FXUS63 KLOT 301143
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
543 AM CST MON NOV 30 2009
.DISCUSSION...
225 AM CST
LONG RANGE FOCUS IS ON AN UPCOMING SNOW EVENT DEVELOPING IN THE SRN
PLAINS AND EJECTING NE ACROSS THE OHIO VALLEY WED NGT INTO THURSDAY.
BUT THE MORE IMMINENT PRIORITY WUD BE TO CLEAR OUT THE SC DECK
ADVECTING SE INTO IL AND EMBEDDED IN THE POST FRONTAL COLD POOL OF
CANADIAN AIR. SEVERAL HOLES EXIST IN THIS FIELD OF CLOUDS AND
CONSIDERING SLOW MOTION OF THIS DECK...GFS APPEARS TO HAVE A BETTER
HANDLE ON CLEARING TODAY THAN THE NAM. STARTING OUT CLOUDY THIS
MORNING MAY TURN TO CLEARING WITH PASSAGE OF THE UPR TROF EARLY THIS
AFTN BUT CLOUDING UP AGAIN TONIGHT AS WARM AIR ADVECTION QUICKLY
RETURNS ON THE WEST SIDE OF THE PASSING RIDGE.
A DIVING UPR JET ACROSS THE DAKOTAS AND UPR MS VLY WILL GENERATE A
WAVE DOWN THE UPR NW FLOW TODAY...PRODUCING AN INCREASE IN CLOUD
COVER AS THIS WAVE APPROACHES LAKE MICHIGAN LATE THIS AFTN. THERE
MAY BE A SMALL RISK OF RAIN OR SNOW THIS EVENING ACROSS PORTIONS OF
NE IL AND NW INDIANA AS THIS WAVE QUICKLY PASSES SE INTO LOWER
MICHIGAN BY MIDNIGHT. THE MORE GENEROUS PORTION OF PCPN WILL BE
NORTH AND EAST OF THE FORECAST AREA. TUESDAY IS EXPECTED TO BE
RATHER UNEVENTFUL WITH PASSAGE OF ANOTHER RIDGE AND MODERATE WARM
AIR ADVECTION RETURNING OUT AHEAD OF THE MIDWEEK SYSTEM.
THE ATTENTION WILL BE FOCUSED ON THIS SYSTEM...OR RATHER DUAL
SYSTEMS...TUES NGT INTO WEDNESDAY. TWO STREAMS OF FLOW MAKE UP THIS
DUAL SYSTEM. A NORTHERN STREAM LOW WILL DIVE SE FROM ALBERTA MONDAY
NIGHT IN THE UPPER NW FLOW WHILE THE SRN STREAM DEVELOPS A CLOSED
LOW OVER SW MEXICO. WHILE THE NRN STREAM APPEARS THREATENING AS IT
DIVES ACROSS THE DAKOTAS TUESDAY...IT INSTEAD MAKES A TURN NE TOWARD
LAKE SUPERIOR TUES NGT INTO WEDNESDAY. HOWEVER THE SRN STREAM SYSTEM
GATHERS GULF MSTR WHILE EJECTING OUT OF MEXICO INTO THE LOWER MS VLY
DURING THAT SAME TIME. THE NAMS HIGHER AMPLITUDE OF THE MAIN UPPER
TROF OVER THE PLAINS BY THAT TIME MAKES THE DIFFERENCE FROM THE
MORE BROADER PATTERN OF THE GFS AND ITS CLOSE ECMWF COUSIN.
EMBEDDED IN THIS HIER AMPLITUDE FLOW...THE NAM IS TRENDING TOWARD
EJECTING THE SFC LOW NORTHEAST ACROSS THE LOWER OHIO VALLEY WED
NGT TO THE DETROIT AREA EARLY THURSDAY. OTHER MODELS TEND TO TAKE
A MORE ROUNDED TRACK NORTHEAST UP THE APPALACHIANS AND WELL EAST
OF ILLINOIS AND INDIANA. THUS WRAPAROUND GULF MSTR WILL BE MORE
APT TO MAKE IT INTO THE FORECAST AREA WITH THE NAM THAN THE GFS OR
ECMWF.
THE CURRENT FORECAST SEEMS GEARED TO A BLEND OF THE GFS WITH THE
NAM. COLD AIR PULLDOWN AS THIS LOW APPROACHES THE OHIO VLY AND
VEERS WINDS TO THE NORTH WILL SUPPORT A SNOWY FORECAST BY WED
EVENING. THIS IS JUST IN TIME FOR THE SRN LOW TO PHASE IN WITH THE
SLOWER MOVING NRN STREAM LOW AND DEEPEN EVEN FURTHER. DAYTIME
HIGHS IN THE LOWER TO MIDDLE 40S WILL PROBABLY NOT COOL ENUF TO
ACCUMULATE ANY SNOW ACCUMULATION UNTIL MIDNIGHT WED NGT. QPF
VALUES OVERNIGHT WED NGT THRU THURSDAY MAY PERMIT AN INCH OR TWO
OF SNOW ACCUMULATION...ESPECIALLY FOR LOCATIONS EAST OF I-39. A
CLOSER CONSENSUS WITH THE NAM WUD LIKELY RESULT IN A HEAVIER
ACCUMULATION WHILE LEANINGS TO THE GFS MAY MEAN NO ACCUMULATION AT
ALL EXCEPT FOR SOME LAKE EFFECT IN NW INDIANA. THIS IS PRETTY
SPECULATIVE YET SINCE MODELS ARE STILL HOLDING OUT ON CONSISTENCY
WITH EACH OTHER. SO AM LEAVING THE SMALL POPS IN PLACE FOR THIS
EARLY EXTENDED PORTION OF THE FORECAST.
