FXUS63 KIWX 022013
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
313 PM EST WED DEC 2 2009
.SHORT TERM...
...TONIGHT THROUGH THURSDAY NIGHT...
WATER VAPOR SHOWS POTENT UPPER LOW LIFTING NORTHEAST OUT OF GULF
COAST REGION INTO MIDWEST WHILE NORTHERN STREAM SHORT WAVE SINKS
SOUTH ACROSS THE DAKOTAS. THESE TWO FEATURES AND MESOSCALE LAKE
EFFECT EVENT WILL BE CONCERNS IN THE SHORT TERM PERIOD.
REGIONAL RADAR MOSAIC SHOWING RAIN INCREASING IN COVERAGE AND
SPREADING NORTH AHEAD OF UPPER WAVE LIFTING OUT OF SOUTH. EXPECT
THIS TO CONTINUE TO SPREAD NORTH ACROSS ALL OF FORECAST AREA THIS
EVENING. FAR NORTHWEST AREAS WILL LIKELY BE SKIMMED BY THIS SYNOPTIC
SYSTEM WITH ONLY LIGHT RAIN AMOUNTS. A LITTLE HIGHER QPF AS YOU GO
FURTHER SOUTH AND EAST ACROSS OUR AREA WITH AMOUNTS NEAR A HALF INCH
POSSIBLE INTO NORTHWEST OHIO.
FORECAST CHALLENGE BECOMES TRANSITION TO SNOW THURSDAY MORNING. 12Z
MODEL SUITE IN RATHER GOOD AGREEMENT ON KEEPING BOUNDARY LAYER WARM
ENOUGH FOR ALL LIQUID ALL AREAS THROUGH JUST ABOUT 12Z THURSDAY.
SURFACE WET BULB TEMPS SHOWN TO REMAIN IN MID AND UPPER 30S THROUGH
ABOUT 15Z BEFORE GRADUALLY BEGINNING TO FALL THROUGH THE DAY. 925MB
WET BULB ZERO LINE MOVES THROUGH A LITTLE QUICKER BUT STILL NOT
UNTIL AT LEAST 12Z IN WEST. 1000-850MB THICKNESS VALUES SIMILAR TO
925MB WET BULB WITH 1300M CRITICAL THICKNESS LINE INTO WESTERN AREAS
NEAR 12Z AND NOT THROUGH EASTERN AREAS UNTIL AFTER 18Z. HAVE USED A
BLEND OF MODEL CONSENSUS FOR TRANSITION WHICH BASICALLY CONTINUES
PREVIOUS TRENDS OF SLOWING CHANGEOVER TO ALL SNOW BY SEVERAL HOURS.
THIS MAKES ACCUMULATING SNOW AWAY FROM LAKE EFFECT AREAS LESS LIKELY
AS DEEPER MOISTURE BEGINS PULLING OUT OF THE AREA AFTER 06Z TONIGHT.
WILL LEAVE A RAIN OR SNOW MENTION IN FAR NORTHWEST TONIGHT BEFORE 12Z
BUT TRANSITION ALL OTHER AREAS TO JUST RAIN. HAVE KEPT A LOW CHANCE
POP OR FLURRY/SPRINKLE MENTION ALL AREAS ON THURSDAY WITH COLD AIR
ADVECTION AND ANY LINGERING MOISTURE...THOUGH MEASURABLE PCPN
BECOMING DOUBTFUL AWAY FROM LAKE EFFECT.
