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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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589 FXUS63 KGRR 192347 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 747 PM EDT Fri Jul 19 2024 .KEY MESSAGES... - Fair weather continues with patchy morning fog possible - Low Precipitation Chances Early Next Week, Better Chances Midweek && .DISCUSSION... Issued at 323 PM EDT Fri Jul 19 2024 - Fair weather continues with patchy morning fog possible High pressure at the surface and through the mid levels will allow fair weather to dominate the weather pattern through Saturday. The forecast question overnight will be fog formation. Winds will be light and there will be a fairly strong inversion overnight. The question is whether there will be enough surface moisture and cooling for fog to form. The surface will be dry enough to preclude any widespread fog. However, there is enough moisture, especially along and south of the I 94 corridor to allow for patchy fog overnight and through the early morning hours Saturday morning. Any fog will lift and dissipate by mid morning. An upper level trough extending across southern Canada and through the upper Great Lakes will drive an associated upper level low through Minnesota tomorrow. This weak trough will trek a boundary into Lower Michigan tomorrow afternoon. While there is some mid level moisture associated with this boundary, dry stable air over southern Michigan will keep any clouds and precipitation further north and allow for the fair weather to continue into Sunday. - Low Precipitation Chances Early Next Week, Better Chances Midweek The first half of the long-term period will be dominated by large scale cyclonic flow from persistent troughing across the eastern United States. This is a favored pattern for diurnally driven scattered showers and thunderstorms Sunday and Monday afternoons, mainly across the northern 2/3 of the CWA just south of a stalled front. Slightly better low-level warm air advection and low-level moisture bring the scattered thunderstorm chances areawide Tuesday afternoon/evening. Favored areas for initiation each day will be wherever low-level convergence is enhanced such as off of the lake breeze. Synoptically, with weak flow aloft, deep layer shear is poor. This supports convection of mainly a pulsey nature occuring. Better synoptic forcing in the form of a reinforcing mid-level wave arrives for Wednesday, with strong confidence in this feature across model solutions. The associated developing surface low crosses into West Michigan bringing the best chance for showers and thunderstorms. This brings our best chance of precipitation for the week Wednesday afternoon and evening. Monitoring will be needed as the approaching wave brings a slightly better mid-level jet. The associated ~30 knots of shear and 1000+ J/kg CAPE shown in some solutions could indicate potential organized convection. Showers and storms wind down Thursday and end by Friday as the mid-level low and surface low pull away from southern Lower Michigan. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 747 PM EDT Fri Jul 19 2024 Based on consistent model guidance, decided to add brief MVFR visibility restrictions to some of our I-94 terminals Saturday morning. As noted previously, this is not a particularly strong signal in the guidance and really was right on the cusp of my deciding to include it. Impacts most likely will be minimal. That said, it does appear that the I-94 corridor could be in a bit of a wind col Saturday morning. This would mean extraordinarily calm conditions and this can be especially conducive to ground fog, especially in areas of depressed terrain. Interestingly, that would include JXN - so it`s not out of the question that this terminal would overperform with brief IFR visibility restrictions. && .MARINE... Issued at 323 PM EDT Fri Jul 19 2024 Lighter winds will continue through Saturday and marine hazards are not expected for the next few days. However, the strong northerly flow from Thursday allowed for upwelling to occur and portions of Lake Michigan`s beaches water temperature will be cooler ranging from the upper 40s to low 60s. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Ceru/Thomas AVIATION...TJT MARINE...Ceru