FXUS63 KIWX 090909
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
409 AM EST WED DEC 9 2009
.SHORT TERM...
...NEAR RECORD SFC LOW PRESSURE TO BRING VERY STRONG WINDS AND
ANOTHER ROUND OF WINTER WEATHER TO THE REGION...
SFC LOW NOW CENTERED OVER NORTHERN IL AT 983 MB /0830Z/...CONTINUES
TO TRACK NE BEING STEERED BY A POTENT MID LATITUDE UPPER TROUGH
AND ASSOCIATED POWERFUL CYCLONICALLY CURVED UPPER FLOW. 00Z RAOB
DATA CONFIRMS 130+ KNOT FLOW OVER THE CENTRAL PORTION OF THE
COUNTRY. IMPLIED FORECAST ASCENT FROM ROBUST SECONDARY CIRCULATION
ON THE LEADING EDGE OF THE JET STREAK...HAS LIKELY SUPPORTED
SIGNIFICANT ASCENT. PEGGED ASCENT FIELDS LIKELY LEAD TO STAUNCH
ADIABATIC COOLING RETARDING THE SN/PL CHANGEOVER TO RAIN YESTERDAY
EVENING. COLD FRONT ALOFT AND THE LEADING EDGE OF A HIGH DESERT EML
CONTINUES TO ADV INTO IL/IN...WITH WIDESPREAD SHOWERS AND ISOLATED
THUNDERSTORMS PRESENT ALONG A SFC TROUGH...AKIN TO A SPRING SYSTEM
DRY LINE. THIS SYSTEM AND ITS TRACK ACTUALLY BEARS SOME RESEMBLANCE
TO THE APR 11 1965 CYCLONE WHICH PRODUCED WIDESPREAD SEVERE WEATHER
TO THE REGION. THE MAIN DIFFERENCE IS OFF COURSE THE MUCH COOLER AND
DRIER THERMAL AND MOISTURE FIELDS. SFC COLD FRONT IS LOCATED IN
EASTERN MO AND WILL CONTINUE TO RAPIDLY PUSH NE TOWARD THE
FA...ENTERING THE WESTERN FA AROUND DAWN. MAIN FORECAST CONCERN
IN THE PERIOD WILL BE THE STRONG GUSTY WINDS TODAY...AND WINTER
WEATHER CONCERNS FROM A BRIEF PERIOD OF DEFORMATION SNOW/LAKE EFFECT
SNOW/AND FREEZING OF ROADWAYS LATER THIS MORNING. HAVE FOLLOWED THE
NAM12 HEAVILY WITH AID FROM THE SREF GIVEN GOOD TRACK RECORD OF LATE
AND PREFERRED THERMAL AND MOMENTUM FIELDS.
COLD FRONT ALOFT WILL PUSH THROUGH THE REGION THIS MORNING
SUPPORTING ANOTHER ROUND OF RAIN...POSSIBLY MIXED WITH SLEET GIVEN
ELEVATED INSTABILITY AND STRONG CONVECTIVE COMPONENT. SFC COLD FRONT
IS EXPECTED INTO THE FA AROUND 12Z...QUICKLY PUSHING EAST THROUGH
THE FA IN 6 HOURS OR LESS. NEAR RECORD/HISTORIC SURFACE LOW PRESSURE
CENTER VALUES EXPECTED AROUND 975 MB WILL CONTINUE TO SUPPORT VERY
STRONG LL WIND FIELDS. NAM 12 GEOSTROPHIC ANALYSIS AT APPROX 1 KFT
INDICATES 95 KNOTS OF GEOSTROPHIC FLOW COINCIDENT WITH STRONG CAA/ A
VERY STRONG SFC PRESSURE GRADIENT/AND LL DRY ADIABATIC LAPSE RATES
WITH THE SFC WIND PARALLEL TO THE ISALLOBARIC WIND FIELD IN THE
PRESENCE OF A DEEPENING SFC LOW. THIS WILL SUPPORT VERY STRONG GUSTY
WINDS BY LATE MORNING. SUSTAINED WINDS OF 35 TO 40 MPH WILL BE
COMMON WITH EXPECTED GUSTS OF 60 TO 70 MPH. ANALOGS TO PAST
EVENTS...12-15-87 AND 4-11-65...CONFIRM WIND GUSTS IN EXCESS OF 60
MPH. THIS IS EXPECTED TO CAUSE SOME TREE DAMAGE WITH STRUCTURAL
DAMAGE POSSIBLE. WINDS WILL PERSIST THROUGH THE AFTERNOON...WANING
SOME BY EVENING. ISSUED A HIGH WIND WARNING EARLIER FOR THIS.
