181
FXUS63 KIWX 210536
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1235 AM EST SAT NOV 21 2009
AVIATION
CONTINUED CHALLENGES WITH FOG FORECASTS OVERNIGHT AS PATCH OF 3-4KFT
CLOUDS ARE DRIFTING ACROSS THE AREA. UPPER SHORT WAVE NEARING KSBN
AT ISSUANCE TIME AND WILL TRAVERSE THE AREA OVERNIGHT. LIFT AHEAD OF
THIS FEATURE ENOUGH TO GENERATE SMALL AREA OF CLOUDS IN ADDITION TO
CLOUDS FROM TODAY ACROSS IL THAT HAVE DRIFTED EAST AND REFUSE TO
DISSIPATE. THESE VFR CIGS ABOUT TO MOVE INTO KSBN AND WILL SLOWLY
WORK TOWARD KFWA NEXT SEVERAL HOURS. WITH THESE CLOUDS DO NOT
EXPECTED IFR VIS DUE TO FOG BUT MVFR STILL POSSIBLE AND STAYED THE
COURSE WITH THOSE FOR NOW. IF CLOUDS BEGIN TO DISSIPATE IN WAKE OF
SHORT WAVE PASSAGE...COULD SEE VIS DROP LATE. WILL MONITOR FOR THESE
TRENDS. OTHERWISE EXPECT WEAK MIXING TO LEAVE BEHIND SCT CLOUDS ON
SATURDAY WITH LIGHT WINDS.
SHORT TERM.../TONIGHT THROUGH SATURDAY NIGHT/
MUCH MORE OPTIMISTIC SHORT TERM PERIOD WITH HIGH TEMPS RETURNING
TO ABOVE NORMAL FOR SATURDAY. UPPER LOW THAT SPOILED THE WORK WEEK
IS CENTERED OVER SOUTHERN ONTARIO WHILE A FOLLOWUP SHTWV IS MOVING
INTO ILLINOIS. THIS FEATURE IS NOT GENERATING AS MUCH CLOUD COVER
AS ANTICIPATED EXCEPT OVER THE NE THIRD OF THE CWA WHERE IT HAS
MOVED INTO AN AREA OF MOISTURE LEFT BEHIND BY RETREATING UPPER
LOW. MODELS INDICATE THIS AREA OF ENHANCED RH THROUGH THE MID
LEVELS TO REMAIN OVERNIGHT AND INTO SATURDAY. WHILE THIS WILL
CURTAILS AN OTHERWISE IDEAL RAD COOLING SETUP COOLING/MOISTURE
STILL SUFFICIENT FOR OVERNIGHT FOG TO DEVELOP. SOUTH OF THICKER
CLOUD POTENTIAL WHERE SKIES SHOULD BE CLEARER WENT SLIGHTLY COOLER
WITH LOWS BUT THIS ALSO SETS UP MORE SIGNIFICANT FOG DEVELOPMENT.
SATURDAY WILL SEE ABV NORMAL TEMPS AS MIXING TO MODEL AVERAGED H92
TEMPS YIELDS HIGHS IN THE MID 50S. GRIDS ARE SLIGHTLY COOLER THAN
THIS IN THE NORTHEAST WHERE MORE CLOUDS ARE EXPECTED AND WARMER IN
SOUTHERN AREAS WHERE TEMPS TODAY ARE REACHING 52-54 DESPITE COOLER
TEMPS ALOFT.
