576
FXUS63 KGRR 011750
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
150 PM EDT TUE APR 1 2025
KEY MESSAGES
- WINTRY MIX LIKELY TUESDAY NIGHT
- CONDITIONAL SEVERE WEATHER THREAT WEDNESDAY AFTERNOON/EVENING
- CHANCE OF RAIN SHOWERS THIS WEEKEND
DISCUSSION
ISSUED AT 352 AM EDT TUE APR 1 2025
- WINTRY MIX LIKELY TUESDAY NIGHT
DRY CONDITIONS ARE EXPECTED THROUGH THE DAY TODAY AS SURFACE RIDGING
MOVES THROUGH THE AREA. PRECIPITATION THEN RETURNS TONIGHT AS A
POTENT UPPER-LEVEL TROUGH DRIVES A SURFACE LOW INTO THE UPPER
MIDWEST. A MID-LEVEL PERTURBATION COMBINED WITH STRONG WARM AIR
ADVECTION WILL SERVE AS THE CATALYST FOR A LATE WINTER EVENT NEAR
AND NORTH OF I96.
SNOW STARTS OFF TOWARDS MIDNIGHT TONIGHT, VERY QUICKLY CHANGING TO
RAIN SOUTH OF I96 AS WARM AIR ADVECTION TAKES HOLD. LITTLE TO NO
ACCUMULATION IS EXPECTED ACROSS THIS PORTION OF THE AREA. EASTERLY
FLOW KEEPS SURFACE COLD AIR IN PLACE LONGER NORTH OF I96, ESPECIALLY
IN OUR HIGHER TERRAIN AREAS SUCH AS LAKE, NEWAYGO, MECOSTA, AND
OSCEOLA COUNTIES. THIS RESULTS IN PRECIPITATION CHANGING OVER TO
FREEZING RAIN TOWARDS DAYBREAK THROUGH THE LATE MORNING/EARLY
AFTERNOON HOURS WHERE PRECIPITATION CHANGES OVER TO RAIN.
BY THE TIME ALL IS SAID AND DONE, THE FORECAST CONTINUES TO FAVOR UP
TO TWO INCHES OF SNOW AND ONE TO TWO TENTHS OF AN INCH OF ICE FOR
THE AREA ROUGHLY NORTH OF A WHITEHALL TO ITHACA LINE WHICH WILL
BRING THE POTENTIAL FOR MORNING COMMUTE IMPACTS. A WINTER WEATHER
ADVISORY MAY BE NEEDED IF TRENDS CONTINUE TO HOLD WITH THE 12Z
GUIDANCE.
- CONDITIONAL SEVERE WEATHER THREAT WEDNESDAY AFTERNOON/EVENING
ATTENTION THEN TURNS TO WEDNESDAY'S CONVECTIVE POTENTIAL WHICH IS A
COMPLICATED FORECAST. A CONDITIONAL RISK FOR SEVERE THUNDERSTORMS
EXISTS MAINLY WEDNESDAY AFTERNOON AND EVENING. WHAT IS KNOWN IS THAT
THE PRESENCE OF A 100 PLUS KNOT MID-LEVEL JET AND 50-70 KNOT LOW-
LEVEL JET WILL CREATE A HIGHLY DYNAMIC ENVIRONMENT ACROSS THE AREA.
THIS WILL RESULT IN 60-80 KNOTS OF DEEP LAYER SHEAR AND 50-70 KNOTS
OF LOW-LEVEL SHEAR ACROSS THE AREA.
IN THE MORNING AND EARLY AFTERNOON HOURS, A FEW HUNDRED JOULES OF
MUCAPE WILL ALLOW FOR ELEVATED THUNDER CHANCES TO DEVELOP. SEVERE
WEATHER IS NOT EXPECTED WITH THIS ACTIVITY THOUGH AN ISOLATED
STRONGER STORM OR TWO CANNOT BE COMPLETELY RULED OUT GIVEN HIGH
SHEAR.
