FXUS63 KIWX 250554
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1254 AM EST FRI DEC 25 2009
.AVIATION...
DEEP LOW PRESSURE LIFTING SLOWLY THROUGH MISSOURI PROMISES STEADY
RAINS OVERNIGHT WHICH HAVE BEGUN AT THE TERMINALS IN THE PAST
HOUR. HEAVIEST PRECIP STILL TIMED FOR MORNING INTO EARLY AFTERNOON
WHERE IFR CIGS ARE EXPECTED TO PREVAIL...BUT BASED ON OBS UNDER
PRECIPITATION UPSTREAM HAVE IMPRVOED PREVAILING VSBYS TO MVFR.
WIND SHEAR STILL BEING CARRIED AS MODELS CONTINUE STRONG 0.5-1KM
WINDS INTO THE AFTERNOON PEAKING AT 60KTS DURING MORNING INTO
MIDDAY. AS DRY SLOT MOVES INTO THE REGION AFTER 18Z STEADY
IMPROVEMENT WITH SFC WINDS VEERING SOUTHERLY BUT CONTINUED GUSTING
25-30 KNOTS. SCATTERED SNOW SHOWERS CONTINUE TO END OF TAF PD AS
COLD AIR RETURNS TO THE AREA.
&&
PREV DISCUSSION... /ISSUED 330 PM EST THU DEC 24 2009/
SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
LOW PRESSURE CENTERED OVER SWRN ARK THIS AFTN WITH A WARM FRONT
EXTENDING NE TO THE UPR OH VALLEY. E-W ORIENTED BANDS OF ZR CONTG
TO DVLP THIS AFTN IN THE STRONG WAA REGIME NORTH OF THE WARM FRONT
AND LIFT NORTH INTO THE DRIER AIR OVER OUR AREA. MODELS HAVE BEEN
UNDER-DOING THIS WAA PRECIP DURING THE PAST 24HRS, THUS FCST POPS
HIGHER AND DUE TO EVAPORATIONAL COOLING... TEMPS A LITTLE LOWER
THAN SUGGESTED BY GUIDANCE THIS EVE. LOW EXPECTED TO LIFT NORTH
INTO EASTERN IA BY 12Z FRI WITH CDFNT ASSOCIATED WITH THIS SYSTEM
PUSHING AHEAD OF IT INTO SWRN INDIANA. WARM SECTOR OF THE STORM
SHOULD REMAIN WELL SOUTH OF OUR CWA, HWVR SFC WINDS EXPECTED TO
VEER TO SE AHEAD OF THE CDFNT ALLOWING FOR SLIGHTLY WARMER
TEMPERATURES TO MOVE INTO THE AREA BEFORE FROPA. BAND OF STRONG
FORCING/DEEP MOISTURE AND LIKELY MOD-HVY RAIN SHOULD SWEEP NE
ACROSS THE CWA AHEAD OF THE CDFNT LATE TONIGHT AND EARLY FRIDAY.
BULK OF MAIN BAND OF HEAVIER PRECIP SHOULD FALL INTO SFC TEMPS
SLIGHTLY ABOVE FREEZING. BUT IT WILL PRBLY BE A CLOSE
CALL...ESPECIALLY ACROSS THE NE WHERE NAM 2M AND BOUNDARY LAYER
TEMPS FCST BLO FREEZING THROUGH THE NIGHT. WILL CONT
WARNINGS/ADVISORIES AS EARLIER ISSUED...ENDING EARLY THIS EVENING
SOUTH AND WEST... MIDDLE OF THE NIGHT CENTRAL...AND 12Z FRI IN THE
NE.
MODELS IN GOOD AGREEMENT ON FRIDAY BRINGING COLDER AIR INTO THE
CWA FROM THE SW ALONG WITH A FAIRLY STRONG UPR LEVEL TROF ROTATING
AROUND LOW TO THE WEST. THIS SHOULD RESULT IN RAIN SHOWERS
CHANGING TO SNOW SHOWERS FROM SW-NE DURING THE AFTN/EVE. DRY SLOT
WILL MOVE ACROSS THE AREA FRIDAY NIGHT BUT WRAP AROUND MOISTURE
MOVES BACK IN BEFORE DAWN SO CHC POPS SOUTH AND LIKELY NORTH
CARRIED THROUGH THE NIGHT.
