375
FXUS63 KGRR 101929
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
329 PM EDT TUE JUN 10 2025
KEY MESSAGES
- MOSTLY DRY THROUGH WEDNESDAY
- SEVERAL ROUNDS OF SHOWERS AND STORMS LATE WEEK
- ELEVATED UNCERTAINTY FOR LATE WEEK TEMPERATURES
DISCUSSION
ISSUED AT 327 PM EDT TUE JUN 10 2025
- MOSTLY DRY THROUGH WEDNESDAY
CONDITIONS WILL BE DRY FOR MOST IF NOT ALL OF THE AREA TODAY. CANNOT
RULE OUT AN ISOLATED SHOWER NORTH OF I96 BUT THAT WILL BE THE
EXCEPTION. A FRONT DROPS SOUTH ACROSS THE AREA ON WEDNESDAY.
HOWEVER, FORECAST HRRR SOUNDINGS SUGGEST A WELL CAPPED ENVIRONMENT
DUE TO A WARM NOSE ALOFT EVEN GIVEN AMPLE LOW-LEVEL MOISTURE. SO
WHILE THE AMPLE LOW-LEVEL WARM ADVECTION WILL BRING HIGHS INTO THE
80S, CONDITIONS WILL REMAIN DRY DURING THE DAYLIGHT HOURS.
- SEVERAL ROUNDS OF SHOWERS AND STORMS LATE WEEK
WE SEE A PATTERN CHANGE WEDNESDAY NIGHT INTO THURSDAY AS MID-LEVEL
FLOW BECOMES ZONAL. A BAROCLINIC ZONE THEN SETS UP ACROSS THE AREA
REINFORCED BY SOUTHERLY FLOW ON THE WARM SIDE AND LAKE-MODIFIED
EASTERLY FLOW ON THE COOL SIDE.
THIS FRONT WILL SERVE AS A FOCUS FOR SHOWERS AND THUNDERSTORMS IN
CONJUNCTION WITH RFQ DIFFLUENCE WEDNESDAY NIGHT INTO THE WEEKEND.
HOWEVER, AS IS COMMON IN THESE ZONAL PATTERNS WITH MORE NEBULOUS
SYNOPTIC FORCING, THE EXACT PLACEMENT OF THE FRONT COVERAGE OF
RAINFALL IS NOT NAILED DOWN. IN PARTICULAR, WE MAY SEE THE FRONT
LIFT NORTH AND MORE WIDESPREAD RAINFALL COVERAGE FRIDAY INTO
SATURDAY AS A TROF AND ASSOCIATED FRONT SWING THROUGH THE REGION.
PWATS AROUND 1.5" WITH MUCAPE AROUND 1000 J/KG WILL BE FAVORABLE FOR
BOTH SHOWERS AND THUNDERSTORMS IN SEVERAL ROUNDS OVER THE LATE WEEK
PERIOD. EPS PROBABILITIES OF RAINFALL OVER 0.5" ARE OVER 50 PERCENT
ACROSS MOST OF THE AREA AND OVER 80% NORTH OF M46. FOR OVER 1"
PROBABILITIES ARE OVER 50% NEAR AND NORTH OF M46. HOWEVER, THIS IS
BOTH A DECREASE AND NORTHWARD SHIFT IN PROBABILITIES COMPARED TO THE
00Z SUITE. THE GEFS ALSO TRENDED NOTABLY DOWNWARD WITH PROBABILITIES
OF WIDESPREAD RAINFALL OVER 0.5" COMPARED TO THE OVERNIGHT RUNS.
IT'S IMPORTANT TO NOTE THOUGH THAT THESE PROBABILITIES ARE BASED ON
COARSE RESOLUTION DATA WHICH DOES NOT ACCOUNT FOR THUNDERSTORMS,
AREAS WITH THUNDERSTORMS AND ESPECIALLY TRAINING THUNDERSTORMS MAY
SEE HIGHER RAINFALL TOTALS. IN SUMMARY, SEVERAL ROUNDS OF SHOWERS
AND STORMS ARE LIKELY THURSDAY THROUGH THE WEEKEND BUT DETAILS AS TO
HOW MUCH RAIN AND STORM COVERAGE REMAIN UNCERTAIN.