THE CRUX OF THE UNCERTAINTY, AND THE BEST SEVERE THUNDERSTORM
POTENTIAL, LIES IN THE EXTENT OF ATMOSPHERIC RECOVERY THAT IS ABLE
TO OCCUR DURING THE AFTERNOON AND EVENING HOURS. SOUTHERLY ADVECTION
IS FORECAST TO LIFT A WARM FRONTAL BOUNDARY NORTH INTO CENTRAL LOWER
MICHIGAN LEADING TO WARMER AND MOISTER AIR ADVECTING INTO THE AREA.
GUIDANCE IS SPLIT ON THE EXTENT THIS OCCURS, AS ANY DESTABILIZATION
WILL BE HIGHLY DEPENDENT ON THE EXTENT OF EARLY DAY CLOUD COVER AND
PRECIPITATION. CAM GUIDANCE DEPICTS A LIKELY QUASI-LINEAR SETUP
WHICH MATCHES THE EXPECTATIONS FROM FORECAST THERMAL AND WIND
PROFILES. THIS LINE OF STORMS WOULD MOVE ACROSS THE CWA BETWEEN
ROUGHLY 4PM AND 1AM.
IF ENOUGH INSTABILITY CAN DEVELOP AHEAD OF THIS LINE FOR CONVECTION
TO BECOME SURFACE BASED, AN ALL HAZARDS SEVERE EVENT IS POSSIBLE.
THE STRONG WINDS ALOFT WOULD FAVOR A DECENT DAMAGING WIND THREAT
FOLLOWED BY A TORNADO THREAT GIVEN LONG STREAMWISE HODOGRAPHS.
HOWEVER, IF SURFACE BASED INSTABILITY DOES NOT DEVELOP AND THESE
STORMS REMAIN ELEVATED, THAT STREAMWISE INFLOW WOULD NOT BE REALIZED
BY THE STORM AND THE SEVERE THREAT WOULD BE TEMPERED. THE BEST
CHANCE FOR ANY SURFACE BASED DESTABILIZATION IF IT OCCURS WOULD BE
NEAR AND SOUTH OF I96, PARTICULARLY I94.
WHILE THE CEILING FOR THIS EVENT IS ELEVATED, CONFIDENCE IN SURFACE
DESTABILIZATION IS LOW GIVEN ITS DEPENDENCE ON MORNING PRECIPITATION
SO CONFIDENCE IN THE OCCURRENCE OF SEVERE WEATHER IS LOWER. THE
OTHER PIECE TO WATCH FOR IS THAT THIS EVENT DOES FIT THE CONCEPTUAL
MODEL FOR GRAVITY WAVE ASSOCIATED CONVECTION (GWAC) WHICH GIVEN THE
STRONG KINEMATICS MEANS THAT IN A WEAKLY STABLE ENVIRONMENT A
GUSTIER STORM STILL CANNOT BE RULED OUT. AS A BETTER PICTURE OF
TONIGHTS PRECIPITATION OCCURS, WE WILL BE ABLE TO NARROW DOWN THE
MAGNITUDE AND PLACEMENT OF ANY SEVERE WEATHER RISK. ALL IN ALL A
HIGHLY COMPLICATED SETUP EXISTS OVER THE NEXT 48 HOURS WITH A
CONDITIONAL SEVERE WEATHER RISK, BUT A NOTABLE FAILURE MODE PRESENT
AS WELL.
- CHANCE OF RAIN SHOWERS THIS WEEKEND
THURSDAY AND FRIDAY REMAIN DRY ACROSS THE AREA AS RIDGING DOMINATES
THE FORECAST. PRECIPITATION THEN RETURNS SATURDAY INTO SUNDAY AS AN
UPPER-LEVEL TROUGH DRIVES A SURFACE LOW ACROSS THE OHIO VALLEY.
TRENDS ARE FOR LIGHT RAIN MAINLY NEAR AND SOUTH OF I96, WITH THE
HEAVIER RAIN MISSING US TO THE SOUTH. OTHERWISE IT WILL BE MILD WITH
HIGHS IN THE 50S THURSDAY THROUGH SATURDAY AND THE UPPER 40S SUNDAY.
