299
FXUS63 KGRR 020747
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
347 AM EDT WED APR 2 2025
KEY MESSAGES
- WINTRY MIX INTO THE MORNING
- CONDITIONAL SEVERE WEATHER THREAT TODAY
- RAIN SHOWERS THIS WEEKEND
DISCUSSION
ISSUED AT 338 AM EDT WED APR 2 2025
- WINTRY MIX INTO THE MORNING
AFTER THE INITIAL BAND OF WARM AIR ADVECTION PRECIPITATION ACROSS
THE AREA, PRECIPITATION HAS BEEN SLOW TO FILL IN ACROSS WEST
MICHIGAN AND UPSTREAM OVER ILLINOIS. DRY EASTERLY FLOW HAS HELPED
LIMIT PRECIPITATION SO FAR. HOWEVER, AS THE SURFACE LOW MOVES INTO
THE UPPER GREAT LAKES PRECIPITATION COVERAGE SHOULD INCREASE IN THE
COMING HOURS. WHILE LIGHT SNOW AND FREEZING RAIN IS STILL EXPECTED
THROUGH LATE MORNING ACROSS THE CURRENT WINTER WEATHER ADVISORY
AREA, THE MAXIMUM ICING IS NOW FAVORED TO BE ON THE ORDER OF AROUND
0.1" GIVEN LESSENED QPF. WILL LEAVE THE CURRENT ADVISORY IN PLACE
GIVEN THE CONTINUED RISK FOR LIGHT FREEZING RAIN/SNOW.
- CONDITIONAL SEVERE WEATHER THREAT TODAY
THE FORECAST AS FAR AS SEVERE WEATHER POTENTIAL TODAY REMAINS
COMPLICATED BY QUESTIONS ON THE EXTENT OF ATMOSPHERIC RECOVERY.
THE FIRST PORTION OF THE CONVECTIVE EVENT IS THIS MORNING AS
ELEVATED INSTABILITY MAKES ITS WAY INTO THE FORECAST AREA. THE
PRIMARY CONCERN WITH THIS PORTION OF THE EVENT GIVEN TRAINING OF
HEAVIER EMBEDDED CELLS. THIS MAY BE ENOUGH FOR MINOR POOR DRAINAGE
AND RIVER FLOODING, ESPECIALLY IF HEAVIER CELLS REPEATEDLY TRAIN
OVER THE SAME AREA. SEE THE HYDROLOGY SECTION FOR MORE DETAILS.
GIVEN AMBIENT DEEP LAYER SHEAR EXCEEDING 50 KNOTS, SMALL HAIL IS
POSSIBLE IN ANY STORMS. THE SETUP IS FAVORABLE FOR GRAVITY WAVE
ASSOCIATED CONVECTION (GWAC) SO A BRIEF GUST FROM AN ELEVATED STORM
IS NOT OFF THE TABLE, HOWEVER PREDICTING THESE SORT OF EVENTS IS
CHALLENGING WITH ANY CERTAINTY BEFORE THE EVENT SO CONFIDENCE IN
GUSTS OCCURING IS LOW.
ATTENTION THEN TURNS TO THE AFTERNOON WHERE A CONDITIONAL RISK OF
SEVERE WEATHER EXISTS, DEPENDING ON WHERE ATMOSPHERIC RECOVERY CAN
OCCUR. WHAT THIS WILL HINGE ON IS WHETHER MORNING CONVECTION CAN
SUPPRESS THE NORTHWARD MOTION OF THE WARM FRONT THIS AFTERNOON AND
EVENING. THE AMBIENT ENVIRONMENT IS VERY DYNAMIC GIVEN 50 PLUS KNOTS
OF DEEP LAYER SHEAR AND OVER 400 M2/S2 OF 0-3KM SRH. HOWEVER, THIS
CAN ONLY BE FULLY REALIZED BY THE STORM IF SUFFICIENT INSTABILITY
EXISTS FOR THE STORM TO BECOME SURFACE BASED.
WHAT WE KNOW IS A LINE OF CONVECTION IS EXPECTED TO CROSS THE CWA IN
THE LATE AFTERNOON AND EVENING HOURS. THE IMPACTS OF THIS LINE
DEPENDS ON THE NORTHWARD EXTENT OF THE WARM FRONT AND SURFACE BASED
INSTABILITY. FOR AREAS THAT DO NOT DESTABILIZE ENOUGH FOR SURFACE
BASED STORMS, CONVECTION WILL REMAIN ELEVATED WITH A LOWER SEVERE
WEATHER THREAT, FOR AREAS THAT DO SEE CLOUDS AND PRECIPITATION CLEAR
OUT LATER TODAY AND DESTABILIZE, THE FULL EFFECTS OF THE VERY STRONG
AMBIENT WINDS WILL BE FELT BY THE STORMS WITH DAMAGING WINDS,
POSSIBLY EXCESS OF 70 MPH, TORNADOES, AND LARGE HAIL POSSIBLE.
