FXUS63 KAPX 221139
AFDAPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
639 AM EST TUE DEC 22 2009
.SYNOPSIS.../ISSUED AT 439 AM/
HIGH PRESSURE WILL BUILD INTO THE WESTERN GREAT LAKES TODAY...AND
WILL PROVIDE THE REGION WITH A TREMENDOUS AMOUNT OF DRY AIR AND
INSIGNIFICANT WEATHER THROUGH WEDNESDAY NIGHT. INCREASING CLOUDS CAN
BE EXPECTED THROUGH THURSDAY AND THURSDAY NIGHT...IN ADVANCE OF AN
APPROACHING WINTER STORM. THIS STORM IS EXPECTED TO BRING A WINTRY
MIX TO THE NORTH WOODS FROM LATE CHRISTMAS EVE THROUGH CHRISTMAS
DAY. LAKE-EFFECT SNOWS WILL DEVELOP BEHIND THIS SYSTEM OVER THE
WEEKEND AND INTO EARLY NEXT WORK WEEK.
SMD
&&
.SHORT TERM.../ISSUED AT 439 AM/...TODAY
ON THE LATEST SURFACE WEATHER MAP...1029 MB HIGH
PRESSURE WAS RIDGED ACROSS MUCH OF ONTARIO. SATELLITE IMAGERY ALONG
WITH SURFACE OBSERVATIONS INDICATE MOSTLY CLEAR SKIES ACROSS EASTERN
UPPER AND FAR NORTHERN LOWER WITH STUBBORN STATUS DECK MIRED ACROSS
THE REMAINDER OF NORTHERN LOWER. APX RADAR SHOWS LAST VESTIGES OF
LIGHT SNOW EXITING FAR SOUTHERN ZONES. THE MAIN SHORT TERM FORECAST
CONCERN REVOLVES AROUND POPS AND SKY COVER TODAY.
NOT A WHOLE LOT GOING ON TODAY WITH RIDGING/DRYING THE GENERAL RULE.
STILL A NORTHWEST FLOW ALOFT IN PLACE BUT HEIGHTS SLOWLY REBOUND. IT
REMAINS COLD ENOUGH FOR LAKE EFFECT PRODUCTION AS 850 MB
TEMPERATURES HOVER BETWEEN -11 AND -12 C. HOWEVER...WITH THE
EXCEPTION OF A BIT OF MOISTURE ADVECTION ACROSS NORTHEAST LOWER
(MEAN 850-700 MB RH 50 TO 60 PERCENT) MUCH OF THE FORECAST AREA IS
VOID OF ANY APPRECIABLE MOISTURE (MEAN 850-700 MB RH 30 TO 40
PERCENT). IN ADDITION...LOW LEVEL FLOW IS WEAK (10 KNOTS OR LESS).
CRUX OF ALL THIS IS THAT THERE MAY BE SOME LIGHT LAKE EFFECT SNOW
SHOWERS OFF OF LAKE HURON THIS MORNING WITH LITTLE TO NO ACTIVITY
THIS AFTERNOON. CLOUD COVER WILL BE TRICKY BUT EXPECT MOST SPOTS TO
SEE AT LEAST PARTIAL CLEARING THROUGH THE DAY. HIGHS GENERALLY IN
THE LOWER AND MIDDLE 20S.
SULLIVAN
&&
.LONG TERM.../ISSUED AT 439 AM/...TONIGHT AND BEYOND
RIDGING WILL BE THE RULE THROUGH WEDNESDAY NIGHT THEN ATTENTION
TURNS TO A WINTER WEATHER SYSTEM MOVING UP FROM THE SOUTH. THE
MAIN LONG TERM FORECAST CONCERNS ARE MINOR OVER THE NEXT COUPLE OF
DAYS THEN THEY REVOLVE AROUND PRECIPITATION TYPE AND TIMING OF
SYSTEM DUE IN ON CHRISTMAS DAY.
TONIGHT THROUGH WEDNESDAY NIGHT...A QUIET STRETCH OF WEATHER WITH
INCREASING RIDGING AT THE SURFACE AND ALOFT. THIS IS EXPECTED TO
LEAD TO CLEAR TO PARTLY CLOUDY SKIES AND SEASONABLE TEMPERATURES.
