FXUS63 KIWX 252014
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
314 PM EST FRI DEC 25 2009
.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
DEEP LOW WAS CENTERED OVER IA THIS AFTN WITH ASSOCIATED STRONG CDFNT
LIFTING NE AHEAD OF IT INTO SWRN PORTION OF CWA. FRONT WILL CONT
TO MOVE NE ACROSS THE CWA LATE THIS AFTN/EARLY THIS EVE WITH BAND
OF RAIN IN ADVANCE OF THE FRONT LIKELY HOLDING TOGETHER AND MOVG
ACROSS THE AREA. STRONG CAA BEHIND THE FRONT WILL RESULT IN CHANGE
OVER OF RAIN SHOWERS TO SCT SNOW SHOWERS LATE THIS AFTN AND THIS
EVE. MID LEVEL DRY SLOT FCST BY MODELS TO MOVE ACROSS THE CWA
OVERNIGHT WITH DEEPER MOISTURE WRAPPING AROUND THE LOW FROM THE
WSW TOWARD MORNING. IN SPITE OF THE DRY SLOT, CONTD MENTION OF CHC
SW- THROUGH THE ENTIRE CWA OVERNIGHT AS -12C H85 TEMPS MOVG INTO
THE AREA WITH MOIST LOW LEVELS SHOULD RESULT IN SOME -SHSN CONTG
WITH HIGHEST POPS NW WHERE DEEPER MOISTURE WILL BE PRESENT THE
LONGEST.
WITH COLD AIR WRAPPING AROUND IA LOW, SYSTEM WILL WEAKEN SAT/SAT NGT
AND SHOULD DRIFT SLOWLY EAST TOWARD THE GRTLKS. CYCLONIC CIRCULATION
EXPECTED TO REMAIN STRONG ENOUGH TO MAINTAIN SOME LIGHT SNOW OR
PERSISTENT SNOW SHOWERS NEAR THE LOW CENTER AS WK SHRTWV'S ROTATE
AROUND IT. TRENDED POPS UP WITH 1-2" OF ACCUM EXPECTED NW AND <1"
SE DURING THIS 24HR PD.
STRONG CAA TONIGHT SHOULD ALLOW TEMPS TO FALL INTO THE L-M20S.
COLD AIR ALOFT AND WELL MIXED/MOIST LOW LEVELS EARLY SATURDAY
SUGGEST TEMPS WILL CLIMB LITTLE FROM OVERNIGHT LOWS WITH HIGHS
RANGING FROM THE U20S NW TO L30S SE. LOW CLOUDS REMAINING TRAPPED
BENEATH INVERSION BASED AROUND 5KFT ALONG WITH CONTD MODERATE MIXING
SHOULD LIMIT TEMP FALL SAT NIGHT... TRENDED MINS UP A BIT TOWARD
LATEST MOS GUIDANCE.
&&
.LONG TERM...
SUNDAY THROUGH FRIDAY
MASSIVE NEGATIVE HEIGHT ANOMALY WILL DOMINATE THE WEATHER THROUGH THE
FIRST PART OF THE LONG TERM PERIOD...WITH SEVERAL FLOW EMBEDDED WEAK
VORT LOBES ACTING TO ENHANCE MESOSCALE SNOW SHOWER PRODUCTION.
GENERAL BLOCKING PATTERN WILL BEGIN TO BREAK DOWN BY MONDAY WITH
EVENTUAL EJECTION OF THE EASTERN CONUS UPPER TROUGH AND A RETURN TO
THE FAVORABLE SPLIT FLOW PATTERN PREVALENT OVER NOAM THIS PAST FALL
SEASON. DOMINATE SIBERIAN NEGATIVE HEIGHT ANOMALY BEARS WATCHING AS
A WESTERN NOAM RIDGE LOOKS TO POSSIBLY SUPPORT CROSS POLAR FLOW BY
MID TO LATE NEXT WEEK...ALLOWING THE POSSIBLE SETUP FOR AN ARCTIC
INTRUSION NEXT WEEKEND BEHIND A DEEP PHASED TROUGH. LIKELY EL NINO
INFLUENCE OBSERVED IN THE PAC CONTINUES TO SUPPORT A POWERFUL MID
LATITUDE UPPER JET...WHICH CONTINUES TO SUPPORT SW CONUS TROUGH
RELOADING AND A PERIODIC WESTERN NOAM RIDGING...WITH AN ATYPICAL
EASTERN BIAS /POSSIBLY ATTRIBUTED TO DOMINATE WESTERN ATLANTIC
BLOCKING. HENCE...FEEL THE ECMWF /AND TO A LESSER EXTENT/ THE GFS
PORTRAY THE GENERAL PATTERN WELL...WITH HINTS TO THIS SOLUTION. HAVE
TRIED TO TAYLOR THE LATER PORTIONS OF THE EXTENDED TO AN EXPECTED
LONG WAVE PHASED TROUGH ADVECTING THROUGH THE REGION BY 6-7...WITH
ANOTHER ROUND OF CP TO POSSIBLY ARCTIC AIRMASS CAA. HAVE FOLLOWED
CLOSEST TO THE ECMWF.