NEXT IS THE WINTER WEATHER CONCERNS. TEMPS WILL QUICKLY FALL BELOW
FREEZING LATE MORNING WEST-EAST WITH THERMAL PROFILES QUICKLY
SUPPORTING SNOW. TAIL END OF THE ASSOCIATED DEFORMATION ZONE IS
EXPECTED TO CLIP THE NW FA LATE MORNING AND EARLY AFTERNOON WITH 1-2
INCHES POSSIBLE. FLOW WILL TURN STRONGLY CONVERGENT OVER LAKE MI
THIS AFTERNOON SUPPORTING A STRONG LAKE ENHANCED SNOW BAND OVER SW
MI. THIS BAND LOOKS TO STAY MOSTLY NORTH OF THE FA. HOWEVER...ANOTHER
1-2 INCHES IS POSSIBLE IN NORTHERN BERRIEN AND CASS COUNTIES. VERY
STRONG GUSTY WINDS WINDS WILL SUPPORT WIDESPREAD BLOWING AND
DRIFTING SNOW WITH VIS RESTRICTIONS EXPECTED WHERE SNOW ACCUMS
OCCUR. IT WILL NOT TAKE MUCH SNOWFALL WITH THESE KIND OF WINDS...AS
ONLY AN INCH WOULD CAUSE SIG VIS REDUCTION. IN ADDITION...CAA OVER
LAKE MI WILL SUPPORT DELTA T/S OF 20-23 C BY LATE TONIGHT WITH A
VIGOROUS LAKE RESPONSE EXPECTED AS LAKE INDUCED CAPES REACH 600-700
J/KG. HOWEVER...STRONG LL WIND WILL LEAD TO MODERATE BAND SHEARING
WITH HEAVIEST ACCUMS LIKELY REMAINING NORTH OF THE FA.
REGARDLESS...CONTINUED STRONG GUSTY WINDS WILL SUPPORT VERY DEGRADED
TRAVEL CONDITIONS WITH ANY SNOWFALL. GIVEN THE ABOVE CONCERNS...HAVE
ISSUED A WW ADV FOR IMPACTS TO TRAVEL.
LAKE EFFECT SNOW CONTINUES INTO THUR AS SFC HIGH PRESSURE BUILDS
SOUTH OF THE REGION...WITH LAKE INDUCED CAPES REMAINING IN THE
600-800 J/KG RANGE. FLOW WILL REMAIN WESTERLY SUPPORTING HEAVIEST
SNOW NORTH OF THE FA. THERE IS TILL SOME QUESTION AS TO EXACT FLOW
ORIENTATION AT THIS POINT BUT FEEL ADDITIONAL ACCUMS WITH BREEZY
CONDITIONS WILL IMPACT TRAVEL IN SW MI. IF HEAVIER BANDS DO SHIFT
FARTHER SOUTH THAN CURRENT EXPECTATIONS...HEAVIER ACCUMS MAY SUPPORT
NEAR WARNING CRITERIA. HOWEVER...IT LOOKS TO BE A LONG DURATION
LIGHT TO MODERATE SNOWFALL EVENT BELOW WARNING CRITERIA AT THIS
POINT. WILL LET THE DAYSHIFT ASSESS.
ARCTIC AIR MASS WILL PUSH INTO THE REGION TONIGHT AND LINGER
THROUGH THUR. GIVEN UPSTREAM OBS AND MOSS TRENDS...HAVE ADJUSTED
HIGHS/LOWS DOWN. TEMPS ARE EXPECTED TO HOVER IN THE TEENS
THUR...WITH WIND CHILLS OF 5 TO 10 BELOW ZERO EXPECTED THU MORNING
AND NIGHT.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
COLDEST AIR WILL BE DEPARTING AT THE START OF THE PERIOD. SW FLOW
WILL STILL BE IN PLACE TO CONTINUE THE CHC OF LAKE EFFECT SNOW
SHOWERS MAINLY ACROSS THE MICH COUNTIES BUT ACCUMS SHOULD NOT BE AN
ISSUE WITH DIMINISHING MSTR AND INVERSION HGTS. H85 TEMPS WILL START
OUT AROUND -14 TO -16 C AT 12Z FRI WARMING TO -1 TO -3 C BY 12Z
SUNDAY. THE RESULT SHOULD BE MODERATING SFC TEMPS BACK CLOSER TO BUT
STILL BELOW NORMAL LEVELS. FRIDAY HIGHS SHOULD MAKE IT INTO THE MID
20S IN MOST LOCATIONS WITH THOSE AREAS THAT HAVE SNOW PACK ACROSS
THE FAR NORTH LIKELY AT LEAST A FEW DEGREES COOLER. BY SATURDAY AND
SUNDAY...THAW SHOULD BE UNDERWAY WITH TEMPS PUSHING BACK TOWARDS
FREEZING IN MANY SPOTS. MODELS NOW POINT TOWARDS DRY FORECAST FOR
SATURDAY AND AFTER COLLABORATION WITH SURROUNDING OFFICES HAVE
REMOVED CHC POPS.
