901
FXUS63 KGRR 140803
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
403 AM EDT TUE OCT 14 2025
KEY MESSAGES
- LIGHT RAIN POSSIBLE TONIGHT
- MORE SUBSTANTIAL SYSTEM TO AFFECT THE AREA INTO THE WEEKEND
- TEMPERATURES A BIT UP AND DOWN
DISCUSSION
ISSUED AT 402 AM EDT TUE OCT 14 2025
- LIGHT RAIN POSSIBLE TONIGHT
AFTER A QUIET WEATHER DAY TODAY OUTSIDE OF SOME AREAS OF MORNING
FOG, RAIN CHANCES INCREASE TONIGHT. THE CHANCES FOR RAIN ARE NOT
HIGH, GENERALLY IN THE 20-50 PCT RANGE. THE PRECIPITATION TONIGHT
IS ASSOCIATED WITH A PUSH OF MID LEVEL MOISTURE ESPECIALLY. BUFKIT
OVERVIEWS SHOW THE BEST JUXTAPOSITION OF MOISTURE/LIFT IN THE
10,000-20,000 FOOT RANGE. THERE IS NOT MUCH MOISTURE ADVECTION
GOING ON BENEATH THAT WITH LOWER RH NOTED AROUND 850MB. THE BEST
PLACES TO SEE LIFT OR IMPLIED LIFT IS ON THE 300K ISENTROPIC
SURFACE AND IN AN INCREASE IN PWAT VALUES TO AROUND 1 INCH. FEEL
THE BEST CHANCES FOR RAIN TONIGHT WILL BE UPSTREAM IN WISCONSIN
AND OVER LAKE MICHIGAN, BUT SOME OF THIS WILL SLIDE INTO WESTERN
LOWER MICHIGAN ESPECIALLY. 4HR MAX REFLECTIVITY FROM THE SPC HREF
SHOWS THIS NICELY. THE 6HR PROBABILITY MATCHED MEAN PRECIPITATION
ALSO SHOWS THAT WHAT PRECIPITATION DOES FALL WILL BE LIGHT,
GENERALLY TRACE AMOUNTS TO PERHAPS A TENTH OF AN INCH.
- MORE SUBSTANTIAL SYSTEM TO AFFECT THE AREA INTO THE WEEKEND
RIDGING ALOFT WILL DOMINATE THE REMAINDER OF THE WORK WEEK WITH
DRY WEATHER EXPECTED FROM WEDNESDAY MIDDAY THROUGH FRIDAY. FOCUS
VERY MUCH IS ON THE SYSTEM FOR FRIDAY NIGHT THROUGH SUNDAY AS
RIDGING IS REPLACED BY A DEEP LONGWAVE TROUGH WHICH WILL BE
OVERHEAD SATURDAY NIGHT INTO SUNDAY. SOUTHWEST UPPER FLOW DEVELOPS
AHEAD OF THE TROUGH FRIDAY NIGHT INTO SATURDAY. THE EVOLUTION OF
THE UPPER TROUGH HAS SOME MODEL DIFFERENCES BETWEEN THE
OPERATIONAL ECMWF AND GFS, BUT WE HAVE SOME THINGS WE CAN NAIL
DOWN AT THIS POINT. THOSE INCLUDE PRECIPITATION WILL MOVE INTO THE
AREA FRIDAY NIGHT AND BE MOST SUBSTANTIAL ON SATURDAY IT APPEARS
AS A COLD FRONT DRIVES THROUGH THE REGION. SHOWERY WEATHER WILL
LINGER INTO SUNDAY AS WE WILL BE BENEATH CORE OF THE UPPER TROUGH.
SOME LOCALLY HEAVY RAIN IS POSSIBLE DURING THIS TIME FRAME AS PWAT
VALUES CLIMB TO 1.5 INCHES. THUNDERSTORMS ARE CERTAINLY POSSIBLE
AHEAD OF THE COLD FRONT AS WELL WITH 850MB DEW POINTS CLIMBING TO
+10C AND MUCAPE VIA THE ECWMF REACHING 1000+ J/KG JUST UPSTREAM.
