865
FXUS63 KGRR 011742
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
142 PM EDT WED JUL 1 2026
KEY MESSAGES
- HOT AND HUMID CONDITIONS CONTINUE
- CHANCES FOR THUNDERSTORMS NEXT SEVERAL DAYS
DISCUSSION
ISSUED AT 404 AM EDT WED JUL 1 2026
- HOT AND HUMID CONDITIONS CONTINUE
WILL MAINTAIN THE ONGOING HEAT WARNING AS IS THROUGH THURSDAY.
CONDITIONS DO NOT LOOK TO CHANGE MUCH IN TERMS OF HEAT INDEX
VALUES GIVEN THE COMBINATION OF WARMTH AND HUMIDITY. 850MB
TEMPERATURES REMAIN NEAR OR ABOVE +20C RIGHT THROUGH FRIDAY
ACTUALLY. DEPENDING ON CLOUD AND PRECIPITATION TRENDS WE MAY NEED
TO EXTEND THE HEADLINE INTO FRIDAY. A COMBINATION OF GFS AND ECMWF
MOS NUMBERS IS LIKELY THE WAY TO GO WHICH PUTS HIGHS IN MOST AREAS
IN THE 90 TO 95 DEGREE RANGE AT LEAST THROUGH THURSDAY. OVERNIGHT
LOWS WILL NOT PROVIDE ANY RELIEF WITH MULTIPLE SITES YESTERDAY
TYING RECORD WARM LOWS, AZO AND BTL AT 76 DEGREES. THE OLD
RECORDS WERE SET IN 2018 AT BOTH SITES. DEW POINTS ARE IN THE 72
TO 75 DEGREE RANGE ACROSS THE AREA AT 400AM AND THIS WILL NOT
CHANGE MUCH EITHER THE NEXT DAY OR TWO. THERE IS A CHANCE OF
SEEING THE DEW POINTS RISE A BIT AS THE STATIONARY BOUNDARY SAGS
OUR DIRECTION. HEAT INDEX VALUES LOOK TO TOP OUT IN THE 100 TO 105
RANGE AT MANY LOCATIONS TODAY AND TOMORROW (POSSIBLY FRIDAY).
BOTTOM LINE THE HEAT WARNING LOOKS GOOD.
- CHANCES FOR THUNDERSTORMS NEXT SEVERAL DAYS
CONVECTIVE TRENDS THE NEXT FEW DAYS ARE NOT AS STRAIGHT FORWARD
AS THE HEAT FORECAST. THE FOCUS THIS MORNING IS ON THE CONVECTION
IN THE PLAINS STATES OVER SD/MN AND IA AT 400AM. THIS COMPLEX OF
STORMS IS EXPECTED TO MOVE EAST AND POTENTIAL TAKE AIM ON CENTRAL
LOWER MICHIGAN LATE THIS AFTERNOON AND EVENING. MODELS ALSO
INDICATE THE POTENTIAL FOR DEVELOPMENT AHEAD OF THE COMPLEX WITH
THESE STORMS ALSO POSSIBLY MOVING INTO CENTRAL LOWER. THE TRUSTY
HREF IS NOT SHOWING SIGNIFICANT ACTIVITY INTO OUR FORECAST AREA
THE NEXT 24 HOURS WITH SOME CONVECTION CERTAINLY POSSIBLE IN THE
NORTHERN HALF OF THE FORECAST AREA (OR NEAR/NORTH OF I-96). THE
FACTOR THAT MAY BE MORE TELLING THAN THE CONVECTION ALLOWING
MODELS HOWEVER THE LOW LEVEL JET. ALL MODELS SHOW AN INCREASE IN
THE 850MB LLJ THIS AFTERNOON AND ESPECIALLY THIS EVENING. SO, WE
WILL RELY ON THE CONCEPTUAL MODEL THAT AN INCREASING LLJ IN
SOUTHWEST LOWER MICHIGAN USUALLY YIELDS SHOWER/THUNDERSTORM
DEVELOPMENT. THE MAIN TIME FRAME OF CONCERN WILL BE THIS AFTERNOON
AND EVENING NEAR/NORTH OF I-96 WITH WIND BEING THE PRIMARY HAZARD
ALONG WITH LOCALLY HEAVY RAIN GIVEN PWAT VALUES OF 1.5+ INCHES.
