963
FXUS63 KGRR 210621
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
221 AM EDT TUE JUL 21 2026
KEY MESSAGES
- LINGERING SHOWERS POSSIBLE THROUGH TONIGHT
- DRY AND COOLER THROUGH SATURDAY, WITH NEXT CHANCE OF RAIN SUNDAY
DISCUSSION
ISSUED AT 220 AM EDT TUE JUL 21 2026
- LINGERING SHOWERS POSSIBLE THROUGH TONIGHT
THE MAIN POTENTIAL OF RAIN (WHICH IN ITSELF MAY BE LIMITED), WILL
WRAP UP EARLY THIS MORNING. THIS IS AS WHATEVER LINE THAT CAN FORM
WITH LOW LEVEL JET DYNAMICS ON THEIR WAY OUT AND THE SHORT WAVE
EXITING THE FORECAST AREA BY 12Z.
A FEW SHOWERS WILL BUBBLE UP DURING THE AFTERNOON HOURS AS WE WILL
HAVE THE LONG WAVE TROUGH OVER THE AREA, WITH SHORT WAVES ROTATING
THROUGH. THERE MAY BE JUST ENOUGH INSTABILITY FOR A FEW RUMBLES OF
THUNDER. HOWEVER THE SUFFICIENT INSTABILITY WILL BE EXITING THE AREA
BY LATE AFTERNOON.
WE WILL NOT CLEAR OUT RIGHT AWAY, AS WE HAVE SOME RESIDUAL LOW LEVEL
MOISTURE LINGERING AROUND TONIGHT INTO EARLY WEDNESDAY. SOME OF THIS
IS ACTUALLY LAKE EFFECT WITH LAKE TEMPS IN THE UPPER TEENS TO LOWER
20S C AND +7C AIR COMING DOWN. THE TRAJECTORY IS MAINLY FROM THE NE,
SO IT SHOULD STAY WEST AND EAST OF THE AREA OFF OF LAKES MICHIGAN
AND HURON.
- DRY AND COOLER THROUGH SATURDAY, WITH NEXT CHANCE OF RAIN SUNDAY
WE SHOULD CLEAR OUT NICELY ON WEDNESDAY, WITH CLOUDS, AND BY THEN
SMOKE ALSO. WE SEE A NICE CANADIAN RIDGE BUILD OVER THE AREA,
BRINGING MUCH COOLER TEMPERATURES AND MUCH DRIER AIR.
WE SEE A LARGE UPPER RIDGE TAKE SHAPE OVER THE PLAINS, AND WE WILL
BE DOWNSTREAM OF THAT RIDGE UNDER A CONFLUENT FLOW. THIS PATTERN
WILL LOCK IN, AND HOLD THEN LIKELY THROUGH THE FIRST HALF OF THE
WEEKEND. WE WILL START OUT COOL, AND GRADUALLY WARM UP AS RETURN
FLOW BRINGS WARMER AIR IN GRADUALLY, ALONG WITH SOME ADDITIONAL
MOISTURE.
THERE IS ACTUALLY DECENT AGREEMENT AMONGST THE VARIOUS MODELS AND
ENSEMBLE MEMBERS THAT WE SEE A STRONG ENOUGH SHORT WAVE FLATTEN THE
UPPER RIDGE TEMPORARILY, AND THEN PUSH A COLD FRONT INTO THE AREA ON
SUNDAY. THIS LOOKS TO BE OUR NEXT CHANCE OF RAIN AFTER
TODAY/TONIGHT.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 141 AM EDT TUE JUL 21 2026
MAIN CHANGES THIS UPDATE WERE TO REMOVE PROB30 THUNDER MENTION AT
MKG/GRR BASED ON RECENT RADAR TRENDS AND HRRR GUIDANCE. THIS SAME
MODEL GUIDANCE LATER DEVELOPS A BAND OF SHOWERS/STORMS ALONG THE
I-94 CORRIDOR (AZO-BTL-JXN TERMINALS) IN THE 10Z TIMEFRAME, SO
HAVE ADDRESSED THIS WITH PROB30 GROUPS AT THOSE TERMINALS.
THUNDERSTORMS ARE NOT THAT FAR NORTH OF THE LAN TERMINAL AT THIS
TIME AND EXPECT AT LEAST A CHANCE FOR THUNDER BASED ON THESE
TRENDS. INTERESTINGLY, THERE IS ANOTHER WINDOW OF POSSIBLE
THUNDERSTORMS AT LAN THIS AFTERNOON, WHICH HAVE BEEN ADDRESSED
WITH ANOTHER PROB30 GROUP.
OTHER UPDATES WERE TO BE SLIGHTLY MORE PESSIMISTIC WITH VISIBILITY
RESTRICTIONS IN SMOKE IN THE SHORT TERM BEFORE THIS AIRMASS GETS
REPLACED WITH POST-COLD FRONTAL WINDS. ALSO THINK THAT JXN COULD
BRIEFLY SEE LLWS THRESHOLDS BEING MET GIVEN CURRENT RELATIVELY
WEAK SURFACE WINDS.
MARINE
ISSUED AT 220 AM EDT TUE JUL 21 2026
WE CONTINUE TO BELIEVE THAT WE ARE LOOKING AT A SOLID SCA AND BEACH
HAZARDS SCENARIO POST FRONTAL TODAY. A GOOD GRADIENT COMBINED WITH
GOOD COLD AIR ADVECTION OVER THE WARMER LAKE WILL STIR UP THE LAKE
PRETTY WELL. CAN NOT RULE OUT GALE GUSTS FOR A FEW HOURS, BUT THAT
WILL BE THE EXCEPTION RATHER THAN THE RULE. WINDS, AND EVENTUALLY
WAVES WILL COME DOWN ON WEDNESDAY.
ONCE THE WIND AND WAVES COME DOWN WEDNESDAY, WE ARE LOOKING AT WINDS
LIKELY STAYING BELOW 20 KNOTS UNTIL LATE SUNDAY.
GRR WATCHES/WARNINGS/ADVISORIES
MI...BEACH HAZARDS STATEMENT THROUGH WEDNESDAY EVENING FOR MIZ037-043-
050-056-064-071.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EDT WEDNESDAY FOR LMZ844>849.
DISCUSSION...NJJ
AVIATION...TJT
MARINE...NJJ
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