- TEMPERATURES A BIT UP AND DOWN
TEMPERATURES WILL BE WARMER THAN NORMAL TODAY WITH HIGHS INTO THE
LOWER 70S IN MANY AREAS. NORMAL HIGHS TODAY ARE 62 AT BOTH GRR
AND AZO. WE COOL A BIT FOR WEDNESDAY AND THURSDAY BACK INTO THE
60S BEFORE RISING AGAIN AHEAD OF THE WEEKEND SYSTEM. HIGHS FRIDAY
AND SATURDAY WILL PUSH BACK TO AROUND 70. MUCH COLDER AIR SETTLES
IN WITH THE TROUGH THIS WEEKEND WITH HIGHS FALLING TO BELOW NORMAL
VALUES INTO THE 50S. SUNDAY NIGHT 850MB TEMPERATURES ACTUALLY DIP
TO -1C OVERHEAD.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 208 AM EDT TUE OCT 14 2025
A COLD FRONT STRETCHES FROM NEAR HOUGHTON LAKE (HTL) TO MUSKEGON
(MKG) AT 06Z. A BAND OF STRATOCUMULUS IS LOCATED NEAR AND AHEAD
OF THE FRONT WITH CLOUD BASES IN THE 3500-6000FT RANGE FOR THE
MOST PART. THE FRONT WILL CONTINUE TO PUSH SOUTH AND EAST TODAY
MOVING THROUGH ALL OF THE TAF SITES BY 18Z. THE STRATOCUMULUS
CLOUDS WILL ALSO PUSH SOUTH WITH THE FRONT.
THE MAIN AVIATION CONCERN IN THIS TAF PERIOD IS THE THREAT OF
STRATUS AND FOG THIS MORNING BETWEEN 06Z AND 15Z OR SO. STRATUS
AND DENSE FOG IS FORMING ALONG THE LAKESHORE (LDM, MBL) AT 06Z AS
THE AIR IS QUICKLY COOLED BEHIND THE FRONT COINCIDENT WITH A ZONE
OF HIGHER LOW LEVEL MOISTURE. AREAS TO THE SOUTHEAST (TEW, JXN)
ARE ALSO FORMING FOG IN AN ZONE OF SCATTERED CLOUDS AHEAD OF THE
STRATOCU. WE FEEL THESE TWO AREAS WILL BE MOST PRONE TO FOG AND
STRATUS THIS MORNING, NAMELY MKG TOWARDS THE LAKESHORE AND LAN/JXN
INLAND. CONFIDENCE IN HOW THIS DEVELOPS IS SOMEWHAT LOW. BOTTOM
LINE IS THAT IFR AND BELOW IS POSSIBLE AT THOSE THREE LOCATIONS
ESPECIALLY.
VFR WEATHER IS EXPECTED FROM THE AFTERNOON THROUGH THE EVENING
HOURS. WINDS WILL BE LIGHT NORTH TODAY AT 4-8 KNOTS.
MARINE
ISSUED AT 402 AM EDT TUE OCT 14 2025
THE POTENTIAL FOR REACHING SMALL CRAFT ADVISORY (SCA) CONDITIONS
THIS EVENING AND TONIGHT IS NOT ZERO, BUT HAVE DECIDED TO HOLD OFF
ON A HEADLINE ISSUANCE. HIGH PRESSURE WILL BE PUSHING INTO THE
REGION FROM THE NORTH THIS EVENING/TONIGHT...AND ON THE LEADING
EDGE THERE IS A TIGHTENING OF THE PRESSURE GRADIENT OVER LAKE
MICHIGAN. WITH TIME TONIGHT THE FLOW WILL BE VEERING FROM NORTH TO
NORTHEAST INCREASING THE OFF SHORE COMPONENT. WE COULD SEE SOME
20 KNOT WINDS OVER THE NEARSHORE WATERS, BUT THIS WILL BE OF
LIMITED TIME SCALE. WAVES WILL INCREASE TO AROUND 3 FEET TONIGHT,
BUT WE FEEL THEY WILL LIKELY REMAIN BELOW CRITICAL THRESHOLDS
(4 FEET). SO, FOR A MARGINAL EVENT OUTSIDE OF THE PEAK BOATING
SEASON WE WILL BE HOLDING OFF ON A HEADLINE FOR NOW. WE WILL BE
WATCHING TRENDS IN MODELED WINDS AND WAVES.
BEYOND TONIGHT, HIGH PRESSURE WILL BRING QUIESCENT CONDITIONS ON
THE BIG LAKE FOR WEDNESDAY AND THURSDAY. THE NEXT TIME FRAME OF
CONCERN WILL BE THURSDAY NIGHT INTO FRIDAY AS SOUTH FLOW PICKS UP
TO SCA LEVELS. FRIDAY NIGHT INTO SATURDAY WE COULD EVEN FLIRT WITH
GALES.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...DUKE
AVIATION...DUKE
MARINE...DUKE
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