FXUS63 KAPX 270003
AFDAPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
703 PM EST THU NOV 26 2009

.SYNOPSIS.../ISSUED AT 324 PM/

COOLER WEATHER HAS ARRIVED AND IS EXPECTED TO REMAIN OVER THE GREAT 
LAKES INTO AT LEAST EARLY DECEMBER. SLOW-MOVING LOW PRESSURE EXITS 
TONIGHT WITH LIGHT RAIN TRANSITIONING TO A LITTLE LIGHT SNOW THIS
EVENING. A FEW LAKE EFFECT SNOW SHOWERS WILL BE LEFT OVER FRIDAY
BUT GRADUALLY END. A BRIEF BREAK OCCURS SATURDAY...AS HIGH PRESSURE
CROSSES THE REGION. THE NEXT LOW PRESSURE SYSTEM WILL MOVE THROUGH
SUNDAY... WITH JUST A TOUCH OF LIGHT RAIN OR SNOW. COLD AIR FLOWS
IN BEHIND THIS SYSTEM FOR NEXT WEEK...WITH SEVERAL PERIODS OF LAKE
EFFECT SNOW POSSIBLE.

JH

&&

.SHORT TERM.../ISSUED AT 324 PM/...TONIGHT

UPPER LOW CONTINUES TO MOVE SLOWLY E/NE AWAY FROM THE AREA WITH
COLD FRONT AND COLDER AIR SWEEPING INTO MICHIGAN ON THE BACKSIDE
OF DEPARTING SYSTEM. AT THE SAME TIME...WEAKENING DEFORMATION AXIS
W/ AXIS OF ENHANCED PCPN WILL BE SLIDING ACROSS CENTRAL/EASTERN
PARTS OF THE AREA. MAIN FORECAST CONCERNS TONIGHT WILL BE
PRECIPITATION CHANCES...P-TYPE ISSUES AND LAKE EFFECT POTENTIAL.

LAST VESTIGES OF SYNOPTIC FORCING SEEN IN THE MID LEVEL OMEGA FIELDS 
EAST OF I-75 THROUGH EARLY THIS EVENING...BEFORE DEPARTING ALL OF 
NORTHERN MICHIGAN BY 06Z.  THIS COINCIDES WITH DEEPEST H8-H5 
MOISTURE AS WELL...WHICH WILL ALSO BE EXITING QUICKLY TO THE EAST.  
THERMAL PROFILES REMAIN CHALLENGING...AS SURFACE BASED WARM LAYER ON 
FCST SOUNDINGS REMAINS IN THE 1.5 TO 2.5K RANGE INTO EARLY EVENING  
...W/ OCCASIONAL CHANGEOVER TO SNOW BASED ON PCPN INTENSITY AS 
COLUMN IS TEMPORARILY DYNAMICALLY COOLED.  COLD AIR ADVECTION SHOULD 
BE ROBUST ENOUGH THIS EVENING TO CHANGE MUCH OF THE PCPN OVER 
INTERIOR AREAS TO ALL SNOW...AS H8 TEMPS DROP TOWARD -5C.  BIGGEST 
QUESTION IS WHETHER THE COLD AIR WILL MOVE IN QUICKLY ENOUGH TO 
INTERACT WITH LINGERING SYNOPTIC MOISTURE TO PRODUCE MUCH IN THE WAY 
OF SNOW.  AT THIS POINT...THAT DOES NOT LOOK TO BE THE CASE AS THE 
BOUNDARY LAYER IS JUST TOO WARM AND THE MOISTURE IS LEAVING TOO 
QUICKLY BEFORE THE REAL COLD AIR ARRIVES.  WILL GO WITH A TRANSITION 
FROM RAIN TO SNOW THIS EVENING...WITH SMALL ACCUM/S POSSIBLE... 
ESPECIALLY ACROSS THE HIGHER TERRAIN.  

LAKE EFFECT SNOW OVERNIGHT SHOULD NOT BE THAT ROBUST...AS H8-H7 
MOISTURE FIELDS DROP QUICKLY TOWARD 50%...WITH DELTA T/S ONLY 
MARGINALLY COLD ENOUGH INTO THE LOWER TEENS.  IN ADDITION... 
SUBSTANTIAL DRYING TAKES PLACE AT THE DENDRITIC GROWTH ZONE ON 
SOUNDINGS AFTER 06Z...LIKELY INHIBITING THE ICE PROCESSES.  SO 
EXPECT SOME LIGHT NORTHWEST FLOW LAKE EFFECT OVERNIGHT WITH ACCUM/S 
GENERALLY LESS THAN ONE INCH.  WILL BE QUITE BREEZY AS COLD AIR 
ADVECTION BEGINS IN EARNEST...AND NORTHWEST WINDS GUST OVER 20 MPH 
AT TIMES.  

