FXUS63 KGRR 290035
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
734 PM EST SAT NOV 28 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...(734 PM EST SAT NOV 28 2009)
VFR CONDITIONS SHOULD PREVAIL THROUGH THE EVENING...WITH HIGH CLOUDS
IN PLACE WITH BASES AT OR ABOVE 15000FT. EXPECTING SOME LIGHT FOG TO
FORM...DROPPING VSBY/S INTO THE MVFR CATEGORY AFTER MIDNIGHT.
CONDITIONS ARE THEN EXPECTED TO RAPIDLY DETERIORATE TOWARD DAYBREAK
AS IFR CONDITIONS DEVELOP. MOIST AIR FLOWING INTO THE STATE ALONG
AND AHEAD OF A COLD FRONT SAGGING INTO THE STATE FROM THE NORTH IS
EXPECTED TO DEVELOP STRATUS. THE STRATUS IS ALREADY SHOWING UP OFF
TO THE NORTH AND WEST...WITH LUDINGTON CARRYING AN 1100 FT OVERCAST.
WILL BE WATCHING THIS CLOUD DECK CLOSELY AS IT PUSHES SOUTH TOWARD
THE TAF SITES.
SUNDAY SHOULD FEATURE IFR CONDITIONS...IF NOT LOWER AS THE COLD
FRONT SAGS SOUTH THROUGH THE AREA. STRATUS...FOG AND RAIN WILL ALL
BE IN PLAY THROUGH THE COURSE OF THE DAY.
&&
.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
