FXUS63 KAPX 260457
AFDAPX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
1157 PM EST FRI DEC 25 2009
.SYNOPSIS.../ISSUED AT 418 PM/
A COMPLEX STORM SYSTEM...CENTERED OVER IOWA...WILL SIT AND SPIN OVER
THE MID WEST STATES THROUGH TOMORROW...BEFORE EDGING CLOSER TOWARD
THE GREAT LAKES ON SUNDAY. A RAIN/SNOW MIX CAN BE EXPECTED INTO
TONIGHT...UNTIL COLDER AIR FILTERS INTO NORTHERN MICHIGAN...TURNING
THINGS OVER TO ALL SNOW SATURDAY. THE WEATHER WILL REMAIN UNSETTLED
IN THIS FASHION INTO THE NEW WORK WEEK.
BERGER
&&
.SHORT TERM.../ISSUED AT 903 PM/...TONIGHT
LOW PRESSURE SPINNING MERRILY AWAY IN WESTERN IOWA. COLD FRONT ARCS
EAST AND SE ACROSS CENTRAL WI AND SOUTHERN LOWER MI...NEARING BIG
RAPIDS AND FLINT. LIGHT PRECIP...MAINLY RAIN/DRIZZLE...CONTINUES
ACROSS MOST OF THE FORECAST AREA. HERE AT THE OFFICE...WE HAD A FEW
HOURS OF SNOW MID/LATE AFTERNOON. BUT...WITH THE DEPARTURE OF SOME
OF THE COLDEST CLOUD TOPS...WE/VE REVERTED BACK TO LIQUID PRECIP
HERE. PRECIP TYPE TRENDS ARE THE MAIN CONCERN.
IT/S A CHALLENGING P-TYPE FORECAST...AS WE HAVE A COUPLE OF
MECHANISMS TO WORRY ABOUT. 1ST...ARE ICE NUCLEI ACTIVATING WITHIN
THE CLOUDS? CLOUD TOP TEMPS PER IR SATELLITE ARE -13-14C...WHICH
SUPPORTS ICE ACTIVATION MOST OF THE TIME. THAT IS PLAYING OUT...WITH
MOST PRECIP BEING JUST FLAT /RAIN/...THOUGH IN BETWEEN THE BETTER
RADAR RETURNS WE ARE STILL SQUEEZING OUT /DRIZZLE/ AT TIMES.
HOWEVER...DRIZZLE MECHANICS (NO ICE ACTIVATION) SHOULD BECOME LESS
COMMON. A BAND OF COLDER CLOUD TOPS (NEAR -20C) IS ROTATING
NORTHWARD ACROSS CENTRAL/SOUTHERN LOWER. AS THAT MOVES IN...DRIZZLE
SHOULD DISAPPEAR. THERE MAY BE A VERY BRIEF WINDOW BEHIND THAT
BEFORE THE AIRMASS JUST GETS TOO COLD. WILL DE-EMPHASIZE
DRIZZLE/FZDZ IN THIS UPDATE.
2ND...THE SURFACE-BASED WARM LAYER. MODEL AND OBSERVED 00Z SOUNDINGS
INDICATE THAT THE ELEVATED WARM LAYER HAS BEEN WIPED OUT. THE
APPROACHING UPPER LOW IS RESULTING IN SIGNIFICANT COOLING IN THE MID
LEVELS. WE/LL AWAIT THE ARRIVAL OF STRONGER COLD ADVECTION FROM THE
SOUTH TO START WIPING OUT THE SURFACE-BASED WARM LAYER. THE COLD
FRONT WILL CONTINUE TO MAKE NORTHWARD PROGRESS...ENTERING THE SW
ZONES IN THE NEXT COUPLE OF HOURS...AND BISECTING EASTERN UPPER MI
FROM NW TO SE BY 12Z.
