888
FXUS63 KGRR 151744
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
144 PM EDT THU MAY 15 2025
KEY MESSAGES
- SEVERE STORMS THIS EVENING
- ANOTHER ROUND OF STORMS POSSIBLE FRIDAY EVENING
- COOL AND CALM EARLY NEXT WEEK
DISCUSSION
ISSUED AT 425 AM EDT THU MAY 15 2025
- SEVERE STORMS THIS EVENING
ONLY SCATTERED SHOWERS EXPECTED TODAY AS SHORTWAVE RIDGE AXIS RESULTS
IN A CAPPING INVERSION INTO THE AFTERNOON. HEIGHTS FALL BY EVENING
AS THE DEEPENING UPPER LOW MOVES ACROSS NORTHERN MINNESOTA AND
THIS, ALONG WITH SFC HEATING AND LOW LEVEL MOISTURE ADVECTION
WILL RESULT IN 2000 TO 3000 J/KG OF CAPE ACROSS THE SOUTHWEST
FORECAST AREA BY EARLY EVENING. DEEP LAYER SHEAR IS PROGGED TO BE
ABOUT 30 KNOTS IN THIS AREA, NOT EXCEPTIONALLY STRONG, BUT
SUFFICIENT FOR ORGANIZED STORMS. 0 TO 1 KM HELICITY VALUES OF 150
TO 200 M2/S2 ARE ALSO PRESENT, SO ROTATING UPDRAFTS ARE EXPECTED
ALONG WITH THEIR ATTENDANT LARGE HAIL AND TORNADO THREAT.
THE HI-RES ARW AND OTHER MODEL GUIDANCE HAS BEEN CONSISTENT WITH
THE TIMING OF A LINE OF STORMS MOVING ALONG OR JUST AHEAD OF AN
OCCLUDED FRONT THAT IS THE FOCUS OF LOW LEVEL CONVERGENCE AND
LIFT, WITH THE ARRIVAL TIME AROUND 00Z TO 01Z AT THE LAKE MICHIGAN
COAST AND BETWEEN 01Z AND 02Z IN GRAND RAPIDS/KALAMAZOO THEN 02Z
TO 03Z FROM LANSING TO JACKSON.
STORM MODE MOST LIKELY WILL BE EVOLVING FROM DISCRETE CELLS TO
QUASI-LINEAR AFTER SUNSET WITH EMBEDDED MESOCYCLONES AND
DOWNBURST/SURGING WINDS. THE POTENTIAL FOR DISCRETE SUPERCELLS
THAT CAN PRODUCE LARGE HAIL AND LONGER TRACK TORNADOES IS LOWER,
BUT CANNOT BE RULED OUT.
- ANOTHER ROUND OF STORMS POSSIBLE FRIDAY EVENING
A SECOND THOUGH DIFFERENT CHARACTER OF SEVERE THUNDERSTORM
ENVIRONMENT COULD SET UP FOR FRIDAY EVENING AS A 500 MB SHORTWAVE
TROUGH ROUNDS THE BASE OF THE LOW AND APPROACHES LOWER MICHIGAN.
FORECAST THERMODYNAMIC PROFILES FRIDAY EVENING AKIN TO THE HIGH
PLAINS WILL FEATURE STEEP LAPSE RATES FROM THE SURFACE TO 600-500
MB, WITH THE WELL MIXED DIURNAL BOUNDARY LAYER IN THE LOWER
ATMOSPHERE NEARLY THE SAME POTENTIAL TEMPERATURE AS AN EML IN THE
MID-LEVELS WHICH ADVECTS IN LATE IN THE DAY. SEVERAL CAMS HAVE BEEN
DEVELOPING ELEVATED AND HIGH-BASED SHOWERS OR STORMS DURING THE
EVENING WITH THE SUPPORT OF THE 500 MB SHORTWAVE. THE MOIST
CONVECTION WOULD BE IN A STRONGLY SHEARED LAYER COLD ENOUGH FOR SOME
HAIL PRODUCTION.
IF STORMS DEVELOP FRIDAY EVENING, CONSIDERABLE DOWNDRAFT POTENTIAL
EXISTS GIVEN ABOUT 8,000 FEET OF DRY AND WELL MIXED AIR UNDERNEATH
THE STORMS (DEEP INVERTED-V SOUNDING). DCAPE MAY BE NEAR 1,000 J/KG
AND INHIBITING STABLE LAYERS FOR DOWNDRAFTS MAY BE LIMITED
ESPECIALLY EARLIER IN THE EVENING. 25 KNOTS OF LOW-LEVEL WIND
MOMENTUM WILL ALSO BE AVAILABLE TO AUGMENT THE SPEED OF THE WINDS
EMANATING FROM DOWNBURSTS. AS SUCH, THERE IS A GUSTY WIND THREAT,
POSSIBLY EVEN ISOLATED SEVERE.
- COOL AND CALM EARLY NEXT WEEK
SFC LOW MOVES EAST SATURDAY NIGHT AND CANADIAN SFC RIDGE REPLACES
IT WITH MUCH COOLER TEMPERATURES. OVERNIGHT LOWS WILL FALL INTO
THE 30S AGAIN EARLY NEXT WEEK AND THERE IS A THREAT OF FROST AND
FREEZING TEMPERATURES ON SUNDAY NIGHT AND POSSIBLY MONDAY NIGHT.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 144 PM EDT THU MAY 15 2025
VFR CONDITIONS ARE EXPECTED WITH SOUTHEAST WINDS AND SCT-BKN CUMULUS
AROUND 3000 TO 5000 FEET THIS AFTERNOON. THUNDERSTORMS MOVE IN
FROM 00-04Z FROM WEST TO EAST TONIGHT. THESE STORMS COULD PRODUCT
GUSTS GREATER THAN 50 KNOTS, LARGE HAIL, AND TORNADOES.
ADDITIONALLY STORMS COULD BRIEFLY BRING MVFR CEILINGS AND IFR
VISIBILITIES. THUNDERSTORMS WILL LINGER OVER ANY ONE LOCATION FOR
ABOUT AN HOUR. WINDS BECOME SOUTHWESTERLY AS THUNDERSTORMS EXIT
TO THE EAST OVERNIGHT WITH CLEARING SKIES.
MARINE
ISSUED AT 425 AM EDT THU MAY 15 2025
THE FOG SHOULD START TO MIX OUT THIS AFTERNOON AS WINDS PICK UP.
THERE IS THE POTENTIAL FOR WIND GUSTS OVER 40 KNOTS LATE THIS
AFTERNOON AND INTO THE EVENING AS STRONG THUNDERSTORMS MOVE
THROUGH. WINDS GUSTING OVER 25 KNOTS AND WAVES GREATER THAN 4
FEET CAN BE EXPECTED FRIDAY INTO SATURDAY.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...OSTUNO
AVIATION...RAH
MARINE...OSTUNO
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