FXUS64 KMEG 230244
AFDMEG
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEMPHIS TN
844 PM CST TUE DEC 22 2009
.DISCUSSION...
LIGHT SHOWERS WERE NOTED OVER NORTHEAST ARKANSAS THIS EVENING.
RAIN WILL LIKELY INCREASE OVERNIGHT ESPECIALLY WEST OF THE
MISSISSIPPI RIVER...HOWEVER MEASURABLE RAINFALL OVER THE REMAINDER
OF THE MIDSOUTH CANNOT BE RULED OUT. THUS THE RAIN FORECAST WILL
REMAIN UNCHANGED. INTENSITY SHOULD PICK UP WEST OF THE RIVER AFTER
4 AM. THE BULK OF HEAVIER RAINFALL WILL WAIT UNTIL THURSDAY TO
AFFECT THE REMAINDER OF THE REGION.
OVERNIGHT TEMPERATURES WILL BE NEAR 50 DEGREES. BUMPED THEM UP
SLIGHTLY FROM PREVIOUS FORECAST. WINDS WILL INCREASE AFTER
MIDNIGHT. NO OTHER CHANGES NECESSARY.
AC
&&
.PREV DISCUSSION... /ISSUED 318 PM CST TUE DEC 22 2009/
DISCUSSION...
AN ACTIVE FEW DAYS LEADING UP TO THE CHRISTMAS HOLIDAY. AT
DISCUSSION TIME...GOES WATER VAPOR IMAGERY SHOWED A CLOSED UPPER
LOW DIVING SOUTH INTO THE GREAT BASIN...PRECEDED BY ANOTHER CLOSED
UPPER LOW TO THE SOUTH MOVING INTO AZ. NOW THAT THESE FEATURES
HAVE COME ASHORE...THEY HAVE BEEN BETTER SAMPLED BY THE UPPER AIR
NETWORK AND THE 12Z MODELS WERE SHOWING TIGHTER AGREEMENT.
THROUGH TONIGHT...THE TWO UPPER LOWS WILL COMBINE TO FORM ONE
MEAN TROF OVER THE FOUR CORNERS REGION. WHILE FORMING ONE LARGE
LONGWAVE TROF...THE CONSTITUENT UPPER LOWS WILL NOT LOSE THEIR
INDIVIDUAL IDENTITIES. INCREASINGLY DIFFLUENT UPPER FLOW DOWNSTREAM
OF THE MEAN UPPER LOW WILL RESULT IN INCREASING HIGH BASED SHOWERS
OVER THE LOWER MS RIVER VALLEY. RADAR MOSAIC INDICATED THAT THIS
ACTIVITY HAD ALREADY FORMED AT DISCUSSION TIME... A FEW HOURS AHEAD
OF SCHEDULE. EXPECT INCREASING COVERAGE OF SHOWERS OVERNIGHT...WITH
THE APPROACH OF STRONGER LIFT AND DEEPENING MOISTURE.
WEDNESDAY WILL SEE THE MAIN UPPER LOW LIFT INTO EASTERN KS/NE...
WHILE THE SOUTHERN LOW/VORT LOBE DROPS INTO SOUTH TX. THIS LATTER
FEATURE WILL BECOME NEGATIVELY TILTED THURSDAY MORNING AND EJECT
THROUGH THE LOWER AND MID MS RIVER VALLEY DURING THE DAY. EXPECT A
SURFACE OCCLUDED FRONT TO EXTEND FROM A 995 TO 1000 MB SURFACE LOW
NEAR THE MO/AR BORDER...SOUTH TO A DEVELOPING SECONDARY SURFACE
LOW OVER CENTRAL MS. A NARROW BAND OF WEAK INSTABILITY...PERHAPS
SURFACED BASED...PERHAPS NOT...WILL EXTEND NORTH UP THE MS DELTA
AHEAD OF THE OCCLUDED FRONT...AND SOUTH OF WARM FRONT LIFTING
THROUGH CENTRAL MS AND WESTERN AL.
WHILE WIND SHEAR WILL BE IMPRESSIVE...UPDRAFT STRENGTH WILL LIKELY
BE MARGINAL AT BEST. NAM FORECASTED MUCAPES ONLY REACH AROUND 100
J/KG AHEAD OF THE OCCLUDED FRONT OVER NORTH MS THURSDAY AFTERNOON.
