FXUS63 KIWX 100856
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
356 AM EST THU DEC 10 2009
.SHORT TERM...
TODAY THROUGH FRIDAY NIGHT
SFC LOW WHICH BROUGHT A VAST ARRAY OF WINTER WEATHER TO THE
CONUS...CONTINUES TO OCCLUDE AS IT PUSHES INTO WESTERN QUEBEC. STRONG
LL PRESSURE GRADIENT IN PLACE IN REPONSE TO SFC RIDGING NOTED BY 3-4MB
3 HOUR PRESSURE TENDENCIES...CONTINUES TO OFFER BREEZY CONDITIONS
WITH MANY PLACES STILL HOVERING IN THE 15-20 KNOT RANGE. CAA
CONTINUES WITH TEMPS BEGINNING TO FALL INTO THE SINGLE DIGITS IN THE
WESTERN FA. H85 TEMPS WILL CONTINUE TO FALL OVER THE FA...WITH
VALUES OF -20 C EXPECTED BY AFTERNOON. CAA OVER THE WARM WATERS OF
LAKE MICH CONTINUES TO SUPPORT A GROWING LAKE REPONSE AS LAKE INDUCED
INSTABILITY CONTINUES TO RISE. SNOW SHOWERS CONTINUE IN PORTIONS OF
SW MI...WITH A BRIEF LULL IN ACTIVITY. LL TROUGH AND HIGHLY
CONVERGENT LL WIND FIELD IN PART TO INCREASINGLY GEOSTROPHIC FLOW
OVER THE LAKE...SUPPORTED HEAVY SNOWS YESTERDAY EVENING. NOW THAT
THE TROUGH FEATURE HAS EXITED THE REGION AND FLOW HAS SLACKENED
SOME...SNOW SHOWER ACTIVITY HAS WANED SOME. HOWEVER...AS LAKE
INDUCED INSTABILITY GROWS...DO EXPECT AN INCREASE IN ACTIVITY.
OTHERWISE...DO EXPECT SOME BREAKS IN THE CLOUD DECK AWAY FROM LAKE
MI FLOW....BY THIS AFTERNOON...WITH SFC HIGH PRESSURE BUILDING INTO
THE REGION. HAVE UTILIZED THE NAM12/LOCAL WRF/AND GFS GIVEN LAKE
EFFECT SNOW SETUP AND VERY GOOD INITIATION AS EVIDENCED IN 00Z
MOMENTUM/THERMAL FIELD COMPARISON.
TODAY...MAIN CONCERN IN THE PERIOD IS ONGOING WINTER STORM WARNING AND
LAKE EFFECT SNOW POTENTIAL. CAA WILL SUPPORT H85 DELTA T/S OF NEARLY
26 C...WITH LAKE INDUCED CAPE VALUES RISING TO NEARLY 800 J/KG.
WESTERLY FLOW WILL SUPPORT LAKE TROUGHINESS OVER THE WEST CENTRAL MI
SHORELINE...WITH HIGHLY CONVERGENT LL FLOW DEVELOPING...SUPPORTING
MAX UVM NEAR THE HOLLAND MKG AREA. THIS WILL FORCE THE MOMENTUM
FIELD TO RESPOND THROUGH A BACKING WIND FIELD...WHICH IS ALREADY
EVIDENT IN SFC OBS...MAINLY FROM GEOSTROPHIC TRENDED FLOW. GROWING
INSTABILITY OVER THE LAKE WILL SUPPORT MAX NEGATIVE OMEGA IN OR NEAR
THE DENDRITIC GROWTH ZONE...AND MODERATE TO HEAVY LAKE EFFECT SNOW
WILL CONTINUE. THIS ONLY CONCERN IS THAT THE BULK OF SNOWFALL WILL
OCCUR NORTH OF THE FA...WITH EXTREME NORTHERN BERRIEN AND CASS
COUNTIES BEING IMPACTED MOST IN THE LOCAL FA. MODEL QPF GUIDANCE AND
BUFR SNOW RATIO PROGS...SUPPORT ANOTHER 1-3 INCHES OF SNOW POSSIBLE
ACROSS NORTHERN BERRIEN AND CASS COUNTIES AND EXTREME NW ST. JOE
COUNTY MI THROUGH TODAY. FLOW LOOKS TO TURN WESTERLY TONIGHT WITH
BANDING SHIFTING FARTHER SOUTH IN A VERY UNSTABLE REGIME GIVEN
RAISED INVERSION HEIGHTS AND EQL OF 10KFT. EXPECTING ANOTHER 1-3
INCHES TONIGHT...WITH LOCALLY HEAVIER AMOUNTS POSSIBLE. IN
ADDITION...GUSTY WESTERLY WINDS WILL CONTINUES TO SUPPORT BLOWING
AND DRIFTING SNOW WITH WHITE OUT CONDITIONS STILL EXPECTED. WILL LET
CURRENT WARNING END TIME REMAIN INTACT. HEADLINES MAY BE NEEDED
TONIGHT...BUT LINGERING QUESTIONS ON FLOW ORIENTATION/HEIGHT
ADJUSTMENT/AND SNOWFALL AMOUNTS PRECLUDES ANY CHANGES ATTM.
