FXUS63 KAPX 232113
AFDAPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
413 PM EST WED DEC 23 2009

.SYNOPSIS.../ISSUED AT 410 PM/

WINTER STORM LIFTING NORTHEAST OUT OF THE MIDWEST WILL BRING A MIX
OF PRECIPITATION TO NORTHERN MICHIGAN LATER CHRISTMAS EVE EVENING
AND INTO CHRISTMAS DAY.

&&

.SHORT TERM.../ISSUED AT 410 PM/...TONIGHT

A COUPLE ISSUES TO TACKLE INTO THE OVERNIGHT...NAMELY REINTRODUCTION 
OF LOWER STRATUS...AS WELL AS SMALL PRECIP POTENTIAL. AFTER A RATHER 
GLOOMY MORNING...STRATUS DECK HAS FINALLY CLEARED THE CWA...SAVE FOR 
SOME GUNKY LAKE-INDUCED STRATOCU HANGING ACRS THE NORTHEAST LOWER 
COASTAL COUNTIES. QUICK PEAK AT SATELLITE PICS ALSO REVEALS 
EXPANSIVE STRATUS/STRATOCU DECK RESIDING OVR MUCH OF LAKE 
HURON...WITH ITS EYES SET ON NORTHERN MICHIGAN OVERNIGHT. SIMILAR TO 
LAST NIGHT...EXPANSIVE LOW LEVEL RIDGE AXIS WILL HOLD FIRM ACRS 
NORTHERN MICHIGAN...WITH SLOWLY VEERING SFC-850MB FLOW TOWARD THE 
EAST/NORTHEAST BY ROUGHLY 09Z OR SO. PER PATTERN RECOGNITION AND 
EXPANSIVE CLOUD SHIELD ALREADY BUTTING UP AGAINST THE LAKE HURON 
SHORE...CANNOT AT ALL ARGUE WITH GOING NOTION OF STRATUS SPILLING 
BACK INTO MUCH OF THE CWA LATER TONIGHT BENEATH SHALLOW INVERSION 
AND CERTAINLY AGAIN AUGMENTED BY CONTINUED (THOUGH WANING) OVERLAKE 
INSTABILITY. FCST RAOBS/MODEL PLAN VIEW SIGNAL OF LIGHT QPF ALSO 
QUITE INTERESTING ACRS MAINLY NORTHEAST LOWER/STRAITS REGION...
LIKELY A CONSEQUENCE OF DEVELOPING BETTER FETCH LENGTH ACRS LAKE 
HURON AND PERHAPS SOME WEAK TERRAIN INFLUENCE ON MEAN EAST/NORTHEAST 
FLOW. DIFFICULT TO ARGUE WITH GUIDANCE ON THIS ONE...ESPECIALLY 
GIVEN EARLIER FLURRIES ON SAME SETUP THIS MORNING...THOUGH FCST 
CLOUD TOP TEMPS ONLY RUNNING -8C OR SO GIVE SOME PAUSE AS TO ICE 
PRODUCTION IN THE SHALLOW CLOUD LAYER. THAT SAID...LACK OF ANY 
MOISTURE INCREASE ABOVE THE INVERSION AND LITTLE SHEAR IN THE CLOUD 
COLUMN COUPLED WITH STILL DECENTLY COLD CLOUD TOPS ARGUE PRECIP 
SHOULD JUST BE IN THE FORM OF SOME LIGHT SNOW FLURRIES (PERHAPS EVEN 
A LITTLE "SNIZZLE"?). OUTSIDE OF NORTHEAST LOWER/STRAITS 
REGION...EXPECT INCREASING HIGHER CLOUD SHIELD THRU THE NIGHT...WITH 
LOWS MUCH WARMER THAN LAST NIGHT...MAINLY TEENS TO LOWER 20S

