FXUS63 KGRR 031159
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
700 AM EST THU DEC 3 2009
LATEST UPDATE...AVIATION...
.SYNOPSIS...(408 AM EST THU DEC 3 2009)
COLDER AIR WILL FILTER INTO THE REGION DURING THE DAY TODAY IN THE
WAKE OF THE DEPARTING AREA OF LOW PRESSURE. THIS COLD AIR MOVING IN
ACROSS THE RELATIVELY WARM WATERS OF LAKE MICHIGAN WILL HELP TO
INDUCE LAKE EFFECT SNOW SHOWERS BEGINNING TODAY.
SNOW SHOWERS WILL INCREASE IN COVERAGE AND INTENSITY TONIGHT AS THE
WINDS BECOME WESTERLY AND A WAVE OF LOW PRESSURE MOVES BY. SOME
LOCATIONS INCLUDING GRAND RAPIDS...MUSKEGON...AND HOLLAND COULD SEE
SNOW ACCUMULATIONS OF UP TO 6 INCHES OF SNOW FROM LATER TODAY
THROUGH THE DAY ON FRIDAY. LESSER AMOUNTS CAN BE EXPECTED ELSEWHERE.
&&
.SHORT TERM...(408 AM EST THU DEC 3 2009)
(TODAY THROUGH FRIDAY)
MAIN CHALLENGE WITH THIS FORECAST PACKAGE IS THE LAKE EFFECT/LAKE
ENHANCEMENT EVENT FOR LATE TODAY THROUGH EARLY FRI. NO MAJOR CHANGES
WERE NEEDED FROM THE PREVIOUS FORECAST. WE DID INCREASE THE SNOW
AMOUNTS JUST A LITTLE FOR THE CORE OF THE AREA EXPECTED TO GET HIT.
DEFORMATION AREA RAINFALL THAT HAS AFFECTED THE AREA MOST OF THE
NIGHT IS NOW IN THE PROCESS OF DIMINISHING AS THE PV ANOMALY LIFTS
INTO THE NE PORTION OF THE COUNTRY. PCPN HAS CONTINUED TO REMAIN
MAINLY RAIN FOR NOW...BUT THE TRANSITION TO SNOW WILL BE OCCURRING
OVER THE NEXT FEW HOURS AS COLD AIR FILTERS IN. THIS COLDER AIR WILL
PRETTY MUCH KEEP TEMPERATURES STABLE THROUGH THE DAY OR EVEN DROP
THEM A COUPLE OF DEGREES.
LAKE EFFECT BAND OFFSHORE CAN ALREADY BE SEEN ON THE RADAR...IN A
N-S ORIENTATION. DELTA T/S ARE LIKELY IN THE MID TEENS CURRENTLY...
AND SHOULD RISE INTO THE UPPER TEENS TO AROUND 20 BY 00Z TONIGHT.
THE ORIENTATION OF THESE BANDS SHOULD SHIFT FROM THE N-S ORIENTATION
TO A GENERAL WEST ORIENTATION BY TONIGHT AS A STRONG SHORT WAVE NOW
ACROSS SOUTH DAKOTA ROTATES TO THE EAST ACROSS THE AREA.
THIS SHORT WAVE IS EXPECTED TO INCREASE MOISTURE LEVELS TO ABOVE 10K
FEET TONIGHT ALONG WITH THE SYNOPTIC FORCING. THIS WAVE IS EXPECTED
TO HAVE A SFC REFLECTION OUT AHEAD OF IT WHICH WILL BEGIN AFFECTING
THE AREA BY EARLY THIS EVENING. FAIRLY GOOD SFC CONVERGENCE ALONG
THE FRONT WILL SHIFT NORTH INTO THE AREA...AND A GOOD DEAL OF LOW
LEVEL FGEN IS EXPECTED TO DEVELOP. MODELS INDICATE STRONG FORCING IN
THE DGZ AFTER 00Z TONIGHT.
THE COMBINATION OF THE SYNOPTIC FORCING...THE LAKE CONTRIBUTION...
AND FAVORABLE MICROPHYSICS ALL POINT TOWARD A DECENT POTENTIAL FOR
ACCUMULATIONS FOR A PORTION OF THE AREA. THE EXACT LOCATION OF THE
HEAVIER SNOW IS SOMEWHAT IN QUESTION DEPENDENT ON THE LOW LEVEL FGEN
BAND EXPECTED TO SET UP. ALL OF THE HIGHER RESOLUTION MODELS DEPICT
THIS MESOSCALE FEATURE A BIT BETTER THAN THE LOWER RESOLUTION
MODELS. EXPECTING A WSW TO WNW FLOW...IT SEEMS AS IF THE WRLY
FAVORED AREAS INCLUDING GRR...BIV...AND MKG WOULD BE FAVORED TO SEE
THE HEAVIER AMOUNTS.
IF ONE LOCATION SEES A HEAVIER BAND SET UP FOR A WHILE...WE COULD
SEE SOME LOCALIZED WARNING AMOUNTS BEING FOUND. RIGHT NOW...WE
EXPECT A SOLID ADVISORY EVENT FOR THE FAVORED LOCATIONS WITH LESSER
AMOUNTS ELSEWHERE. WE DO EXPECT THAT MOST OF THE CWFA WILL SEE SOME
MEASURABLE SNOW. WITH THIS BEING THE FIRST BIGGER MEASURABLE
EVENT...AN ADVISORY MAY BE NEEDED FOR MORE LOCATIONS DUE MORE TO
IMPACT THAN SNOW AMOUNTS ALONE. THIS WILL CONTINUE INTO FRIDAY
MORNING BEFORE SNOW SHOWERS DIMINISH IN INTENSITY AS THE WAVE MOVES
BY AND THE MOISTURE DEPTH SHRINKS.