LAKE EFFECT AREAS POSE THEIR OWN CHALLENGES FOR THIS EVENT. LAKE
ENHANCED BAND STILL LOOKS PLAUSIBLE TOWARD 12Z THU AS SYNOPTIC LOW
EXITS THE EAST AND COLD AIR ADVECTION BEGINS IN WEST. MUCH COLDER
AIR OVER NORTHERN LAKE MICHIGAN WILL BE QUICKLY MOVING SOUTH ACROSS
LAKE AS LOW LEVEL FLOW QUICKLY BACKS FROM NORTHEAST TO NORTHWEST AND
EVENTUALLY WEST. ITS THE PERIOD FROM ABOUT 09Z TO 18Z THAT IS OF
SOME CONCERN IN FAR NW AREAS AS MODELS 925MB PLUME ANALYSIS INDICATE
GOOD LIFT AND MOISTURE WITH LONG FETCH. QUESTION IS WHETHER DELTA T
VALUES WILL BE COLD ENOUGH THIS EARLY FOR GOOD INSTABILITY AND HOW
FAST MID LEVEL SYNOPTIC MOISTURE DRIES OUT AND WHETHER ANY ORGANIZED
BAND CAN FORM. GIVEN THE QUICKLY BACKING WINDS EXPECT ANY LAKE PLUME
TO BE RATHER TRANSITORY EARLY WHICH WOULD LIMIT ANY ACCUMULATIONS.
IN ADDITION...WET BULB TEMPS LOOK TO STILL BE IN LOW TO MID 30S
WHICH MAY ALLOW ANY SNOW TO MIX WITH RAIN AT TIMES OR MELT QUICKLY.
HAVE CONTINUED LIKELY POPS IN FAVORED LAKE EFFECT REGION WITH ONLY
SMALL ACCUMS. FLOW BECOMES MORE WESTERLY THU NIGHT WHICH SHOULD
SHIFT ANY LAKE EFFECT INTO EXTREME NORTHERN INDIANA AND MAINLY
SOUTHWEST LOWER MICHIGAN. BERRIEN AND CASS REMAIN FAVORED LOCATIONS
WITH SOME ACCUMS POSSIBLE THU NIGHT DEPENDING AGAIN ON AMOUNT OF
MOISTURE IN MIXED LAYER GIVEN SHORTEST FETCH POSSIBLE ACROSS LAKE.
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
BRUNT OF THE COLD BLAST WILL BE SETTLING OVER THE AREA AT THE START
OF THE PERIOD. 850 MB TEMPS OF -12 TO -14C WILL LEAD TO A COLD DAY
ACROSS THE AREA COMPARED TO WHAT WE HAVE SEEN RECENTLY. AVERAGE
HIGHS THIS TIME OF YEAR ARE IN THE UPPER 30S SO DEFINITELY BELOW
NORMAL. MOST AREAS WILL BE DRY EXCEPT FOR LOCATIONS IN FAR SOUTHERN
LOWER MI...WHERE LAKE EFFECT MACHINE WILL BE IN FULL SWING WITH
DELTA T'S AROUND 20 C. GIVEN SHORT FETCH IN THE WSW TO SW
FLOW...AMOUNT OF MSTR TO BE CONTRIBUTED TO THESE BANDS REMAINS
TRICKY. AS SUCH HAVE MAINTAINED LIKELY POPS FRIDAY IN BERRIEN
COUNTY. HIGHEST POPS WILL REMAIN ACROSS NORTHERN AND CNTRL OF THE
COUNTY WHERE A FEW INCHES OF ACCUMULATION WILL BE POSSIBLE. THE
CHANCES FOR SNOW WILL CONTINUE INTO SATURDAY MORNING WITH A SLOW
DOWNWARD TREND AS THE FLOW BEGINS TO SHIFT...DELTA T'S AND MSTR
DECREASES. FOR THE REMAINDER OF THE AREA...HAVE KEPT WITH PARTLY
CLOUDY SKIES AS DRY AIRMASS SHOULD ALLOW FOR SUNSHINE BUT STILL COOL
TEMPS.
A FAST MOVING WAVE WILL ARRIVE SOMETIME MONDAY OR MONDAY NIGHT. AT
THIS POINT IT APPEARS TO BE MSTR STARVED AND WILL PROBABLY DO LITTLE
MORE THAN ALLOW FOR SLIGHTLY WARMER TEMPS AHEAD OF IT AND A
REINFORCING SHOT OF COLD AIR BEHIND IT. PAST GRIDS HAD THIS HANDLE
SO WILL LEAVE CHC POPS MON/MON NGT. SOME POTENTIAL TO REMOVE POPS
FROM MONDAY NIGHT BUT GIVEN VARIANCE OF MODELS LATELY DON'T WANT TO
MESS AROUND WITH IT.