LAWRENCE

&&

.LONG TERM.../ISSUED AT 410 PM/...THURSDAY AND BEYOND

BIG MIDWEST STORM FOR THE CHRISTMAS HOLIDAY PERIOD THE OBVIOUS ISSUE 
DU JOUR.  WATER VAPOR IMAGERY SHOWS MAIN UPPER LOW WITH SOUTHERN 
BRANCH OF SPLIT FLOW ACROSS WESTERN NORTH AMERICA OVER THE DESERT 
SOUTHWEST THIS AFTERNOON...WITH A LEAD SHORT EXTENDING FROM THE 
CENTRAL HIGH PLAINS SOUTHEAST INTO THE LOWER MISSISSIPPI VALLEY.  
NORTHERN BRANCH SHORT WAVE OVER ALBERTA/MONTANA DROPPING SOUTHEAST 
DOWN THE FRONT SIDE OF A NARROW WEST COAST RIDGE WILL KICK OUT AND 
EVENTUALLY MERGE WITH SOUTHERN BRANCH WAVE TO SPIN UP A STRONG LOW 
OVER THE UPPER MIDWEST BY CHRISTMAS NIGHT.  ONCE THE MAIN UPPER LOW 
PARKS ITSELF OVER THE UPPER MIDWEST...LOOKS LIKE IT WILL BE SLOW TO 
MOVE OUT WITH EFFECTS FROM THIS STORM LINGERING THROUGH THE 
WEEKEND.  FORECAST WILL REVOLVE AROUND TRYING TO REFINE PRECIP 
TYPE/TIMING FORECAST A BIT...WITH A SURGE OF LOW LEVEL WARM AIR INTO 
NORTHERN MICHIGAN THURSDAY NIGHT INTO FRIDAY...ALONG WITH THE 
POTENTIAL FOR SUBSTANTIAL DRY SLOTTING LATER CHRISTMAS DAY.

CHRISTMAS EVE (THURSDAY)...SURFACE LOW SPINS UP ACROSS THE LOWER 
MISSISSIPPI VALLEY THURSDAY MORNING...LIFTING NORTHWARD INTO THE 
VICINITY OF CENTRAL IOWA BY CHRISTMAS MORNING.  MAIN PRECIPITATION 
SHIELD AHEAD OF THIS SYSTEM WILL LIKELY BE JUST WEST/SOUTHWEST OF 
THE FORECAST AREA MUCH OF THURSDAY AND THURSDAY EVENING...AS DRY LOW 
LEVEL SOUTHEAST TRAJECTORIES WILL CONTINUALLY TRY AND INHIBIT DEEP 
LAYER SATURATION UNTIL AFTER MIDNIGHT WHEN LOW LEVEL INFLOW BEGINS 
TO POINT IN OUR DIRECTION.  LOOKS LIKE QUITE A VIRGA STORM FOR A 
WHILE ESPECIALLY ACROSS LOWER MICHIGAN...WITH GREATEST THREAT FOR 
MEASURABLE PRECIPITATION OCCURRING THURSDAY NIGHT ACROSS ABOUT THE 
SOUTHWEST HALF OF THE FORECAST AREA.  OTHER THAN SOME LAKE INDUCED 
FLURRIES IN SHALLOW INSTABILITY OFF LAKE HURON...WILL KEEP FAR 
EASTERN UPPER AND FAR NORTHEAST LOWER DRY THROUGH THURSDAY NIGHT.  
WILL CARRY CHANCE POPS ACROSS THE REST OF EASTERN UPPER AND 
BASICALLY ALONG THE I-75 CORRIDOR IN NORTHERN LOWER...WITH LIKELY 
POPS ACROSS MUCH OF NORTHWEST LOWER WHERE LOW LEVEL SATURATION MOST 
LIKELY TO OCCUR DURING THE NIGHT.  AS FOR PRECIP TYPE...LOW LEVEL 
WARM NOSE BEGINS TO NUDGE INTO NORTHWEST LOWER DURING THE 
AFTERNOON...AND SPREAD ACROSS MUCH OF THE FORECAST AREA EARLY 
CHRISTMAS MORNING.  THIS WARM LAYER ALSO COINCIDES WITH THE LOW 
LEVEL DRY LAYER...SO WILL BE A BATTLE BETWEEN WARM ADVECTION AND 
COOLING DUE TO EVAPORATION/MELTING.  THINK THE BIGGEST ISSUES WILL 
BE ALONG-WEST OF THE US-131 CORRIDOR WHERE THE COMBINATION OF 
HIGHEST QPF/DEEP MELTING LAYER/SUBFREEZING SURFACE TEMPERATURES WILL 
LINE UP.  IN THIS AREA MENTIONED POSSIBILITY OF LIGHT SNOW/LIGHT 
FREEZING RAIN AS EARLY AS TOMORROW AFTERNOON...THEN TRANSITIONED TO 
MOSTLY FREEZING RAIN THURSDAY NIGHT...ANTICIPATING THAT SURFACE 
TEMPERATURES WILL HANG ON NEAR OR JUST A LITTLE BELOW FREEZING MUCH 
OF THE NIGHT.  MAY SEE TEMPERATURES CLIMB ABOVE FREEZING IN LOWER 
ELEVATIONS NEAR LAKE MICHIGAN LATE DUE TO EASTERLY DOWNSLOPING 
WINDS.  FARTHER EAST...PRECIP WILL BE LIGHTER AND ALOT MAY NOT 
MATERIALIZE UNTIL LATE WITH LOW LEVEL DRY WEDGE.  IF PRECIP WERE TO 
REACH THE GROUND...FORECAST WARM LAYER OF SUFFICIENT DEPTH/MAGNITUDE 
TO MELT PRECIP THOUGH SOME CONCERNS WITH A SUB-ZERO WET BULB PROFILE 
(THOUGH PRECIP MAY NOT BE HEAVY ENOUGH TO REALLY ERODE THIS 
SUFFICIENTLY).  SO A GOOD TUG OF WAR BETWEEN VARIOUS PROCESSES... 
THOUGH FORTUNATELY QPF OVERNIGHT WILL LIKELY NOT BE SUBSTANTIAL.  
FOR NOW WILL MENTION BOTH LIGHT SNOW/LIGHT FREEZING RAIN.  ACROSS 
EASTERN UPPER...ANY PRECIP SHOULD FALL AS ALL SNOW AS LOW LEVEL 
WARMING NOT EXPECTED TO ARRIVE UNTIL LATE.

