FXUS63 KIND 241102
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
602 AM EST THU DEC 24 2009
.UPDATE...ISSUED FREEZING RAIN ADVISORY FOR THE NORTHEAST PORTION OF
THE WARNING AREA BASED ON RADAR TRENDS AND SUBFREEZING TEMPS/LARGE
SURFACE DEWPOINT DEPRESSIONS. WETBULB ZERO LINE HAS BEEN HOLDING
STEADY JUST NORTHEAST OF A LAF TO GEZ LINE...AND USED THAT AS A
GUIDE. MAY TAKE A WHILE FOR RAIN TO BEGIN REACHING THE GROUND DUE TO
NEAR SURFACE DRY AIR...BUT RAIN SHOULD EVENTUALLY MAKE IT...WITH AT
LEAST A FEW HOUR PERIOD OF FREEZING RAIN THIS MORNING INTO THE EARLY
AFTERNOON...AND LIGHT ICE ACCUMULATIONS.
&&
.AVIATION...DISCUSSION FOR THE 12Z TAFS
WILL KEEP RAIN IN THE WHOLE PERIOD BASED ON RADAR TRENDS.
MODELS...MOS AND TRENDS FAVOR VFR CEILINGS AND VISIBILITIES
DETERIORATING TO MVFR OR WORSE TONIGHT WHEN THE OCCLUDED FRONT IS
EXPECTED TO APPROACH FROM THE WEST. WILL KEEP LOW LEVEL WIND SHEAR
IN UNTIL AFTER 20Z WHEN THE SURFACE PRESSURE GRADIENT WILL INCREASE
BRINGING THE SUSTAINED EAST WINDS TO NEAR 20 KNOTS AND GUSTS TO NEAR
30 KNOTS. GUSTY WINDS SHOULD THEN CONTINUE THROUGH THE PERIOD.
&&
.PREV DISCUSSION...AT 08Z...TEMPERATURES ACROSS THE FORECAST AREA
RANGED FROM AROUND 30 NORTHEAST...TO THE UPPER 40S SOUTHWEST...UNDER
CLOUDY SKIES AND AN EASTERLY BREEZE. NATIONAL 88D MOSAIC SHOWED
BROAD SWATH OF PRECIPITATION ORGANIZING AHEAD OF DEVELOPING CYCLONE
OVER NORTHEAST TEXAS...EXTENDING FROM THE SABINE RIVER NORTHEASTWARD
INTO CENTRAL ARKANSAS...THE OHIO/MISSISSIPPI CONFLUENCE...AND INTO
SOUTHWEST INDIANA...COINCIDENT WITH A DEVELOPING ROBUST LOW LEVEL
JET AND A BROAD PLUME OF ISENTROPIC LIFT.
FORECAST CHALLENGES OF THE DAY ARE LINGERING PRECIP TYPE ISSUES
TODAY...AS WELL AS POPS AND TEMPS THROUGHOUT THE SHORT TERM...AND
WINDS TONIGHT AND FRIDAY.
MODELS WERE IN DECENT AGREEMENT REGARDING DEVELOPMENT AND
PROGRESSION OF MAJOR MISSISSIPPI VALLEY CYCLONE...BUT GFS...AS IS
ITS TENDENCY...APPEARS TO BE BETTER HANDLING THE STRONG/RAPID
CYCLOGENESIS AND ALSO APPEARS TO HAVE A BETTER HANDLE ON THE LOW
LEVEL THERMAL ENVIRONMENT...AND SO LEANED TO IT FOR THIS FORECAST.
LOW WILL CONTINUE DEVELOPMENT AND LIFT QUICKLY NORTHWARD NEXT 36
HOURS...DURING WHICH TIME IT WILL RAPIDLY OCCLUDE...BECOME
VERTICALLY STACKED...AND THEN BEGIN TO WEAKEN FRIDAY NIGHT. BROAD
PLUME OF ISENTROPIC LIFT TO OUR SOUTHWEST WILL PUSH INTO THE AREA
TODAY AND INTO THE OVERNIGHT...AND AS SUCH...PRECIPITATION IS A NEAR
CERTAINTY FOR MUCH OF THE AREA TODAY...AND THE ENTIRE AREA TONIGHT.
AM CONCERNED THAT MODELS AND MOS GUIDANCE ARE NOT HANDLING SHALLOW
DRY AIR OVER NORTHEAST FORECAST AREA AND TO OUR EAST VERY WELL.
DEWPOINT AT MIE HAS DROPPED TO 21 OVERNIGHT...AND EVEN LOWER
DEWPOINTS PRESENT JUST TO THE EAST. THUS...HAVE RETAINED THE CHANCE
OF FREEZING RAIN LATER THAN INITIALLY FORECAST...INTO MID AFTERNOON.
WETBULB ZERO LINE WILL COMMAND CLOSE MONITORING TODAY AS
PRECIPITATION PUSHES INTO THE AREA.
