FXUS63 KGRR 290501
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1200 AM EST SUN NOV 29 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(321 PM EST SAT NOV 28 2009)
A WEAK COLD FRONT WILL DRIFT ACROSS THE REGION TONIGHT AND EARLY 
SUNDAY.  BEHIND THE FRONT LIGHT RAIN IS EXPECTED TO DEVELOP ON 
SUNDAY.  THE RAIN SHOULD BECOME MIXED WITH AND THEN CHANGE OVER TO 
SNOW LATE SUNDAY AFTERNOON INTO SUNDAY EVENING.  THE LIGHT SNOW IS 
EXPECTED TO CONTINUE ON AND OFF THROUGH MONDAY NIGHT.  ANY 
ACCUMULATIONS FROM SUNDAY NIGHT THROUGH MONDAY NIGHT WILL BE LESS 
THAN AN INCH.  

&&

.SHORT TERM...(321 PM EST SAT NOV 28 2009)
(TONIGHT THROUGH MONDAY NIGHT)
MAIN FOCUS WAS ON THE AFFECTS OF A COLD FRONT AND SHORT WAVE COMING 
THROUGH TONIGHT AND SUNDAY.  ALSO NEEDED TO CONSIDER LAKE EFFECT 
POTENTIAL BEHIND THE SHORT WAVE FOR SUNDAY NIGHT INTO MONDAY NIGHT.

A WEAK COLD FRONT WAS CROSSING WISCONSIN THIS AFTERNOON WITH LITTLE 
WEATHER ASSOCIATED WITH IT.  HOWEVER...A SHORT WAVE THAT WAS OVER 
THE LAKE WINNIPEG REGION TODAY WILL CATCH UP TO THE FRONT BY SUNDAY 
AND ADD MOISTURE AND LIFT TO THE SYSTEM AS IT COMES ACROSS LOWER 
MICHIGAN.  WILL KEEP THE FORECAST DRY FOR TONIGHT AS ANY MOISTURE 
WILL REMAIN SHALLOW.  HOWEVER...WILL INCREASE POPS TO LIKELY SUNDAY 
AFTERNOON AS THE SHORT WAVE ARRIVES WITH DEEPER MOISTURE.  HAVE ALSO 
ADDED THE CHANCE FOR A MIXTURE ACROSS THE NORTHERN PORTIONS OF THE 
CWA AS THICKNESS VALUES FALL BY LATE IN THE DAY.

THE LAKE EFFECT POTENTIAL BEHIND THE SHORT WAVE APPEARS RATHER 
PALTRY.  THIS IS MAINLY DUE TO AN ANTICYCLONIC FLOW THAT DEVELOPS 
RATHER QUICKLY.  THERE MAY BE A SMALL WINDOW AROUND MIDNIGHT WHERE A 
FEW SNOW SHOWERS DEVELOP...OTHERWISE JUST FLURRIES ARE EXPECTED.

THE MODELS ARE IN POOR AGREEMENT BY MONDAY AFTERNOON INTO MONDAY 
NIGHT.  THE GFS IS MUCH MORE AGGRESSIVE WITH ANOTHER COLD 
FRONT/SHORT WAVE AS IT PHASES A WAVE RIDING OVER THE RIDGE OVER THE 
ROCKIES.  MEANWHILE THE NAM DOES NOT PHASE THE WAVE AND SHOWS LITTLE 
SURFACE REFLECTION.  HAVE LEFT THE CHANCE POPS GOING FOR MAINLY 
MONDAY AFTERNOON AND MONDAY NIGHT AS THERE COULD BE A LITTLE 
ASSISTANCE FROM THE LAKE TO ANY LIGHT SNOW.  

OVERALL...BOTH OF THESE SYSTEMS WILL ONLY PRODUCE LIGHT PCPN.  ANY 
SNOW WILL RANGE FROM JUST FLURRIES TO LESS THAN A HALF INCH OF SNOW 
FROM BOTH SYSTEMS.

&&

.LONG TERM...(321 PM EST SAT NOV 28 2009)
(TUESDAY THROUGH SATURDAY)
A COMPLEX AND ACTIVE WX PATTERN WILL EVOLVE MID TO LATE WEEK. THE 
KEY TO THE FCST FOR WEDNESDAY NIGHT AND THURSDAY IS IN THE TIMING 
AND EVOLUTION OF THE UPPER LEVEL PATTERN WHICH WILL HAVE SIGNIFICANT 
IMPACT ON THE EVENTUAL TRACK OF THE GULF LOW. 12Z GFS GUIDANCE 
SUGGESTS THAT THE NORTHERN AND SOUTHERN STREAMS WILL ALREADY COME 
INTO PHASE BY 12Z THURSDAY... RESULTING IN A DEEP LONGWAVE TROUGH 
OVER OUR REGION BY THEN. 