SO PRECIP WILL CHANGE FROM RAIN TO SNOW FROM SW TO NE...BUT ALSO
OVER THE HIGHER TERRAIN FIRST (WHERE SURFACE-BASE WARM LAYER IS
ALREADY SHALLOWER). WE CAN SEE THIS TRANSITION DOWNSTATE ON THE GRR
RADAR...WITH A MORE CELLULAR LOOK TO RAIN/SLEET AREAS...AND A MORE
/FEATHERY/ LOOK TO THE SNOW AREA ALONG IT/S SW FLANK. HAVE ALREADY
SLOWED THIS TRANSITION VS THE EARLIER FORECAST. THIS WOULD ALSO GIVE
US RELATIVELY LITTLE TIME FOR ACCUMS BEFORE THE DRY-SLOT MAKES
PRECIP SPORADIC BY 09Z-12Z. WILL REDUCE THE (ALREADY FAIRLY SMALL)
ACCUMS.
JZ
&&
.LONG TERM.../ISSUED AT 418 PM/...SATURDAY AND BEYOND
SATURDAY...COLD AIR, MOISTURE, AND THE SFC LOW STILL TO THE SW OF
THE REGION. SO WILL EXPECT THAT WITH THE ENTIRE SOUNDING TOT EH LEFT
OF THE FREEZING LINE THAT THERE WILL BE SNOW SHOWERS SCATTERED
AROUND THE FORECAST. WINDS CONTINUE OUT OF THE SOUTH, SO WILL HOLD
OFF THE SNOW ENHANCEMENT. THAT MAIN CHANCES WILL BE ALONG THE TRACK
OF THE LOW WHICH LOOKS LIKE NORTHERN LAKE MICHIGAN, SO PORTIONS OF
NW LOWER AND E UPPER.
SATURDAY NIGHT...THE UPWARD DYNAMIC FORCING CONTINUES TO FOCUS NEAR
NW LOWER AND E UPPER. WITH THE 850-700 MB LAYER STILL ABOVE 70% RH
AND WITH THE WIND STILL SSE, WON'T PROBABLY SEE ANY LAKE ENHANCEMENT
OVER LAKE HURON, ALTHOUGH MAYBE NEAR DRUMMOND ISLAND. THE 1000-850MB
STREAMLINES ARE TOO CURVED FOR ANY FETCH IN E UPPER OTHERWISE AND IS
OFFSHORE IN NW LOWER.
SUNDAY...WILL SEE HOW THIS PANS OUT, BUT THE LOW CONTINUES TO MOVE
OVER N LOWER WITH THE CORE BY 00Z, GETTING TO EAST SIDE OF THE
STATE. SO THIS WILL CONTINUE THE PROBABLY SCATTERED SNOW SHOWERS
WITH THE WEAKENING LOW WITH THE FILLING OVER THE REGION. ONCE THE
SFC LOW MOVES INTO N LAKE HURON THE WINDS BEGIN TO TURN NW IN E
UPPER AND NW LOWER. THIS WILL ALLOW LES TO BEGIN TO DEVELOP BY THE
AFTERNOON.
SUNDAY NIGHT...LES LOOKS TO BE THE BEST BET AS THE 850 MB
TEMPERATURES ARE AROUND -10C WITH NW OR NNW WINDS. THE PROBLEM THAT
THE MODELS ARE STARTING TO SHOW ARE THE WINDS SHIFTING FROM WNW TO
ALMOST NNW PRETTY QUICKLY INITIALLY. THEN THEY SETTLE A BIT SO THERE
COULD BE SOME DECENT ACCUMULATION BY MORNING AFTER THE COLD FRONT
PASSES THROUGH.
MONDAY...WE HAVE GOOD WINDS AND GOOD TEMPERATURES, FOR LAKE EFFECT.
SO WILL PROBABLY HAVE SOME SNOW BANDS, BUT THE AMOUNTS WILL PROBABLY
BE MODERATE AT BEST, WITH BOTH THE GFS, AND NAM SHOWING THAT THE
850-700 MB LAYER RH IS LESS THAN 40% AFTER 18Z. THIS MAY NOT SQUASH
THE LE CONVECTION, BUT IT WILL PUT A DAMPER ON HAVING ANY HEAVIER
AMOUNTS FOR THE AFTERNOON. OVERNIGHT, THE WINDS CONTINUE FROM THE NW
STEADILY, BUT WITH WHAT THE GFS SAYS IS RH VALUES IN THE 850-700 MB
LAYER OF LESS THAN 20%. WOULDN'T BE SURPRISED IF IT CLEARS A BIT BY
12Z.