THE PRIMARY FORECAST CHALLENGE IS WHERE WILL DESTABILIZATION OCCUR?
A PERUSAL OF 00Z GUIDANCE STILL SUGGESTS WHERE IS NOT CERTAIN, AND
IS DEPENDENT ON OUTFLOW FROM MORNING CONVECTION AND CLOUD COVER.
CONSENSUS IS NEAR AND SOUTH OF I94 HAS THE BEST CHANCE TO SEE
SURFACE BASED STORMS AND THE ASSOCIATED SEVERE WEATHER. HOWEVER,
SOME SOLUTIONS SUCH AS THE NAM SUITE DO BRING SURFACE BASED STORMS
AND THE BEST SEVERE THREAT INTO THE I96 CORRIDOR.
IT'S IMPORTANT TO NOTE THAT WHILE THE CEILING OF THE EVENT IS
ELEVATED GIVEN THE STRONG WINDS ALOFT, THE QUESTIONS OF
DESTABILIZATION MEANS WHO SEES SEVERE WEATHER IS UNCERTAIN AND SOME
OR ALL OF THE AREA MAY NOT SEE SEVERE STORMS TODAY. CLOSE MONITORING
OF CLOUD COVER TRENDS, PRECIPITATION TRENDS, AND ATMOSPHERIC
RECOVERY WILL BE NEEDED THROUGH THE DAY TO FINE TUNE THE EXACT
THREAT AREA.
- RAIN SHOWERS THIS WEEKEND
THURSDAY AND FRIDAY REMAIN DRY ACROSS THE AREA AS RIDGING DOMINATES
THE FORECAST. WE THEN SEE A LOW PRESSURE SYSTEM CROSS THE OHIO
VALLEY FRIDAY NIGHT INTO SUNDAY WITH THE RAIN SHIELD REACHING INTO
LOWER MICHIGAN. WIDESPREAD RAINFALL IS LIKELY, WITH AREAS NEAR AND
SOUTH OF I96 HAVING A 30-50 PERCENT CHANCE OF EXCEEDING 1 INCH OF
RAINFALL. IT WILL BE MILD WITH HIGHS IN THE 50S THROUGH SATURDAY
FALLING INTO THE 40S BY SUNDAY.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 200 AM EDT WED APR 2 2025
A BAND ON SNOW IS CURRENTLY MOVING THROUGH NORTHERN PORTIONS OF
THE AREA IMPACTING MOP, RBQ, LDM AND NORTH WITH ACCUMULATIONS
AROUND 1 TO 2 INCHES OVER THE NEXT FEW HOURS. RAIN AND SNOW
SHOWERS WILL THEN EXPAND OVER THE AREA EARLY THIS MORNING WITH A
WINDOW OF FREEZING RAIN POSSIBLE EARLY THIS MORNING FOR MKG, GRR,
AND LAN. FREEZING RAIN ACCUMULATIONS ARE MORE LIKELY NORTH OF
THESE SITES.
ANY FROZEN PRECIPITATION TRANSITIONS TO RAIN THIS MORNING WITH
SOME EMBEDDED THUNDERSTORMS. CEILINGS WILL GRADUALLY DROP TO LIFR
VALUES WITH BRIEF PERIODS OF LIFR POSSIBLE. THERE IS SOME
UNCERTAINTY IN THE TIMING OF THUNDERSTORMS THROUGHOUT THE DAY, BUT
A LULL IS POSSIBLE WEDNESDAY AFTERNOON BEFORE THUNDERSTORMS
RETURN IN THE EVENING.
LOW LEVEL WIND SHEAR WILL BE PRESENT THROUGHOUT THE DAY INITIALLY
FROM THE SOUTHEAST AND THEN BECOMING SOUTHWESTERLY WEDNESDAY
EVENING AS THE WARM FRONT MOVES NORTH OF THE AREA. SURFACE WINDS
CURRENTLY FROM THE EAST GUSTING TO AROUND 25 KNOTS WILL INCREASE
WITH GUSTS AROUND 30-35 KNOTS THIS MORNING BEFORE SHIFTING TO THE
SOUTHWEST WEDNESDAY EVENING.
GRR AIRPORT DSS UPDATE:
THERE IS A SLIGHT TIME ADJUSTMENT FOR THE WINDOW OF FREEZING RAIN
THAT WAS PROVIDED EARLIER. THE BEST WINDOW FOR ANY FREEZING RAIN
WILL BE BETWEEN 5-8AM BEFORE WARMER TEMPERATURES CAUSE A
TRANSITION TO RAIN. OTHERWISE NO OTHER CHANGES TO THE PREVIOUS
FORECAST.
EAST TO SOUTHEAST WINDS GUSTING AROUND 25 KNOTS CONTINUE WITH
GUSTS INCREASING TO AROUND 30 KNOTS WEDNESDAY MORNING.