FINAL FOCUS WILL TURN TOWARD NEXT SOMEWHAT DEEPER TROUGH SET TO DIG
INTO THE PLAINS AS THE MONDAY SYSTEM IS MOVING THROUGH. GFS SHOWS A
RATHER POTENT SYSTEM TAKING SHAPE AND AFFECTING MUCH OF THE EASTERN
US. GFS ENSEMBLE MEMBERS FOR PRECIP CHANCES DEPICT 60 TO 70% CHANCE
OF A TENTH OF AN INCH OR MORE MAINLY ON WEDNESDAY. WHILE THIS WOULD
LEAD NORMALLY TO INCREASED CONFIDENCE...THE FACT THAT THE MEDIUM
RANGE MODELS HAVE BEEN DOING RATHER HORRIBLE IN TERMS OF CONSISTENCY
OF LATE AND THAT THIS AREA IS LIKELY TO CHANGE IN LOCATION OVER THE
NEXT SEVERAL DAYS...MAKES IT HARD TO LEAN THAT HEAVILY ON GUIDANCE
POINT TOWARDS ABOVE CLIMO POPS. NOW THAT BEING SAID...GIVEN THE
SIGNS OF THE ACTIVE PATTERN AND LARGE PIECE OF NORTHERN STREAM
ENERGY SET TO BREAK OFF AND DROP TOWARDS THE AREA...STAGE MAY BE SET
FOR A SOMETHING TO BE MONITORED IN LATER FORECASTS. FOR NOW HAVE
WENT UNDER CLIMO/GUIDANCE VALUES AND INTRODUCED 30 POPS TUES
NGT/WEDS WITH PLENTY OF TIME TO WATCH EVOLUTION OF THE MODELS.
ONE THING TO NOTE IS LARGE POLAR LOW THAT WILL BE MOVING ACROSS
NORTHERN CANADA TOWARDS THE END OF THIS FORECAST PERIOD WITH A CORE
OF -40 C 850 MB TEMPS. WILL SOME OF THIS MAKE IT DOWN OUTSIDE THE
LONG TERM PERIOD...STAY TUNED.
&&
.AVIATION...
MODELS CONTINUE TO GRADUALLY BACK OFF ON PCPN WITH DEEP SYSTEM
MOVING BY TO OUR SOUTH TONIGHT. MODELS HAVE ALSO SLOWED COLD AIR
INTRUSION IN LOWER LEVELS DELAYING CHANGEOVER TO ALL SNOW. CIGS WILL
GRADUALLY LOWER THIS AFTERNOON AND EVENING. RAIN WITH VIS
RESTRICTIONS WILL LIKELY HOLD OFF AT TAF SITES UNTIL EARLY EVENING.
RADAR SHOWING RETURNS JUST SOUTH OF KFWA BUT MOST REPORTING SITES
NOT INDICATING ANY RAIN REACHING SURFACE WITH DRY NORTHEAST LOW
LEVEL FLOW. HAVE BACKED UP ONSET OF PCPN A FEW HOURS ALONG WITH
SLOWED TIMING FOR MVFR CIGS. EXPECT WITH NIGHTTIME COOLING AND
SATURATION THAT CIGS AND EVENTUALLY VIS WILL REACH MVFR LEVELS
OVERNIGHT. HEAVIEST PCPN WILL BE FROM KFWA SOUTH AND EAST. LOW LEVEL
THICKNESS AND WET BULB TEMPS FROM 12Z MODEL SUITE SUGGEST ANY
CHANGEOVER TO SNOW WILL BE CLOSER TO 12Z AT KSBN AND POSSIBLY AS
LATE AS 16 TO 18Z AT KFWA. LEFT A MIX IN AT KSBN AND KEPT KFWA ALL
RAIN. COULD SEE PERIODS OF ALL SNOW LATE MORNING ON AT KSBN
DEPENDING ON LAKE EFFECT MOISTURE PLUME AND STRONGER LIFT.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 7 AM EST FRIDAY FOR LMZ043-046.
&&
$$
SHORT TERM...LASHLEY
LONG TERM...FISHER
AVIATION...LASHLEY
