022
FXUS63 KGRR 200504
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
104 AM EDT MON JUL 20 2026
KEY MESSAGES
- STORMY MONDAY NIGHT
- UPPER TROUGHING CONTINUES
DISCUSSION
ISSUED AT 256 PM EDT SUN JUL 19 2026
- STORMY MONDAY NIGHT
A VIGOROUS UPPER SHORTWAVE TROUGH ROUNDS THE TOP OF AN UPPER HIGH
CENTERED OVER COLORADO TONIGHT AND THEN PHASES WITH TROUGHING
OVER EASTERN CANADA ON MONDAY. A SURFACE LOW DEEPENS AS IT MOVES
NORTH OF LAKE SUPERIOR MONDAY AFTERNOON, WITH A TRAILING COLD
FRONT TO FOCUS CONVECTION ACROSS WISCONSIN. THERE IS SOME
UNCERTAINTY ON THE STRENGTH AND TIMING OF THE CONVECTION AS IT
CROSSES LAKE MICHIGAN AND MOVES INTO LOWER MICHIGAN MONDAY
EVENING.
THE HI-RES CONVECTIVE-ALLOWING MODELS SHOW SEVERAL HOURS OF SPREAD
ON TIMING, FROM LATE AFTERNOON TO LATE EVENING, SO CONFIDENCE IS
LOW, BUT THE FORECAST BLEND HAS THE HIGHER POPS MOVING IN AROUND
MIDNIGHT. DEEP LAYER SHEAR IS FORECAST TO BE GREATER THAN 35
KNOTS ALONG WITH MODEST INSTABILITY DURING THE EVENING, WANING
OVERNIGHT.
THE MAIN THREAT APPEARS TO BE DOWNBURST WINDS ASSOCIATED WITH
BOWING LINE SEGMENTS ALONG WITH LARGE HAIL. THE THREAT SHOULD BE
ENDING TUESDAY MORNING AS THE COLD FRONT PUSHES SOUTH.
- UPPER TROUGHING CONTINUES
THE LARGE SCALE PATTERN OF RIDGING ACROSS THE SW CONUS AND
TROUGHING ACROSS THE NW CONUS SHOULD KEEP THE GREAT LAKES REGION
IN A NORTHWEST FLOW PATTERN 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.
AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 104 AM EDT MON JUL 20 2026
SMOKE CONTINUES TO SUPPORT MVFR CONDITIONS AT AZO/MKG AND IFR AT
GRR. GIVEN PERSISTENCE FORECAST FROM PREVIOUS DAYS, ESPECT
CONDITIONS TO REMAIN THE SAME THROUGH THE NIGHT IF NOT DETERIORATE
SLIGHTLY NEAR DAYBREAK. MIXING THEN INCREASES FAVORING VFR
CONDITIONS AT ALL TERMINALS BEGINNING MID TO LATE MORNING. A LINE
OF STORMS POTENTIALLY ARRIVES FROM THE WEST AFTER 00Z TUESDAY,
HOWEVER EXISTENCE OF TIMING AND STORMS REMAINS UNCERTAIN. GIVEN
THIS HAVE ELECTED TO GO PROB30 AT GRR/MKG TO START AND CAN RE-
EVAUATE WITH FUTURE PACKAGES. GUSTY WINDS FROM THE SOUTH TO AROUND
20 KNOTS ARE EXPECTED TODAY, WITH LOCALLY HIGHER WINDS AND MFVR
AND LOWER CONDITIONS POSSIBLE IN ANY STORMS TONIGHT.
MARINE
ISSUED AT 256 PM EDT SUN JUL 19 2026
WINDS AND WAVES WILL BE INCREASING ON MONDAY AND A SCA/BHS WILL
BE NEEDED FROM MONDAY INTO WEDNESDAY. SOUTH WINDS ON MONDAY WILL
GO WEST BY TUESDAY MORNING THEN NORTHWEST TUESDAY AFTERNOON, AND
THEN NORTH TUESDAY NIGHT, WHEN GALES ARE POSSIBLE ALONG WITH WAVES
BUILDING OVER 6 FEET. CONDITIONS SHOULD RAPIDLY IMPROVE ON
THURSDAY AS HIGH PRESSURE 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.
MARINE...NONE.
DISCUSSION...OSTUNO
AVIATION...THOMAS
MARINE...OSTUNO
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