257
FXUS63 KGRR 251941
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
341 PM EDT FRI APR 25 2025
KEY MESSAGES
- EVENING STORMS THEN DRYING OUT FOR THE WEEKEND
- FROST POTENTIAL SATURDAY NIGHT
- THUNDERSTORM POTENTIAL MONDAY NIGHT AND TUESDAY
DISCUSSION
ISSUED AT 341 PM EDT FRI APR 25 2025
- EVENING STORMS THEN DRYING OUT FOR THE WEEKEND
CONVECTION HAS COMMENCED THIS AFTERNOON, POISED JUST OFF TO OUR
SOUTH ACROSS THE FAR SOUTHERN ROW OF MICHIGAN COUNTIES. MUCAPE
VALUES ARE ON THE ORDER OF 1000-2000 J/KG SO WE HAVE PLENTY OF
INSTABILITY. DEEP LAYER SHEAR IS ON THE ORDER OF 30 KNOTS, SO WE
HAVE HAD OCCASIONAL CORES ALOFT THAT HAVE BEEN WORTH MONITORING,
BUT NOTHING SEVERE YET. GIVEN SOLID INSTABILITY AND MARGINAL SHEAR
THERE WILL BE PERIODS THIS EVENING WHERE A STRAY CORE MAY PULSE
TOWARDS SEVERE LEVELS. OVERALL THOUGH, OUR SEVERE THREAT IS QUITE
LOW. STORMS WILL CONTINUE FROM NOW THROUGH 7-8PM BEFORE MOVING
EAST AND/OR DIMINISHING. THERE MAY BE SOME WRAP AROUND SHOWERS ON
THE BACKSIDE OF THE DEPARTING LOW TONIGHT, BUT SCATTERED POPS
(30-40 PCT) AT BEST SHOULD COVER THAT THREAT.
OTHERWISE, WE ARE LOOKING AT DRY WEEKEND AS HIGH PRESSURE SLIDES
EAST ACROSS THE GREAT LAKES. NEXT CHANCE FOR PRECIPITATION SHOULD
NOT COME UNTIL MONDAY NIGHT.
- FROST POTENTIAL SATURDAY NIGHT
THERE WILL BE THE POTENTIAL FOR SOME PATCHY FROST IN THE COUNTIES
WE HAVE ACTIVE FOR FROST/FREEZE HEADLINES FOR SATURDAY NIGHT. THE
COUNTIES WE ARE ISSUING HEADLINES FOR ARE FROM THE
MUSKEGON/KENT/MONTCALM/GRATIOT ROW TO THE SOUTH. AT THIS TIME
THOUGH WE ARE HOLDING OFF ON ANY HEADLINES AT ALL AND WE WILL
ASSESS THE THREAT FURTHER TONIGHT AND INTO SATURDAY. AS IT STANDS
NOW LOW TEMPERATURES LOOK TO BE 34 TO 36 DEGREE RANGE THAT WOULD
EQUATE TO AN ADVISORY IF THESE FORECAST LOW TEMPERATURES HOLD. THE
CENTRAL LOWER MICHIGAN COUNTIES ARE COLDER, BUT THE GROWING SEASON
HAS NOT PROGRESSED ENOUGH UP THERE AT LAST CHECK TO BRING THEM
INTO THE FOLD. BOTTOM LINE IS THERE IS A CHANCE OF FROST SATURDAY
NIGHT BUT WE WILL HOLD OFF FOR NOW AND ISSUE GOING FORWARD IF
CONFIDENCE INCREASES.
- THUNDERSTORM POTENTIAL MONDAY NIGHT AND TUESDAY
THE GRR FORECAST AREA IS IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS
BOTH MONDAY NIGHT AND AGAIN ON TUESDAY. MONDAY NIGHT THE
CONVECTION WILL BE COMING IN LIKELY IN A DECAYING PHASE AFTER
GENERATING EARLY ON MONDAY UPSTREAM. ON TUESDAY, THE CONVECTION
WILL GO UP ON AN ADVANCING FRONT IN OUR SOUTH AND EAST, SO IT WILL
ONLY BE A PORTION OF THE AREA THAT WILL HAVE A THREAT FOR SEVERE
WEATHER. THE UPPER WAVE DRIVING THE COLD FRONT LOOKS FAIRLY
POTENT. MONDAY NIGHT CONVECTION LOOKS ELEVATED WITH MARGINAL SHEAR
VALUES SO CANNOT RULE OUT SOME NEAR SEVERE HAIL.