EXPECT AND AREA OF RAIN...WITH EMBEDDED THUNDER. BEST INSTABILITY
WILL REMAIN CLOSER TO THE GULF COAST. FOR THE MIDSOUTH...THE MAIN
STORY WILL BE THE STRONG PRESSURE GRADIENT WINDS. 12Z MAV GUIDANCE
HAS MODERATED PROGGED WIND SPEEDS SINCE YESTERDAY/S RUN. LATEST
MAV GUIDANCE APPEARS MORE REASONABLE GIVEN THE WIDESPREAD RAIN AND
STABLE BOUNDARY LAYER. NONETHELESS...EXPECT WINDS TO REACH WIND
ADVISORY CRITERIA ON WEDNESDAY NIGHT AND THURSDAY.
THE UPPER LOW SHOULD LIFT RAPIDLY INTO THE NORTHERN MS RIVER
VALLEY BY THURSDAY NIGHT. A DRY SLOT SHOULD EFFECTIVELY END PRECIP
CHANCES ACROSS THE MIDSOUTH BY MIDEVENING...BUT MAY SEE SUFFICIENT
RESIDUAL LOW LEVEL MOISTURE AND MIDLEVEL LIFT FOR SPRINKLES OR A
FEW RAIN SHOWERS. NORTHEAST AR MAY EVEN SEE A FEW SNOW FLAKES MIXING
IN. VERY LIGHT...NON MEASURABLE SNOW SHOWERS MAY OCCUR FURTHER
EAST ACROSS NORTHERN WEST TN AFTER MIDNIGHT THURSDAY NIGHT.
ANOTHER UPPER LOW WILL DIVE SOUTH FROM CANADA INTO THE BASE OF THE
MEAN UPPER TROF THURSDAY NIGHT...EJECTING INTO THE OZARK REGION BY
CHRISTMAS MORNING. THIS WILL DRIVE A SURFACE ARCTIC COLD FRONT
THROUGH THE MIDSOUTH DURING THE AFTERNOON. MOISTURE WILL REMAIN
LIMITED...BUT CANNOT RULE OUT ISOLATED SNOW SHOWERS CHRISTMAS
MORNING OVER NORTHEAST AR...THE MO BOOTHEEL AND NORTHERN WEST TN.
HAVE UNDERCUT GFS MEX GUIDANCE TEMPS BY A FAIR AMOUNT AREAWIDE...
GIVEN CLOUDY SKIES ACROSS THE NORTH AND MODERATE TO STRONG COLD
ADVECTION OVER THE ENTIRE MIDSOUTH.
THE WEEKEND WILL SEE VERY BROAD AND DEEP LONGWAVE TROF OVER THE
EASTERN TWO THIRDS OF THE U.S...WHICH BOTH THE GFS AND ECMWF
BREAK DOWN BY TUESDAY. THIS GFS/ECMWF SOLUTIONS WOULD BRING
WARMER TEMPS AND A CHANCE OF RAIN TO THE MIDSOUTH TOWARD THE
MIDDLE OF NEXT WEEK. HAVE GONE A LITTLE SLOWER WITH THIS SUGGESTED
WARM UP...AS THE MODELS ARE OFTEN TO QUICK TO MIX OUT ARCTIC
AIRMASSES.
PWB
AVIATION...
00Z TAF CYCLE
VFR CIGS WILL BEGIN TO DETERIORATE LATER THIS EVENING AND INTO
WEDNESDAY MORNING FROM WEST TO EAST AS THE NEXT STORM SYSTEM
APPROACHES FROM THE WEST. MVFR CIGS ALONG WITH INCREASING LIGHT
RAIN CHANCES CAN BE EXPECTED THIS EVENING ALONG AND WEST OF THE
MISSISSIPPI RIVER AND SPREADING TO SITES EAST OF THE RIVER AFTER
MIDNIGHT. CIGS SHOULD LOWER FURTHER ON WEDNESDAY WITH IFR CIGS
POSSIBLE AT WESTERN TAF SITES. RAIN SHOULD ALSO BECOME
INCREASINGLY WIDESPREAD ACROSS THE AREA...ESPECIALLY BY WEDNESDAY
AFTERNOON. WINDS WILL ALSO INCREASE AND BECOME QUITE GUSTY OUT OF
THE SOUTHEAST LATER TONIGHT AND ESPECIALLY ON WEDNESDAY. VISBYS
SHOULD REMAIN VFR AT MOST SITES...BUT MAY DROP TO MVFR BY
TOMORROW. THIS WILL BE CLOSELY MONITORED THROUGH THE PERIOD.
JLH
&&
.AVIATION...
&&
.PRELIMINARY POINT TEMPS/POPS...
MEM 52 58 52 56 / 80 90 80 100
MKL 49 57 50 57 / 50 80 70 100
JBR 50 56 50 52 / 90 90 90 100
TUP 46 59 51 61 / 30 60 60 100
&&
.MEG WATCHES/WARNINGS/ADVISORIES...
AR...NONE.
MO...NONE.
MS...NONE.
TN...NONE.
&&
$$