TOWARDS THE END OF THE PERIOD...MUCH UNCERTAINTY REMAINS IN NEXT
UPPER LOW TO DROP OUT OF CANADA. MED RANGE MODELS ALL TRY TO DIG THE
LOW GENERALLY JUST SOUTH OF HUDSON BAY WITH TROUGH EXTENDING SOUTH
INTO THE GREAT LAKES. TIMING ISSUES...STRENGTH OF TROUGH AND AMOUNT
OF COLD AIR ALL MAKE THE FORECAST RATHER TRICKY. GFS IS MOST
AGGRESSIVE ON COLD AIR WITH 850 MB TEMPS DROPPING BACK TOWARDS -15 C
BY 16/00Z. ECMWF AND GFS ENSEMBLE MORE IN THE -6 TO -8 C RANGE.
SINCE MAIN PUSH OF COLDEST AIR IS WELL INTO DAY 6 AND MORE DAY 7 AND
BEYOND...WILL HOLD OFF ON INTRODUCING ANY NEW POPS. MEX GUIDANCE IS
RIGHT AT CLIMO VALUES AND WOULD LIKE TO SEE IT A BIT HIGHER THAN
CLIMO TO GIVE ADDED SUPPORT.
&&
.AVIATION...
FLIGHT CONDITIONS AT BOTH SITES WILL NOT BE THE BEST OVER THE NEXT
24 HOURS. SURGE OF WARM AIR HAS FINALLY ARRIVED AND IS SWITCHING
THE MIX OF SNOW AND SLEET OVER TO ALL RAIN. TAMDAR SOUNDING
RECENTLY FROM KFWA SHOWED A LARGE WARM LAYER ABOVE 4000 FT. AS A
RESULT HAVE WENT JUST RAIN AT BOTH SITES WITH CONTINUATION OF SE
FLOW OF WARMER AIR EXPECTED. CIGS WILL REMAIN AOB 1000 FT FOR THE
NIGHT AND INTO MUCH OF THE DAY WEDS. WINDS JUST ABOVE THE SURFACE
ARE RATHER STRONG AND EXPECTED TO CONTINUE TO INCREASE. LOCAL
SHEAR ALERT PROGRAM SUGGESTS SHEAR UPWARDS OF 50 TO 60 KTS AT KSBN
AND 50 KTS AT KFWA THROUGH AT LEAST 12Z. HAVE ADDED LLWS MENTION
AT BOTH SITES THROUGH 12Z FOR NOW AND MAY NEED TO EXTEND A BIT
PAST THAT PRIOR TO THE ARRIVAL OF THE COLD FRONT. PRECIP WILL
TAPER TO PERIOD OF DRY CONDITIONS AND SOME DRIZZLE AT TIMES UNTIL
THE FRONT APPROACHES WHEN ADDITIONAL SHOWERS MAY ARRIVE FOLLOWED
BY A QUICK SWITCH TO SNOW AND SFC WINDS INCREASING AND BECOMING
SW. BEYOND 12Z FEW CHANGES MADE OTHER THAN TO INCREASE WIND GUSTS
TO 40 KTS...WHICH MAY NOT BE HIGH ENOUGH.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...HIGH WIND WARNING FROM 10 AM EST /9 AM CST/ THIS MORNING TO 7 PM
EST /6 PM CST/ THIS EVENING FOR INZ003>009-012>018-020-
022>027-032>034.
WINTER WEATHER ADVISORY FROM NOON EST /11 AM CST/ TODAY TO 9 PM
EST /8 PM CST/ THIS EVENING FOR INZ003>005.
MI...HIGH WIND WARNING FROM 10 AM THIS MORNING TO 7 PM EST THIS
EVENING FOR MIZ077>081.
WINTER WEATHER ADVISORY FROM NOON TODAY TO 9 PM EST THIS EVENING
FOR MIZ079.
WINTER WEATHER ADVISORY FROM NOON TODAY TO 7 PM EST THURSDAY FOR
MIZ077-078.
OH...HIGH WIND WARNING FROM 10 AM THIS MORNING TO 7 PM EST THIS
EVENING FOR OHZ001-002-004-005-015-016-024-025.
LM...STORM WARNING FROM 9 AM THIS MORNING TO 7 PM EST THIS EVENING
FOR LMZ043-046.
GALE WARNING UNTIL 9 AM EST THIS MORNING FOR LMZ043-046.
&&
$$
SHORT TERM...JC
LONG TERM...FISHER
AVIATION...JC
