287
FXUS63 KGRR 030556
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
156 AM EDT THU SEP 3 2026
KEY MESSAGES
- HEAT THROUGH THIS EVENING, SOME STORMS OVERNIGHT
- PERIODIC STORMS THURSDAY AFTERNOON INTO LATE NIGHT
- SHORT BREAK MIDDAY FRIDAY, THEN MORE RAIN CHANCES
DISCUSSION
ISSUED AT 254 PM EDT WED SEP 2 2026
- HEAT THROUGH THIS EVENING, SOME STORMS OVERNIGHT
SURFACE DEW POINTS HAVE OVERACHIEVED THIS AFTERNOON COMPARED TO MOST
MODEL GUIDANCE, AND AS A RESULT HEAT INDICES HAVE NUDGED HIGHER.
WIDESPREAD INDICES OF 95 TO 100 ARE OCCURRING AND WILL CONTINUE TO
OCCUR ACROSS SOUTHERN LOWER MICHIGAN THROUGH THIS AFTERNOON AND
EVENING GIVEN AIR TEMPS IN THE UPPER 80S TO LOW 90S AND DEW POINTS
OF 70 TO 75 MAKING IT FEEL PRETTY MISERABLE IN THE SUN. REDUCE
STRENUOUS OUTDOOR ACTIVITIES THROUGH THE EVENING.
IN SPITE OF FAVORABLE MLCAPE VALUES OF 1500-2500 J/KG THIS AFTERNOON
AS WELL AS 0-6 KM SHEAR VALUES OF 40-50 KTS, SOME MLCIN OF 100-200
J/KG IS STILL PRESENT NORTH OF I-96 WHERE SOME CONVECTION HAS
OCCURRED BUT HAS LARGELY BEEN HELD IN CHECK. A LLJ OF 30-35 KTS IS
PRESENT OVERHEAD OUR REGION, THOUGH IT IS MORE CONVERGENT OVER SE
LOWER MICHIGAN TOWARD THE THUMB REGION. THAT IS WHERE SCATTERED
STRONG TO SEVERE STORMS ARE MOST LIKELY TO DEVELOP INTO THIS
EVENING. MUCH OF OUR REGION WILL BE STORM FREE THROUGH EARLY TONIGHT
WITH THE EXCEPTION OF NORTH OF M-20 AND NEAR/EAST OF US 127.
BEYOND MIDNIGHT TONIGHT, THE LLJ OVER WISCONSIN INCREASES BACK TO 30-
35 KTS AND ANGLES OVER LAKE MICHIGAN. SCATTERED SHOWERS/STORMS MAY
DEVELOP ESPECIALLY FROM MUSKEGON TO LANSING DURING THE 05Z-12Z TIME
FRAME. MOST ARE NOT LIKELY TO REACH SEVERE LEVELS. MODEL SOUNDINGS
DO SUPPORT GOOD CAPE THROUGH THE HAIL GROWTH REGION BUT AN INVERSION
AROUND 850 MB WILL LIKELY (THOUGH NOT WITH 100% CERTAINTY) LIMIT
DAMAGING WIND POTENTIAL. LOCALIZED DOWNPOURS MAY LEAD TO A FEW MINOR
LOWLAND AND/OR STREET FLOODING OCCURRENCES OVERNIGHT.
