FXUS63 KGRR 221115
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
615 AM EST TUE DEC 22 2009
LATEST UPDATE...AVIATION...
.SYNOPSIS...(330 AM EST TUE DEC 22 2009)
AN UPPER AIR DISTURBANCE PASSING BY TO THE SOUTH OF MICHIGAN WILL
BRING LIGHT SNOW TO AREAS MAINLY SOUTH OF INTERSTATE 96 TODAY WITH
JUST A FEW FLURRIES POSSIBLE ELSEWHERE. HIGH PRESSURE WILL BRING DRY
WEATHER TONIGHT THROUGH WEDNESDAY NIGHT.
A LOW PRESSURE SYSTEM MOVING UP THE MISSISSIPPI RIVER VALLEY WILL
BRING OUR AREA POTENTIAL FOR A WINTRY MIX OF SNOW... SLEET...
FREEZING RAIN AND RAIN LATE THURSDAY INTO FRIDAY. SIGNIFICANT SNOW
WITH THIS SYSTEM WILL STAY WELL TO OUR WEST. HOWEVER THERE IS
POTENTIAL FOR FREEZING RAIN ON CHRISTMAS EVE WHICH COULD POTENTIALLY
CREATE VERY HAZARDOUS TRAVEL CONDITIONS FROM CHRISTMAS EVE INTO
CHRISTMAS DAY. IT WILL TURN COLDER WITH INTERMITTENT SNOW SHOWERS
LATE FRIDAY THROUGH THE WEEKEND.
&&
.SHORT TERM...(330 AM EST TUE DEC 22 2009)
(TODAY THROUGH THURSDAY AFTERNOON)
OUR PRIMARY SHORT TERM FCST CONCERNS INVOLVE POTENTIAL FOR LIGHT
SNOW ACROSS OUR SOUTHERN CWFA TODAY AND THEN TO TIME PCPN INTO OUR
CWFA THURSDAY AFTERNOON. FCST TWEAKS INCLUDE RAISING POPS TO LIKELY
FOR LIGHT SNOW ACROSS OUR SOUTHERN CWFA FOR TODAY BASED LARGELY ON
SHORT RANGE GUIDANCE TRENDS CORROBORATED WITH RGNL RADAR TRENDS OFF
TO OUR WSW. WE HAVE ALSO REMOVED POPS FROM THE FCST FOR THURSDAY
MORNING.
RGNL RADAR TRENDS AND SFC OBS INDICATE A LARGE AREA OF LIGHT SNOW
ACROSS FAR SOUTHERN WI AND NORTHERN IL EARLY THIS MORNING. LIGHT
SNOW IS ALREADY MOVING INTO OUR EXTREME SW CWFA. THIS AREA OF SNOW
WILL CONTINUE TO EXPAND OFF TO THE EAST TO ESE AND IMPACT OUR
SOUTHERN CWFA (PARTICULARLY SOUTH OF I-96) LATER THIS MORNING INTO
THIS AFTERNOON AS SUGGESTED BY SHORT RANGE GUIDANCE TRENDS. DECENT
MID LEVEL (700-500 MB) FRONTOGENETICAL FORCING IS NOTED OFF TO OUR
WEST THIS MORNING WHICH CORRESPONDS WELL TO THE AREA OF SNOW. THE
MID LEVEL FGEN WILL STRENGTHEN SOUTH OF I-96 LATER TODAY.
LIGHT ACCUMULATIONS OF AROUND AN INCH ARE THE MOST PROBABLE OUTCOME
TODAY SOUTH OF I-96. HOWEVER GIVEN THE NATURE OF MID LEVEL FGEN
BANDED SNOW AND RGNL RADAR TRENDS/SFC OBS... I WOULD NOT BE
SURPRISED TO SEE A COUPLE OF LOCALLY HIGHER AMOUNTS. THE DAY SHIFT
WILL NEED TO MONITOR RADAR/GUIDANCE TRENDS ON THIS CLOSELY.
THE HIGH PRESSURE TO OUR NORTH WILL DOMINATE OUR WX PATTERN TONIGHT
THROUGH WEDNESDAY NIGHT RESULTING IN PARTLY CLOUDY SKIES AND
SEASONABLY COOL CONDITIONS. EASTERLY FLOW AND MODERATING H8 TEMPS
WILL ELIMINATE POTENTIAL FOR ANY LES.
