879
FXUS63 KGRR 031728
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
128 PM EDT FRI JUL 3 2026
KEY MESSAGES
- THUNDERSTORM CHANCES CONTINUE THROUGH THE HOLIDAY WEEKEND
- WARM AND HUMID CONDITIONS TO PERSIST
DISCUSSION
ISSUED AT 415 AM EDT FRI JUL 3 2026
- THUNDERSTORM CHANCES CONTINUE THROUGH THE HOLIDAY WEEKEND
THUNDERSTORM CHANCES WILL CONTINUE EACH DAY FROM TODAY THROUGH
SUNDAY ACROSS SOUTHWEST LOWER MICHIGAN. WE ARE IN A
MARGINAL/SLIGHT RISK OF SEVERE WEATHER TODAY AND A GENERAL
THUNDER RISK FOR SATURDAY/SUNDAY VIA THE STORM PREDICTION CENTER.
A DIFFUSE STATIONARY BOUNDARY REMAINS IN PLACE ACROSS THE
SOUTHERN GREAT LAKES THIS MORNING WHICH IS BEING AUGMENTED BY
THUNDERSTORM OUTFLOW. RICH BOUNDARY LAYER MOISTURE REMAINS IN
PLACE WHICH WILL AID MODERATE INSTABILITY ONCE AGAIN TODAY AND
OVER THE WEEKEND AS WELL. IT IS NOT UNTIL WE GET INTO SUNDAY NIGHT
AND MONDAY BEFORE WE GET INTO LESS HUMID/UNSTABLE AIR.
THUNDERSTORMS TODAY WILL BE DRIVEN BY WEAK SHORTWAVES MOVING
THROUGH THE UPPER FLOW AND LOCALIZED CONVERGENCE AT THE SURFACE.
THE SPC HREF SHOWS A LULL DURING THE MORNING HOURS IN THE WAKE OF
THE CURRENT ACTIVITY WITH A DIURNAL BOOST TO THE ACTIVITY THIS
AFTERNOON AND EVENING, ESPECIALLY FOR AREAS NEAR AND SOUTH OF
I-96. MACHINE LEARNING OUTPUT VIA NADOCAST SHOWS WIND AS THE CLEAR
MAIN THREAT.
SATURDAY AND SUNDAY THE THUNDERSTORM CHANCES CONTINUE WITH
SATURDAY'S THREAT BEING DRIVEN BY CONVECTIVE VORT'S AND SUNDAY'S
BY A STRONGER WAVE MOVING THROUGH. INSTABILITY IS STILL FAIRLY
SIGNIFICANT BOTH DAYS WITH THE GFS SHOWING NORTH OF 2,000 J/KG OF
MUCAPE. CANNOT RULE OUT SEVERE WEATHER EITHER DAY, ESPECIALLY ON
SUNDAY WHEN CONVECTION WILL GET MORE OF A SYNOPTIC BOOST FROM A
MID LEVEL WAVE AND A SURFACE COLD FRONT.
HEAVY RAIN POTENTIAL WILL EXIST TODAY THROUGH SUNDAY AS WELL WITH
PWAT VALUES NEAR 2 INCHES ALL THREE DAYS. THE FLOODING THREAT
WOULD BE SHORT TERM EXCESSIVE RAIN WHERE STORM DRAINS WILL NOT BE
ABLE TO KEEP UP WITH THE VOLUME OF WATER.
- WARM AND HUMID CONDITIONS TO PERSIST
850MB TEMPERATURES REMAIN WARM TODAY AND ON THE FORTH. HIGHS TODAY
WILL STILL REACH THE 90S OVER MUCH OF THE AREA. 80S WILL BE MORE
COMMON ON SATURDAY. WE WILL MAINTAIN THE CURRENT HEAT ADVISORY AS
IS.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 128 PM EDT FRI JUL 3 2026
A COMPLEX FORECAST IS UNDERWAY ASSOCIATED WITH THE TIMING OF
THUNDERSTORMS TODAY. A LINE OF STORMS ACROSS ILLINOIS IS ONGOING
WITH ADDITIONAL DEVELOPMENT OUT AHEAD OF IT. TRACKING THIS LINE OF
STORMS BRINGS IT TO MKG/BIV AROUND 20Z AND PROGRESSING EAST WITH
TIME, WHICH THE RRFS/RRFS-MPAS SEEM TO BE THE ONLY GUIDANCE
HANDLING THIS WELL. ADDITIONAL DEVELOPMENT IS POSSIBLE AHEAD OF
THIS LINE WHICH WE ARE ALREADY SEEING UPSTREAM. HAVE PROGRESSED TO
TEMPO TSRA FOR AZO/BTL/JXN WHERE THE BEST ENVIRONMENT IS AHEAD OF
THIS LINE AND PROB30S FOR MKG/GRR/LAN HAVE BEEN MAINTAINED.
AMENDMENTS WILL BE MADE AS NEEDED. STORMS WILL BE CAPABLE OF WINDS
IN EXCESS OF 40 KNOTS, AS WELL AS MVFR AND LOWER CONDITIONS.
DEPENDING ON HOW THE AFTERNOON STORMS EVOLVE, ONE OR MORE
ADDITIONAL ROUNDS OF STORMS ARE POSSIBLE AFTER 00Z, HOWEVER
CONFIDENCE IS LOW. OTHER THAN THAT THERE ARE SOME SIGNALS FOR FOG
TO DEVELOP NEAR AND NORTH OF MKG OVERNIGHT. SOUTHWEST WINDS TO 15
KNOTS WILL CONTINUE THROUGH THE AFTERNOON BEFORE WINDS BECOME
LIGHT AND VARIABLE OVERNIGHT.
MARINE
ISSUED AT 415 AM EDT FRI JUL 3 2026
A FAIRLY LIGHT WIND REGIME IS EXPECTED FOR THE HOLIDAY WEEKEND.
WINDS FOR THE MOST PART WILL BE IN THE 5 TO 15 KNOT RANGE FROM
TODAY THROUGH SUNDAY. THERE IS A BRIEF WINDOW THIS EVENING WHERE
SOUTHWEST WINDS INCREASE ALOFT AND SOME OF THIS WIND COULD MIX TO
THE SURFACE. ON SATURDAY WE MAY SEE A SOUTHWEST WIND OF 10 TO 20
KNOTS DEVELOP. OVERALL THOUGH IT LOOKS LIKE WAVES OF 1-3 FEET OR
LESS THROUGH THE HOLIDAY WEEKEND GIVEN THE LIGHTER WINDS. WE
THEREFORE ARE NOT EXPECTING ANY WIND/WAVE EVENTS TO ADVISORY
LEVELS. WE WILL SEE OCCASIONAL THUNDERSTORMS TODAY THROUGH SUNDAY,
SOME MARINERS AND BEACH GOERS ALIKE (BOTH OF WHICH WILL BE
PLENTIFUL THIS WEEKEND) WILL NEED TO KEEP AN EYE TO THE SKY FOR
THE THREAT OF LIGHTNING.
GRR WATCHES/WARNINGS/ADVISORIES
MI...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR MIZ046-051-052-
056>059-064>067-071>074.
MARINE...NONE.
DISCUSSION...DUKE
AVIATION...THOMAS
MARINE...DUKE
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