FXUS63 KIWX 220259
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
959 PM EST MON DEC 21 2009
.UPDATE...
ZONES/GRIDS BEING UPDATED TO INCREASE POPS LATER TONIGHT INTO THE
FIRST PART OF TUESDAY MORNING.
MONITORING OF UPSTREAM OBSERVATIONS AND SAT DATA SHOWS A RATHER
COMPACT BUT STRONG SHORT WAVE MOVING ACROSS NE NEBRASKA. SOMEWHAT
EXPANDING AREA OF SNOW AND EVEN A BIT OF SLEET AND FREEZING RAIN
EVERY ONCE IN A WHILE...HAS BEEN SEEN ACROSS PORTIONS OF IOWA WITH
SOME SPOTS PUSHING 1SM VSBY. NEW NAM12 SHOWING THIS NARROW BUT
FAIRLY IMPRESSIVE AREA OF DEEPER MSTR AND LIFT EXTENDING CLEAR
BACK INTO THE DAKOTAS. SOME ENHANCED RADAR RETURNS SHOWING UP
ACROSS IOWA NEAR THE CIRCULATION AND IR/WATER VAPOR ALL POINTING
TOWARDS POTENTIAL INCREASING TREND AS WELL. GIVEN ALL THIS AND
AFTER COLLABORATION...WILL INCREASE TO LIKELY POPS FOR LIGHT SNOW
STARTING AROUND 8Z AND CONTINUING TO 14Z IN WESTERN THIRD TO HALF
OF THE AREA AND EXPAND CHC POPS FURTHER EAST. AT THE MOMENT WILL
KEEP ACCUMULATIONS AROUND AN INCH BUT WILL NEED TO MONITOR THIS AS
EXTENDED PERIOD OF LIGHT SNOW COULD CONTINUE INTO TUESDAY WHICH
COULD ALLOW FOR A FEW INCHES. WILL LET MID SHIFT LOOK THINGS OVER
FURTHER.
OTHER MINOR CHANGES INCLUDE INCREASED SKY COVER TO 100 PERCENT
THROUGH TOMORROW GIVEN ABUNDANCE OF CLOUD COVER AND NUDGE UP TEMPS
SLIGHTLY WITH SAME CLOUDY SKIES AND LITTLE OVERALL FALLOFF
EXPECTED.
&&
.PREV DISCUSSION... /ISSUED 629 PM EST MON DEC 21 2009/
AVIATION...
LL MSTR ABUNDANT ACROSS THE AREA WITH CIGS AT BOTH SITES SITTING
AROUND 1500 FEET. GIVEN UPSTREAM TRENDS...AND LOOK AT MODEL DATA
SEE NO REASON FOR THIS TO CHANGE SO HAVE KEPT CIGS FAIRLY STEADY.
AREA OF LGT SNOW WORKING SE TOWARDS THE REGION LATER TONIGHT STILL
LOOKS TO TAKE AIM ON THE TAF SITES. HOWEVER...NOT A WHOLE LOT
GOING ON OVERALL WITH IT AS VSBYS DROP INTO THE 2 TO 4 SM RANGE
AND CIGS IN SOME LOCATIONS ACTUALLY RISE TO MVFR OR VFR. SUSPECT
THINGS WILL FILL BACK IN OVER TIME HENCE THE ABOVE MENTIONED
CONTINUATION OF 1500 FT CIGS. PRECIP SHOULD BE GONE BY 18Z WITH
JUST LINGERING VSBY/CIG ISSUES.
PREV DISCUSSION... /ISSUED 454 PM EST MON DEC 21 2009/
SHORT TERM...
