854
FXUS63 KGRR 202356
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
ISSUED BY NATIONAL WEATHER SERVICE TOPEKA KS
756 PM EDT MON JUL 20 2026
KEY MESSAGES
- STORMS TONIGHT
- UPPER TROUGHING CONTINUES THROUGH NEXT WEEK
DISCUSSION
ISSUED AT 258 PM EDT MON JUL 20 2026
- STORMS TONIGHT
A VIGOROUS UPPER SHORTWAVE TROUGH IS PHASING WITH TROUGHING OVER
EASTERN CANADA, WHILE A DEEPENING SURFACE LOW NORTH OF LAKE
SUPERIOR DRIVES A COLD FRONT INTO A MOIST AND UNSTABLE AIRMASS
ACROSS WISCONSIN. THE CONVECTIVE ALLOWING MODELS SHOW A LINE OF
STORMS INITIATING IN THAT AREA THIS AFTERNOON THEN MOVING
SOUTHEAST ACROSS LAKE MICHIGAN AND INTO WESTERN LOWER MICHIGAN
THIS EVENING. THEY ALSO SHOW A GENERAL WEAKENING TREND AS
INSTABILITY DECREASES THIS EVENING, ALTHOUGH SHEAR PROFILES REMAIN
IMPRESSIVE.
THE MAIN THREAT APPEARS TO BE DOWNBURST WINDS ASSOCIATED WITH
BOWING LINE SEGMENTS ALONG WITH ISOLATED LARGE HAIL IN THE
STRONGEST, MOST PERSISTENT UPDRAFTS. THE THREAT SHOULD BE ENDING
TUESDAY MORNING AS THE COLD FRONT PUSHES THROUGH.
- UPPER TROUGHING CONTINUES THROUGH NEXT WEEK
THE HEAT AND HUMIDITY OF LAST WEEK LOOKS TO BE GONE FOR A WHILE
WITH ALL THE LONG RANGE MODELS SHOWING A PERSISTENT PATTERN OF
RIDGING ACROSS THE SW CONUS AND TROUGHING ACROSS THE NE CONUS.
THIS WILL KEEP THE GREAT LAKES REGION IN A NORTHWEST FLOW REGIME
FOR THE NEXT WEEK AT LEAST, WITH OCCASIONAL COLD FRONT PASSAGES
THAT COULD FOCUS CONVECTION. THE NEXT ONE APPEARS TO BE NEXT
WEEKEND. OVERALL, A COOLER AND DRIER THAN NORMAL WEATHER REGIME
FOR THE REST OF THE MONTH IS EXPECTED.
AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 756 PM EDT MON JUL 20 2026
MVFR VISIBILITY WITH SMOKE MAY BE RETURNING THIS EVENING WITH
BOUNDARY LAYER MIXING SETTLING DOWN, AND THERE ARE 4SM TO 8SM VIS
REPORTS TO THE SOUTHWEST IN THE CHICAGO TO SOUTH BEND AREA, WHERE
OUR AIR WILL BE COMING FROM. SMOKE IS LIKELY TO BE LESS OF A CONCERN
ON TUESDAY.
BASED ON LATEST FORECAST TRENDS INCLUDING GUIDANCE FROM THE WOFS,
HRRR, AND RRFS, THE THUNDERSTORM THREAT IS BEING PUSHED LATER INTO
THE NIGHT, AND REMAINS LOW-CONFIDENCE ENOUGH TO KEEP TS AS A PROB30
FOR NOW. SO FAR THE CONVECTION IN NORTHEAST WISCONSIN HAS BEEN
FAIRLY LIMITED IN COVERAGE AND INTENSITY, PERHAPS DUE TO THE EFFECTS
OF TWO ROUNDS OF THUNDERSTORMS TODAY IN EASTERN IOWA AND NORTHERN
ILLINOIS. INSTABILITY ALOFT AND MIDLEVEL MOISTURE IS NONETHELESS
EXPECTED TO INCREASE TONIGHT AND MAY STILL SUPPORT SCATTERED
THUNDERSTORM DEVELOPMENT.
MARINE
ISSUED AT 258 PM EDT MON JUL 20 2026
SCA CONTINUES THROUGH WEDNESDAY EVENING. WE MAY NEED A GALE
WARNING FOR STRONG NORTH WINDS TUESDAY NIGHT AS THE PRESSURE
GRADIENT TIGHTENS BETWEEN THE DEPARTING LOW AND THE ADVANCING
HIGH. CONDITIONS WILL QUICKLY IMPROVE ON THURSDAY AS THE HIGH
BUILDS IN.
GRR WATCHES/WARNINGS/ADVISORIES
MI...AIR QUALITY ALERT UNTIL MIDNIGHT EDT TONIGHT FOR MIZ037>040-
043>046-050>052-056>059-064>067-071>074.
BEACH HAZARDS STATEMENT THROUGH WEDNESDAY EVENING FOR MIZ037-043-
050-056-064-071.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EDT WEDNESDAY FOR LMZ844>849.
DISCUSSION...OSTUNO
AVIATION...CAS
MARINE...OSTUNO
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