874
FXUS63 KGRR 091154
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
754 AM EDT SAT AUG 9 2025
KEY MESSAGES
- HOT AND HUMID WITH CHANCES FOR STORMS THROUGH SUNDAY
- RAIN CHANCES LATE MONDAY THROUGH TUESDAY
- TEMPS CLOSER TO NORMAL WITH DRIER AIR MASS LATE NEXT WEEK
DISCUSSION
ISSUED AT 330 AM EDT SAT AUG 9 2025
- HOT AND HUMID WITH CHANCES FOR STORMS THROUGH SUNDAY
LATEST RADAR HAS A LINE OF SHOWERS AND STORMS ALONG A MID LEVEL
MOISTURE BOUNDARY THAT IS ASSOCIATED WITH A NEGATIVELY TILTED MID
LEVEL SHORT WAVE. THAT TROUGH IS DUE TO AN UPPER LEVEL LOW
SITUATED OVER SOUTHERN CANADA, JUST NORTH OF THE US AND CANADIAN
BORDER. THAT LOW WILL CONTINUE TO MOVE ALONG THE BORDER AS IT
PROGRESSES EASTWARD.
A POSITIVELY TILTED RIDGE EXTENDING THROUGH THE MID ATLANTIC WILL
CONTINUE TO BRING STRONG, HUMID, SOUTHERLY FLOW THROUGH LOWER
MICHIGAN THIS WEEKEND. THIS WILL KEEP MAX TEMPS 10 TO 15 DEGREES
ABOVE NORMAL AND HEAT INDICES INTO THE MID TO UPPER 90S. AS
STATED BEFORE, HOWEVER, IT SHOULD REMAIN BELOW HEAT ADVISORY
CRITERIA.
THE BOUNDARY BETWEEN THE TWO ABOVE MENTIONED AIR MASSES WILL
EXTEND THROUGH THE UPPER GREAT LAKES. AS THE GRADIENT TIGHTENS,
WINDS WILL CONTINUE TO INCREASE. THAT WILL BRING WIND GUSTS
UPWARDS OF 25 MPH THIS AFTERNOON.
WHILE HOT, HUMID AIR WILL MOVE OVER THE AREA THIS AFTERNOON, THE
UPPER LEVEL RIDGE, WHICH LATEST MODELS HAVE FAIRLY DRY MID
LEVELS, SHOULD STIFLE CONVECTION TODAY.
THE EXCEPTION WILL BE ALONG THE BOUNDARY THAT WILL CLIP THE
WESTERN PORTION OF UPPER LOWER MICHIGAN AND WILL INCLUDE THE NW
COUNTIES CONTAINING THE POINTS. FOR THESE REASONS, AMONG OTHERS,
SPC HAS UPGRADED THIS REGION TO A MARGINAL RISK FOR SEVERE STORMS
UNTIL 12Z SUNDAY.
THE BEST CHANCE WILL BE LATE SATURDAY, EARLY SUNDAY AS THE HIGH
BREAKS DOWN AND MEAGERLY TREKS EASTWARD. MOISTURE CONVERGENCE
SHOULD COUPLE WITH THE WARM FLOW AND SHOULD BE AIDED BY SHORTWAVES
AND A LOW LEVEL JET THOUGH THERE REMAINS SOME QUESTION ABOUT ITS
STRENGTH AND TIMING.
THE HIGH WILL KEEP THE LOW IN CHECK WITH MOISTURE STREAMING IN
THE ABOVE MENTIONED REGION. SOME PRECIPITATION SHOULD CONTINUE
THROUGH THE WESTERN PORTIONS OF SOUTHERN MICHIGAN INTO MONDAY
MORNING. HOWEVER, GIVEN THE LACK OF INSTABILITY SPC HAS KEPT THE
REGION ONLY IN GENERAL THUNDER.
