092
FXUS63 KGRR 181745
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
145 PM EDT SUN MAY 18 2025
KEY MESSAGES
- MILD AND DRY TODAY AND MONDAY
- APRIL-LIKE WEEK AHEAD: CHILLY, OCCASIONALLY WET, AND BREEZY
DISCUSSION
ISSUED AT 312 AM EDT SUN MAY 18 2025
- MILD AND DRY TODAY AND MONDAY
UPPER TROUGHING SLOWLY PULLS AWAY FROM THE REGION TODAY INTO
MONDAY. MUCH OF THE REGION WILL HAVE MOSTLY CLOUDY SKIES TODAY,
ESPECIALLY NEAR AND NORTH OF I-96. THIS IS DUE TO EXTENSIVE
MOISTURE IN THE 925-850MB LAYER HANGING TOUGH AROUND THE REGION,
AS EVIDENT BY RAP13 MODEL GUIDANCE. SOUTH OF I-96, A BETTER
CHANCE AT SOME SUNSHINE EXISTS, AND THAT IS PARTICULARLY TRUE WEST
OF I-69. HIGHS ARE ANTICIPATED TO BE AROUND 60 FOR CENTRAL LOWER
MI AND LOW TO PERHAPS MID 60S SOUTH OF I-96 AND AWAY FROM THE
LAKE. FOR MONDAY, A MIX OF CLOUDS AND SUN IS FORECAST WITH SIMILAR
TEMPERATURES AS UPPER RIDGING BRIEFLY MOVES IN.
- APRIL-LIKE WEEK AHEAD: CHILLY, OCCASIONALLY WET, AND BREEZY
WE'LL BE HEADING BACKWARDS IN THE UPPER PATTERN EVOLUTION TO MORE
OF AN APRIL REGIME ACROSS THE GREAT LAKES. AN UPPER LOW IS
FORECAST TO DEVELOP ACROSS THE MIDWEST ON TUESDAY AS OUR BRIEF
UPPER RIDGING GETS SQUASHED. THE LEFT EXIT REGION OF AN UPPER JET
MOVES INTO THE REGION LATE TUESDAY AS THE EASTERN EDGE OF THE 500
MB CLOSED LOW APPROACHES, BRINGING COUNTERCLOCKWISE 850MB FLOW
AROUND IT TO PULL SOME GULF MOISTURE NORTHWARD AND WRAPPING AROUND
AN OCCLUDING SURFACE LOW.
THE LATEST MODEL GUIDANCE IS TRENDING SLIGHTLY FURTHER NORTH WITH
THIS OCCLUDING LOW, AND HENCE THE QPF IS BUMPING A BIT HIGHER
ESPECIALLY FOR AREAS NEAR AND SOUTH OF I-96. CURRENT ECE ENSEMBLE
GUIDANCE DEPICTS A 60-70% PROBABILITY FOR 0.50" OR MORE OF RAIN
MAINLY NEAR AND SOUTH OF I-96 FROM TUESDAY AFTERNOON INTO
WEDNESDAY. AROUND 20% OF THE ECE MEMBERSHIP SUPPORTS 1.00" OR MORE
OF RAIN AS WELL, AND THE 00Z DETERMINISTIC ECMWF FALLS INTO THAT
MEMBERSHIP ENVELOPE WITH AROUND 1.00" FORECAST FOR MANY AREAS NEAR
AND WEST OF US 131. THERE MAY BE A SHARP NORTHERN EDGE/CUTOFF TO
THE HIGHER RAIN TOTALS, SO SOME VARIABILITY IS EXPECTED ACROSS THE
REGION. ANY TREND BACK TOWARD THE SOUTH WILL BRING RAIN TOTALS
DOWN QUITE A BIT, SO WILL HAVE TO SEE IF MODELS WILL LOCK INTO A
SOLUTION SOON.
