276
FXUS63 KGRR 020002
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
802 PM EDT TUE APR 1 2025
KEY MESSAGES
- WINTER WEATHER TONIGHT
- SEVERE WEATHER TOMORROW
DISCUSSION
ISSUED AT 352 PM EDT TUE APR 1 2025
- WINTER WEATHER TONIGHT
A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR AREAS NORTH OF I-96
TONIGHT THROUGH NOON ON WEDNESDAY FOR A WINTRY MIX OF SNOW
CHANGING TO SLEET AND FREEZING RAIN. ICE ACCUMULATIONS MAY
APPROACH A QUARTER INCH ACROSS PARTS OF OSCEOLA, CLARE AND
ISABELLA COUNTIES BY LATE WEDNESDAY MORNING BEFORE TEMPERATURES
GET ABOVE FREEZING.
WARM ADVECTION/ISENTROPIC ASCENT INCREASES THIS EVENING WITH SNOW
EXPECTED TO BREAK OUT AFTER MIDNIGHT GENERALLY NORTH OF I-96.
THERMAL PROFILES SHOW THAT SNOW WILL MIX WITH SLEET AND FREEZING
RAIN BY DAYBREAK WITH GENERALLY 1 TO 3 INCHES OF SNOW ACROSS THE
ADVISORY AREA. ELEVATED INSTABILITY DURING THE MORNING COULD LEAD
TO SOME HEAVIER PRECIP RATES, WITH ICE PELLETS AND HEAVY FREEZING
RAIN CAUSING TRAVEL IMPACTS, PRIMARILY ACROSS THE HIGHER
ELEVATIONS OF OSCEOLA AND CLARE COUNTIES. WE WILL HAVE TO WATCH
PRECIP TRENDS DURING THE MORNING FOR THE POTENTIAL FOR HEAVY
FREEZING RAIN CAUSING POWER OUTAGES.
DEW POINTS ARE STARTING OUT IN THE TEENS TONIGHT AND WILL TAKE A
WHILE TO GET ABOVE FREEZING ON WEDNESDAY WITH THE SURFACE HIGH
ADVECTING COLD, DRY AIR INTO THE NORTHERN FORECAST AREA.
EVENTUALLY THE LOW LEVEL COLD ADVECTION GOES NEUTRAL AND RAIN
RATES AND DIURNAL WARMING BEGINS THE MELTING PROCESS.
- SEVERE WEATHER TOMORROW
AS THE WINTER WEATHER THREATS WIND DOWN NORTH OF I-96, THE SEVERE
WEATHER THREAT RAMPS UP SOUTH OF I-96. THE CONVECTIVE ALLOWING
MODELS SHOW TWO MAIN BATCHES OF CONVECTION, ONE AROUND 12Z AND
ANOTHER AROUND 00Z, OR A BIT LATER.
THE FIRST ROUND OF STORMS DURING THE MORNING IS ELEVATED AND THE
PRIMARY THREAT IS MINOR FLOODING OF POOR DRAINAGE AREAS THAT ARE
STILL SATURATED FROM THE RAIN ON SUNDAY, ALONG WITH SMALL HAIL.
THIS MOVES EAST DURING THE AFTERNOON AND THE CONDITIONAL
PROBABILITY FOR SEVERE WEATHER FROM THE LATER ROUND OF STORMS WILL
DEPEND ON HWO MUCH AIR MASS RECOVERY OCCURS DURING THE AFTERNOON.
THE CURRENT THINKING IS THAT THERE WILL BE SEVERAL HOURS DURING
THE LATE AFTERNOON INTO THE EARLY EVENING WHEN SFC HEATING IS
POSSIBLE. THE SHEAR PROFILES AND HODOGRAPHS SHOWN BY MOST MODEL
GUIDANCE ACROSS THE SOUTHERN HALF OF THE FORECAST AREA AT THAT
TIME ARE FRIGHTENING WITH OVER 65 KNOTS OF DEEP LAYER SHEAR AND
0-1 KM HELICITY IN THE 400 TO 500 RANGE! ANY DEEP UPDRAFTS
OCCURRING AT THAT TIME CERTAINLY HAVE THE POTENTIAL FOR
SIGNIFICANT SEVERE WEATHER. THE CAMS INDICATE A LINEAR MODE OF
CONVECTION TOMORROW EVENING, WITH THE POTENTIAL FOR DISCRETE CELLS
AS WELL.