LONG TERM.../SUNDAY THROUGH FRIDAY/
GENERAL SOUTHWEST FLOW REGIME OF LATE WILL BEGIN TO BREAK DOWN
DURING IN THE PERIOD. STRONG LL TEMPERATURE GRADIENT OVER THE
NORTHERN PAC WILL SET THE STAGE FOR A SUBTLE PATTERN CHANGE AS A
WEAK SFC WAVE NEAR THE EASTERN ALEUTIANS INTERACTS WITH A
STRENGTHENING UPPER LEVEL IMPULSE PUSHING OVER THE WESTERN
ALEUTIANS. ORIENTATION OF THE STRENGTHENING UPPER LEVEL JET WILL
SUPPORT DEEPENING OF THE AFOREMENTIONED UPPER LEVEL TROUGH WITH
INCREASING NW LL FLOW SUPPORTING AMPLE CAA...WITH TROUGHING EXPECTED
INTO THE WESTERN US BY EARLY NEXT WEEK. GIVEN THE POSITION OF THE
EXPECTED UPPER LEVEL JET OVER THE WESTERN CONUS WITH WIDESPREAD
DOWNSTREAM RIDGING ALREADY IN PROGRESS...EXPECT A PERIOD OF UPPER
LEVEL TROUGH DIGGING AS DEPICTED IN GEM AND ECMWF PROGS. DEGREE OF
DIGGING AND AFFECT ON THE PROGRESSIVE NATURE OF THE FLOW IS STILL
YET TO BE DETERMINED. IN ADDITION...CLOSING OF THE UPPER LEVEL WAVE
AS SUPPORTED IN NEARLY ALL DETERMINISTIC RUNS LENDS CREDENCE TO A
SEMI SPLIT FLOW PATTERN WITH THE BULK OF CAA RESIDING WELL NORTH OF
THE REGION. A SHIFT TO AT OR BELOW NORMAL TEMPERATES IS WARRANTED IN
DAYS 5-7. HOWEVER...THE VERY COLD PROGS IN THE GFS MAY BE TOO
AGGRESSIVE GIVEN CONCERNS ON SYSTEM EVOLUTION. BOTTOM LINE...HAVE
HELD CLOSER TO ECMWF NUMBERS...WITH A HEAVY TREND TO CLIMO. THIS
WILL CERTAINLY SUPPORT A CHANCE OF MIXED PRECIP LATE IN THE PERIOD.
HOWEVER...AT THIS POINT ACCUMULATING SNOWFALL LOOKS TO REMAIN NORTH
OF THE REGION AT THIS POINT AS THE FLOW WILL REMAIN SOMEWHAT
PROGRESSIVE.
SUNDAY THROUGH MONDAY...GOMEX DISTURBANCE WILL EJECT TOWARD THE
EASTERN OH VALLEY WITH AN INCREASE IN HIGH AND MID LEVEL CLOUDS
EXPECTED. WARM PROFILES WILL SUPPORT TEMPS IN THE 50S...WITH THE
AMOUNT OF INSOLATION DICTATING THE DEGREE OF T RISE HEAVILY. A FEW
SOLUTIONS SUGGEST THE FAR EASTERN FA COULD GET CLIPPED BY A PERIOD
OF LIGHT RAIN LATE IN THE DAY. HOWEVER...CONCERNS ON DRY PROFILES
AND TRACK VARIABILITY DOES NOT WARRANT POP ADDITION. EXPECT ANOTHER
MILD DAY ON MON...WITH INCREASING MID AND HIGH CLOUDS LIKELY
LIMITING SHARPER T RISES IN DISTURBED SW FLOW.
TUE-FRI...PREFER A TREND TO AN ECMWF SOLUTION GIVEN PREFERRED
HANDLING OF UPPER LEVEL MOMENTUM FIELDS. SLOWER ARRIVAL OF THIS
SYSTEM IS PREFERRED GIVEN NORTHERN STREAM WAVE SPLIT AND GIVEN
LIKELY CLOSING OF THE UPPER LEVEL CIRCULATION. MAIN CHANGES TO THE
GRIDS TO REFLECT THIS SOLUTION WERE TO WARM TEMPS TUE AND SLIGHTLY
WED...AND SHIFT SNOW MENTION TO THE THE LATER PERIODS. WITH
CONTINUOUS SIGNALS SUPPORTING PROLONG NEGATIVE MSLP AND HEIGHT
ANOMALIES OVER THE GREAT LAKES THROUGH THE PERIOD...FEEL IT WAS
PRUDENT TO RAISE POPS TO 40 IN MANY PERIODS GIVEN CLIMO NUMBERS
ACROSS THE FA NOW AT OR ABOVE 30 PER 12 HOUR.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
SHORT TERM...LUDINGTON
LONG TERM...JC
AVIATION...LASHLEY
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