGHT RAIN IS EXPECTED TO SPREAD ACROSS OUR
AREA FROM THE SOUTHWEST LATE TUESDAY AND TUESDAY NIGHT. TEMPERATURES
WILL DROP THROUGH THE EVENING AND THERE IS SOME POTENTIAL FOR A
WINTRY MIX OR LIGHT SNOW IN THE NORTH AFTER MIDNIGHT. THERE ARE
SIGNIFICANT DIFFERENCES BETWEEN THE GFS AND ECMWF WEDNESDAY THROUGH
THURSDAY WITH THE POSSIBLE DEVELOPMENT OF A SURFACE LOW OVER THE
NORTHERN GULF AND CONTINUED RAIN CHANCES THROUGH WEDNESDAY INTO
THURSDAY. FOR NOW WL LEAN TOWARD THE GFS WITH SLIGHTLY WARMER
TEMPERATURES AND THE RAIN TAPERING OFF WEDNESDAY NIGHT BEFORE
INCREASING FROM THE SOUTH AGAIN THURSDAY AS ANOTHER SHORTWAVE HELPS
DEVELOP A STRONGER SURFACE LOW OVER THE NORTHERN GULF. THERE MAY
AGAIN BE SOME WINTRY MIX PRECIPITATION WEDNESDAY NIGHT INTO THURSDAY
MORNING. /22/
&&
.AVIATION...
IFR CONDITIONS WILL PREVAIL ALONG AND BEHIND A SQUALL
LINE IN ERN MS WHILE A COLD FRONT CROSSING THE ARKLATEX STARTS
RACING EWD OVERNIGHT. SSE SURFACE WINDS OF 25KTS WILL CONTINUE AHEAD
OF THE SQUALL LINE AND THEN SHIFT TO THE SW AT 15-25KTS. WINDS WILL
GRADUALLY BECOME WLY AT 15-25KTS WITH HIGHER GUSTS AS THE THE FRONT
PASSES TONIGHT. THE IFR CEILINGS OF 2-3K FEET SHOULD PERSIST FOR
MUCH OF CHRISTMAS MORNING WITH INCREASING CAA AND NWLY WINDS.
CEILINGS SHOULD BECOME BROKEN AT 4-6K FEET AFTER 17Z ALONG THE MS
RIVER WITH IMPROVING CONDITIONS SPREADING EWD THROUGH THE AFTERNOON.
VFR CONDITIONS WILL RESUME FRIDAY NIGHT AND THROUGH THE WEEKEND./40/
&&
.PRELIMINARY POINT TEMPS/POPS...
JACKSON 34 43 27 51 / 61 9 12 9
MERIDIAN 36 44 26 51 / 68 10 12 10
VICKSBURG 34 44 29 51 / 33 8 11 8
HATTIESBURG 36 48 26 53 / 55 9 10 7
NATCHEZ 34 43 27 52 / 15 7 10 7
GREENVILLE 32 41 28 47 / 19 10 12 10
GREENWOOD 33 39 27 48 / 41 11 13 11
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...LAKE WIND ADVISORY UNTIL 3 PM CST FRIDAY FOR MSZ026>033-036>039-
042>066-072>074.
WIND ADVISORY UNTIL 3 AM CST FRIDAY FOR MSZ018-019-025-034-035-
040-041.
LA...LAKE WIND ADVISORY UNTIL 3 PM CST FRIDAY FOR LAZ015-016-023>026.
WIND ADVISORY UNTIL 3 AM CST FRIDAY FOR LAZ007>009.
AR...WIND ADVISORY UNTIL 3 AM CST FRIDAY FOR ARZ074-075.
&&
$$
