FXUS63 KGRR 272023
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
330 PM EST FRI NOV 27 2009

LATEST UPDATE...ALL EXCEPT AVIATION...

.SYNOPSIS...(330 PM EST FRI NOV 27 2009)
AFTER QUIET WEATHER TONIGHT AND SATURDAY...RAIN WILL RETURN TO THE 
FORECAST SUNDAY WITH THE APPROACH OF ANOTHER COLD FRONT. THERE IS 
POTENTIAL FOR SIGNIFICANTLY COLDER CONDITIONS BY THE END OF THE 
COMING WORK WEEK...WITH LAKE EFFECT SNOW A DISTINCT POSSIBILITY. 

&&

.SHORT TERM...(330 PM EST FRI NOV 27 2009)
(TODAY THROUGH SATURDAY)
MAIN FORECAST CONCERN IS SKY COVER. NO SIGNIFICANT CHANGES WERE MADE 
TO THE PREVIOUS FORECAST. 

APPEARS THAT LAKE ENHANCED CLOUDINESS WILL PERSIST AT LEAST THROUGH 
THE AFTERNOON HOURS. KBIV HAD RECENTLY REPORTED LIGHT SNOW IN A 
HORIZONTAL CONVECTIVE ROLL INDUCED SNOW BAND. NO ADDITIONAL 
ACCUMULATIONS ARE EXPECTED. ANY LINGERING LAKE EFFECT PRECIPITATION 
WILL SHUT DOWN BY THIS EVENING AS INCREASINGLY ANTICYCLONIC FLOW 
WORKS INTO THE AREA. WE CONTINUE TO EXPECT CLEARING TO COMMENCE WELL 
BEFORE SUNRISE SATURDAY...ALLOWING FOR MINIMUM TEMPERATURES BELOW 
FREEZING. RELATIVELY CLEAR CONDITIONS SHOULD CONTINUE DURING THE DAY 
SATURDAY.

&&

.LONG TERM...(330 PM EST FRI NOV 27 2009)
(SATURDAY NIGHT THROUGH FRIDAY)

DRY WX IS ANTICIPATED SATURDAY NIGHT BEFORE A WEAK LOW PRESSURE 
SYSTEM BRINGS A CHC OF SHOWERS SUNDAY. A COUPLE OF SHORTWAVES WILL 
DIVE IN FROM THE NW AND BRING A CONTINUED CHC FOR PCPN SUNDAY NIGHT 
THROUGH MONDAY NIGHT...ALTHOUGH DUE TO LACK OF MOISTURE MOST OF 
THAT TIME PERIOD WILL BE DRY. PREDOMINANTLY DRY WX WILL CONTINUE 
TUESDAY THROUGH WEDNESDAY. 

12Z GFS GUIDANCE HAS TRENDED MUCH COLDER FOR LATE IN THE WEEK. 12Z 
ECMWF GUIDANCE CONTINUES TO LOOK COLD AND HAS 850 MB TEMPS DOWN TO 
-12 TO -14 C FROM THURSDAY NIGHT THROUGH NEXT WEEKEND. 12Z FIM 
GUIDANCE TAKES 850 MB TEMPS DOWN TO AT LEAST -10 C BY THURSDAY 
EVENING TOO. 

THEREFORE... BASED ON ALL OUR LATEST MEDIUM RANGE GUIDANCE AND 
TRENDS INFORMATION OUR CONFIDENCE IS INCREASING THAT OUR FIRST SHOT 
OF MUCH COLDER AIR AND POTENTIALLY OUR FIRST SIGNIFICANT LAKE EFFECT 
SNOW EVENTS WILL OCCUR LATE NEXT WEEK. LES POTENTIAL WILL BE 
MODULATED BY NUMEROUS OTHER FACTORS INCLUDING INVERSION HEIGHTS... 
DEPTH OF MOISTURE... UPSTREAM RH AND WIND SPEED/DIRECTION AND SHEAR 
BY THEN WHICH ARE MUCH TOO EARLY TO DETERMINE AT THIS TIME. 

&&

.AVIATION...(1230 PM EST FRI NOV 27 2009)
THE MAIN CHALLENGES IN THE AVIATION FORECAST IS WHETHER TO INCLUDE 
FUEL ALTERNATE CIGS AOB 2000 FT IN THE VERY SHORT TERM AND THEN 
TIMING THE END OF THE MVFR CEILINGS.

CURRENT SATELLITE INDICATES LAKE EFFECT CLOUDS OVER NEARLY ALL OF 
LOWER MI. CIGS DECREASE FROM SE TO NW ACROSS THE AREA. BELIEVE BEST 
CHANCE FOR CIGS BELOW 2000 FT WILL BE AT GRR AND LAN PRIOR TO 21Z. 
NOT CERTAIN ENOUGH TO INCLUDE IN THOSE TAFS AT THIS POINT...BUT AN 
AMENDMENT MAY BE NEEDED SHORTLY AFTER THE ROUTINE ISSUANCE.

OTHERWISE...CLOUDINESS IS EXPECTED TO END TONIGHT WHEN WINDS WILL 
SWITCH TO A W/SW DIRECTION AND HIGH PRESSURE WILL BUILD INTO THE 
REGION. CONFIDENCE IS LOW REGARDING THE EXACT TIMING...BUT BEST 
GUESS IS 00-03Z. FOR BREVITY...THIS TRANSITION IS NOT INCLUDED IN 
THE CURRENT TAFS. EXPECT VFR CIGS AND VSBYS TO PREDOMINATE MAINLY 
AFTER 06Z.

&&

.MARINE...(330 PM EST FRI NOV 27 2009)
WILL ALLOW THE SCA TO EXPIRE AS SCHEDULED AT 5 PM BASED ON 
OBSERVATIONS AND LOCAL RUN OF THE GLERL WAVE MODEL.

&&

.HYDROLOGY...(330 PM EST FRI NOV 27 2009)
NO HYDRO ISSUES IN THE SHORT TERM. PRECIPITATION SUNDAY SHOULD 
REMAIN LIGHT.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY ST. JOSEPH MANISTEE UNTIL 5 PM EST 
     FRIDAY AFTERNOON.

&&

$$

SYNOPSIS:     TJT
SHORT TERM:   TJT
LONG TERM:    LAURENS
AVIATION:     TJT
MARINE:       TJT
HYDROLOGY:    TJT