102 FXUS63 KGRR 070755 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 355 AM EDT Fri Aug 7 2026 .KEY MESSAGES... - Showers and storms possible this afternoon through Saturday - Storms possible Sunday into Monday - Trending slightly cooler and drier into mid next week && .DISCUSSION... Issued at 354 AM EDT Fri Aug 7 2026 - Showers and storms possible this afternoon through Saturday Small chances for showers and thunderstorms exist this afternoon and early evening to the southeast of Grand Rapids. Areas from Kalamazoo to Lansing and Jackson stand the best chances to see this activity but it is not certain. The HREF does not have a good handle of convective chances today. The HRRR and other high resolution models seem to be picking up on a signal for this area where MUCAPE values may exceed 1500 j/kg. If storms develop not expecting severe weather given low shear and only modest instability. Tonight there is a threat that some stronger storms may try to advect in from the west overnight along and ahead of a cold front. Machine learning schemes are not bullish on severe weather today or tonight though and the SPC only has our area in a general thunder outlook. Shear remains weak tonight. - Storms possible Sunday into Monday A better chance at some stronger storms looks to occur in the Sunday into Monday time frame as a warm front sets up to our southwest. This is when surface dew points (around 70) and PWAT values (1.75 to 2.00 inches) peak in the 7 day forecast. Embedded shortwaves in a generally zonal upper flow will likely aid in thunderstorm initiation and maintenance. A 25-35 knot low level jet will also aid storms. MUCAPE values will push towards or potentially exceed 2000 j/kg. Sunday night and Monday will likely be the best chance at storms. SPC maintains a general thunder outlook for us on Sunday and Monday as well. - Trending slightly cooler and drier into mid next week We trend a bit cooler into mid week as 850mb temperatures cool slightly from the upper teens (Sunday night) to the lower teens by Thursday. GFS MOS guidance has highs back into the 70s at GRR on Thursday. The surface pattern looks fairly diffuse Tuesday into Wednesday which will trend towards ridging by Thursday. Overall the focus of the entire 7 day forecast is on periodic thunderstorm chances. Some locally heavy rain will be possible, especially from Sunday into Monday. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 211 AM EDT Fri Aug 7 2026 There at two main forecast concerns with this set of (06z-06z) TAFs. The first concern is the threat of fog and stratus this morning mainly in the 09Z to 15Z time frame. The second area of focus is the chance of showers and storms over portions of the area in the 21Z to 03Z time frame. As for the fog, it has formed across portions of the area already with visibilities ranging from MVFR to LIFR. A continued expansion to the fog and developing stratus should occur through sunrise which is around 640am this morning. Expecting most TAF sites to at least reach MVFR conditions with areas of IFR/LIFR. The fog should be shallow in nature and should burn off rather quickly in the early August sun. By 15Z, we expect most if not all areas to be back to VFR. The next concern is the chance for showers and storms this afternoon and evening between 21Z and 03Z. At this time confidence was not high enough to put showers/storms in the TAFs, but we will be monitoring forecast trends. Some models are showing activity developing and moving east affecting AZO, BTL, LAN and JXN during this time frame. If confidence increases a PROB30 group could be included in the 12Z TAFs. Otherwise, VFR conditions are expected outside of those two concerns. Winds will be southwest today at 5-15 knots. && .MARINE... Issued at 354 AM EDT Fri Aug 7 2026 For the most part we expect conditions to remain below advisory levels through the next 3 to 4 days. The first time frame that may approach advisory levels is tonight when high resolution models pick up on an increase in the 850mb low level jet to 25-30 knots. Usually overnight low level jet increases in the heart of the summer result in building waves. Tonight looks to be no different with the Wavewatch3 indication 3 to 3.3 foot waves developing. We will be watching this time frame for any increase in wind and correspondingly the waves. The next time frame we will be monitoring will be Sunday when an increase in southwesterly winds may push conditions to advisory levels. BUFKIT overviews are showing southwest winds of 15-25 knots which usually pushes waves towards the 4 foot mark. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Duke AVIATION...Duke MARINE...Duke

NWS GRR Office Area Forecast Discussion