CHRISTMAS DAY (FRIDAY)...DEEP LAYER SATURATION ARRIVES FOR A LITTLE 
WHILE BEFORE DRY SLOT COMES IN DURING THE AFTERNOON...THOUGH 
QUESTIONS LINGER REGARDING MOISTURE DEPTH (COULD STILL BE ENOUGH 
MOISTURE TO SUPPORT SOME LIGHT MEASURABLE PRECIPITATION).  WARM 
LAYER ALSO ENCOMPASSES MUCH OF THE FORECAST AREA FRIDAY 
MORNING...THOUGH EVAPORATIVE COOLING ON INITIAL SATURATION AND 
MELTING TRYING TO PUSH THERMAL PROFILES BACK BELOW FREEZING.  NOT 
GOING TO TRY AND PICK WHICH WAY TO GO AT THIS POINT...AND 
ESSENTIALLY KEEP RAIN/SNOW IN THE FORECAST FOR FRIDAY...WITH 
FREEZING RAIN MENTION IN THE MORNING ACROSS EASTERN UPPER...AND IN 
THE HIGHER TERRAIN ALL DAY ACROSS HIGHER TERRAIN OF NORTHERN LOWER 
WHERE TEMPERATURES MAY LINGERING RIGHT AROUND FREEZING.  FOR FRIDAY 
NIGHT COLDER AIR SWEEPS IN FROM THE SOUTH...BUT MOISTURE DEPTH 
ISSUES STILL LINGER.  SO PLAN TO MENTION LIGHT SNOW/DRIZZLE/FREEZING 
DRIZZLE.

STILL LOOKS LIKE A MOSTLY ADVISORY LEVEL EVENT...AND STILL TOO
EARLY FOR THOSE TYPES OF HEADLINES.