TEMPS WILL SLOWLY RISE TONIGHT TO THE M-U30S BY FRIDAY MORNING.
BASED ON UPSTREAM OBS BUMPED HIGHS UP A BIT FOR FRIDAY INTO THE
U30-L40S. NO CHANGE TO EARLIER FCST MINS FRI NGT...EXPECTED IN THE
L-M20S.
925MB WINDS FCST AROUND 50KT LATE TONIGHT AND EARLY FRIDAY...HOWEVER
SFC BASED INVERSION SHOULD LIMIT MIXING SO WHILE EXPECTING WINDY
CONDITIONS, WINDS SHOULD STAY BLO ADVISORY CRITERIA.
LONG TERM...
SOME MINOR CHANGES MADE IN THE LONG TERM PERIOD TO REFLECT OVERALL
SYNOPTIC PATTERN CONCERNS GIVEN A BLOCKED PATTERN INTERACTING WITH A
POTENT MID/UPPER LEVEL JET. POWERFUL 190 KNOT PLUS UPPER LEVEL JET
WILL CONTINUE TO SUPPORT STAUNCH HEIGHT RISES INTO WESTERN
NOAM...SUPPORTING A VERY STALE FLOW REGIME OVER THE CONUS INTO EARLY
NEXT WEEK AS LONG MERIDONAL NORTHERLY FLOW IS SUPPORTED ON THE
BACKSIDE OF THE 2 STD H5 NEGATIVE HEIGHT ANOMALY..WITH MASSIVE
ATLANTIC BLOCKING. MEANWHILE HEIGHT ADJUSTMENT OVER THE EASTERN PAC
WILL FAVOR A SOUTHWARD BIAS TO MID/UPPER FLOW IN THAT REGION WITH A
DIGGING SW CONUS TROUGH DEVELOPING BY EARLY NEXT WEEK...SUPPORTING
SPLIT FLOW AND THE EVENTUAL BREAKDOWN OF THE WESTERN NOAM RIDGE.
LOCAL SYNOPTIC INFLUENCE WILL BE A LONG PERIOD /2-3 DAYS/ OF DEEP
CYCLONIC FLOW WITH SEVERAL CHANCES FOR SNOW SHOWERS AT THE BEGINNING
OF THE PERIOD PER SEVERAL FUJIWARA TYPE ROTATING DISTURBANCES IN THE
GREAT LAKES/MIDWEST. OCCLUDING SFC CYCLONE...WITH SUFFICIENT
MOISTURE...WILL SUPPORT A TOTAL OF 1-2 INCHES OF SNOWFALL FROM
SEVERAL ROUNDS OF SNOW SAT-SUN...WITH A TRANSITION TO NW FLOW SUNDAY
NIGHT...SETTING THE STAGE FOR LAKE EFFECT SNOW IN THE NW ZONES.
TEMPS ARE EXPECTED TO REMAIN BELOW SEASONAL NORMS...BUT THERE IS AN
EXPECTED DELAY IN CAA GIVEN THE OCCLUDED NATURE OF THE SYSTEM
SUPPORTING WEAK AIRMASS MODERATION AND AN END TO NORTHERLY FLOW
INFLUENCE ACROSS THE UPPER MIDWEST.
SAT-SUN...HAVE RAISED POPS SOME GIVEN AFOREMENTIONED PATTERN
SUPPORTING 1-3 ROUNDS OF SNOW SHOWER ACTIVITY WITH PASSING MID LEVEL
IMPULSES IN CYCLONIC FLOW. ACCUMULATION FROM EACH DISTURBANCE IS
EXPECTED TO BE LIGHT WITH AN INCH AT MOST...TOTAL ACCUMULATION
LIKELY 1 TO POSSIBLY 2 INCHES. A FEW PLACES MAY SEE UP TO 3 IF
DURATION AND INTENSITY IS MAXIMIZED...BUT HAVE OPTED FOR LIGHTER
AMOUNTS IN THE GRIDS ATTM. EXPECT CLOUDY CONDITIONS WITH SMALL
DIURNAL TEMP RANGES GIVEN A WELL MIXED BL WITH AMPLE CLOUD COVER.
