291
FXUS63 KGRR 072345
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
745 PM EDT THU AUG 7 2025
KEY MESSAGES
- MOST STAY DRY, OFF AND ON SLIGHT CHANCES FOR SHOWERS AND STORMS
DISCUSSION
ISSUED AT 307 PM EDT THU AUG 7 2025
- MOST STAY DRY, OFF AND ON SLIGHT CHANCES FOR SHOWERS AND STORMS
OVERALL OUR AFTERNOON CHANCES FOR POP UP THUNDERSTORMS IS LOW AND
WILL BE MAINLY CONFINED TO THE 127 CORRIDOR. OTHERWISE DRY
CONDITIONS ARE EXPECTED FOR THE REST OF THE AFTERNOON AND EVENING.
LATE TONIGHT INTO FRIDAY, CHANCES ARE DECREASING WITH THE LATEST
GUIDANCE, THEREFORE DECREASED POPS FOR TOMORROW IN THE 20 TO 30
PERCENT RANGE. WHAT WE SEE FOR RAIN AND STORMS WILL DEPEND ON
CONVECTION AS IT EXITS WISCONSIN, BUT EVENT THEN CHANCES AREN'T
TOO HIGH ON THAT SIDE OF THE LAKE EITHER. WHILE WE HAVE A MORE HOT
AND HUMID AIR MASS DEVELOPING OVER THE AREA, WE LACK ANY
SIGNIFICANT SOURCE OF LIFT WITHIN THE UPPER LEVEL RIDGE. HEIGHTS
WILL CONTINUE TO RISE INTO THE WEEKEND UNTIL WE MOVE MORE INTO
SOUTHWEST FLOW SUNDAY INTO MONDAY. COMPARED TO YESTERDAY THERE
WERE SIGNS OF A STRONGER TROUGH MOVING THROUGH THE AREA, BUT TODAY
THOSE HAVE BACKED OFF KEEPING US IN SOUTHWEST FLOW WITH THE MAIN
TROUGH AXISES PASSING TO THE NORTH. THIS HAS CAUSE A DOWNWARD
TREND IN THE POPS (20 TO 40 PERCENT) FOR THE BEGINNING OF NEXT
WEEK. TO SUMMARIZE, SOME MAY SEE RAIN AND THUNDERSTORMS BUT MOST
STAY DRY AT LEAST THROUGH THE WEEKEND. ANY RAIN THAT IS OBSERVED
LIKELY WON'T AMOUNT TO MUCH WITH AMOUNTS LIKELY UNDER A QUARTER OF
AN INCH.
AS MENTIONED IT WILL BECOME HOT AND HUMID ESPECIALLY OVER THE
WEEKEND WITH HEAT INDICES IN THE 90S. SATURDAY SOME AREAS MAY SEE
HEAT INDEX VALUES NEAR 100, THE BEST CHANCES FOR THESE HIGHER HEAT
INDICES ARE ALONG AN ALLEGAN TO GRAND RAPIDS TO ALMA LINE.
AVIATION /00Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 745 PM EDT THU AUG 7 2025
EXPECTING MOSTLY VFR (WITH POSSIBLE EXCEPTIONS BELOW) AS ANY CLOUD
BASES WILL BE AT OR ABOVE 4,000 FEET. ABOUT 15 KNOTS OF WIND SHEAR
MAY BE PRESENT BELOW 1,000 FEET BETWEEN 03 AND 12 Z. SOME, BUT NOT
ALL MODELS, DEVELOP SHOWERS OR THUNDERSTORM CELLS AROUND MKG AND
GRR AFTER 06 Z TONIGHT, WEAKENING AROUND 12 Z. THESE WOULD BE
BASED ON THE TRANSPORT OF RELATIVELY MOIST (CLOUDY) AND UNSTABLE
AIR AROUND 5,000 FEET. ADDITIONAL SCATTERED SHOWERS/THUNDERSTORMS
MAY DEVELOP BETWEEN GRR AND LAN AFTER 18 Z WITH DAYTIME HEATING.
TEMPORARY MVFR TO IFR VISIBILITY MAY OCCUR WITH MODERATE TO HEAVY
RAIN IF THESE THUNDERSTORMS DEVELOP. BOTH POTENTIALS GET A PROB30
FOR NOW.
MARINE
ISSUED AT 307 PM EDT THU AUG 7 2025
A FEW THUNDERSTORM CELLS COULD DEVELOP OVER LAKE MICHIGAN DURING THE
EARLY MORNING HOURS OF FRIDAY. THESE POTENTIAL STORMS WOULD ARISE
FROM RELATIVELY MOIST AND UNSTABLE AIR FLOWING IN ABOVE THE
MARINE LAYER. THEY ARE NOT EXPECTED TO BE SEVERE.
WINDS MOSTLY FROM THE SOUTH ARE EXPECTED FRIDAY AND THROUGH THE
WEEKEND. SATURDAY MAY BE THE BREEZIEST, AND MODELS SHOW A
POSSIBILITY FOR 3-5 FT WAVES AND HIGH SWIM RISK NEAR BIG AND LITTLE
SABLE POINTS (NORTH OF WHITEHALL TOWARD LUDINGTON). HOWEVER, THE
MODELED WAVES MAY BE A BIT TOO HIGH, AS PREVIOUS 90-DEGREE DAYS OVER
THE LAND WITH SOUTH WINDS RESULTED IN STABILITY OVER THE WATER, A
LACK OF STRONGER WINDS MIXING TOWARD THE WATER, AND MORE OF A 2-4
FOOT WAVE REGIME WITH MODERATE SWIM RISK.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...RAH
AVIATION...CAS
MARINE...CAS
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