ELSEWHERE ACROSS THE FA.....EXPECT VERY COLD TEMPS WITH ONLY A VERY
SLIGHT DIURNAL RISE. HAVE LOWERED HIGHS A TAD TO REFLECT CONCERNS ON
CAA. SOME SUN MAY BE POSSIBLE LATE TODAY...ESPECIALLY IN THE SW.
EXPECT WIND CHILL READINGS OF 5 TO 10 BELOW THIS MORNING AND AGAIN
FRIDAY MORNING. LOOK FOR VERY COLD READINGS TONIGHT WITH LOWS IN THE
SINGLE DIGITS. EVEN THOUGH SKIES WILL CLEAR ACROSS THE SOUTHERN
THIRD OF THE FA...A MIXED BL IN THE PRESENCE OF VERY LITTLE SNOW
COVER WILL TEND TO KEEP TEMPS FROM CRASHING BELOW ZERO.
FRIDAY...WARMING PROFILES AND LOWERING INVERSION HEIGHTS WILL
SUPPORT A SLOW WANING TREND IN LAKE EFFECT SNOW. ANOTHER INCH OR TWO
WILL BE POSSIBLE OVER THE CURRENTLY WARNED AREA...ESPECIALLY WESTERN
CASS COUNTY. BUFR DATA STILL INDICATES DELTA T/S OVER 20C...AND
GIVEN STRONG MODEL BIAS TO END LAKE EFFECT EVENTS TOO
SOON...SNOWFALL TOTALS MAY BE HIGHER THAN CURRENT EXPECTATIONS. WILL
DEFER ANY CHANGES TO THE DAYSHIFT...GIVEN THE NEED FOR MORE
OBSERVATIONAL DATA CLOSER TO THE PERIOD. OTHERWISE...LOOK FOR
CONTINUED COLD CONDITIONS WITH PARTLY TO MOSTLY SUNNY SKIES SOUTH OF
THE LAKE FETCH.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
WAA WILL BE UNDERWAY AT THE START OF THE PERIOD WITH PARTLY CLOUDY
SKIES AND HIGH TEMPS RETURNING BACK TO NEAR FREEZING FOR SATURDAY.
WARMEST SURGE OF AIR WILL ARRIVE SUNDAY INTO MONDAY AHEAD OF THE
NEXT SYSTEM SET TO AFFECT THE REGION. WHILE SOLUTIONS VARY ON THE
EXACT TRACK AND EFFECTS OF THIS SYSTEM IN THE 2ND HALF OF THE
EXTENDED...MODELS AGREE AT LEAST ON 850 MB TEMPS CLIMBING NEAR OR
ABOVE 0 C AND 1000-850 MB THICKNESS VALUES ABOVE 1300 M. MEX
GUIDANCE POINTS TOWARDS HIGHS WELL INTO THE 40S BOTH SUNDAY AND
MONDAY AND WHILE NOT A LARGE STRETCH DEPENDING ON THE EXACT
TRACK...AM VERY HESITANT TO JUMP ON THAT BOAT GIVEN WHAT MAY STILL
BE A COOL BOUNDARY LAYER. AS A RESULT HAVE INCREASED TEMPS SOMEWHAT
BUT REMAINING UNDER MEX GUIDANCE. IN TERMS OF PRECIP WILL LEAVE CHC
POPS IN FOR MONDAY AS FRONT APPROACHES. GIVEN ABOVE DETAILS AND
COLLABORATION HAVE WENT WITH RAIN/SNOW MIX. CLOUD COVER MAY BE
TRICKY DURING THE PERIOD AS WARM FRONT MOVES THROUGH WITH MODELS
SHOWING POTENTIAL FOR A FAIR AMOUNT OF CLOUD COVER BY SUNDAY. WILL
REMAIN CONSERVATIVE FOR NOW.
