336 FXUS63 KGRR 041821 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 221 PM EDT Sat Jul 4 2026 .KEY MESSAGES... - Pop-up Thunderstorms This Afternoon and Evening - Showers and Thunderstorms Mainly South Tonight into Sunday - Dry Monday through Wednesday, Showers and Thunderstorm Chances Return Late Wednesday Night into Thursday && .DISCUSSION... Issued at 123 PM EDT Sat Jul 4 2026 - Pop-up Thunderstorms This Afternoon and Evening A surface trough over the area and weak cold front will sink south this afternoon. Already seeing building cumulus and showers developing north of I-96. Surface based CAPE will increase to 1000 to 1500 J/kg this afternoon. Shear however is lacking. Therefore not expecting anything organized or severe, just some general pop-up thunderstorms with lightning and brief heavy downpours as the main concern. Thunderstorms will generally taper off around sunset with the chance for lingering showers and storms across southern Michigan. - Showers and Thunderstorms Mainly South Tonight into Sunday As mentioned showers and thunderstorms could linger in southern Michigan overnight due to a disturbance moving through northern Illinois under the surface trough. HREF probabilities are not high though so it is possible that areas along I-94 could remain dry. Sunday we`ll see another diurnal trend with storms mainly focused along and east of a Kalamazoo to St. Johns line. Instability will only be around 1000 J/kg and with similar shear values to today do not expect any severe weather. - Dry Monday through Wednesday, Showers and Thunderstorm Chances Return Late Wednesday Night into Thursday High pressure builds in for Monday through Wednesday. The ridge weakens Wednesday night with an approaching trough. There are some timing differences with this shortwave moving through sometime in the late Wednesday night/Thursday timeframe. The timing will impact whether we see lingering rain chances for Friday or if we`ll see dry conditions. Overall with this system there will be a weak low level jet, and upper level jet divergence may be displaced. Overall not seeing a concern for a severe risk at this time. High temperatures through the week will largely be in the 80s with lows in the 50s and 60s. A nice break from the hot temperatures this past week. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 102 PM EDT Sat Jul 4 2026 Earlier MVFR cigs have broken up with scattered low clouds likely to persist into the afternoon. After 20z, scattered pop up thunderstorms are likely, especially for LAN/JXN, however confidence in terminal impacts to a particular terminal remains low. As such, the earlier PROB30s remain in place with amendments made as needed. Overnight, signals suggest pockets of low clouds may (30%) develop tonight. Have added SCT MVFR clouds for now and will add restrictions if confidence increases. Any clouds will lift/break up Sunday morning after daybreak. && .MARINE... Issued at 220 PM EDT Sat Jul 4 2026 Areas of dense fog have developed over Lake Michigan impacting the lakeshore areas. Expect periods of reduced visibilities from Holland to Manistee this afternoon before clearing this evening. The Marine Dense Fog Advisory may need to be extended further south. Thunderstorms will be possible this afternoon and evening before tapering off around sunset. Waves will remain below 3 feet through next week. Northerly winds Sunday afternoon and Monday afternoon may briefly approach Small Craft Advisory criteria toward Big and Little Sable. Northerly winds are largely expected through Monday with winds potentially becoming easterly each night. Tuesday winds become westerly then southwesterly for Wednesday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Dense Fog Advisory until 8 PM EDT this evening for LMZ846>849. && $$ DISCUSSION...RAH AVIATION...Thomas MARINE...RAH

NWS GRR Office Area Forecast Discussion