374
FXUS63 KGRR 011953
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
353 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 /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 150 PM EDT TUE APR 1 2025
HIGH CONFIDENCE FOR VFR CONDITIONS AT ALL TERMINALS THROUGH 00Z.
THIS WOULD ALSO BE THE CASE FOR SOUTHERN TERMINALS (AZO-BTL-JXN)
THROUGH 06Z. THE MAIN CHANGE THIS UPDATE WAS TO ADD SOME DETAIL
AFTER 06Z WHEN PRECIPITATION TYPES COULD BECOME ESPECIALLY
VARIABLE, PARTICULARLY AT THE MKG-GRR-LAN TERMINALS, AS THIS MARKS
THE EXPECTED TRANSITION ZONE BETWEEN FREEZING/FROZEN
PRECIPITATION TO THE NORTH AND MAINLY LIQUID PRECIPITATION TO THE
SOUTH. THERE IS A LOW PROBABILITY FOR A BRIEF WINDOW OF ZR OR PL
AT ONE OR MORE OF THESE TERMINALS OVERNIGHT, BUT THIS IS FAR TOO
UNCERTAIN TO CARRY EXPLICITLY IN THE TERMINAL FORECASTS AT THIS
TIME.
AS NOTED PREVIOUSLY, PRECIPITATION ONSET TIMES AND INITIAL
CHARACTERISTICS ARE HIGHLY UNCERTAIN GIVEN THE CURRENTLY DRY
AIRMASS IN PLACE AND DEPENDENCE ON PRECIPITATION INTENSITY AMONG
OTHER THINGS. THAT SAID, AGREE WITH PREVIOUS THINKING THAT RAIN
SHOULD BE THE PREDOMINANT PRECIPITATION TYPE AFTER 12Z AND HAVE
ALSO INCLUDED PROB30 FOR THUNDERSTORMS AT ALL TERMINALS TO
ACCOMPANY THIS. LOW LEVEL WIND SHEAR COULD BE QUITE SUBSTANTIAL
OVERNIGHT AND WELL INTO WEDNESDAY MORNING AND THIS WILL LATER BE
COMPLICATED BY THE PRESENCE OF WHAT SHOULD BE MOSTLY ELEVATED
THUNDERSTORMS.
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...TJT
MARINE...OSTUNO
HYDROLOGY...AMD
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