605
FXUS63 KGRR 090807
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
407 AM EDT TUE JUN 9 2026
KEY MESSAGES
- SCATTERED SHOWERS AND STORMS TODAY
- STRONG TO SEVERE STORMS POSSIBLE WEDNESDAY AND THURSDAY
- TURNING COOLER FOR FRIDAY THROUGH MONDAY
DISCUSSION
ISSUED AT 407 AM EDT TUE JUN 9 2026
- SCATTERED SHOWERS AND STORMS TODAY
SCATTERED CONVECTION CONTINUES TO OCCUR EVEN AT THIS HOUR (3AM)
DUE TO A SLIGHT INCREASE IN THE LOW LEVEL JET AND WEAK INSTABILITY
THAT REMAINS IN PLACE. WE ARE NOT EXPECTING ANYTHING WIDESPREAD
THROUGH DAYBREAK BUT SHOWERS AND A FEW STORMS WILL CONTINUE TO
PERCOLATE GIVEN THE HI-RES MODELS SHOWING A 25-35 KNOT LLJ THROUGH
DAYBREAK.
THE FOCUS WILL THEN TURN TO THE AFTERNOON AND EVENING AS THE LOW
LEVEL JET REDEVELOPS ACROSS THE SOUTHERN HALF OF THE FORECAST AREA
(I-96 SOUTHWARD). THE LOW LEVEL JET WILL BE A FOCUS FOR CONVECTION
ACROSS THE SOUTHERN CWA, WHILE A MID LEVEL SHORTWAVE TROUGH WILL
BRING AN INCREASE IN STORMS FOR THE EASTERN HALF OF THE FORECAST
AREA. SO, MUCH OF THE AREA WILL SEE SHOWERS AND STORMS THIS
AFTERNOON AND EVENING, ONCE THE MORNING LOW CLOUDS LIFT. DEEP
LAYER SHEAR IS NOT STRONG TODAY SO NOT EXPECTING ORGANIZED SEVERE
WEATHER. SPC HAS US IN GENERAL THUNDER AND THAT MATCHES OUT
THINKING.
- STRONG TO SEVERE STORMS POSSIBLE WEDNESDAY AND THURSDAY
STRONG TO SEVERE STORMS WILL BE POSSIBLE BOTH WEDNESDAY AND
THURSDAY. THE STORM PREDICTION CENTER HAS THE AREA IN A SLIGHT
RISK ON WEDNESDAY AND AN ENHANCED RISK ON THURSDAY.
A WARM FRONT WILL LIFT THROUGH THE AREA ON WEDNESDAY WHICH WILL
PROVIDE A FOCUS FOR CONVECTION. THE LLJ RAMPS UP TO 35 TO 45 KNOTS
AT LEAST WITH SOME MODELS SHOWING A CONVECTIVELY ENHANCED JET OF
OVER 50 KNOTS. A COUPLE ROUNDS OF STORMS APPEAR POSSIBLE DURING
THE AFTERNOON/EVENING AND INTO THE OVERNIGHT. WE ARE MOST LIKELY
LOOKING AT A LINEAR SYSTEM MOVING OUR DIRECTION FROM WI/IL WITH
WIND BEING THE PRIMARY THREAT. DEEP LAYER SHEAR IS NOT ALL THAT
STRONG WEDNESDAY AFTERNOON/EVENING, BUT UPPER LEVEL DIFFLUENCE
WILL AID THE MAINTENANCE OF THE STORMS. MUCAPE VALUES WILL LIKELY
REACH THE 2,000 TO 3,000 J/KG RANGE.
THURSDAY THE PARAMETER SPACE IS EVEN BETTER WHICH IS WHY THE SPC
HAS US IN A ENHANCED RISK FOR SEVERE WEATHER. MUCAPE VALUES WILL
INCREASE TO 3,000+ J/KG WITH DEEP LAYER SHEAR INCREASING TO BETTER
THAN 40 KNOTS IN THE EVENING. GIVEN THE CAPE/SHEAR BALANCE AND
VALUES ALL HAZARDS ARE IN PLAY. THE COLD FRONT LOOKS TO BE THE
PRIMARY FORCING MECHANISM AND IT MOVES THROUGH THE AREA THURSDAY
NIGHT.