WE HAVE REMOVED POPS FROM THE FCST FOR THURSDAY MORNING. AT THIS
TIME WE WILL MAINTAIN POPS FOR MUCH OF OUR CWFA FOR A WINTRY MIX OF
PCPN BEGINNING THURSDAY AFTERNOON. HOWEVER A CONSENSUS BLEND OF 00Z
SHORT RANGE GUIDANCE SUGGESTS THE MUCH BETTER CHC FOR PCPN WILL HOLD
OFF UNTIL CHRISTMAS EVE. MINIMAL TRAVEL IMPACTS ARE EXPECTED THROUGH
THURSDAY AFTERNOON.
&&
.LONG TERM...(330 AM EST TUE DEC 22 2009)
(THURSDAY NIGHT THROUGH MONDAY)
ONLY MADE A FEW TWEAKS TO PRECIP TYPE AND POPS AS SLOW MOVING LOW
DOMINATES THE WEATHER ACROSS THE GREAT LAKES THROUGH THE PERIOD.
WENT WITH A COMPROMISE OF GFS AND NAM GUIDANCE...WITH SNOW AND MIXED
PRECIP ACROSS THE NORTHERN FORECAST AREA AND FREEZING RAIN TO RAIN
ACROSS THE SOUTH ON THURSDAY NIGHT AS EAST WINDS CONTINUE TO FEED
COLD AND DRY AIR IN FROM SFC HIGH RETREATING ACROSS EASTERN CANADA.
AFTER A BURST OF WAA/ISENTROPIC LIFT PRECIP THURSDAY NIGHT...THE DRY
SLOT SHOULD WORK IN ON FRIDAY REDUCING POPS TO CHANCE WITH TEMPS
ABOVE FREEZING DURING THE DAY. RAIN CHANGING TO WET SNOW DURING THE
AFTERNOON AS COOLER AIR MOVES IN ALOFT BY 00Z SATURDAY.
SOME LAKE ENHANCED WRAP AROUND SNOWS FOR THE WEEKEND WITH ARCTIC AIR
ARRIVING ON SUNDAY HELPING TO PRODUCE WIDESPREAD SNOW SHOWERS AND
SOME ACCUMS OF A FEW INCHES AS THE UPPER LOW MOVES THROUGH.
&&
.AVIATION...(615 AM EST TUE DEC 22 2009)
SOME SNOW SHOWERS EXPECTED ACROSS SOUTHERN LOWER MICHIGAN TODAY AS
WEAK LOW PRESSURE MOVES THROUGH. GENERALLY VFR AT MKG AND GRR WITH
SOME MVFR AND AREAS OF IFR AT TIMES FROM AZO AND BTL TO JXN. LIGHT
SNOW COULD CONTINUE INTO THE EVENING ACROSS SOUTHERN LOWER MICHIGAN.
&&
.MARINE...(330 AM EST TUE DEC 22 2009)
WINDS AND WAVES WILL NOT POSE A HAZARD TO MARINERS UNTIL THURSDAY
AND FRIDAY AS A LOW PRESSURE PRESSURE SYSTEM MOVES IN RESULTING IN
SIGNIFICANTLY HIGHER WIND AND WAVE ACTION LATE IN THE WEEK.
&&
.HYDROLOGY...(330 AM EST TUE DEC 22 2009)
CONCERN FOR ICE DEVELOPMENT THAT WOULD LEAD TO ICE JAMS IS MITIGATED
BY MAX TEMPS MAINLY IN THE 30S THROUGH FRIDAY... RESULTING IN LOW
ICE JAM POTENTIAL. PCPN THURSDAY THROUGH FRIDAY WILL NOT BE
SIGNIFICANT ENOUGH TO CAUSE HYDRO ISSUES.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE
LM...NONE.
&&
$$
SYNOPSIS: LAURENS
SHORT TERM: LAURENS
LONG TERM: OSTUNO
AVIATION: OSTUNO
MARINE: LAURENS
HYDROLOGY: LAURENS