THE GENERAL PATTERN THURS NGT THRU EARLY FRIDAY KEEPS US IN CYCLONIC
FLOW WITH STEEP LAPSE RATES SUPPORTING SCT FLURRIES. RIDGING MOVING
ACROSS THE MS VLY LATE FRIDAY AND FRIDAY NIGHT SHUD SHUT THIS PCPN
DOWN AND START RETURNING WAA FROM THE PLAINS. THIS USUALLY MEANS
THAT ANOTHER SYSTEM IS WORKING ACROSS THE PLAINS ENROUTE TO THE
MIDWEST. QUESTIONS AS TO HOW FAST WE WARM UP BEFORE PCPN BEGINS WITH
THIS LATE WEEKEND OR POST WEEKEND SYSTEM WILL NEED TO BE CONSIDERED
WITH THE NEXT FEW MODEL RUNS.
RLB
&&
.AVIATION...
545 AM CST
1200 UTC TAFS...MAIN CONCERN FOR TODAY WILL FOCUS ON WINDS.
A WEAK SFC RIDGE MOVING THROUGH THE AREA HAS BROUGHT WEAKENING
WINDS THIS MORNING. HOWEVER...SFC TROUGH MOVING THROUGH THE REGION
LATER THIS AFTERNOON WILL BRING INCREASING WINDS...GUSTING INTO
THE UPPER TEENS TO NEAR 20KT. WIND DIRECTION WILL BACK FROM NWLY
THIS MORNING TO SWLY FOLLOWING THE PASSAGE OF THE TROUGH AXIS.
WINDS WILL REMAIN SWLY FOR THE REMAINDER OF THE PERIOD...THOUGH
SPEED WILL GRADUALLY DECREASE AFTER SUNSET AND THROUGH THE
OVERNIGHT HOURS.
SKIES ARE SLIGHTLY PROBLEMATIC AS A LARGE HOLE DEVELOPED IN THE
AC/ST DECK OVER NERN IL/NWRN IN. ALL SITES...EXCEPT RFD WILL START
OUT SKC-FEW...WHILE RFD REMAINS UNDER AN OVC DECK. LATEST METARS
INDICATE BASES OF 3500-4500FT. THE OVC DECK WILL SPREAD EWD
THROUGH THE MORNING...SPREADING OVER THE ERN SITES BY 15-16Z...BUT
SHOULD REMAIN VFR.
NO PCPN OR OBSTRUCTIONS TO VISIBILITY ARE LIKELY THROUGH THE PERIOD.
KREIN
&&
.MARINE...
245 AM CST
A RIDGE OF HIGH PRESSURE EXTENDS FROM THE SOUTH HIGH PLAINS
THROUGH THE GREAT LAKES REGION. THIS RIDGE AS BROUGHT A BRIEF
RESPITE FROM THE STRONGER WINDS...LOWERING WINDS TO 10-20KT. AS
THE RIDGES MOVES TO THE EAST TODAY...A LOW PRESSURE SYSTEM WILL
DROP OUT OF THE CANADIAN ROCKIES AND PUSHES INTO THE UPPER GREAT
LAKES BY EARLY THIS EVENING. THIS WILL STRENGTHEN THE PRESSURE
GRADIENT OVER THE LAKE ALLOWING WINDS TO INCREASE TO ARND 25KT
AGAIN THIS EVENING AND TONIGHT. AS THIS LOW MOVES OFF TO THE EAST
TONIGHT...ANOTHER...STRONGER LOW WILL DROP OUT OF THE SOUTHERN
CANADIAN ROCKIES AND QUICKLY TRACK ACROSS LAKE SUPERIOR BY TUESDAY
NIGHT. THIS SYSTEM WILL DRAG A STRONG COLD FRONT ACROSS LAKE
MICHIGAN WEDNESDAY...TURNING WINDS MORE WESTERLY TO NORTHWESTERLY
AND INCREASING TO AT LEAST 25 KT. GUSTS TO 30KT ARE POSSIBLE WITH
THIS SYSTEM...AND CONDITIONS WILL NEED TO BE MONITORED CLOSELY FOR
FURTHER STRENGTHENING AND POSSIBLE GALE FORCE WINDS.
KREIN
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 6 AM MONDAY.
SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...3 PM MONDAY TO MIDNIGHT TUESDAY.
&&
$$