JK

&&

.LONG TERM.../ISSUED AT 324 PM/...FRIDAY AND BEYOND

FRI THRU SUN...OVERALL RATHER TRANQUIL PERIOD OF WX...WITH MAIN 
ISSUE LINGERING LAKE EFFECT POTENTIAL EARLY FRIDAY...FOLLOWED BY 
SMALL PRECIP CHANCES INTO SAT NIGHT/SUN. BRIEF DUMP OF COLDER AIR 
EXPECTED TO BE ON THE WANE QUICKLY INTO THE DAY ON FRIDAY...WITH 
RAPID LOSS OF MOISTURE AND OVERLAKE INSTABILITY THRU THE AFTN. 
CERTAINLY CAN FORESEE SOME NUISANCE LIGHT SNOW SHOWERS EARLY 
ON...BUT WITH MOISTURE STRIPPING OUT ABOVE -5C AND DIURNAL MIXING OF 
THE BOUNDARY LAYER (I.E. INCREASING T/TD SPREADS DOWN LOW)...
PROBABLY LOOKING AT JUST PLAIN LAKE-DRIVEN CLOUD COVER LINGERING 
INTO THE AFTN...WITH EVEN THAT ENCOUNTERING INCREASINGLY DRY AIR AND 
ANTICYCLONIC FLOW REGIME. THUS WILL CALL IT BECOMING PARTLY CLOUDY 
OUTSIDE THE NORTHWEST FLOW LAKE BELTS...WITH TEMPS MAINLY UPR 
30S/LOW 40S.

HIGH PRESSURE/SHORTWAVE RIDGING PROGGED TO SHIFT INTO THE AREA FRI 
NIGHT INTO SAT...WITH INCREASING WARM ADVECTION DOWN LOW. WILL HAVE 
TO BE CAREFUL AS SOME OF THAT WARMING MAY TRY TO GO INTO LOWER CLOUD 
PRODUCTION...BUT WILL ATTEMPT TO KEEP THINGS OPTIMISTIC AT THIS 
POINT AND CALL IT PARTLY CLOUDY (HIGH CLOUDS OVERHEAD)...WITH TEMPS 
BACK IN THE 40S ALL SPOTS. A BIT MORE INTERESTING SETUP INTO SAT 
NIGHT WITH CONTINUED LOW LEVEL WARM ADVECTION LIKELY GOING INTO THE 
PRODUCTION OF LOWERING STRATUS DECK. FCST RAOBS FROM THE GFS 
FOLLOWING EARLIER TRENDS SHOWING POTENTIAL FOR A DRIZZLY (FREEZING 
DRIZZLE?) SCENARIO DURING THIS TIMEFRAME...AND PATTERN RECOGNITION 
OF WARMER AIR RETURNING OVER SHALLOW RETREATING COLDER AIRMASS ALSO 
SUPPORTS THIS NOTION (SORT OF THE CLASSIC DRIZZLE SETUP). 
OTHERWISE...WILL LOOK FOR SMALL PRECIP CHANCES INTO THE DAY ON SUN 
AS NEXT SHORTWAVE/MOISTURE-STARVED COLD FRONT PUSH THRU THE 
AREA...WITH THERMAL PROFILES SUGGESTING MORE OF A LIGHT RAIN 
SCENARIO TO THE SOUTH AND MORE RAIN/SNOW NORTH (THOUGH WITH AMOUNTS 
QUITE LIGHT). 

LATER PERIODS (SUN NIGHT THRU THU)...FAIRLY ACTIVE PERIOD...THOUGH 
NOT OVERLY SO...WITH MAIN CONCERNS INITIALLY FOCUSED ON LAKE EFFECT 
POTENTIAL EARLY IN THE WEEK...FOLLOWED BY INCREASING HINTS OF 
STORMINESS TO ROUND OUT THE WORK WEEK (POSSIBLE PATTERN CHANGER?). 
FIRST UP...00Z GUIDANCE COMING INTO RATHER GOOD AGREEMENT REGARDING 
BRIEF DUMP OF COLDER AIR TO START THE NEW WORK WEEK AS RIDGING 
BUILDS THRU THE WESTERN CONUS. SETUP APPEARS RATHER FAVORABLE FOR AT 
LEAST A BRIEF PERIOD OF POTENTIAL LIGHT ACCUMULATING LAKE EFFECT 
SNOW...PARTICULARLY SOMETIME MONDAY WITH APPROACH OF ADDITIONAL UPR 
SUPPORT. FCST RAOBS (GFS BUFR AND CRUDE ECMWF SOUNDINGS) SUGGEST 
DECENT OVERLAKE INSTABILITY WITH H85-H8 TEMPS CRASHING TOWARD -10C 
TO -12C AND INVERSION HEIGHTS BRIEFLY TICKING UP TOWARD 7KFT...
HIGHEST EASTERN UPR WHERE SLIGHTLY DEEPER MOISTURE PROGGED TO 
RESIDE. OF COURSE...THE SPECIFICS CAN AND WILL CHANGE TO SOME 
DEGREE...BUT CERTAINLY WORTH CONTINUED MENTION FOR SNOW SHOWERS. 