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 AM EDT TUE APR 1 2025
A STRONG LOW-LEVEL JET DEVELOPS TONIGHT AS A DEEP SURFACE LOW
MOVES INTO THE UPPER GREAT LAKES. EASTERLY OFFSHORE FLOW WILL
DOMINATE THROUGH EARLY WEDNESDAY AFTERNOON BEFORE BECOMING
SOUTHERLY AND THEN WESTERLY WEDNESDAY NIGHT BEHIND A COLD FRONT.
IN THE EASTERLY FLOW PORTION OF THIS SYSTEM, SPECIFICALLY EARLY
WEDNESDAY MORNING THROUGH EARLY WEDNESDAY AFTERNOON FORECAST
SOUNDINGS SUGGEST THE POTENTIAL TO MIX INTO 35-40 KNOT WINDS. A
GALE WATCH HAS BEEN ISSUED FOR ALL NEARSHORE ZONES GIVEN THIS.
CONDITIONS HAZARDOUS TO SMALL CRAFT THEN CONTINUE AFTER ANY
POTENTIAL GALES SUBSIDE INTO THURSDAY.
HYDROLOGY
ISSUED AT 250 PM EDT MON MAR 31 2025
WITH ANOTHER ROUND OF WIDESPREAD RAIN COMING UP ON WEDNESDAY, WE
NEED TO BE THINKING ABOUT THE CAPACITY OF OUR RIVERS TO HANDLE ALL
THIS WATER. AS OF MONDAY AFTERNOON, THE MUSKEGON RIVER IS ALREADY AT
NEAR OR SLIGHTLY ABOVE-NORMAL LEVELS, WHILE THE GRAND AND KALAMAZOO
RIVERS ARE AT NEAR TO SLIGHTLY BELOW NORMAL LEVELS FOR THIS TIME OF
YEAR. ENSEMBLE GUIDANCE IS IN PRETTY GOOD AGREEMENT ON AT LEAST
ANOTHER INCH OR SO OF RAIN COMING UP ACROSS A LARGE PORTION OF OUR
BIG 3 WATERSHEDS. IF THIS COMES TO PASS, OUR RIVERS SHOULD BE ABLE
TO HANDLE THINGS RELATIVELY SMOOTHLY, WITH ONLY THE LOWER MUSKEGON
RIVER (NEWAYGO AND BRIDGETON) LOCATIONS RISING TO BANKFULL BUT NOT
REACHING MINOR FLOOD LEVELS LATER THIS WEEK.
HOWEVER, BECAUSE MUCH OF THIS PRECIPITATION WILL BE DRIVEN BY
CONVECTION, WE FULLY EXPECT SOME BULLSEYES/LOCALIZED AREAS TO
APPROACH 2 INCHES OF RAIN DURING THE WEDNESDAY AND WEDNESDAY NIGHT
TIMEFRAMES. IF RAIN TOTALS APPROACH 2 INCHES OVER THE GRAND OR
KALAMAZOO BASINS, THE MAINSTEM RIVERS SHOULD STILL MOSTLY BE OK, BUT
SOME OF THE SMALLER TRIBUTARY STREAMS - ESPECIALLY AROUND THE
LANSING AREA, SUCH AS THE RED CEDAR AND SYCAMORE CREEK - WOULD
APPROACH FLOOD LEVELS. SIMILARLY, IF THESE 2 INCH RAIN TOTALS FALL
UP OVER THE MUSKEGON RIVER, WE'D LIKELY PUSH BRIDGETON AND NEWAYGO
WELL INTO MINOR FLOOD STAGE.
WE'LL BE CLOSELY MONITORING EXPECTED RAIN TOTALS OVER THE NEXT 36
HOURS BEFORE THE STORM BEGINS, BUT NOW IS THE TIME FOR ANY FOLKS
LIVING OR PLAYING NEAR WEST MICHIGAN RIVERS TO PREPARE FOR LIKELY
RISING WATER LEVELS LATER THIS WEEK.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...GALE WATCH FROM LATE TONIGHT THROUGH WEDNESDAY AFTERNOON FOR
LMZ844>849.
DISCUSSION...THOMAS
AVIATION...TJT
MARINE...THOMAS
HYDROLOGY...AMD
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