CLOUDY SKIES TO PREVAIL THIS EVENING AS WEAKENING SHRTWV TRACKS TO
OUR NE THROUGH THE GREAT LAKES WHILE LLEVEL MOISTURE REMAINS TRAPPED
UNDER SUBSIDENCE ALOFT. AS ENERGY OVER THE INTERMOUNTAIN WEST
BEGINS TO ORGANIZE AHEAD OF MID WEEK SYSTEM SOUTHERLY FLOW INTO THE
GREAT PLAINS SETS UP WARM ADVECTION/ISENTROPIC ASCENT REGION ALREADY
FORMING UP OVER THE DAKOTAS AND SW MINNESOTA...AND IS PROGGED TO
PROPAGATE SE AND ALLOW DEVELOPMENT OF LIGHT SNOW TUESDAY MORNING OVER
MUCH OF THE CWA. WHILE ASCENT REMAINS OVER THE AREA THROUGH MUCH OF
THE DAY IT WEAKENS WHILE REFOCUSING TO OUR SW AS MID WEEK SYSTEM
ORGANIZES FURTHER. ANY SNOW AMOUNTS RECEIVED EXPECTED TO BE LIGHT
AT THIS TIME WITH FURTHER MONITORING WARRANTED AS BUFR DATA DOES
INDICATE WEAK UVM INTO A MOIST DGZ AND W/V LOOP DOES SHOW A DECENT
SHRTWV OVER THE NORTHERN PLAINS ATTM. WILL GRID ACCUMS UP TO AN INCH
OVER NORTHWEST AREAS..LESSER AMOUNTS ELSEWHERE. IF THIS WAVE DOES
MANAGE TO OVERACHIEVE ADVISORY LEVEL IMPACT IS STILL NOT
ANTICIPATED.
AS FOR TEMPS...AT THE SFC EASTERLY FLOW WILL UNDERCUT WAA ALOFT AND
PREVENT A SIGNIFICANT WARMUP KEEPING HIGHS IN THE LOW TO MID 30S FOR
TUESDAY AND SIMILARLY PERSISTENT CLOUD COVER WILL HELP HOLD LOW TEMPS
IN THE MID 20S FOR TONIGHT AND TUESDAY NIGHT.
LONG TERM...
WEDNESDAY THROUGH MONDAY...THE MAIN CONCERN THIS PERIOD CONTINUES TO
BE THE POTENTIAL FOR A WINTER STORM WEDNESDAY THROUGH FRIDAY. FOR
THIS PACKAGE...FAVOR A BLEND OF THE GFS ENSEMBLES AND THE
OPERATIONAL ECMWF. GIVEN THE GFS RUN TO RUN TRENDS AND THE BASIC
TENDENCY FOR THE GFS TO LIFT OUT THIS TYPE OF SYSTEM TOO FAST...
BELIEVE THE BULK OF THE PRECIPITATION WILL FALL FROM THURSDAY
AFTERNOON INTO FRIDAY MORNING. GIVEN THE EVOLVING MORE SUPPRESSED
PATTERN...CONCERNS PERSIST FOR THE COLD WEDGE OF AIR LINGERING OVER
THE REGION AS WARM AS MOIST AIR SURGES NORTH...ESPECIALLY WITH A
1040 SFC HIGH NEAR JAMES BAY. NCEP MODELS HAVE A HISTORY OF TRYING
TO MIX OUT THE SHALLOW COLD LAYER TOO FAST IN A SCENARIO LIKE THIS
AS IN THE EVENT THAT HAPPENED ON WEDNESDAY LESS THEN 2 WEEKS AGO.
AFTER COLLABORATION WITH SURROUNDING OFFICES...HAVE DECIDED TO
HANDLE IN A STRONGLY WORDED SPS. FREEZING RAIN AND SLEET ARE STILL
POSSIBLE FROM WEDNESDAY NIGHT INTO LATE THURSDAY NIGHT OVER NORTHERN
AREAS. THE PRECIPITATION SHOULD CHANGE TO ALL RAIN FRIDAY BEFORE THE
FRONT MOVES IN FROM THE SOUTHWEST...CHANGING THE RAIN TO ALL SNOW.
THE AREA INITIALLY SHOULD BE DRYSLOTTED FRIDAY...BUT WRAP AROUND
MOISTURE AND COLD AIR SHOULD BE SUFFICIENT FOR A CHANCE FOR SNOW
INTO THE WEEKEND PER GFS ISENTROPIC 290K ANALYSIS.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SHORT TERM...LUDINGTON
LONG TERM...SKIPPER
AVIATION...FISHER
UPDATE...GREENAWALT/FISHER