WX LOOKS TO CLEAR RATHER RAPIDLY LATER TUE INTO WED AS SHORTWAVE 
RIDGING BUILDS THRU THE GREAT LAKES...WITH WED POTENTIALLY A RATHER 
NICE DAY AS DRY AIR WINS OUT. THEREAFTER...MORE QUESTIONS THAN 
ANSWERS REGARDING EVOLUTION OF THE UPR PATTERN WED NIGHT ONWARD...
WITH GUIDANCE STRUGGLING SEVERELY WITH PRONOUNCED SPLIT FLOW PATTERN 
AND DEGREE OF POTENTIAL PHASING TO SPIN UP A RATHER POTENT STORM 
SOMEWHERE NEARBY. KEY APPEARS TIED TO HOW MUCH ENERGY GETS EJECTED 
FROM THE SOUTHWEST/NORTHERN MEXICO AND AT WHAT TIME INTERVAL...WHICH 
CERTAINLY WILL AFFECT DEGREE OF PHASING DOWNSTREAM. INTERESTING TO 
NOTE RECENT RUNS OF GFS LINING UP MORE AND MORE WITH GFS ENSEMBLE 
MEAN (AND TO SOME DEGREE THE ECMWF...THOUGH THAT SOLUTION A BIT LESS 
AMPLIFIED). AT THIS JUNCTURE...WILL INTRODUCE SMALL CHANCE POPS FOR 
RAIN OR SNOW NEXT THURSDAY AND SEE HOW THINGS SHAKE OUT THE NEXT FEW 
DAYS. HIGH TEMPS TO AVERAGE AT OR JUST A BIT ABOVE NORMAL THRU THE 
PERIOD...WITH INCREASING HINTS OF SIGNIFICANTLY COLDER WEATHER TO 
ARRIVE JUST BEYOND.

LAWRENCE

&&

.MARINE.../ISSUED AT 324 PM/

SCA WINDS AND WAVES EXPECTED TONIGHT OVER ALL OF NORTHERN MICHIGAN 
NEARSHORE WATERS AS CORE OF STRONGEST 950MB WINDS MOVE ACROSS THE 
AREA WITH STRONG COLD AIR ADVECTION. SOME AREAS ALONG LAKE MICHIGAN 
MAY BE IN THE HIGH SCA RANGE THROUGH EARLY EVENING...BUT SHOULD DROP 
BACK A BIT OVERNIGHT.  ANY LINGERING RAIN WILL CHANGE TO SNOW...AS 
TEMPERATURES DROP TOWARD THE FREEZING MARK.  WIND AND WAVES 
DIMINISHING ON FRIDAY AS HIGH PRESSURE AND A WEAKENING PRESSURE 
GRADIENT MOVE INTO THE WESTERN LAKES...THOUGH CAN FORESEE THE NEED
TO EXTEND SCA THRU THE AFTN ON THE HURON SIDE. SOME SMALL POTENTIAL
FOR SMALL CRAFT CONDITIONS TO RETURN TO PORTIONS OF THE AREA BY
LATE SUNDAY NIGHT INTO MONDAY AS ANOTHER QUICK SHOT OF COLDER AIR
ARRIVES...BUT CONFIDENCE IN THIS SCENARIO RATHER LOW AT THIS
POINT.

JK/LAWRENCE

&&

.AVIATION.../ISSUED AT 703 PM/...VALID FOR 00Z TAFS

LOW PRESSURE CENTERED ACROSS NRN LAKE HURON WILL SLOWLY WEAKEN AND
MOVE EASTWARD INTO ONTARIO BY FRIDAY. WRAP-AROUND PRECIP WITH
THIS SYSTEM WILL SLOWLY WORK EASTWARD ACROSS NRN LOWER MICHIGAN
TONIGHT WITH SYNOPTIC PRECIP ENDING AT PLN/TVC BETWEEN 03Z AND
06Z...AND APN AFTER 09Z. PRECIP WILL BE MAINLY SNOW...ALTHOUGH A
MIX WILL PERSIST THROUGH MID EVENING UNTIL COLDER AIR ARRIVES.

THEREAFTER...COLDER AIR FILTERING INTO THE REGION WILL GET THE
LAKE EFFECT MACHINE GOING TONIGHT...WITH LAKE SNOW SHOWERS
ANTICIPATED TONIGHT AT TVC AND /TO A LESSER EXTENT/
PLN...DIMINISHING ON FRIDAY. 

CEILING HEIGHTS A BIT PROBLEMATIC. GENERALLY MVFR ANTICIPATED AT
TVC/PLN THROUGH TONIGHT...IMPROVING TO VFR ON FRIDAY. APN MAY
REMAIN IFR AT LEAST THIS EVENING GIVEN THE DEEPER MOISTURE SLOWLY
ROTATING THROUGH THE REGION. MIGHT IMPROVE TO MVFR OVERNIGHT BUT
HAVE GONE A BIT MORE PESSIMISTIC IN THE TAF.

ADAM

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 11 AM EST FRIDAY FOR LMZ323-341-342-
     344>346.
LH...SMALL CRAFT ADVISORY UNTIL 11 AM EST FRIDAY FOR LHZ345-347>349.
LS...SMALL CRAFT ADVISORY UNTIL 11 AM EST FRIDAY FOR LSZ321-322.

&&

$$