385 FXUS63 KGRR 310645 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 245 AM EDT Sat Oct 31 2026 .KEY MESSAGES... - Slight chance for rain this weekend - Warmer and wetter by mid-week - Limited forecast certainty from mid-week onward && .DISCUSSION... Issued at 245 AM EDT Sat Oct 31 2026 - Slight chance for rain this weekend Current radar this morning shows isolated and mostly light elevated showers crossing Lake MI and entering Lower MI. Upstream VWPs such as KMKX/TMKE indicate strong lower tropospheric veering indicative of forced isentropic ascent. The 31/00Z DTX sounding showed a dry lower troposphere; this should result in spotty precipitation amounts around a trace for Lower Michigan into today. Trick or treating tonight does not appear at risk of a washout. Sunday looks similar in terms of hit or miss light rain. A weak and poorly phased upper trough and attendant PV max will cross Lower MI. It`s not out of the question that a better coverage of rain will result, but ensemble guidance such as the ECE has been trending drier and this may speak to the continued dry lower tropospheric conditions still expected. - Warmer and wetter by mid-week GOES-W satellite shows a phasing and meridionally deep upper trough off the west coast about to move onshore. It will cross the Rockies when a well developed Bermuda High allows increasingly favorable moisture transport from the Gulf. The moist transport will be augmented by troughing in the lee of the Rockies in response to the approach of the upper trough. Consequently, we will be looking at seasonably very large precipitable water values by Monday night, with ECE mean values reaching or exceeding the 99th percentile relative to climatology. Not surprisingly, precipitation chances go up considerably around this time thanks to the increased moisture and forcing for ascent. Precipitation efficiency will be good but there is some question about total amounts given that the trough will be fairly progressive. Nonetheless, this is normally when fall leaves and storm drains do their annual clogging dance. Thus, nuisance flooding is certainly possible from quick rainfall accumulations of even an hour or less. Severe weather is not expected and there is some question about whether there will be enough conditional instability for any thunderstorms in the first place. We still expect anomalously warm temperatures early this week. To illustrate, an expected high of 70 at Grand Rapids on Tuesday would be about 15 degrees above normal. - Limited forecast certainty from mid-week onward Starting in the Wednesday timeframe, the previously mentioned organized and phased upper trough appears to weaken while at the same time there is background unphasing of the northern and southern streams. There is a wide variety of possible forecast scenarios during this transition. One tricky possibility would be the development of a cutoff low to focus precipitation chances. However, predictability for a targeted and relatively impactful outcome such as this is very poor, so the best compromise at this point is keeping PoPs in the 20 to 30 percent range for the latter part of the week. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 126 AM EDT Sat Oct 31 2026 No changes to previous thinking. Probability of VFR at all terminals through 12Z: 95 percent Probability of VFR at all terminals through 18Z: 90 percent Probability of IFR at any terminals through 18Z: 3 percent Brief light rain is possible at some of the terminals this morning with no associated visibility or ceiling restrictions anticipated. As noted previously, fog this morning looks unlikely due to a combination of increasing low to mid-level cloudiness and stronger nocturnal boundary layer winds; these factors should mitigate outgoing longwave radiation flux necessary for radiation fog. && .MARINE... Issued at 245 AM EDT Sat Oct 31 2026 No concerns in the short term. Winds and waves could reach or exceed Small Craft Advisory criteria as early as Monday afternoon however. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...TJT AVIATION...TJT MARINE...TJT

NWS GRR Office Area Forecast Discussion