019
FXUS63 KGRR 040610
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
210 AM EDT FRI SEP 4 2026
KEY MESSAGES
- SHOWERS/STORMS THROUGH LATE AFTERNOON, THEN OVERNIGHT/FRIDAY AM
- LIKELY DRY FRIDAY AFTERNOON; SCATTERED STORMS POSSIBLE LATE
DISCUSSION
ISSUED AT 231 PM EDT THU SEP 3 2026
- SHOWERS/STORMS THROUGH LATE AFTERNOON, THEN OVERNIGHT/FRIDAY AM
THROUGH THE END OF THE AFTERNOON, THE MOST CONCENTRATED AREAS FOR
STRONGER CONVECTION WILL BE NEAR/NORTH OF I-96 AND EAST OF US 131
WHERE SCATTERED DAMAGING WIND GUSTS AND LARGE HAIL WILL BE POSSIBLE.
IN THIS REGION, EFFECTIVE SHEAR VALUES OF 40-45 KTS ARE PRESENT
ALONG WITH SBCAPE OF 2000-3000 J/KG. SURFACE VORTICITY ENHANCEMENTS
ALONG ANY OUTFLOW BOUNDARIES COULD ALSO AID IN A ROTATIONAL
COMPONENT TO STRONGER THUNDERSTORMS WITH A TORNADO NOT OUT OF THE
QUESTION ESPECIALLY ACROSS CENTRAL AND SOUTH CENTRAL LOWER MI. THERE
IS A CAM SIGNAL FOR SOME SWATHS OF CONVECTIVE WIND GUSTS EXCEEDING
60 MPH EAST OF US 131 INTO LATE AFTERNOON OR EARLY EVENING BEFORE
ENDING.
REDEVELOPMENT OF OVERNIGHT STORMS IS QUITE LIKELY. THIS ROUND OF
STORMS WILL BE FUELED BY AN INCREASING LLJ (30-40 KTS) OVER
WISCONSIN THAT WILL MOVE OUR DIRECTION, INTERSECTING A LARGELY
STATIONARY BOUNDARY OVER THE REGION. MODEL SIM REFS ARE INDICATING A
FEW POSSIBLE OUTCOMES INCLUDING A QLCS OR ELONGATED/TRAINING
CONVECTIVE EVENT, THE LATTER BEING MORE CONCERNING IN TERMS OF AN
URBAN AND POOR DRAINAGE FLOOD RISK. AREAS THAT WOULD BE MOST
SUSCEPTIBLE TO LOCALIZED FLOODING OVERNIGHT AND INTO FRIDAY MORNING
WOULD BE ALONG US 10 (WHERE 1"-2" OCCURRED TODAY) AS WELL AS THE
GREATER LANSING AREA WHERE SEVERAL ROUNDS OF THUNDERSTORMS HAVE
OCCURRED. HREF 6 HR PMM RAINFALL INDICATES 1"-2" ESPECIALLY NEAR AND
WEST OF US 131, THOUGH MAX 6 HR QPF FROM THE MEMBERSHIP INDICATES
AREAS OF 2"-3" OR SLIGHTLY MORE. PLACEMENT IS NOT CERTAIN AT THIS
TIME, AND COULD SHIFT EAST. IN TERMS OF A QLCS RISK, THERE IS
SOME SIGNAL FOR THIS TO OCCUR IN THE 09Z-13Z FRIDAY TIME FRAME.
NAM3KM AND HRRR SOUNDINGS AHEAD OF THIS POTENTIAL FEATURE INDICATE
400-500 J/KG OF CIN, LIKELY INDICATING STRONG WINDS WILL NOT MIX
DOWN TO THE SURFACE. HAIL AND HEAVY DOWNPOURS/LOCALIZED FLOODING
WOULD BE MORE LIKELY THREATS.