PWAT VALUES IN THE 1.75 TO 2.00+ RANGE WILL MAKE HEAVY RAIN AND
LOCALIZED FLOODING A THREAT WITH ALL STORMS THIS WEEK. THE HIGHEST
MOISTURE CONTENT WILL BE THURSDAY INTO THURSDAY NIGHT WHEN
TORRENTIAL DOWNPOURS ARE POSSIBLE.
- TURNING COOLER FOR FRIDAY THROUGH MONDAY
WE TURN COOLER BEHIND THURSDAY NIGHTS COLD FRONT. FRIDAY AND
SATURDAY, TEMPERATURES MAY REMAIN NEAR NORMAL. BY SUNDAY AND
MONDAY HOWEVER WE WILL LIKELY BE SLIGHTLY BELOW NORMAL. HIGHS ON
MONDAY WILL LIKELY HOLD IN THE MIDDLE 70S.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 212 AM EDT TUE JUN 9 2026
2 MAIN CONCERNS THE NEXT 24 HOURS...THE POTENTIAL FOR LOW
CEILINGS AND THREAT OF THUNDERSTORMS. LOW CEILINGS ARE EXPECTED TO
DEVELOP AND/OR SPREAD INTO THE AREA OVER THE COURSE OF THE
REMAINDER OF THE NIGHT AND INTO THE MORNING HOURS OF TUESDAY.
CEILINGS WILL LIKELY DIP TO IFR AT MOST TAF SITES DURING THE 09Z
TO 16Z TIME FRAME. WE EXPECT IMPROVING CEILINGS DURING THE
AFTERNOON ON TUESDAY AS THE LOW CEILINGS LIFT/SPREAD NORTHWARD.
AS FOR THUNDERSTORMS, THERE ARE TWO DISTINCT TIME FRAMES, ONE IS
THE REST OF TONIGHT AND THE OTHER IS THIS AFTERNOON. FOR THE
REMAINDER OF THE NIGHT THE STORMS SHOULD BE SCATTERED AND ON THE
WEAK SIDE. THIS AFTERNOON, STRONGER STORMS ARE ANTICIPATED. KAZO,
KBTL, KLAN AND KJXN WILL BE MOST AFFECTED. STORM CHANCES ARE
HIGHEST AT THESE TAF SITES FROM 18Z TO 23Z.
MARINE
ISSUED AT 407 AM EDT TUE JUN 9 2026
WINDS AND WAVES LOOK TO REMAIN BELOW ADVISORY LEVELS TODAY,
TONIGHT AND THROUGH WEDNESDAY MORNING. IT IS DURING THE AFTERNOON
ON WEDNESDAY WHEN WINDS AND WAVES BEGIN TO RAMP UP. BY WEDNESDAY
EVENING SMALL CRAFT ADVISORIES AND BEACH HAZARD STATEMENTS WILL
LIKELY BE NEEDED. THE INCREASE IN WINDS WILL BE DUE TO A
TIGHTENING PRESSURE GRADIENT BETWEEN A PLAINS TROUGH AND A HIGH OF
THE MIDDLE ATLANTIC COAST. WAVES WILL REACH THE 4 FOOT THRESHOLD
IN THE EVENING AND THROUGH THE OVERNIGHT FROM HOLLAND NORTHWARD.
THERE IS THE POTENTIAL FOR DENSE MARINE FOG TODAY GIVEN VERY
MOIST AIR MOVING OVER COLDER LAKE WATERS. HOLDING OFF ON A MARINE
DENSE FOG ADVISORY AT THIS POINT, BUT WE WILL BE MONITORING
WEBCAMS.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...NONE.
DISCUSSION...DUKE
AVIATION...DUKE
MARINE...DUKE
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