AS THE UPPER LOW MOVES EAST ON WEDNESDAY, ENSEMBLE GUIDANCE
STRONGLY SUPPORTS A PHASING OF THIS SYSTEM WITH AN UPPER LOW SOUTH
OF HUDSON BAY, AND THAT MAY ESSENTIALLY PARK THIS SYSTEM OVERHEAD
THROUGH THURSDAY WITH PERIPHERAL INFLUENCE ON THE BACK SIDE OF IT
ON FRIDAY INTO SATURDAY. THAT WILL LEAD TO PERIODIC LIGHT RAIN
SHOWERS AND DRIZZLE. ECE 850MB TEMPERATURES CRASH BY THURSDAY
INTO SUBZERO TERRITORY, WHICH IS VERY ANOMALOUS AND QUITE COLD FOR
MID TO LATE MAY. IF THAT OCCURS, TEMPERATURES MAY STRUGGLE TO GET
OUT OF THE 40S ON THURSDAY, AS THE LATEST DETERMINISTIC ECMWF IS
INDICATING.
THROUGHOUT THE TUESDAY THROUGH THURSDAY PERIOD, BREEZY CONDITIONS
ARE EXPECTED. A FAIRLY DECENT PRESSURE GRADIENT FORCE ACROSS
MICHIGAN, NORTH OF THE OCCLUDING LOW, WILL ENSURE BRISK EASTERLY
SURFACE FLOW TUESDAY AND WEDNESDAY, WHICH OFTEN OVERACHIEVES IN A
CORRIDOR FROM SAGINAW BAY TO LANSING AND GRAND RAPIDS. WIND GUSTS
MAY REACH 30 TO 40 MPH ACROSS THE REGION. BY THURSDAY, WINDS
SWITCH TO THE NW AND COULD ALSO GUST ABOVE 30 MPH. THAT WILL MAKE
THURSDAY'S TEMPERATURES POTENTIALLY FEEL EVEN COLDER THAN
FORECAST.
AVIATION /18Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 145 PM EDT SUN MAY 18 2025
WE ARE CONTINUING A THEME OF PERSISTENT MVFR CEILINGS INTO THE
OVERNIGHT HOURS FOR OUR MOST INLAND TERMINALS (LAN/JXN/BTL). BY
21Z THIS AFTERNOON, THERE COULD BE A SIGNIFICANT CUTOFF BETWEEN
MVFR AT THOSE LOCATIONS AND VFR/NO CEILINGS IMMEDIATELY WEST AT
GRR/AZO. THE GOOD NEWS IS THERE'S A LOW CHANCE OF CEILINGS
DROPPING BELOW 2000 FT AGL (FUEL ALT THRESHOLD) AT ANY OF THE
TERMINALS WHICH IS CERTAINLY MORE OPTIMISTIC THAN YESTERDAY.
MKG STANDS THE BEST CHANCE OF REMAINING PREDOMINANTLY VFR THROUGH
THE PERIOD DUE TO THE CURRENT CLEARING EFFECTS OF A LAKE BREEZE
THAT WILL EVENTUALLY YIELD TO N-NE BACKGROUND GRADIENT FLOW THIS
EVENING.
MARINE
ISSUED AT 312 AM EDT SUN MAY 18 2025
THE NEXT PERIOD FOR HAZARDS TO MARINERS WILL LIKELY HOLD OFF UNTIL
TUESDAY AS EASTERLY FLOW INCREASES OVER THE LAKE, POTENTIALLY
GETTING HIGH ENOUGH FOR SCA CRITERIA, THOUGH HIGHER WAVE ACTION
WILL BE PUSHED OUT OVER THE OPEN WATERS. WAVE ACTION WILL LIKELY
BUILD WEDNESDAY INTO THURSDAY AS FLOW SHIFTS NORTH TO NORTHWEST,
POTENTIALLY LEADING TO AN EXTENDED SCA FOR THAT PERIOD.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...TJT
AVIATION...HOVING
MARINE...HOVING
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