THE EXCEPTION TO THIS WILL BE TONIGHT...WITH LIGHT WINDS LEADING TO
VERY GOOD RADIATIONAL COOLING CONDITIONS. LOWS GENERALLY IN THE
SINGLE DIGITS ABOVE ZERO...BUT COULD CERTAINLY SEE SOME SPOTS FALL
WELL BELOW ZERO.
THURSDAY INTO THIS WEEKEND...ATTENTION WILL TURN TO A SYSTEM
CURRENTLY EVIDENT ON WATER VAPOR LOOP ACROSS NORTH CENTRAL CANADA.
EXTENDED MODELS CONTINUE TO DIG THIS SYSTEM INTO THE SOUTHERN
ROCKIES THEN INTO THE SOUTHERN PLAINS BEFORE LIFTING IT NORTH
NORTHEASTWARD INTO THE WESTERN GREAT LAKES BY THE END OF THE WEEK.
EXTENDED GUIDANCE IS NOW DECIDEDLY ON A MORE WESTERN TRACK (ACROSS
WISCONSIN) BRINGING WARM AIR ALOFT INTO THE FORECAST AREA.
HOWEVER...VERTICAL STACKING AND SURFACE OCCLUSION WILL MAKE IT TOUGH
FOR WARM AIR TO MAKE IT TO THE SURFACE. IN ADDITION...DRY EASTERLY
FLOW LOOKS LIKE IT WILL CAUSE MASSIVE EVAPORATIVE COOLING THROUGH
THE COLUMN WHICH MAY OVERCOME THE WARM AIR ALOFT ENOUGH TO RESULT IN
SNOW OR SLEET TO BEGIN THE EVENT. THERE IS STILL WAY TOO MUCH
UNCERTAINTY TO PIN DOWN TOO MUCH DETAIL AT THIS TIME. IT DOES LOOK
LIKE IT WILL TAKE SOME TIME TO REALIZE PRECIPITATION...DUE TO THE
DRYING SOUTHEASTERLY FLOW AROUND STRONG SURFACE RIDGE (1040 MB) TO
OUR NORTH ACROSS ONTARIO. THEREFORE...HAVE DELAYED ONSET OF PRECIP
UNTIL LATER CHRISTMAS EVE OR EVEN OVERNIGHT (ACTUALLY WOULD NOT BE
SURPRISED IF NORTHEAST FORECAST AREA HAD TO WAIT UNTIL AFTER 12Z
FRI). WILL CONTINUE TO ALLOW FOR ALL FORMS OF PRECIPITATION
(SN/RN//FZRA/PL) INTO CHRISTMAS DAY AS THE AMOUNT AND DEPTH OF
WARMING REMAINS UNCERTAIN. EXTENDED MODELS THEN VARY AS TO WHAT
HAPPENS AFTER INITIAL SURGE (MAINLY DURING CHRISTMAS DAY) AS SYSTEM
LIKELY STALLS OUT ACROSS THE REGION WHILE WEAKENING. PRECIP SHOULD
FALL IN THE FORM OFF ALL SNOW CHRISTMAS NIGHT AND CONTINUE RIGHT
INTO THE WEEKEND.
SULLIVAN
&&
.MARINE.../ISSUED AT 439 AM/
SURFACE RIDGE WILL RESULT IN A LIGHT EASTERLY/NORTHEASTERLY FLOW
ACROSS THE UPPER LAKES THROUGH WEDNESDAY EVENING. WINDS WILL BEGIN TO
INCREASE LATER WEDNESDAY NIGHT INTO CHRISTMAS EVE OUT AHEAD OF LOW
PRESSURE APPROACHING FROM THE SOUTH.
AJS
&&
.AVIATION.../ISSUED AT 637 AM/...VALID FOR 12Z TAFS
HIGH PRESSURE WILL PROVIDE IMPROVING CONDITIONS FOR THE TERMINAL
SITES OVER THE NEXT FEW HOURS. LINGERING LOW END VFR TO LOCALLY
MVFR CEILINGS WILL GIVE WAY TO SOLIDLY VFR CONDITIONS BY LATER
THIS MORNING AS MUCH DRIER AIR BACKS INTO THE AREA ON DEVELOPING
LIGHT NORTH/NORTHEAST FLOW.
AJS
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
LH...NONE.
LS...NONE.
&&
$$