- LIKELY DRY FRIDAY AFTERNOON; SCATTERED STORMS POSSIBLE LATE
THE SURFACE BOUNDARY IN PLACE TODAY LOOKS TO SLIDE SOUTH TOWARD I-94
AND THE MI/IN BORDER BY LATE FRIDAY. SUBSIDENCE IN THE WAKE OF
MORNING RAIN ON FRIDAY WILL LIKELY INHIBIT CONVECTIVE DEVELOPMENT
FRIDAY AFTERNOON OUTSIDE OF AN ISOLATED POP UP SHOWER OR STORM THAT
COULD OCCUR ON ANY RESIDUAL OUTFLOW BOUNDARIES THAT REMAIN IN PLACE
DURING DAYTIME HEATING. PREDICTABILITY OF THESE IS LOW. BEST
INDICATIONS ARE SCATTERED SHOWERS AND THUNDERSTORMS COULD DEVELOP
LATE AFTERNOON/EVENING AND INTO FRIDAY NIGHT NEAR AND SOUTH OF A
GRAND RAPIDS TO LANSING LINE AFTER SUFFICIENT DAYTIME HEATING. A
HRRR SOUNDING NEAR LANSING AROUND 21Z INDICATES QUITE A BIT OF DCAPE
AT 1200 J/KG WITH FAIRLY SUBSTANTIAL 0-3 KM SHEAR OF 35 KTS. AN
ISOLATED SEVERE THUNDERSTORM CANNOT BE RULED OUT NEAR AND SOUTH OF
GRR TO LAN WITH DAMAGING WIND GUSTS THE PRIMARY HAZARD.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 209 AM EDT FRI SEP 4 2026
ANOTHER NIGHT OF PATCHY FOG IN PLACE AT 06Z, SOME OF WHICH IS
LOCALLY DENSE WITH VISIBILITIES AROUND 1/2 MILE. WE MAY SEE SOME
MVFR FOG AT THE TAF SITES EARLY THIS MORNING BUT IN LARGE PART THE
LOWER CEILINGS AND VISIBILITIES ASSOCIATED WITH FOG SHOULD REMAIN
OVER CENTRAL LOWER MICHIGAN.
THE BIGGER THREAT TO AVIATION INTERESTS WILL BE THUNDERSTORMS.
STORMS HAVE BEEN WORKING THIS WAY THROUGH WISCONSIN OVERNIGHT AND
WE EXPECT THAT TREND TO CONTINUE. SHOWERS AND THUNDERSTORMS SHOULD
MOVE INTO THE AREA BETWEEN 07Z AND 10Z AND CONTINUE INTO THE
DAYLIGHT HOURS OF FRIDAY MORNING. BY 16Z TO 18Z THE STORMS SHOULD
BE MOVING OFF TO THE SOUTH AND EAST OF THE AREA. MVFR CONDITIONS
AS THE STORMS MOVE THROUGH ARE LIKELY WITH IFR AND LOWER CERTAINLY
POSSIBLE. VERY HEAVY RAIN RATES ARE POSSIBLE WHICH WILL AFFECT
VISIBILITY AS WELL AS THE POTENTIAL FOR STRONGER WINDS (IN EXCESS
OF 40 KNOTS) AND HAIL (TO AROUND 1" IN DIAMETER).
VFR WEATHER WILL RETURN THIS AFTERNOON IN THE WAKE OF THE MORNING
THUNDERSTORM ACTIVITY. BOTTOM LINE...WE ARE LOOKING AT ACTIVE
WEATHER AT THE TAF SITES ESPECIALLY BETWEEN 08Z AND 16Z.
MARINE
ISSUED AT 231 PM EDT THU SEP 3 2026
WINDS AND WAVES SHOULD STAY BELOW HAZARDOUS LEVELS FOR MARINERS
THROUGH THE WEEKEND. MARINERS SHOULD STAY ABREAST OF THUNDERSTORM
POTENTIAL FROM THIS AFTERNOON INTO FRIDAY NIGHT AND HAVE PLANS TO
SEEK SAFE HARBOR WHEN NECESSARY.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...HOVING
AVIATION...DUKE
MARINE...HOVING
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