&&
.LONG TERM...(408 AM EST THU DEC 3 2009)
(FRIDAY NIGHT THROUGH WEDNESDAY)
THE PRIMARY FORECAST CHALLENGE DEALS WITH THE SNOWFALL COVERAGE
SATURDAY AND THE NEXT POTENTIAL STORM FOR EARLY NEXT WEEK.
THE LOW LEVEL FLOW WILL BE BACKING FROM WEST TO SOUTHWEST FRIDAY
NIGHT INTO SATURDAY. WITH THE COLDEST 850 MB AIR OVER SOUTHERN LAKE
MI 12Z SAT... THE LAKE EFFECT SHOULD STILL BE ONGOING AT THAT TIME.
THE MODELS SHOW A MOIST THERMAL TROUGH AT 700 MB ARRIVING SAT.
THIS COMBINED WITH INCREASING FETCH AS THE FLOW TURNS
SOUTHWEST...SHOULD MAINTAIN THE SNOW SHOWERS FOR THE LAKESHORE
COUNTIES...ESPECIALLY NORTH OF BIV. WILL FEATURE LIKELY POPS THERE
AS IT APPEARS MOST LOCATIONS SHOULD SEE SOME MEASURABLE SNOWFALL.
THE SUNDAY NIGHT INTO MONDAY SYSTEM APPEARS TO BE SPEEDING UP WITH
TIME. THE HIGH RES EURO HAS IT MOVING IN SUN NIGHT WITH THE GFS
SIMILAR AND STRONGER. WILL FEATURE CHC OF SNOW MOVING IN LATER SUN
NIGHT AND CONTINUING INTO MONDAY.
&&
.AVIATION...(700 AM EST THU DEC 3 2009)
A COUPLE OF CONCERNS WITH THE AVIATION FORECAST. FIRST IS THE IFR
CONDITIONS OCCURRING FROM KLAN TO KJXN. THE STORM RESPONSIBLE FOR
THESE LOWER CEILINGS IS MOVING AWAY. THUS THE DURATION OF THE IFR
CONDITIONS IS EXPECTED TO REMAIN LIMITED. ABUNDANT LOW LEVEL
MOISTURE WILL CREATE RATHER WIDESPREAD MVFR CONDITIONS THROUGH THE
MORNING. SOME IMPROVEMENT TO VFR COULD OCCUR FROM KLAN TO KJXN THIS
AFTERNOON AS DRIER AIR TRIES TO WORK IN AND THE EVENT TAKES MORE OF
A LAKE EFFECT APPEARANCE.
THE LAKE EFFECT SNOW SHOWERS WILL BE ON THE INCREASE LATER THIS
AFTERNOON AND EVENING AND WILL BECOME WIDESPREAD TONIGHT. THE
LOWEST CONDITIONS ARE EXPECTED FROM KMKG TO KGRR...AND POSSIBLY KAZO
WHERE EVENTUAL IFR OR LOWER CONDITIONS ARE PREDICTED. SOUTHWEST
WINDS TONIGHT AT KAZO AND WEST WINDS AT KMKG WILL ENHANCE THE LIFT
BETWEEN THE TWO LOCATIONS...STRENGTHENING THE SNOW SHOWERS. WILL
NEED TO MONITOR THE WINDS FROM KAZO TO KBTL TO KJXN AS A RISK FOR
GUSTS OVER 25 KNOTS EXISTS.
ALSO WE LOSE THE MOISTURE AT THE -15 DEG C LEVEL THIS MORNING INTO
THE AFTERNOON...AND THIS RAISES THE RISK FOR SOME ICING.
THE MAIN POTENTIAL ICING LAYER WOULD BE FROM 3000 FT TO ABOUT 10000
FT.
&&
.MARINE...(408 AM EST THU DEC 3 2009)
SMALL CRAFT ADVISORY REMAINS IN EFFECT AND WILL LIKELY HAVE TO BE
EXPANDED IN TIME THROUGH FRIDAY NIGHT. CORE OF STRONGEST WINDS ALOFT
HAS SHIFTED OUT OF THE AREA...AND WINDS ARE NOW BEGINNING TO
GRADUALLY DIMINISH. THIS TREND WILL CONTINUE INTO EARLY THIS EVENING
BEFORE WINDS PICK UP ONCE AGAIN AHEAD OF THE NEXT WAVE OF LOW
PRESSURE. WINDS WITH THE NEXT SYSTEM LOOK TO REMAIN AT OR BELOW 30
KNOTS.
&&
.HYDROLOGY...(408 AM EST THU DEC 3 2009)
NO HYDROLOGY ISSUES EXPECTED THROUGH THE PERIOD. RIVERS ARE ALL WELL
WITHIN THEIR BANKS...AND ARE EXPECTED TO REMAIN SO AS RAINFALL
AMOUNTS WITH THIS SYSTEM HAVE GENERALLY REMAINED UNDER HALF AN INCH.
IT APPEARS THAT ALMOST ALL PRECIPITATION FROM NOW THROUGH THE
WEEKEND WILL BE SNOW...AND THIS WILL NOT IMPACT RIVER LEVELS FOR
NOW.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY ST. JOSEPH TO MANISTEE THROUGH THURSDAY.
&&
$$
SYNOPSIS: NJJ
SHORT TERM: NJJ
LONG TERM: MJS
AVIATION: MJS
MARINE: NJJ
HYDROLOGY: NJJ