AS AN ASIDE, TOMORROW MARKS THE 48TH ANNIVERSARY OF THE LAST F4
TORNADO IN MICHIGAN.
HEAVY RAIN COULD ALSO CAUSE SOME MINOR FLOODING BY TOMORROW
EVENING. SEE HYDRO SECTION BELOW FOR DETAILS.
AVIATION /00Z TAFS THROUGH 00Z THURSDAY/
ISSUED AT 802 PM EDT TUE APR 1 2025
QUITE AN IMPACTFUL FORECAST PERIOD COMING UP FOR THE TERMINALS
OVER THE NEXT 24 HOURS. THE FIRST 6 HOURS THROUGH 06Z SHOULD BE
QUIET WITH VFR CONDITIONS, AND INCREASING WINDS FROM THE EAST.
PRECIPITATION WILL LIKELY START TO MOVE IN FROM SW TO NE AFTER
05-06Z IN THE FORM OF SNOW. IT WILL BE AN HOUR OR TWO IN DURATION
ALONG I-94, AND 2-3 HOURS ALONG I-96. SOME LIGHT FREEZING RAIN
WILL BE POSSIBLE FOR AN HOUR OR TWO ALONG I-96, BEFORE CHANGING TO
RAIN LIKELY BY 12Z.
SHOWERS WILL BE FAIRLY WIDESPREAD MOST OF THE DAY, WITH THUNDER
STORMS BECOMING POSSIBLE AFTER 14-15Z. CONDITIONS WILL DETERIORATE
QUICKLY GOING DOWN LIKELY TO LIFR, IF NOT VLIFR. WINDS WILL REMAIN
GUSTY THROUGH THE DAY. CONDITIONS WILL IMPROVE A BIT AFTER 20-21Z
AS THE WARM FRONT MOVES THROUGH THE TERMINALS. WE THEN HAVE SOME
LOW LEVEL WIND SHEAR WITH 60 KNOTS AT 2K FT FROM THE SSW, AND THE
SFC WINDS FROM THE SE. ADDITIONAL STORMS ARE LIKELY, BUT PROBABLY
JUST AFTER 00Z THU.
MARINE
ISSUED AT 352 PM EDT TUE APR 1 2025
REPLACED THE GALE WATCH WITH A GALE WARNING FOR LATE TONIGHT
THROUGH WEDNESDAY EVENING. SOUTHEAST WINDS WILL GUST TO 35 KNOT
GALES AT TIMES. THE OFFSHORE COMPONENT OF THE WINDS WILL KEEP THE
HIGHEST WAVES WELL OFFSHORE, WITH 4 TO 6 FOOT WAVES MOSTLY
CONFINED TO OUT BEYOND A COUPLE MILES FROM SHORE.
THERE COULD ALSO BE WINDS GUSTING OVER 40 KNOTS WEDNESDAY EVENING
AS A LINE OF THUNDERSTORMS MOVES ACROSS THE LAKE. HAIL AND EVEN
WATERSPOUTS ARE POSSIBLE WITH THESE STORMS.
A SMALL CRAFT ADVISORY WILL BE NEEDED TO REPLACE THE GALE WARNING
LATER WEDNESDAY NIGHT. CONDITIONS WILL IMPROVE ON THURSDAY AS
HIGH PRESSURE BUILDS IN AND WINDS DECREASE TO LESS THAN 25 KNOTS
DURING THE AFTERNOON.
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 FROM 2 AM TO NOON EDT WEDNESDAY FOR
MIZ037>040-043>046-051-052.
MARINE...GALE WARNING FROM 4 AM TO 11 PM EDT WEDNESDAY FOR LMZ844>849.
DISCUSSION...OSTUNO
AVIATION...NJJ
MARINE...OSTUNO
HYDROLOGY...AMD
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