EXTENDED (TUESDAY THROUGH FRIDAY)...TUESDAY, 500 MB HEIGHTS BUILD
WITH THE SFC HIGH BUILDING INTO THE REGION. SO WILL GO WITH THE
CHANCE OF SNOW SHOWERS FOR THE MORNING. SYNOPTIC MOISTURE SHOULD
WANE, SO WILL THINK THAT THERE COULD BE SOME CLEARING THROUGH THE
DAY AND INTO THE NIGHT. WEDNESDAY, THE HIGH MOVES TO THE EAST AND A
WARM FRONT MOVES THROUGH UPPER MICHIGAN. WITH ANOTHER 500MB WAVE
MOVING OUT OF THE CENTRAL ROCKIES. THE BULK OF WEDNESDAY WILL BE
DRY, BUT THERE IS A CHANCE FOR SOME SNOW WITH THE FRONT AND THE 500
MB WAVE. THURSDAY, THE NEXT SYSTEM AND COLD FRONT WILL MOVE THROUGH
THE REGION AND LOOKS LIKE IT WILL KICK OFF SNOW. THE 500 MB
SHORTWAVE TRAILING THE FRONT WILL HELP TO KEEP THE SNOW GOING.
FRIDAY, MORE ENERGY DIVES INTO THE 500 MB TROUGH AND CUTS THE LOW
OFF. WHILE THE MAIN ENERGY WILL BE CLOSER TO THE EAST COAST, THE
LOWS CORE WILL BE IN WISCONSIN, ALLOWING FOR MORE SNOW SHOWERS AS IT
PUSHES INTO MICHIGAN BY THE EVENING.
JSL
&&
.MARINE.../ISSUED AT 418 PM/
WINDS ALONG THE LAKE MICHIGAN SHORE ARE BEGINNING TO DROP BELOW
GALE CRITIERIA, SO WILL TAKE A COUPLE OF THE SOUTHERN ZONES FOR US
OUT OF THE GALES AND PUT UP SOME SCA. OTHERWISE, AS THE AFC LOW
APPROACHES THE FORECAST AREA, THE GRADIENT WILL SLACKEN AND WINDS
WILL DROP OFF THROUGH SUNDAY.
JSL
&&
.AVIATION.../ISSUED AT 1154 PM/...VALID FOR 06Z TAFS
MAIN AREA OF RAIN (WITH SNOW ON THE BACK EDGE) WILL LIFT OUT OF
NORTHERN MICHIGAN DURING THE OVERNIGHT HOURS. ONGOING IFR/MVFR
CONDITIONS WILL IMPROVE SOMEWHAT AS THIS HAPPENS. HOWEVER...AM
WATCHING AN AREA OF MIXED SN/FZRA GETTING GOING DOWNSTATE. WILL
NEED TO KEEP AN EYE ON THIS...FOR NOW DO NOT HAVE IT IMPACTING THE
TAF SITES...BUT COULD BE CLOSE AT TVC THIS MORNING. OTHERWISE
MAINLY MVFR FOR THE UPCOMING DAY.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...GALE WARNING UNTIL 5 AM EST SATURDAY FOR LMZ341.
SMALL CRAFT ADVISORY UNTIL 5 AM EST SATURDAY FOR LMZ323-342-
344>346.
LH...GALE WARNING UNTIL 5 AM EST SATURDAY FOR LHZ345>348.
SMALL CRAFT ADVISORY UNTIL 5 AM EST SATURDAY FOR LHZ349.
LS...GALE WARNING UNTIL 5 AM EST SATURDAY FOR LSZ321-322.
&&
$$
