Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 292311
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
711 PM EDT WED OCT 29 2014

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 343 PM EDT WED OCT 29 2014

MOSTLY CLOUDY SKIES AND CHILLY TEMPERATURES WILL CONTINUE INTO
THURSDAY NIGHT. A STRONG COLD FRONT WILL COME THROUGH THE AREA
FRIDAY MORNING BRINGING A PERIOD OF MIXED RAIN AND SNOW THAT WILL
LIKELY CHANCE TO ALL SNOW BEFORE THE PRECIPITATION COMES TO AN END
BY LATE AFTERNOON. IT WILL BE VERY WINDY ON HALLOWEEN TOO. SKIES
SHOULD CLEAR FRIDAY NIGHT AND WE WILL SEE THE COLDEST TEMPERATURES
OF THE SEASON TO DATE.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY NIGHT)
ISSUED AT 343 PM EDT WED OCT 29 2014

THE PRIMARY ISSUE IS THE PRECIPITATION EVENT ON FRIDAY. A MIX OF
RAIN AND SNOW IS EXPECTED FRIDAY MORNING THAT WILL LIKELY BECOME
ALL SNOW BEFORE IT ENDS BY LATER AFTERNOON. SOME MINOR
ACCUMULATIONS AREA POSSIBLE FRIDAY...MOST OF THAT BEING NORTH OF
INTERSTATE 96.

THE PHASING OF A STRONGLY DIGGING NORTHERN STREAM WAVE WITH A
SOUTHERN STREAM PACIFIC SYSTEM RESULTS IN A FAIR AMOUNT OF MID
LEVEL DYNAMICS FOR LATE THURSDAY NIGHT INTO MIDDAY FRIDAY. THERE
IS MORE THAN ENOUGH MOISTURE AROUND TO BRING BETWEEN .25 AND .50
INCHES OF PRECIPITATION TO MOST OF THE CWA. THE NAM HAS BEEN THE
WEAKEST OF THE MODELS WITH THIS SYSTEM AND SINCE THE MODELS
OVERALL DO NOT HANDLE ARCTIC ORIGIN WAVES ALL THAT WELL THE STRONG
GFS/ECMWF SEEMS TO BE THE BETTER WAY TO GO.

AS FOR THE QUESTION OF PRECIPITATION TYPE... I LOOK AT THE HEIGHT
OF THE 0C ISOTHERM IN THE MODEL SOUNDINGS AS MY PRIMARY TOOL. THIS
SHOWS THE HEIGHT FALLING TO NEAR 1000 FT AGL BY LATE MORNING SO
WITH IT THAT CLOSE TO THE GROUND I HAVE TO BELIEVE MOST OF THE
PRECIPITATION WILL BECOME SNOW BY THEN. SINCE THAT IS TOWARD THE
END OF THE EVENT... ACCUMULATIONS WILL BE LIMITED. AREAS NORTH OF
INTERSTATE 96 HAVE THE HIGHEST POTENTIAL FOR SNOW ACCUMULATIONS. I
WOULD THINK 1 TO 2 INCHES IN THE HIGHER ELEVATIONS WOULD BE THE
LIMIT BUT WE WILL HAVE TO WATCH THIS.

ONE OTHER ASPECT TO THIS EVENT IS THERE IS SOME CONVECTIVE
INSTABILITY AS THE COLD AIR COMES IN. THE GFS MOST UNSTABLE CAPE
SHOWS AS MUCH AS 300 J/KG OVER OVER SOUTHERN LAKE MICHIGAN AND
INTO AREAS SOUTH OF GRAND RAPIDS BY 18Z FRIDAY. I ADDED
THUNDERSTORMS TO OUR FORECAST FOR AREA SOUTH AND WEST OF GRAND
RAPIDS TO COVER THIS ISSUE.

THE OTHER CONSIDERATION IS THE WIND... THERE IS 50 TO 60 KNOTS IN
THE 1000 TO 2000 AGL LAYER BY LATE MORNING OR EARLY AFTERNOON AND
GIVEN THIS IS DURING THE DAY AND THERE IS STRONG COLD ADVECTION...
I HAVE TO BELIEVE A LOT OF THIS WILL MIX TO THE GROUND SO I WOULD
THINK A WIND ADVISORY WOULD BE NEEDED. TO EARLY FOR THAT YET
THROUGH. I DID INCREASE WIND GUSTS TO NEAR 40 MPH FOR NOW THROUGH.