AS MENTIONED...MODELS VARY GREATLY ON HANDLING OF NEXT POTENTIAL
COLD SHOT STARTING MAINLY MONDAY NIGHT. TEMP PROFILES DO CONFIRM AT
LEAST SOME COOLING. HOWEVER...GFS IS MUCH MORE AGGRESSIVE AND
DRAMATIC ON COLD AIR WITH 850 MB TEMPS DROPPING BACK TO -16 TO -18 C
BY TUES NIGHT COMPARED TO THE BRUNT OF THE COLD AIR REMAINING NE OF
THE AREA AND 850 TEMPS ONLY DROPPING TO -2 TO -4 C WITH SIGNS OF
WARMING ALREADY BY THE END OF THE PERIOD. GIVEN THIS DEGREE OF
VARIANCE...HARD TO GRAB ONTO ONE SOLUTION AS GIVEN HISTORY PAST
SEVERAL WEEKS ROLLER COASTER OF TEMPS IS EXPECTED. WILL STAY ON
WARMER SIDE FOR NOW AND CONTINUE WITH PREV GRIDS. IF COLDER TEMPS DO
ARRIVE THEN LAKE EFFECT WILL BECOME A CONCERN WITH ADDITION OF POPS
BEING NEEDED STARTING MONDAY NIGHT.
&&
.AVIATION...
DEPARTING SFC CYCLONE CONTINUES TO SUPPORT CAA INTO THE
FA...RESULTING IN LAKE EFFECT SNOW ACROSS THE NORTH...WITH
LINGERING WEAK VERTICAL ASCENT PER CONTINUED STRONG MECHANICAL
MIXING OVER THE REMAINDER OF THE FA. HIGH RH BOUNDARY LAYER WILL
NOT BEGIN TO DRY OUT UNTIL MID TO LATE MORNING WITH LIGHT SNOW
ACTIVITY EXPECTED TO PERSIST ACROSS MUCH OF THE FA...WITH MVFR TO
IFR VIS EXPECTED. OTHERWISE...NW AREAS WILL SEE CONTINUED LIGHT TO
MODERATE LAKE EFFECT SNOW SHOWERS GIVEN INCREASING LAKE INDUCED
INSTABILITY. BULK OF ACTIVITY IS EXPECTED TO REMAIN NORTH OF
SBN...WITH MAIN VIS RESTRICTIONS FROM BLSN THERE.
SFC HIGH PRESSURE WILL BUILD INTO THE REGION ON THUR...WITH VFR
CONDITIONS OVER THE MAJORITY OF THE FA...SAVE THE NNW WHERE LAKE
EFFECT CLOUDS AND SNOW SHOWERS WILL CONTINUE TO SUPPORT MVFR TO IFR
CONDITIONS. SBN WILL BE ON THE EDGE OF SNOW VIS RESTRICTIONS...BUT
GIVEN DIURNAL COOLING AND SLIGHT VEERING IN THE WIND PROFILE...DO
EXPECTED AT LEAST MVFR CIGS/VIS WITH POSSIBLE IFR CONDITIONS
RETURNING BY EVENING.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...WINTER STORM WARNING UNTIL 7 PM EST THIS EVENING FOR MIZ077>079.
OH...NONE.
LM...GALE WARNING UNTIL 7 PM EST THIS EVENING FOR LMZ043-046.
&&
$$
SHORT TERM...JC
LONG TERM...FISHER
AVIATION...JC
