FXUS64 KJAN 260343 AAA
AFDJAN
AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE JACKSON MS
943 PM CST FRI DEC 25 2009
.DISCUSSION...
UPDATE:
THE FORECAST IS ON TRACK AS WEAK HIGH PRESSURE AND DRY WESTERLY FLOW
MAINTAIN CONTROL OF THE WEATHER OVER THE ARKLAMISS. TEMPERATURES ARE
COOLING AT A SLIGHTLY FASTER RATE THAN FORECAST...BUT SOME HIGH THIN
CIRRUS STREAMING ACROSS THE AREA IN THE SUBTROPICAL STREAM COULD
INTERRUPT NOCTURNAL COOLING ENOUGH TO KEEP TEMPERATURES FROM FALLING
BELOW FORECASTED LOWS. THE UPDATED AVIATION DISCUSSION IS BELOW.
/EC/
PREVIOUS DISCUSSION...
SURFACE HIGH(1020MB) ALONG THE MIDDLE TX COAST WILL
BUILD NEWD ALONG THE GULF COAST TONIGHT IN THE WAKE OF OUR CHRISTMAS
EVE STORM SYSTEM NOW SPINNING THROUGH THE UPPER MS VALLEY. SATELLITE
VISIBLE IMAGES SHOWING A VERY NICE CLEARING OF THE CAA STRATOCU WAS
DEPARTING OUR NERN COUNTIES LEAVING ONLY SCATTERED THIN CIRRUS IN
PLACE. WLY SURFACE WINDS HAVE SLACKED UP TO GENERALLY LESS THAN 15
MPH AND HAVE TERMINATED THE LAKE WIND ADVY. DRY AIR SPREADING ACROSS
THE CWFA AND HAVE LOWERED DEWPOINTS A BIT MORE THAN GUIDANCE
FORECASTS AS THE HIGH PRESSURE PASSES SOUTH OF THE REGION.
LOW TEMPS SHOULD EASILY REACH M-U20S AS FLOW COMING STRAIGHT OFF THE
EXTENSIVE SNOW COVER OVER N TX/OK. OTHERWISE...THE WEAK SURFACE HIGH
SLIDES INTO NRN FL SATURDAY AFTERNOON ALLOWING OUR LOW LEVEL FLOW TO
BACK AROUND TO THE SW AS HIGHER LEVEL MOISTURE INCREASES MORE
RAPIDLY. HIGHS WILL ALSO BE A TAD WARMER SATURDAY AFTERNOON REACHING
CLOSE TO NORMS. ELEVATED UPGLIDE ON THE 315-325K CONTINUES THROUGH
SATURDAY NIGHT WITH SOME SPRINKLES/LIGHT RAIN POSSIBLY REACHING THE
GROUND OVER OUR SRN CWFA WELL AFTER MIDNIGHT WHEN TEMPS WILL BE
REBOUNDING FROM EARLIER LOWS JUST BELOW FREEZING. NAM HOLDS ALL
RAINFALL GENERALLY S OF THE COAST WHILE THE ECMWF WAS WETTER AND THE
GFS WAS A SOLID COMPROMISE OF THE TWO...SO THE MODEL OF CHOICE.
ON SUNDAY...A FRESH SURGE OF COLD AIR ARRIVES BY AFTERNOON WITH THE
PASSAGE OF A SHORTWAVE ROTATING AROUND THE GREAT LAKES UPPER LOW.
COLDER THAN NORMAL TEMPERATURES RETURN FOR THE START OF THE WEEK WITH
A 1030MB+ SURFACE HIGH MOVING OVER THE CENTRAL PLAINS SNOW FIELDS AND
INTO THE LOWER MS VALLEY BY LATE MONDAY. LOWS WILL GENERALLY BE BACK
INTO THE 20S AND HIGHS 45 TO 55 FROM SUNDAY NIGHT INTO TUESDAY.
SHORTWAVE RIDGING ALOFT IS EXPECTED TO DEVELOP OVER OUR REGION
TUESDAY TO ALLOW THE START OF SOME MODIFYING TEMPS BY WEDNESDAY.
HOWEVER...MOISTURE AND CLOUDS INCREASING FROM THE WEST TUESDAY
AFTERNOON COULD SHUT DOWN MUCH OF THE WARMING. BOTH THE GFS AND
ECMWF BRING PRECIPITATION BACK INTO OUR CWA TUESDAY NIGHT THROUGH
WEDNESDAY WITH QPF AMOUNTS OF ONE HALF TO ONE INCH. OBVIOUSLY...THE
TIMING OF THE PRECIPITATION AND JUST HOW MUCH TEMPS MODIFY WILL BE A
HUGE FACTOR TO OUR EVENTUAL OUTCOME. THE ECMWF IS STRONGER WITH THE
SHORTWAVE TROUGH THAN THE GFS AND DEVELOPS A SFC LOW FARTHER NORTH
OVER THE WESTERN GULF. WILL HAVE TO MONITOR THESE FACTORS CLOSELY
NEXT WEEK AS WE END 2009./40/
THE REST OF THE PREVIOUS DISCUSSION HINTS AT THE ISSUES AHEAD...
BOTH MODELS HAVE CRITICAL THICKNESSES JUST NORTH OF OUR AREA EARLY
WEDNESDAY AND WELL NORTH OF WHERE THE SIGNIFICANT RAINFALL IS
EXPECTED. AGAIN WL NOT INCLUDE MENTION OF WINTRY MIX PRECIPITATION
WITH THIS PACKAGE BUT FUTURE MODEL RUNS MAY END UP TRENDING COLDER.
BY WEDNESDAY NIGHT BOTH GFS AND ECMWF HAVE SFC LOWS JUST SOUTH OF OUR
CWA BUT WITH THE ECMWF BEING OVER SOUTHERN LOUISIANA AND THE GFS
SOUTH OVER THE NORTHERN GULF WATERS. THE RAIN WILL END FROM THE WEST
THURSDAY AS THE SFC LOW AND SHORTWAVE TROUGH SHIFT EAST. THE ECMWF
HAS A SIGNIFICANTLY LARGER AMPLITUDE UPPER LEVEL TROUGH OVER THE
CENTRAL CONUS FRIDAY AND IS MUCH COLDER OVER OUR REGION THAN THE GFS
BUT FRIDAY LOOKS DRY. /22/
&&
.AVIATION...VFR CONDITIONS WITH GENERALLY LIGHT WINDS WILL PREVAIL
THROUGH SATURDAY NIGHT AS HIGH PRESSURE REMAINS OVER THE AREA. /EC/
&&
.JAN WATCHES/WARNINGS/ADVISORIES...
MS...NONE.
LA...NONE.
AR...NONE.
&&
$$