- RAIN CHANCES LATE MONDAY THROUGH TUESDAY
THE UPPER LEVEL LOW WILL CONTINUE TO MOVE TO THE EAST AS THE HIGH
FINALLY WEAKENS. THE BEST CHANCE FOR WIDESPREAD MOISTURE WILL
COME LATE MONDAY INTO TUESDAY AS STRONG AREAS OF POTENTIAL ENERGY
SHOULD COUPLE WITH ANOMALOUS PWATS UPWARDS OF 1.5 TO 2 INCHES
ACCORDING TO NAEFS. THERE IS A COPIOUS AMOUNT OF MOISTURE WITH
THIS SYSTEM. WHILE NOT IN OUR AREA, WPC HAS ISSUED A MODERATE
EXCESSIVE RAINFALL OUTLOOK SUNDAY NIGHT INTO MONDAY FOR IOWA AND
NORTHWESTERN ILLINOIS. THAT AIR MASS WILL THEN MOVE INTO SOUTHERN
MICHIGAN. DUE TO THIS, LOWER MICHIGAN IS IN THE DAY 4 MARGINAL
RISK FOR EXCESSIVE RAINFALL. SO WILL NEED TO KEEP WATCH AS THIS
SITUATION DEVELOPS.
- TEMPS CLOSER TO NORMAL WITH DRIER AIR MASS LATE NEXT WEEK
MODELS CONTINUE TO BE UNCERTAIN PAST TUESDAY. HOWEVER, LINGER
SHOWERS EARLY WEDNESDAY ASIDE, THE SECOND HALF OF THE WEEK IS
TRENDING DRIER, WITH TEMPERATURES CLOSER TO NORMAL.
AVIATION /12Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 745 AM EDT SAT AUG 9 2025
VFR WILL CONTINUE TO DOMINATE THROUGH THE TAF PERIOD. THERE IS A
CHANCE FOR SOME SHOWERS AND STORM LATE SATURDAY NIGHT INTO SUNDAY.
HOWEVER THEY SHOULD REMAIN TO THE NORTHWEST OF THE TAF SITES.
WINDS WILL INCREASE LATE THIS MORNING OUT OF THE SOUTH AND SUBSIDE
THIS EVENING, AROUND 00Z.
MARINE
ISSUED AT 300 AM EDT SAT AUG 9 2025
A MODERATE TO HIGH SWIM RISK WILL BE BUILD THIS MORNING NORTH OF
GRAND HAVEN WITH SOUTH WINDS 15 TO 25 KNOTS. THIS WILL BUILD WAVES
INTO AT LEAST THE 2 TO 4 FT RANGE AND POSSIBLY 3 TO 5 FEET. IT'S
POSSIBLE THAT WITH THE HOT WEATHER OVER THE WEEKEND, THE
RELATIVELY COOLER (70 DEGREE) WATER TEMPERATURES MAY CREATE A BIT
OF STABILITY IN THE LOWER ATMOSPHERE WHICH WOULD SUBDUE THE HIGHER
END OF THE WIND FORECAST RANGE AND THUS KEEP WAVES MORE SO IN THE
2 TO 4 FOOT RANGE, WHICH IS STILL A MODERATE SWIM RISK, AS
CURRENTS IN THE WATER MOVING ALONG-SHORE AND OUT AGAINST SOUTH
PIER STRUCTURES WILL ALSO EXIST.
THUNDERSTORMS FROM WISCONSIN COULD ATTEMPT TO CROSS LAKE MICHIGAN
SATURDAY AFTERNOON OR EVENING. IT'S LIKELY THEY WILL DIMINISH IN
INTENSITY AS THEY DO SO, BUT COULD PRODUCE AN AREA OF GUSTY WINDS
AND WIND SHIFTS IN THEIR WAKE.
GRR WATCHES/WARNINGS/ADVISORIES
MI...BEACH HAZARDS STATEMENT FROM 11 AM EDT THIS MORNING THROUGH THIS
EVENING FOR MIZ037-043-050.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM THIS MORNING TO 11 PM EDT THIS
EVENING FOR LMZ847>849.
DISCUSSION...CERU
AVIATION...CERU
MARINE...CERU
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page