EXTENDED FORECAST (SATURDAY THROUGH WEDNESDAY)...FILLING SURFACE LOW 
FORECAST TO BE IN THE VICINITY OF THE IOWA/ILLINOIS BORDER SATURDAY 
MORNING WITH COLDER AIR WRAPPING INTO MICHIGAN FROM THE SOUTHWEST.   
ENTIRE SYSTEM WILL SLOWLY SPIN ITS WAY ACROSS THE UPPER MIDWEST/ 
GREAT LAKES THROUGH THE WEEKEND...WAITING TO GET KICKED OUT BY 
NORTHERN BRANCH HEIGHT FALLS ROTATING AROUND POLAR VORTEX NORTH OF 
HUDSON BAY.  THIS WILL KEEP THE THREAT OF LIGHT SNOW/SNOW SHOWERS 
GOING THROUGH THE WEEKEND (POSSIBLY WITH SOME FREEZING DRIZZLE FOR 
PART OF SATURDAY WITH LINGERING EFFECTS OF DRY SLOT).  SUNDAY LOOKS 
INTERESTING AS LOW LEVEL TEMPERATURES CONTINUE TO COOL (POSSIBLE 
850MB TEMPERATURES IN THE -10C TO -12C RANGE)...THE INCREASING 
INSTABILITY OVER THE LAKES COMBINED WITH LINGERING LARGE SCALE 
MOISTURE WILL SET THE STAGE FOR SOME LAKE ENHANCED SNOW SHOWERS.  
LOW LEVEL FLOW WILL BE WEAK...THUS SMALL SCALE ORGANIZATION WILL 
PREDOMINATE AND BE THE DRIVING FORCE BEHIND SNOWFALL POTENTIAL.   
LOOKING INTO EARLY NEXT WEEK...PRETTY GOOD AGREEMENT IN THE LONG 
RANGE GUIDANCE WITH RESPECT WITH TO AN ARCTIC BOUNDARY COMING IN THE 
SIDE DOOR IN THE MONDAY/TUESDAY TIME FRAME...HOW SIGNIFICANT A PUSH 
OF COLD AIR WE GET IS MORE UNCERTAIN AND TIED TO EVOLUTION OF POLAR 
VORTEX AND ANY SHORT WAVES ROTATING AROUND THE WEST SIDE.  WILL 
FOCUS SNOW SHOWER CHANCES IN THE MONDAY-WEDNESDAY TIME FRAME AROUND 
THE TYPICAL SNOWBELTS...AND TREND TEMPERATURES COLDER THROUGH THE 
PERIOD.  

JPB

&&

.MARINE.../ISSUED AT 410 PM/

EAST/SOUTHEAST GRADIENT WIND PICKS UP LATER CHRISTMAS EVE INTO THE 
NIGHTTIME HOURS...WITH GALE FORCE WINDS LIKELY WITHIN LAKE MICHIGAN/ 
HURON NEARSHORE ZONES BY CHRISTMAS MORNING.  WILL ISSUE A GALE WATCH 
FOR THURSDAY NIGHT THROUGH FRIDAY.

JPB

&&

.AVIATION.../ISSUED AT 150 PM/...VALID FOR 18Z TAFS

FCST IS LARGELY CONTINUITY WITH 12Z TAFS.

THIS AFTN: MVFR STRATOCU GRADUALLY MIXING OUT TO SCT. IMPROVEMENT TO 
VFR EXPECTED SHORTLY AT TVC. 25K FT CIRRUS WILL OVERSPREAD THE 
TERMINALS IN LIGHT N-E BOUNDARY LAYER (BL) FLOW.

TONIGHT: VFR TO START THEN MVFR STRATOCU EXPECTED TO MOVE BACK IN FM 
E TO W. CIRRUS CIGS GRADUALLY YIELD TO MULTI-LAYERED MID LEVEL 
ALTOCU/ALTOST ABOVE LOW-LEVEL LAKE CLDS. LIGHT E BL FLOW.

THU THRU 18Z: DIURNAL MIXING AND DOWNSLOPE FLOW AT SHOULD ERODE MVFR 
STRATOCU AT PLN/TVC...REVEALING MULTI-LAYERED 8-12K FT MID-LEVEL 
OVC. E BL FLOW WILL BEGIN INCREASING.

JH/JPB

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...GALE WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY AFTERNOON FOR 
     LMZ323-341-342-344>346.
LH...GALE WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY AFTERNOON FOR 
     LHZ345>349.
LS...NONE.

&&

$$