- PERIODIC STORMS THURSDAY AFTERNOON INTO LATE NIGHT
THERE ARE SOME MIXED SIGNALS REGARDING THURSDAY'S DAYTIME STORM
CHANCES, LEADING TO LESS CONFIDENCE THAN DESIRED (EG. NBM POPS ARE
AROUND 30%). DEEP LAYER SHEAR OF AROUND 40 KTS WILL BE PRESENT NORTH
OF I-96. HREF MEAN SBCAPE VALUES ARE LESS SUBSTANTIAL THAN TODAY BUT
STILL 1000-2000 J/KG. WE DO HAVE UPPER JET DIVERGENCE MOVING THROUGH
WHICH COULD AID IN THE DEVELOPMENT OF SOME ORGANIZED CONVECTION
DURING THE MIDDAY TO AFTERNOON PERIOD. THE LOW LEVEL JET WEAKENS TO
20-25 KTS. THERE IS AN INCOHERENT SIGNAL AMONGST HREF MEMBERS AS TO
THE PLACEMENT AND INTENSITY OF CONVECTION TOMORROW. THE HRRR/RRFS DO
BRING IN SOME ORGANIZED SWATHS OF STORMS WITH 60+ MPH GUSTS DURING
THE AFTERNOON, WHILE THE OTHER CAMS ARE NOT SUPPORTIVE. AT THIS
POINT, THE SPC MARGINAL RISK SEEMS TO COVER THE SPATIAL THREAT WELL,
WITH SOME ISOLATED/SCATTERED INSTANCES OF STRONG WIND GUSTS AND HAIL
POSSIBLE.
AFTER 00Z, A STRONGER NOCTURNAL LLJ DEVELOPS TO OUR WEST AND ANGLES
IN DURING THE LATE NIGHT HOURS. VERY HIGH PWAT VALUES ARE SHOWN BY
THE 12Z ECMWF DURING THIS TIME, WITH 2.00-2.50" MOVING IN. VERY
HEAVY DOWNPOURS AND SOME STREET FLOODING MAY DEVELOP IF ORGANIZED
CONVECTION GETS GOING ON THE NOSE OF THE LLJ THURSDAY NIGHT INTO
FRIDAY MORNING. LARGE HAIL ALSO LOOKS TO BE A THREAT WITH THESE
POTENTIAL STORMS.
- SHORT BREAK MIDDAY FRIDAY, THEN MORE RAIN CHANCES
A DECENT MODEL SIGNAL EXISTS FOR A BREAK IN THE RAIN CHANCES LATE
FRIDAY MORNING INTO THE EARLY AFTERNOON PERIOD. DAYTIME HEATING ON
FRIDAY COULD BRING SOME POP-UP SHOWERS AND THUNDERSTORMS BY
EVENING WITH PERHAPS ADDITIONAL RAIN CHANCES OVERNIGHT ALONG A
POTENTIAL SURFACE BOUNDARY IN THE AREA.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 156 AM EDT THU SEP 3 2026
SKIES ARE PARTLY CLOUDY AS WE APPROACH 06Z ACROSS SOUTHWEST LOWER
MICHIGAN WITH VFR BASES. THE CLOUDS ARE GENERALLY IN THE 5,000 TO
10,000 FOOT LAYER AND ARE ASSOCIATED WITH A WEAK FRONT IN THE
AREA. THE FRONT IS PRODUCING SHOWERS AND A FEW THUNDERSTORMS
MAINLY NEAR I-96. THERE IS A CHANCE THESE SHOWERS AND STORM EXPAND
THROUGH THE REMAINDER OF THE NIGHT AND WE WILL BE WATCHING THAT
CLOSELY. OTHERWISE SOME PATCHY LIGHT FOG HAS FORMED ACROSS THE
AREA.
AS WE PROGRESS INTO THE DAYTIME HOURS OF THURSDAY, THE SHOWERS AND
STORMS THAT DEVELOP OVERNIGHT WILL LIKELY END WITH VFR WEATHER
EXPECTED. ANOTHER ROUND OF HEAT OF THE DAY SHOWERS AND STORMS WILL
BE POSSIBLE DURING THE AFTERNOON 18Z-22Z.
MARINE
ISSUED AT 245 PM EDT WED SEP 2 2026
NO HAZARDOUS WINDS OR WAVES ARE EXPECTED FOR THE NEXT SEVERAL
DAYS WITH THE HIGHEST WAVES OF UP TO 2 FEET OCCURRING THIS
EVENING. HOWEVER, MARINERS WILL NEED TO BE AWARE OF THUNDERSTORM
CHANCES THROUGH SATURDAY.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...HOVING
AVIATION...DUKE
MARINE...HOVING
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