SUN-MON...BROAD UPPER TROUGH WILL SUPPORT CONTINUED CHANCES FOR SNOW
SHOWERS WITH A SFC TROUGH /POSSIBLY A GREAT LAKES MOBILE TROUGH
HYBRID/ EXPECTED TO ADVECT SOUTHWARD INTO THE FA BY LATE SUN. CAA
AND VEERING LL WINDS WILL SUPPORT LAKE ENHANCEMENT WITH A PURE LAKE
MI RESPONSE SUNDAY NIGHT. NAM AND GFS H925-H85 THERMAL/MOMENTUM/AND
FORCING PROGS CONTINUE TO SUPPORT A DECENT LAKE REPONSE WITH A
PERIOD OF DEEP UVM SUNDAY NIGHT INTO MONDAY...IN THE PRESENCE OF
NEARLY 400 J/KG OF LAKE INDUCED CAPE. THIS MAKES SENS GIVEN RAISED
INVERSION HEIGHTS AND LONGER TRAJECTORY FLOW COMBINED WITH AN
ADVANCING UPPER LEVEL IMPULSE. FEEL THAT A 1-2 INCH SNOW MENTION
IS WARRANTED WITH POSSIBLE HIGHER ACCUMS. HAVE RAISED POPS TO LIKELY
IN THE NW ZONES WHERE FLOW/FORCING/AND DURATION BEST OVERLAP. LOOK
FOR HIGHS GENERALLY IN THE MID TO UPPER 20S WITH LOWS IN THE LOWER
20S TO UPPER TEENS. RATHER STRONG SFC PRESSURE GRADIENT COMBINED
WITH STRONG LL FLOW IN THE LOWEST 1-3 KM WILL CONTINUE TO SUPPORT A
WELL MIXED BL.
TUE-FRI...SFC HIGH PRESSURE WILL BUILD INTO THE REGION TUE
SUPPORTING A LIGHT FLOW REGION WITH COLD THERMAL FIELDS IN PLACE.
EXPECTING COOLER HIGHS GIVEN LACK OF APPRECIABLE MIXING. POSSIBLE
INSOLATION MAY ADD A FEW DEGREES. DEVELOPING DISTURBED NW FLOW WILL
SUPPORT SEVERAL SMALL SCALE WAVES WITH LIKELY MID AND HIGH CLOUD
ASSOCIATION. DIGGING SW CONUS WAVE WILL EJECT COINCIDENT WITH A
NORTHERN STREAM WAVE. TIMING AND PHASE POTENTIAL IS STILL
UNCERTAIN...BUT CURRENT ENSEMBLE AND MODEL TRENDS STILL SUPPORT A
LONG WAVE PHASED TROUGH ACROSS THE CONUS WITH SNOW CHANCES
INCREASING WED NIGHT THROUGH FRI. DID ADD POPS ON FRIDAY PER COLLAB
AND GIVEN A TYPICAL AND EXPECTED SECONDARY CP-ARCTIC AIRMASS PUSH
INTO THE REGION...WHICH ALSO HAS THE SUPPORT OF AO INDEX PROGS FROM
THE MEAN GEFS ENSEMBLE.
&&
.AVIATION...
DEEP LOW OVER IOWA WILL REMAIN NEARLY STNRY THROUGH THIS TAF PD.
A STRONG CDFNT WAS LIFTING NE AHEAD OF THE LOW ACROSS SWRN
INDIANA. THIS SHOULD MOVE THROUGH SBN AND FWA TERMINALS AROUND 00Z
SHIFTING WINDS FROM SE TO SSW. BAND OF RAIN SHOWERS OUT AHEAD OF
THE CDFNT WILL ROTATE THROUGH THE AREA THIS AFTN CAUSING VSBYS TO
LOWER TO 3SM OR LESS. SNOW SHOWERS SHOULD DEVELOP SHORTLY AFTER
FROPA AND CONT IN MOIST CAA REGIME THROUGH THE NIGHT AND INTO
SAT... THOUGH ATTM EXPECT THE SNOW TO BE LIGHT WITH MVFR
CONDITIONS PREVAILING.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...GALE WARNING UNTIL 7 PM EST THIS EVENING FOR LMZ043-046.
&&
$$
SHORT TERM...JT
LONG TERM...JC
AVIATION...ARNOTT
