772
FXUS63 KGRR 180548
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
148 AM EDT THU SEP 18 2025
KEY MESSAGES
- VERY WARM TEMPERATURES AGAIN ON THURSDAY.
- A LITTLE COOLER FRIDAY INTO SATURDAY. WARMER WITH INCREASING RAIN
CHANCES BY THE END OF THE WEEKEND.
DISCUSSION
ISSUED AT 318 PM EDT WED SEP 17 2025
MID LEVEL RIDING AND SFC HIGH PRESSURE OVERHEAD WILL SUPPORT LIGHT
AND VARIABLE WINDS AND OPTIMAL RADIATIONAL COOLING TONIGHT, ALLOWING
NIGHTTIME MINS TO DROP DOWN INTO THE 50S. FOG POTENTIAL TONIGHT WILL
BE THROUGH RADIATIONAL PROCESSES AND MOST FAVORABLE IN LOW LYING
AREAS. MID LEVEL SHORT WAVE ENERGY WILL CAUSE SOME SUPPRESSION OF
THE MID LEVEL RIDGE AXIS ACROSS THE NORTHERN GREAT LAKES TONIGHT AND
WILL DRIVE A WEAK COLD FRONT SOUTH INTO CENTRAL LOWER MI BY LATE
THURSDAY AFTERNOON. AN AXIS OF LOW LEVEL MOISTURE IS FORECAST TO
ADVECT INTO THE FRONTAL BOUNDARY AND RESULT IN WEAK INSTABILITY AS
THE FRONT ADVANCES INTO CENTRAL LOWER MI. HI RES MODEL GUIDANCE
SUGGESTS ENHANCED LOW LEVEL FRONTAL CONVERGENCE AIDED BY FLOW OFF
SAGINAW BAY WILL RESULT IN SCATTERED LATE DAY CONVECTION ACROSS THE
TRI CITIES, MT PLEASANT AND CLARE. A FEW SOLUTIONS ACTUALLY SUGGEST
SOME RESIDUAL CONVECTION PUSHING SOUTHWARD TOWARD FLINT AND LANSING
BY EVENING WITH SOME EROSION OF THE MID LEVEL CAP. OTHERWISE
PREFRONTAL WARMTH AND RESPECTABLE MIXING HEIGHTS WILL RESULT IN
ANOTHER VERY WARM DAY WITH HIGHS POSSIBLY WELL INTO THE 80S.
MID LEVEL RIDGING IS FORECAST RE EXPAND ACROSS LOWER MI THURS NIGHT
INTO FRIDAY. THE STRENGTH OF THE NORTHEASTERLY GRADIENT ACROSS LAKE
HURON WILL HOLD THE LOWER TROPOSPHERIC FRONT OVER LOWER MI DESPITE
THE INCREASING MID LEVEL HEIGHT FIELD. THIS WILL RESULT IN A
RESPECTABLE THERMAL GRADIENT ACROSS SOUTHERN MICHIGAN. LOCATIONS
AROUND KALAMAZOO AND BATTLE CREEK ARE LIKELY TO REMAIN IN THE WARM
SECTOR, RESULTING IN HIGHS IN THE LOW 80S AGAIN WHILE TEMPS FROM
CENTRAL MICHIGAN ACROSS THE THUMB REGION MAY BE STUCK IN THE 60S.
THE DEPTH OF MOISTURE TRAPPED UNDER A DEEP FRONTAL INVERSION WILL
RESULT IN MORE CLOUD COVER ACROSS MUCH OF THE AREA. MODEL SOUNDINGS
HAVE SOME INDICATIONS OF A DRIZZLE POTENTIAL THURS NIGHT INTO FRIDAY
FROM CENTRAL MICHIGAN/TRI CITIES ACROSS THE THUMB.
THE BLOCKING PATTERN WHICH HAS HELD STRONG MID LEVEL RIDGING
OVERHEAD FOR THE LAST WEEK WILL GRADUALLY BREAK DOWN THIS WEEKEND AS
THE MID LEVEL FLOW BECOMES MORE PROGRESSIVE. THE UPPER LOW NOW OVER
THE NORTHERN PLAINS WILL LIFT ACROSS THE NORTHERN GREAT LAKES THIS
WEEKEND, DRIVING MID LEVEL HIGH FALLS ACROSS LOWER MI. SOUTHERLY
FLOW WILL ALSO ADVECT A LITTLE DEEPER MOISTURE INTO THE GREAT LAKES
TOWARD SUNDAY, WARRANTING A THE NEXT CHANCE FOR RAIN. RESIDUAL LOW
LEVEL DRY AIR ASSOCIATED WITH DEPARTING HIGH PRESSURE TO THE EAST
SUPPORT A CONTINUED DRY FORECAST THROUGH AT LEAST THE AFTERNOON
SATURDAY.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 148 AM EDT THU SEP 18 2025
CALM TO LIGHT AND VARIABLE WINDS CONTINUE INTO THURSDAY MORNING
WITH A BRIEF WINDOW AROUND SUNRISE FOR SLIGHTLY REDUCED
VISIBILITIES. WINDS BECOME MORE NORTHWESTERLY THIS AFTERNOON WITH
FEW TO SCT CUMULUS AROUND 4000 TO 6000 FEET EXPECTED THIS
AFTERNOON. ANY SHOWERS AND THUNDERSTORMS THIS AFTERNOON LOOK TO BE
NORTH OF TAF SITES, BUT GRR AND LAN HAVE A 20 PERCENT CHANCE THIS
AFTERNOON WITH BETTER CHANCES TO THE NORTH. WINDS THEN SHIFT TO
THE NORTHEAST THURSDAY NIGHT BEHIND THE COLD FRONT. THERE IS THE
POTENTIAL FOR FOG TO DEVELOP THURSDAY NIGHT INTO FRIDAY MORNING
ACROSS MUCH OF THE AREA.
MARINE
ISSUED AT 328 AM EDT WED SEP 17 2025
WINDS BUILD TOMORROW BEHIND THE BACKDOOR COLD FRONT WITH
NORTHERLY WINDS AROUND 10 TO 20 KNOTS. EASTERLY WINDS THEN RETURN
UNTIL MORE SOUTHWESTERLY FLOW DEVELOPS SUNDAY AND CONTINUES INTO
NEXT WEEK. WITH THIS CHANGE IN THE WIND THERE WILL ALSO BE CHANCES
FOR SHOWERS AND EVEN A FEW THUNDERSTORMS. AT THIS TIME SMALL
CRAFT ADVISORY CONDITIONS ARE NOT EXPECTED OVER THE NEXT WEEK.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...RAH
AVIATION...RAH
MARINE...RAH
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page