THIS IS SIGNIFICANT BECAUSE IT WOULD BE CONDUCIVE TO THE POTENTIAL 
FOR THE GULF COAST LOW TO TAKE A MUCH FURTHER NORTHWESTWARD TRACK 
THROUGH THE OHIO VALLEY REGION WEDNESDAY NIGHT INTO THURSDAY WHICH 
COULD IMPACT OUR AREA. CONVERSELY... IT IS NOTED THAT 12Z ECMWF 
GUIDANCE HAS TRENDED FURTHER EAST TO SUGGEST THIS WILL BE AN EAST 
COAST SYSTEM. THIS STILL SEEMS LIKE THE MOST LIKELY OUTCOME AND IS 
ALSO SUPPORTED BY 12Z FIM GUIDANCE. NEVERTHELESS GIVEN THE 
DISCREPANCIES IN MEDIUM RANGE GUIDANCE AND LACK OF RUN TO RUN 
CONTINUITY...WE WILL NEED TO MONITOR THE SYSTEM AND GUIDANCE TRENDS 
CLOSELY.  

CONFIDENCE REMAINS HIGH THAT WE WILL HAVE BELOW NORMAL TEMPS 
THURSDAY THROUGH SATURDAY WITH POTENTIAL FOR SOME LAKE EFFECT SNOW 
SHOWERS AS 850 MB TEMPS FALL TO AROUND -10 TO -12 C BY THURSDAY 
NIGHT AND FRIDAY. LES POTENTIAL WILL BE AFFECTED BY NUMEROUS OTHER 
FACTORS INCLUDING INVERSION HEIGHTS... DEPTH OF MOISTURE... AND 
UPSTREAM RH. THOSE SPECIFICS ARE STILL TOO EARLY TO DETERMINE. LES 
POTENTIAL WILL BE MITIGATED SOMEWHAT BY BRISK WINDS THAT COULD HAVE 
A SIGNIFICANT WESTERLY COMPONENT RESULTING IN LIMITED FETCH AND 
AIRMASS RESIDENCE TIME OVER LAKE MI.  

&&

.AVIATION...(1200 AM EST SUN NOV 29 2009)
DIFFICULT AVIATION FORECAST THE NEXT 24 HOURS. COLD FRONT STRETCHES 
FROM FAR NORTHERN LOWER MICHIGAN SOUTHWEST INTO IOWA. STRATUS AND 
FOG CONTINUES TO DEVELOP ALONG AND AHEAD OF THE FRONT. STRATUS HAS 
PUSHED INTO LUDINGTON...FREMONT AND BIG RAPIDS. THE STRATUS IS 
SPREADING SOUTH BUT HAS NOT MADE IT INTO MUSKEGON YET...BUT IT 
SHOULD SHORTLY. LOOKING A MODEL RH PROGS THE STRATUS WILL TRY TO 
HOLD OFF MOST OF THE NIGHT SPREADING INTO THE REMAINDER OF THE TAF 
SITES TOWARD DAYBREAK. 

IFR CONDITIONS ARE EXPECTED TO PREVAIL MOST OF THE DAY ON 
SUNDAY...IMPROVING TOWARD EVENING AS DRIER AIR WORKS IN FROM THE 
NORTHWEST. RAIN WILL LIKELY BREAK OUT ALONG THE FRONT AROUND MIDDAY 
LASTING MOST OF THE AFTERNOON.

&&

.MARINE...(321 PM EST SAT NOV 28 2009)
WINDS AND WAVES WILL STAY RELATIVELY LOW THROUGH TONIGHT AND MOST OF 
SUNDAY AS A WEAK COLD FRONT CROSSES THE LAKE.  HOWEVER...CONDITIONS 
WILL BEGIN TO WORSEN LATE SUNDAY AND INTO MONDAY AS COLD ADVECTION 
AND WEST NORTHWEST WINDS ARE ESTABLISHED.  A SCA MAY BE NEEDED BY 
SUNDAY EVENING.

&&

.HYDROLOGY...(321 PM EST SAT NOV 28 2009)
NO HYDRO ISSUES EXPECTED AS PCPN THROUGH MONDAY NIGHT WILL REMAIN 
LIGHT.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.

&&

$$

SYNOPSIS:     JK
SHORT TERM:   JK
LONG TERM:    LAURENS
AVIATION:     DUKE
MARINE:       JK
HYDROLOGY:    JK