FLOW WILL TURN NW LATE SUNDAY AND SUPPORT THE ORGANIZATION OF LAKE
EFFECT SNOW SHOWERS. PROGGED BUFR INVERSION HEIGHTS AROUND 10 KFT
FOR AN 8 HOUR WINDOW WOULD LIKELY SUPPORT SOME HEAVIER ACTIVITY IF
THE PROGGED THERMAL AND MOMENTUM FIELDS COME TO FRUITION. HAVE OPTED
TO RAISE POPS TO 50 IN THE NW ZONES...AND WILL AWAIT FURTHER
OBS/GUIDANCE FOR FURTHER ADJUSTMENT. CYCLONIC FLOW COMBINED WITH THE
ADDITION OF A MID LEVEL VORT LOBE COULD VERY WELL SUPPORT SOME
DECENT ACCUMS SUNDAY NIGHT AND WILL NEED TO BE WATCHED. INVERSION
HEIGHTS DO FALL QUICKLY MONDAY MORNING AND THIS MAY BE A LARGE
LIMITING FACTOR.
MON-WED...DEEP LAYER FLOW STARTS TO BECOME MORE PROGRESSIVE AS THE
EASTERN CONUS TROUGH PHASES AND LIFTS NE. SFC HIGH PRESSURE WILL
SUPPORT CLEARING ACROSS THE SOUTH WITH NORTHERN AREAS LIKELY
REATTAINING A LK MI INFLUENCE. HAVE ADJUSTED LOWS SLIGHTLY BELOW
NORMAL GIVEN RADIATIONAL COOLING CONCERNS AND COOL DAYTIME HIGHS.
WED-THU...FORECAST MODELS AND ENSEMBLES CONTINUE TO HIGHLIGHT THE
EJECTION OF A SW CONUS TROUGH TOWARD THE REGION COINCIDENT WITH
ANOTHER NORTHERN STREAM SYSTEM. WAS RELUCTANT TO ADD POPS GIVEN THE
PERIOD AND LARGE UNCERTAINTY STILL PRESENT...BUT WAS LIMITED BY
COLLABORATION. SEMI-ACTIVE PATTERN DOES SUPPORT A 2-3 DAY WAVE
PERIOD AND PRECIP CHANCES DO FIT WITH THIS CONCERN. HAVE EXTENDED
POPS BACK INTO WED NIGHT TO HIGHLIGHT TIMING UNCERTAINTY...WHICH
WILL ULTIMATELY DEPEND ON THE STRENGTH OF THE ASSOCIATED MID/UPPER
LEVEL JET AND LL BAROCLINIC SETUP. OTHERWISE...LOOK FOR TEMPS AROUND
NORMAL IN THIS PERIOD.
AVIATION...
BANDS OF RAIN CONTG TO DVLP IN WAA ZONE NE OF INTENSIFYING LOW
OVER THE ARKLATEX AND MOVE ACROSS NRN INDIANA. LOW LEVELS REMAIN
DRY RESULTING IN RATHER LIGHT PRECIP REACHING THE GROUND...MAINLY
IN THE FORM OF ZR- AND IP- WITH VFR FLYING CONDITIONS. EXPECT THIS
TO REMAIN THE CASE INTO THIS EVE WHEN WAA AND STRENGTHENING
WINDS/MIXING SHOULD RESULT IN TEMPS RISING ABOVE FREEZING. VFR
CONDITIONS SHOULD CONT THROUGH THE EVE. BAND OF HEAVY RAIN
EXPECTED AHEAD OF CDFNT SHOULD MOVE THROUGH LATE TONIGHT CAUSING
FLYING CONDITIONS TO LOWER TO IFR. VERY STRONG WIND FIELD WILL BE
HELD MAINLY ALOFT BY LOW LEVEL INVERSION BUT SHOULD RESULT IN LLWS
IN THE AREA OVERNIGHT AND FRIDAY.
&&
.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...LUD