IN THE SHORT TERM THE SHORTWAVE THAT IS CAUSING THE SHOWERS IS
LEAVING THE AREA AND SHORTWAVE RIDGING MOVES IN. VISIBLE
SATELLITE IMAGES SHOW OPEN CELL CU TO OUR NORTH MOVING SOUTH AND
WINDS ARE FORECAST TO BECOME NORTH THIS EVENING SO ALL OF THE
LEADS ME TO BELIEVE THERE WILL BE A FEW HOURS OF CLEARING TONIGHT
INLAND OF US-131. TOWARD MORNING WINDS BECOME MORE WESTERLY SO THE
LAKE CLOUDS WILL THEN MOVE INLAND SO EXPECT MOSTLY CLOUDY SKIES ON
THURSDAY.

.LONG TERM...(SATURDAY THROUGH WEDNESDAY)
ISSUED AT 343 PM EDT WED OCT 29 2014

A RATHER PROGRESSIVE PATTERN IS IN PLACE THROUGH THE LONG TERM
PERIOD. WE BEGIN ON SATURDAY WITH AN UPPER TROUGH OVERHEAD ALONG
WITH VERY COLD AIR IN PLACE. AN UPSTREAM UPPER RIDGE QUICKLY SLIDES
IN FOR LATE IN THE WEEKEND INTO EARLY NEXT WEEK. FOLLOWING THAT A
TROUGH MOVES THROUGH FOR TUESDAY/WEDNESDAY.

IN TERMS OF THE SENSIBLE WEATHER...SATURDAY WILL BE QUITE COLD WITH
HIGHS ONLY AROUND 40 DEGREES EXPECTED. FEEL THE NORTH-NORTHEAST FLOW
WILL LIKELY KEEP LAKE EFFECT PRECIPITATION OUT OF THE FORECAST AREA
OVER LAKE MICHIGAN AND OVER IN SOUTHEAST LOWER MI.

A PERIOD OF QUIET WEATHER WILL CONTINUE THROUGH THE WEEKEND AS A
SURFACE HIGH DRIFTS THROUGH GREAT LAKES. EXPECTING DRY WEATHER
THROUGH THE WEEKEND. HIGHS SATURDAY AND SUNDAY WILL BE 10 TO 15
DEGREES BELOW NORMAL.

EARLY NEXT WEEK HAVE SHOWERS IN THE FORECAST FOR MONDAY THROUGH
TUESDAY AS A SURFACE LOW AND COLD FRONT PIVOT THROUGH THE AREA.
MONDAY NIGHT AND TUESDAY LOOK TO BE THE BEST CHANCES FOR SHOWERS
WHICH IS THE TIME FRAME WHEN THE COLD FRONT WILL BE MOVING THROUGH.
HIGHS EARLY NEXT WEEK WILL BE BACK UP TOWARD NORMAL...IN THE LOWER
50S IN MOST AREAS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 703 PM EDT WED OCT 29 2014

VFR WEATHER TO DOMINATE THE WEATHER THROUGH THE PERIOD. PATCHY
MVFR CLOUDS AS A RESULT OF LAKE MOISTURE COULD OCCUR NEAR THE
LAKESHORE...BUT BASED ON TRENDS...VFR CONDITIONS HAVE EXPANDED.

PRESSURE GRADIENT WILL WEAKEN TONIGHT SO THE WINDS WILL CONTINUE
TO DIMINISH.

LOOKING AHEAD...A FAST MOVING WAVE OF LOW PRESSURE ARRIVES THU NIGHT
INTO FRI WITH IMPACTS LIKELY TO AVIATORS.

&&

.MARINE...
ISSUED AT 500 PM EDT WED OCT 29 2014

I HAVE CANCELLED THE SMALL CRAFT ADVISORY AS WINDS AND WAVES ARE
DIMINISHING IN THE NEAR SHORE AND WITH RIDGING BUILDING IN TONIGHT
I WOULD EXPECT WINDS AND WAVES TO CONTINUE TO DECREASE INTO THE
EARLY EVENING HOURS.

WINDS WILL RAMP UP AGAIN BY EARLY FRIDAY MORNING AS A STRONG COLD
FRONT MOVES THROUGH THE AREA. I EXPECT WINDS OF GALE FORCE TO
FOLLOW THE COLD FRONT. THERE IS ENOUGH INSTABILITY FOR A SCATTERED
THUNDERSTORMS SO I ADDED THOSE TO THE FORECAST TOO.


&&

.HYDROLOGY...
ISSUED AT 343 PM EDT WED OCT 29 2014

WHATEVER QPF WE WILL SEE THIS WEEK WILL BE LIGHT SO IT SHOULD HAVE
NO IMPACT ON AREA RIVERS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...GALE WARNING FROM 8 AM FRIDAY TO 5 AM EDT SATURDAY FOR
     LMZ844>849.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...DUKE
AVIATION...MJS
HYDROLOGY...WDM
MARINE...WDM






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