005 FXUS63 KGRR 211835 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 235 PM EDT Tue Apr 21 2026 .KEY MESSAGES... - Showers and a few storms yet through this evening - Showers and storms Friday afternoon and Friday night - Confidence increasing in a wet system late Monday into Tuesday && .DISCUSSION... Issued at 235 PM EDT Tue Apr 21 2026 - Showers and a few storms yet through this evening The line of showers and a few isolated storms that developed to our North and West have done so a bit earlier than expected. Mesoscale analysis of typical parameters like MU CAPE indicates no instability around, even with lightning ongoing. Forecast soundings show a couple hundred J/kg of CAPE based around 650 mb or so. Mid level lapse rates of 8.0-9.0C/km are also helping the cause. It seems that the threat with any storm this afternoon would be some hail, or downburst given the dry low levels that could help accelerate and downward wind. It seems that the band of showers and isolated storms should push south of the forecast area by mid evening as a sfc front becomes involved, and helps to push it out, along with the developing cold pool. We are then looking at a couple of mainly dry and warm days coming up for the area tomorrow and Thursday. We see the long wave upper ridge push toward the area, helping to bring a good deal of sunshine toward the area. Even though the front moves through this evening, we will actually warm a couple of degrees on Wednesday compared to today. That is because of the building heights, more sunshine, and really no cold air advection behind the front. The front will lift back north as a warm front on Thursday. It is then that we will see temperatures make a run at 80 degrees again. There is a non-zero chance of a shower on Thursday as the warm front moves through. - Showers and storms Friday afternoon and Friday night We are still expecting the next batch of showers and storms to arrive Friday afternoon and evening for the forecast area. We are still expecting northern and southern branch energy to phase over the Northern Plains. We then see left over energy from the southern stream get steered NE toward the area on Friday. This is what will drive the front in. The timing of the front is favorable coming in during peak heating. Instability could build to over 1000 J/kg ahead of the front. However, effective deep layer shear is quite low, less than 20 knots. This lack of shear will limit the amount of potential severe weather. Also, we do not see a good solid short wave come right at us, as it will be more focused to our NW. Showers and a few storms will linger into Friday night, before clearing out by Saturday. We then are in between systems from Saturday through the first part of Monday as the upper low stays over the Upper Midwest, and we have to wait for additional energy to arrive early next week for our next good chance of rain. It does cool off some behind the Friday night front, but not much as the much colder air stays up in Canada. - Confidence increasing in a wet system late Monday into Tuesday The upper low does look to drive the next bit of southern stream energy coming in off of the Pacific up toward the area late on Monday. This has been fairly consistent over the last couple of days. The system will have a low level flow that will draw a good deal of moisture out of the Gulf. This looks to be a fairly wet system for much of the forecast area. Too early to tell if a severe weather threat will be present given the uncertainty 7 days out. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 137 PM EDT Tue Apr 21 2026 A broken line of showers has been observed tracking torts MKG/GRR as of present. There was lightning with this line earlier, but satellite trends suggest that risk has diminished. Have gone prevailing SHRA PROB30 TSRA to account for the isolated thunder potential. Moved up timing given radar trends given poor handling by short range guidance. Overnight, light winds and clear skies appear to be conducive to fog formation. MVFR is likely at all terminals, with the potential for IFR and lower. The worst conditions will be at AZO and BTL. Fog should burn off by mid to late Wednesday morning. && .MARINE... Issued at 235 PM EDT Tue Apr 21 2026 We will be leaving the ongoing Small Craft Advisory up this afternoon to go until its expiration time. We are still getting a few SCA wind gusts at the lakeshore, and the wave model shows we drop below 4 ft around expiration time. Our next marine headline event looks to ramp up in the Thursday night time frame ahead of the incoming front. It is expected to possibly last then into Friday night behind the front, before diminishing. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 5 PM EDT this afternoon for LMZ844>849. && $$ DISCUSSION...NJJ AVIATION...Thomas MARINE...NJJ

NWS GRR Office Area Forecast Discussion