PERIODS OF HEAVY RAIN WILL BE POSSIBLE TONIGHT...WITH PRECIPITABLE
WATER VALUES NEAR OR ABOVE 200 PERCENT OF NORMAL...AND AN EXTREMELY
STRONG /60-70+KT/ LOW LEVEL JET NOSING OVER THE FORECAST AREA. A
WIDESPREAD ONE TO PERHAPS TWO INCH RAINFALL APPEARS LIKELY...WITH
THE HIGHEST AMOUNTS OVER THE SOUTHWESTERN PORTION OF THE AREA. LOWER
WABASH IS CURRENTLY FORECAST TO GO INTO MINOR FLOOD WITH A LESSER
RAINFALL AMOUNT...BUT FROST DEPTH OBSERVATION AT IND INDICATES THAT
TOPSOIL HAS THAWED HERE...AND IT HAS BEEN SIGNIFICANTLY WARMER TO
THE SOUTHWEST...SO FROZEN GROUND SHOULD NOT BE A MAJOR CONCERN FOR
RUNOFF POTENTIAL. CONSIDERED BUT WILL HOLD OFF ON FLOOD WATCH FOR
WESTERN THIRD OR WESTERN HALF FOR THE MOMENT...AND CONSULT WITH DAY
SHIFT FORECASTERS AND HYDROLOGIST.
OCCLUDED FRONT SHOULD BE LIFTING THROUGH THE FORECAST AREA DURING
CHRISTMAS MORNING...BRINGING AN END TO WIDESPREAD AND HEAVIER
PRECIPITATION...AND BEGINNING STRONG COLD ADVECTION...CHANGING
REMAINING PRECIPITATION OVER TO SNOW IN THE WEST IN THE
MORNING...AND EVERYWHERE BY LATE AFTERNOON. PRECIP TYPE WILL REMAIN
SNOW THROUGH THE SHORT TERM...AS THE UPPER LOW AND ASSOCIATED COLD
POOL SLOWLY PUSH EAST...LEADING TO CHANCES OF SNOW SHOWERS THROUGH
SUNDAY NIGHT.
MOS IS AT A MAJOR DISADVANTAGE FOR THIS TEMPERATURE FORECAST...AS A
SIGNIFICANT GRADIENT AND STRONG WARM ADVECTION WILL BE THE RULE FOR
THE FIRST TWO PERIODS...FOLLOWED BY STRONG COLD ADVECTION TOMORROW
AND INTO THE SHORT TERM. LEANED TOWARD A BLEND OF GFS 2-METER
TEMPS...TEMPERED WITH MODEL SURFACE WETBULB TEMPS DURING
PRECIPITATION PERIODS...AND AS A RESULT...EXPECT A 15 DEGREE RANGE
ACROSS THE AREA TODAY ON HIGHS...AND A TEN DEGREE RANGE ON LOWS
TONIGHT...WHICH WILL LIKELY OCCUR IN MANY AREAS DURING THE EVENING
OR EARLY NIGHTTIME HOURS...AS OCCLUSION APPROACHES AND POWERS
THROUGH THE AREA. AS SUCH...HIGHLY NONDIURNAL TEMPERATURE FORECAST
DEPICTED IN GRIDS THROUGH FRIDAY.
IN THE LATTER PORTION OF THE SHORT TERM...LEANED TOWARD A
COMBINATION OF OPERATIONAL GFS AND GFS ENSEMBLE MINIMUMS...AS COLD
POOL REMAINS OVER THE AREA...AND IS EVEN STRENGTHENED BY A
REINFORCING SHOT OF COLD AIR LATE IN THE WEEKEND/EARLY NEXT WEEK AS
A STRONG ARCTIC HIGH DROPS SOUTH INTO THE CENTRAL U.S. IN THE WAKE
OF THE DEPARTING UPPER LOW.
FINALLY...BOTH GRADIENT WINDS AND POTENTIAL GUSTS LOOK TO FLIRT WITH
ADVISORY CRITERIA TONIGHT INTO FRIDAY...AS SURFACE PRESSURE GRADIENT
AND WINDS ALOFT STRENGTHEN. APPEARS AT THIS TIME THAT LOW LEVEL
INVERSION WILL ACT TO LIMIT MIXING OF STRONGER WINDS TO THE
SURFACE...BUT THIS INVERSION LIFTS AND WEAKENS ON FRIDAY...AND IF WE
WERE TO GET DRY SLOTTED...SIGNIFICANT GUSTS...PERHAPS APPROACHING 40
KNOTS...WOULD BE POSSIBLE. AT THIS TIME...EXPECT GUSTS IN THE AREA
OF 30-35 KNOTS AT MOST THROUGH FRIDAY AFTERNOON...BUT WILL HAVE TO
MONITOR FOR ADVISORY POTENTIAL AS TIME GOES ON.
&&
.IND WATCHES/WARNINGS/ADVISORIES...FREEZING RAIN ADVISORY
INZ021-030-031-038>042-048-049-057 THRU 21Z.
&&
$$
UPDATE...NIELD
PUBLIC...NIELD
AVIATION...KOCH