- ELEVATED UNCERTAINTY FOR LATE WEEK TEMPERATURES
THE QUESTIONS ON FRONTAL POSITIONING ALSO RAISE QUESTIONS ON LATE
WEEK TEMPERATURES. 25TH-75TH PERCENTILE SPREAD IN TEMPERATURES
EXCEEDS 5F AND IN SOME CASES 10F ACROSS THE CWA BETWEEN THURSDAY AND
SATURDAY. AS SUCH, ENSEMBLE BASED GUIDANCE LIKE NBM WILL SMOOTH OUT
THE MORE STARK GRADIENT WITH WIDESPREAD "MIDDLE OF THE ROAD"
TEMPERATURES. DETERMINISTIC GUIDANCE BETTER REPRESENTS THE EXPECTED
SCENARIO WITH HIGHS IN THE 60S-LOW 70S NORTH OF THE FRONT AND HIGHS
IN THE MID 70S-80S SOUTH. NAILING DOWN FRONTAL POSITION WILL BE KEY
TO TEMPERATURES IN THE LONG TERM PORTION OF THE FORECAST.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 154 PM EDT TUE JUN 10 2025
A MID LEVEL DISTURBANCE IS WORKING FROM WEST TO EAST THROUGH THE
NORTHERN GREAT LAKES THIS AFTERNOON. THE MID LEVEL WAVE IS
PUSHING A SURFACE TROUGH THROUGH SOUTHWEST LOWER MICHIGAN THIS
AFTERNOON. NEAR AND BEHIND THE TROUGH (WHICH STRETCHES FROM CHEBOYGAN
TO CADILLAC TO FREMONT) THERE ARE PLENTY OF BOTH CUMULUS AND
STRATOCUMULUS WITH BASES RANGING FROM NEAR 2,000 FEET AT CADILLAC
TO 4,000 TO 5,000 FEET. WE ARE EXPECTING MAINLY VFR CEILINGS
ABOVE 3,500 FEET AT THE TAF SITES THIS AFTERNOON. AS WE MOVE
TOWARDS EVENING WE EXPECT ALL OF THE TAF SITES TO SCATTER OUT AND
CLEAR, BETWEEN 22Z AND 02Z.
CLEAR SKIES WILL PREVAIL OVERNIGHT WITH SOME ALTOCUMULUS SHOWING
UP TOWARDS DAYBREAK WITH BASES NEAR AND ABOVE 9,000 FEET. THESE
CONDITIONS WILL PERSIST THROUGH THE MORNING HOURS OF WEDNESDAY.
SOUTHWEST TO WEST WINDS THIS AFTERNOON OF 10 TO 20 KNOTS WILL
SUBSIDE QUICKLY THIS EVENING BECOMING LIGHT TONIGHT. WINDS RAMP UP
QUICKLY LATE TONIGHT AFTER 09Z WITH SOUTHWEST WINDS OF 15-30
KNOTS DEVELOPING. WINDS WILL PEAK AROUND 18Z ON WEDNESDAY WITH
GUSTS TOWARDS 30 KNOTS POSSIBLE.
MARINE
ISSUED AT 327 PM EDT TUE JUN 10 2025
THE MAIN FOCUS OF THE MARINE FORECAST IS A PERIOD OF STRONGER
SOUTHWEST FLOW THAT DEVELOPS LATE TONIGHT AND PERSISTS INTO
WEDNESDAY. WE HAVE OPTED TO ISSUE BOTH A BEACH HAZARDS STATEMENT AND
A SMALL CRAFT ADVISORY FROM 600AM WEDNESDAY TO 400PM WEDNESDAY.
WINDS INCREASE TO 40 KNOTS AT 1,000 FEET. ALL OF THIS WIND WILL NOT
MIX DOWN, BUT WE FEEL SOUTHWEST WINDS TO 15-25 KNOTS ARE LIKELY
WHICH SHOULD RESULT IN A 3-5 FOOT WAVE FIELD NORTH OF SOUTH HAVEN.
HIGHEST WAVES WILL BE NORTH OF HOLLAND. THESE CONDITIONS WILL BE
HAZARDOUS TO BOTH SWIMMERS AND BOATERS. THERE IS SOME CONCERN THAT
THIS WIND BEING PRIMARILY WARM AIR ADVECTION MAY NOT MIX DOWN WELL,
BUT WE FELT CONFIDENT ENOUGH TO GO WITH THE HEADLINES. BEYOND THE
WEDNESDAY EVENT, WINDS AND WAVES ARE LIKELY BELOW ADVISORY TYPE
CRITERIA WEDNESDAY NIGHT INTO FRIDAY MORNING.
GRR WATCHES/WARNINGS/ADVISORIES
MI...BEACH HAZARDS STATEMENT FROM WEDNESDAY MORNING THROUGH WEDNESDAY
AFTERNOON FOR MIZ037-043-050-056-064.
AIR QUALITY ALERT FROM MIDNIGHT TONIGHT TO MIDNIGHT EDT
WEDNESDAY NIGHT FOR MIZ050-056-057-064-071.
MARINE...SMALL CRAFT ADVISORY FROM 6 AM TO 4 PM EDT WEDNESDAY FOR
LMZ845>849.
DISCUSSION...THOMAS
AVIATION...DUKE
MARINE...THOMAS
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