989
FXUS63 KGRR 210536
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
136 AM EDT TUE OCT 21 2025
KEY MESSAGES
- SHOWERS EXPECTED TONIGHT INTO TUESDAY
- LAKE ENHANCED SHOWERS WITH A CHANCE OF STORMS LATER TUESDAY INTO
WEDNESDAY
- COOL WITH ADDITIONAL CHANCES FOR SHOWERS LATE WEEK
DISCUSSION
ISSUED AT 323 PM EDT MON OCT 20 2025
- SHOWERS EXPECTED TONIGHT INTO TUESDAY
AN LEADING SHORTWAVE OVERNIGHT PAIRED WITH AN OCCLUDING FRONTAL
REFLECTION WILL BRING THE FIRST ROUND OF RAIN INTO THE FORECAST.
THIS LEADING SHORTWAVE MARKS THE ARRIVAL OF NOTABLE UPPER-LEVEL
TROUGHING (500 MB HEIGHTS BELOW THE 10TH PERCENTILE) ACROSS THE
REGION. THIS OCCLUDING FRONT WILL LEAD TO A BAND OF SHOWERS ACROSS
THE AREA. INSTABILITY LOOKS RATHER LIMITED KEEPING THUNDER OUT OF
THE FORECAST. HIGHEST TOTALS WILL BE APPROACHING 0.5 INCHES ACROSS
THE NORTHWESTERN CWA CLOSER TO THE OCCLUSION, WITH LOWER TOTALS
SOUTH AND EAST. SOUTHERLY WINDS TUESDAY MORNING SHIFT TO WESTERLY
DURING THE DAY. BUFKIT OVERVIEW SUGGEST WE SHOULD BE ABLE TO MIX
GUSTS TO 30-35 MPH DOWN MAKING FOR A WINDY DAY.
- LAKE ENHANCED SHOWERS WITH A CHANCE OF STORMS LATER TUESDAY INTO
WEDNESDAY
BEHIND THE COLD FRONT, VERY COLD AIR INFILTRATES THE REGION AS 850
MB TEMPERATURES FALL BELOW ZERO CELSIUS. COMBINED WITH THE PASSAGE
OF A VORTICITY MAXIMA ASSOCIATED WITH THE LARGE SCALE TROUGHING LAKE
ENHANCED SHOWERS ARE LIKELY. IN ADDITION, A FEW HUNDRED JOULES OF
LAKE INDUCED INSTABILITY WILL LEAD TO THE POTENTIAL FOR EMBEDDED
THUNDERSTORMS MAINLY NEAR THE LAKESHORE. THIS MUCH COLDER AIR WILL
ALSO KEEP TEMPERATURES DOWN WITH MIDWEEK HIGHS IN THE UPPER 40S TO
NEAR 50. THE SURFACE LOW IS SLOW TO DEPART KEEPING SHOWERS ONGOING
THROUGH WEDNESDAY.
HOWEVER, IN PARTICULAR THE TUESDAY AFTERNOON/EARLY EVENING PERIOD
NEEDS TO BE MONITORED. THERE IS DECENT CONSENSUS AMONG THE 12Z CAMS
THAT A BROKEN LINE OF POST FRONTAL CONVECTION WILL DEVELOP IN THE
AFTERNOON AND SWEEP EAST IN THE STRONG FLOW. 500 MB TEMPS NEAR -30C
WILL BE SUFFICIENT FOR AN ISOLATED THUNDER RISK. IN ADDITION, CANNOT
RULE OUT GRAUPEL AND/OR SMALL HAIL DEVELOPMENT IN STRONG UPDRAFT
CORES. STRONG UPDRAFTS MAY ALSO BE ABLE TO MIX DOWN WINDS IN EXCESS
OF 40 MPH AS THIS HAPPENS GIVEN THE STRONG LOW-LEVEL FLOW.
- COOL WITH ADDITIONAL CHANCES FOR SHOWERS LATE WEEK
SHOWERS WILL CONTINUE INTO THURSDAY AS A PV MAXIMA PROVIDES
ADDITIONAL FORCING FOR SHOWER DEVELOPMENT. ADDITIONAL WAVES ARE
LIKELY THROUGH THE WEEKEND KEEPING AT LEAST LOW SHOWER CHANCES IN
THE FORECAST. HIGHS SLOWLY BEGIN CLIMBING BACK TOWARDS 60 LATE WEEK
AS WARM AIR ADVECTION BEGINS.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 126 AM EDT TUE OCT 21 2025
LIGHT SHOWERS HAVE BEGUN TO MOVE THROUGH THE REGION AS FRONTAL
BANDS APPROACH. EXPECT PERIODS OF MVFR CIGS AND VSBYS UNTIL 10Z
WITH IMPROVING CONDITIONS BY 12Z. ANOTHER ROUND OF LOWER CLOUDS
WITH SHOWERS WILL MOVE IN DURING THE LATE AFTERNOON TIMEFRAME
WITH AREAS OF MVFR CONDITIONS. THERE IS A CHANCE FOR AN ISOLATED
STORMS SO HAVE INCLUDED PROB30 GROUPS TO REPRESENT THIS POTENTIAL.
SOUTH/SOUTHWEST LLWS OF 40 KNOTS WILL CONTINUE FOR THE NEXT FEW
HOURS. THE LOW LEVEL JET CAUSING THIS SHEAR WILL MOVE EASTWARD
AFTER 10Z, ENDING THE THREAT OF LLWS. GUSTY WINDS HAVE BEGUN TO
MIX DOWN TO THE SURFACE WITH WIND GUSTS OF 20 TO 25 KTS ALREADY AT
MKG AND AZO. THESE WINDS WILL BEGIN TO INFILTRATE THE OTHER TAF
SITES OVERNIGHT. EXPECT GUSTY WINDS TO INCREASE TO UPWARDS OF
35KTS AND CONTINUING THROUGH TUESDAY. THERE WILL BE IMPROVING
CONDITIONS LATE TUESDAY WITH MORE SHOWERS TUESDAY NIGHT INTO
WEDNESDAY WITH MVFR CIGS AND VSBYS EXPECTED.
MARINE
ISSUED AT 323 PM EDT MON OCT 20 2025
THE SMALL CRAFT ADVISORY WILL CONTINUE THROUGH 8 AM TUESDAY AND THEN
BE REPLACED WITH A GALE WARNING THAT WILL RUN THROUGH WEDNESDAY
EVENING. TIGHT PRESSURE GRADIENT AND COLD AIR ADVECTION WILL COMBINE
TO BRING 30 TO 40 KNOT WINDS DOWN TO THE WATER. EXPECT STRONG WAVE
ACTION TUESDAY AND WEDNESDAY ALONG WITH A CHANCE OF WATERSPOUTS. THE
BETTER CHANCE FOR WATERSPOUTS WILL BE LATE WEDNESDAY AFTERNOON AND
EVENING WHEN THE WINDS THROUGH THE LOW/MID LEVELS DECREASE BELOW 35
KNOTS.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 AM EDT THIS MORNING FOR LMZ844>849.
GALE WARNING FROM 8 AM THIS MORNING TO 2 AM EDT THURSDAY FOR
LMZ844>849.
DISCUSSION...THOMAS
AVIATION...CERU
MARINE...OSTUNO
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