BEYOND TODAY, ADDITIONAL SHOWER AND THUNDERSTORM CHANCES LOOK TO
CONTINUE OFF AND ON THROUGH SUNDAY. A STATIONARY BOUNDARY SAGS
INTO THE REGION FROM THE NORTH FROM TODAY INTO THURSDAY AND LIKELY
REMAINS NEARBY THROUGH SUNDAY. THIS FRONT WILL LIKELY BE A FOCUS
FOR STORMS AS WILL PERIODIC LARGELY CONVECTIVELY DRIVEN SHORTWAVES
WORKING THROUGH A SOUTHWEST FLOW INITIALLY THAT TRANSITIONS TO
ZONAL WITH TIME.
SPC HAS CENTRAL LOWER MICHIGAN IN AN ENHANCED RISK FOR SEVERE
WEATHER TODAY AND PORTIONS OF THE AREA IN A SLIGHT RISK FOR
THURSDAY. CONFIDENCE IN THE MORPHOLOGY OF THE CONVECTION IS NOT
HIGH THE NEXT 48 HOURS BUT THERE IS POTENTIAL FOR SEVERE WEATHER
FOR SURE.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 142 PM EDT WED JUL 1 2026
NO SIGNIFICANT CHANGES FOR THIS UPDATE. WE EXPECT ABOUT A 90 PERCENT
CHANCE OF VFR CONDITIONS AT ALL THE TERMINALS THOUGH 00Z...EXCEPT
FOR 75 PERCENT AT MKG. WE CURRENTLY ARE WATCHING A SUPERCELL
THUNDERSTORM OVER WISCONSIN THAT HAS ABOUT A 30 PERCENT CHANCE OF
MAKING IT ACROSS LAKE MICHIGAN AND A LESSER CHANCE THAN THAT OF
AFFECTING THE MKG TERMINAL PRIOR TO 21Z.
WE EXPECT SYNOPTIC WIND GUSTS TO RESUME SHORTLY AND LAST INTO
EARLY EVENING. PREDICTABILITY FOR THUNDERSTORMS AFTER 00Z REMAINS
POOR WITH A WIDE VARIETY OF MODEL SOLUTIONS. WE CARRIED A PROB30
FOR SOME TERMINALS AFTER 06Z TONIGHT FOR REMNANT, OUTFLOW-DRIVEN
CONVECTION. BUT AGAIN, THERE REMAINS IS A LOT OF UNCERTAINTY
INVOLVED.
MARINE
ISSUED AT 404 AM EDT WED JUL 1 2026
AT THIS TIME HAVE DECIDED TO HOLD OFF ON A SMALL CRAFT ADVISORY
AND BEACH HAZARDS STATEMENT FOR MAINLY TONIGHT, BUT IT WILL BE
CLOSE TO CRITERIA NORTH OF GRAND HAVEN. IT LOOKS TO BE TRENDING
TOWARDS A TYPICAL SUNRISE SURPRISE TYPE OF EVENT. IN THESE
EVENTS, THE OVERNIGHT LOW LEVEL JET AIDES IN DEVELOPING SURFACE
WINDS THAT IN TURN BUILDS A WAVE FIELD. THE WAVES LOOK TO BE
LIKELY 2-4 FEET WITH CHANCES INCREASING FOR 3-5 FOOTERS. GIVEN
THIS IS AN INCREASE AND ITS BORDERLINE WILL HOLD OFF FOR NOW, BUT
MARINERS CAN EXPECT SOME CHOPPY CONDITIONS EARLY THURSDAY MORNING
NORTH OF GRAND HAVEN. CONDITIONS LOOK TO BE BELOW ADVISORY LEVELS
LATER THURSDAY AND INTO FRIDAY. THE OUTLOOK FOR THE HOLIDAY
WEEKEND ON THE BIG LAKE LOOKS GOOD AT THIS POINT WITH LIGHTER
WINDS AND LOWER WAVE CONDITIONS TYPICAL OF MID SUMMER.
GRR WATCHES/WARNINGS/ADVISORIES
MI...EXTREME HEAT WARNING UNTIL 8 PM EDT THURSDAY FOR MIZ037>040-
043>046-050>052-056>059-064>067-071>074.
MARINE...NONE.
DISCUSSION...DUKE
AVIATION...TJT
MARINE...DUKE
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