018
FXUS63 KGRR 021455
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1055 AM EDT WED APR 2 2025
KEY MESSAGES
- WINTRY MIX INTO THE MORNING
- CONDITIONAL SEVERE WEATHER THREAT TODAY
- RAIN SHOWERS THIS WEEKEND
UPDATE
ISSUED AT 1041 AM EDT WED APR 2 2025
BASED ON MDOT WEBCAMS AND CURRENT OBS, WE WILL KEEP THE REMAINING
FOUR COUNTIES IN THE WINTER WEATHER ADVISORY UNTIL IT EXPIRES AT
NOON.
AS FOR THE SEVERE THREAT, IT APPEARS THE OVERALL THREAT IS REDUCED
AS INSTABILITY WILL BE LACKING THIS AFTERNOON WHEN THE MAIN BATCH
OF STORMS COMES THROUGH. CURRENT ELEVATED STORMS ARE NOT PRODUCING
ANYTHING SIGNIFICANT EITHER OVER US OR TO THE WEST WHERE RADAR
SIGNATURES SHOW GRAVITY WAVE PROPAGATION CURRENTLY MOVING ACROSS
LAKE MICHIGAN. THESE DID NOT HAVE A DISCERNIBLE SURFACE WIND
RESPONSE OVER WISCONSIN, BUT WILL BEAR WATCHING FOR STRONG WINDS
REACHING THE SURFACE AS THEY COME THROUGH OUR AREA.
BACK TO THE AFTERNOON...WE EXPECT LITTLE IN THE WAY OF AIR MASS
RECOVERY AS A STEADY PARADE OF SHOWERS AND THUNDERSTORMS CONTINUE
MOVING THROUGH WITH NO SIGNIFICANT BREAKS OR CLEARING UNTIL AT
LEAST THE EVENING. STRONG SHEAR PROFILES WILL STILL EXIST SO
TRENDS FOR CONVECTION WILL HAVE TO BE MONITORED THROUGH THE
EVENING, ESPECIALLY CLOSER TO THE SFC WARM FRONT APPROACHING THE
I-94 CORRIDOR.
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
0.1-0.2" 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 /12Z TAFS THROUGH 12Z THURSDAY/
ISSUED AT 714 AM EDT WED APR 2 2025
SOME POCKETS OF MIXED PRECIPITATION HAVE BEEN OBSERVED OVER THE
PAST HOUR, BUT WE SHOULD SEE A TRANSITION TO ALL RAIN WITH THE
WIDESPREAD RAIN CURRENTLY MOVING INTO AZO, BTL, JXN, AND GRR.
THERE IS STILL A BRIEF WINDOW THIS MORNING FOR FREEZING RAIN NORTH
OF THE TAF SITES. AFTER SUNRISE, ANY FREEZING RAIN SHOULD
TRANSITION TO RAIN WITHIN A FEW HOURS AS TEMPERATURES WARM.
WITH THE RAIN COMES PLENTY OF LOW LEVEL WIND SHEAR WHICH WILL BE
PRESENT THROUGHOUT THE DAY AND INTO TONIGHT. CEILINGS WILL
GRADUALLY DROP TO LIFR VALUES WITH BRIEF PERIODS OF LIFR POSSIBLE
THIS AFTERNOON AND EVENING. THUNDERSTORMS ARE EXPECTED LATER THIS
MORNING AND CONTINUE OFF AND ON THROUGH THE DAY. THERE IS A RISK
FOR SEVERE STORMS MAINLY BETWEEN 18Z WED - 3Z THU. THE HIGHEST
RISK WILL BE FOR AREAS ALONG AND SOUTH OF A AZO TO JXN LINE.
DAMAGING WINDS, HAIL, TORNADOES, AND HEAVY RAINFALL ARE ALL
POSSIBLE. THE SEVERE RISK COULD BE LIMITED BY THIS MORNING'S ROUND
OF RAIN AND THUNDERSTORMS IF WE DO NOT SEE A BREAK IN THE
PRECIPITATION.
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 MIZ039-040-045-
046.
MARINE...GALE WARNING UNTIL 11 PM EDT THIS EVENING FOR LMZ844>849.
UPDATE...OSTUNO
DISCUSSION...THOMAS
AVIATION...RAH
MARINE...THOMAS
HYDROLOGY...AMD
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