THE TIME FRAME OF CONCERN WILL BE TUESDAY AFTERNOON AS THE
MOISTURE CONSOLIDATES ALONG THE FRONT AND INSTABILITY JUMPS TO IN
EXCESS OF 2000 J/KG. DEEP LAYER SHEAR ON TUESDAY IS HIGH AROUND 50
KNOTS PER THE GFS. THE COMBINATION OF CAPE/SHEAR IS SUFFICIENT FOR
ALL HAZARDS. THE QUESTION MARK AS IS ALWAYS THE CASE IN THESE
EVENTS IS WHETHER OR NOT THE CLOUDS AND PRECIP CLEAR OUT ENOUGH ON
TUESDAY TO BUILD THE INSTABILITY TO FORECAST LEVELS. BOTTOM LINE
WE ARE WATCH MONDAY NIGHT AND ESPECIALLY TUESDAY CLOSELY.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 147 PM EDT FRI APR 25 2025
WE ARE STARTING THIS FORECAST PERIOD OFF WITH WIDESPREAD VFR
CONDITIONS ACROSS ALL OF OUR TERMINALS. THIS MOST DEFINITELY WILL
NOT LAST THROUGH THE ENTIRE PERIOD. WE EXPECT THAT CUMULUS CLOUDS
WILL BUILD, AND HELP TO PRODUCE A FEW SHOWERS AND STORMS FOR ALL
OF THE TERMINALS EXCEPT KMKG AND KGRR. THE MOST LIKELY TIME FOR
THOSE SHOWERS AND STORMS WILL BE ROUGHLY FROM 20-24Z. THE COVERAGE
WILL BE SUCH THAT WE DECIDED TO USE A PROB30 TO ACCOUNT FOR IT.
THE SHOWERS/STORMS OVER THE SE WILL LIKELY MOVE OUT NO LATER THAN
00Z. SHORTLY AFTER THAT, THE NORTHERN PERIPHERY OF THIS SYSTEM
WILL BRING A FEW SHOWERS OVER THE KMKG AND KGRR TERMINALS THIS
EVENING. SHORTLY AFTER THAT RAIN MOVES IN, WE WILL SEE LOWER
CEILINGS PUSH IN. THESE CEILINGS WILL DROP DOWN TO AROUND LOW END
MVFR TO HIGHER END IFR TONIGHT. WINDS WILL BECOME FROM THE NNW AND
BECOME GUSTY WITH GUSTS UP TO 25-28 KNOTS. THE CEILINGS WILL THEN
SLOWLY LIFT LATE TOMORROW MORNING AND TOMORROW AFTERNOON,
EVENTUALLY TO VFR.
MARINE
ISSUED AT 341 PM EDT FRI APR 25 2025
NORTH WINDS ARE BEGINNING TO FILL IN ACROSS LAKE MICHIGAN THIS
AFTERNOON. LOW PRESSURE CONSOLIDATES THIS AFTERNOON ACROSS THE
SOUTHERN GREAT LAKES AND MOVES EAST THIS EVENING. PEAK WINDS WILL
OCCUR THIS EVENING BUT A STRONGER NORTH FLOW WILL PERSIST INTO
SATURDAY. NORTH WINDS OF 15 TO 30 KNOTS WILL BE COMMON TONIGHT
AND SATURDAY MORNING. WE HAVE A SMALL CRAFT ADVISORY (SCA) IN
EFFECT THROUGH 800PM WHICH LOOKS GOOD. WE MAY NEED TO EXTEND THE
SCA FOR AN HOUR OR TWO IN THE FAR SOUTH SATURDAY EVENING, BUT AT
THIS POINT THINKING IS IT LOOKS GOOD.
WINDS AND WAVES WILL BE BELOW ADVISORY CRITERIA SATURDAY NIGHT AND
SUNDAY AS HIGH PRESSURE DRIFTS THROUGH THE REGION. SUNDAY NIGHT
INTO MONDAY SOUTH WINDS TAKE HOLD AND WE MAY NEED HEADLINES ONCE
AGAIN.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT SATURDAY FOR LMZ844>849.
DISCUSSION...DUKE
AVIATION...NJJ
MARINE...DUKE
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