MARINE
ISSUED AT 338 AM EDT WED APR 2 2025
THE GALE WARNING REMAINS IN EFFECT THROUGH WEDNESDAY EVENING, WITH
WINDS FORECAST TO INCREASE TO GALE FORCE IN THE COMING HOURS.
HOWEVER, WAVES WITH THE GALE FORCE WINDS WILL BE LOWER GIVEN THE
WINDS WILL BE PRIMARILY OFFSHORE, WITH WAVES OVER 5 FEET MAINLY
SEVERAL MILES OFFSHORE AND BEYOND. A SMALL CRAFT ADVISORY WILL BE
NEEDED WEDNESDAY NIGHT INTO THURSDAY MORNING AFTER THE GALE
WARNING, WITH GUSTS EXCEEDING 25 KNOTS EXPECTED AND WAVES
BUILDING IN THE NEARSHORE AS WINDS FLIP TO WESTERLY. HIGH PRESSURE
THEN CASES WINDS AND WAVES TO SUBSIDE INTO THURSDAY AFTERNOON.
THE OTHER CONCERN IS FOR POTENTIAL SEVERE THUNDERSTORMS OVER THE
LAKE THIS AFTERNOON AND EVENING. A LINE OF STORMS WILL DEVELOP
BEHIND THE CURRENT SHOWERS AND STORMS. GUSTS IN EXCESS OF 40
KNOTS, HAIL, AND WATERSPOUTS ARE POSSIBLE WITH THIS LINE THOUGH
IT IS NOT CERTAIN IF THIS WILL OCCUR.
HYDROLOGY
ISSUED AT 352 PM EDT TUE APR 1 2025
SEVERAL ROUNDS OF SHOWERS AND STORMS ARE EXPECTED TO SWEEP ACROSS
LOWER MICHIGAN BETWEEN WEDNESDAY MORNING AND LATE WEDNESDAY
EVENING. WE'RE EXPECTING MOST LOCATIONS TO RECEIVE BETWEEN 1 AND
1.5 INCHES OF RAIN DURING THIS TIME, THOUGH DEPENDING ON HOW THE
CLUSTERS OF THUNDERSTORMS EVOLVE SOME LOCATIONS COULD EASILY 2.5
INCHES OR MORE. IF THUNDERSTORMS MOVE OVER THE SAME AREAS
REPEATEDLY, WE MAY OVERWHELM LOCAL DRAINAGES AND RESULT IN SOME
GENERAL FLOODING CONCERNS AS WE GO THROUGH THE DAY WEDNESDAY.
AS THE RAIN THAT FALLS TOMORROW STARTS MAKING ITS WAY INTO OUR
RIVERS, WE'LL BE MONITORING FOR POSSIBILITY OF OVERFLOWING SOME OF
THE RIVERS. CURRENTLY, THE MUSKEGON RIVER IS THE ONLY LARGE RIVER
SYSTEM IN OUR AREA THAT IS RUNNING HIGHER THAN NORMAL - MOSTLY DUE
TO RECENT HEAVY RAINS AND SNOWMELT IN NORTHERN LOWER MICHIGAN. IF
RAIN TOTALS TOMORROW IN THIS AREA START TO SURPASS THE EXPECTED 1
INCH TOTALS, WE MAY BE LOOKING AT PUSHING SOME OF THE LOWER RIVER
AREAS (NEWAYGO AND BRIDGETON) INTO THE MINOR/NUISANCE FLOODING
CATEGORY.
MEANWHILE, MOST OF THE RIVERS IN THE GRAND AND KALAMAZOO RIVER
WATERSHEDS ARE NEAR OR SLIGHTLY BELOW AVERAGE FOR THIS TIME OF YEAR,
SO WE'VE GOT A DECENT AMOUNT OF SPACE IN THESE RIVERS TO FILL UP.
HOWEVER, IF RAIN TOTALS ACROSS A LARGE AREA START TO PASS THE 2 INCH
MARK, WE MAY EVENTUALLY START TO SEE SOME MINOR FLOODING AT A FEW
SPOTS AROUND LANSING AND DOWNSTREAM IN COMSTOCK PARK. HOWEVER, IF
RAIN TOTALS STAY IN THE 1 TO 1.5 INCH RANGE IN THIS AREA, WE'LL
BRING WATER LEVELS UP TO BANKFULL BUT THAT WILL PROBABLY BE ABOUT
IT.
GRR WATCHES/WARNINGS/ADVISORIES
MI...WINTER WEATHER ADVISORY UNTIL NOON EDT TODAY FOR MIZ037>040-
043>046-051-052.
MARINE...GALE WARNING UNTIL 11 PM EDT THIS EVENING FOR LMZ844>849.
DISCUSSION...THOMAS
AVIATION...RAH
MARINE...THOMAS
HYDROLOGY...AMD
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