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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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054 FXUS63 KGRR 201934 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 334 PM EDT Sat Jul 20 2024 .KEY MESSAGES... - Showers and storms possible north of I 96 Sunday afternoon - Scattered Storms Possible Monday/Tuesday, Better Chance Wednesday +&& .DISCUSSION... Issued at 300 PM EDT Sat Jul 20 2024 - Showers and storms possible north of I 96 Sunday afternoon Fair weather will continue over the next 24 hours, however high pressure will shift to the east as a moisture boundary associated with an upper level trough treks from the south. Low level moisture overnight should allow for another round of patchy morning fog. While some high clouds should limit the spread there could be some minor reductions to visibility Sunday morning. Any fog will clear out by mid morning as the before mentioned weak boundary moves southwards. While dewpoints will increase tomorrow leading to higher humidity, it should be dry enough for any showers and storms to remain north of I 96 and begin to form Sunday afternoon. Any storms are not expected to be severe with around a half an inch or less of QPF expected. - Scattered Storms Possible Monday/Tuesday, Better Chance Wednesday Monday and Tuesday`s main impact will be in the form of scattered afternoon convection. MUCAPE values exceeding 1000 J/kg will be supportive of scattered afternoon thunderstorms. A weak shortwave crossing northern MI will provide a slight forcing enhancement there Tuesday. Otherwise, given the lack of notable synoptic features, thunder chances will be largely driven by localized convergence such as from the lake breeze. With bulk shear of 20 knots or less, storms should mainly be pulsey in nature. By Wednesday, a reinforcing mid-level wave drives a cold front through the CWA in the later portion of the day bringing our best chance of showers and thunderstorms. Where uncertainty, and the need for monitoring comes in, is the extent of deep layer shear and organized convection. Solid model consensus exists in 1000 + J/kg of MUCAPE given the ample low-level moisture. The GFS/GEM and their associated ensembles suggest a slightly stronger mid-level jet and 30-35 knots of shear which would support organized convection. The ECMWF and its ensemble are weaker on the mid-level jet and by extension shear. We will continue to watch overall trends and possible support for stronger storms if confidence grows in the GFS/GEM solution. A bit of uncertainty as to how quickly the showers diminish on Thursday as the ECMWF wants to close off the upper-low slowing its exit while the other GEM/GFS keep an open wave and a faster exit. Will have low PoPs mainly across the eastern CWA given the uncertainty. Dry conditions expected Friday and Saturday as surface and upper-level ridging take hold. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1254 PM EDT Sat Jul 20 2024 VFR expected the next 24 hours. SCT cumulus in the 6-8kft that are presently developing will diminish after sunset with just a BKN cirrus layer remaining through the end of the TAF window. Winds will be below 10 knots today becoming light and variable tonight with some form of westerly component dominating the light winds. The one possible exception is MKG where SW winds ahead of a stalled front bring moisture off the lake. A period of MVFR or lower fog is possible, however confidence in restrictions does not rise to the level needed for TAF inclusion (only 20-30 percent). Given the favorable setup and moisture profile will highlight a window of 6SM BR near daybreak and future packages can add restrictions if confidence grows. && .MARINE... Issued at 315 PM EDT Sat Jul 20 2024 Light winds are expected due to high pressure overhead. Winds and waves will increase a tad late Sunday as a weak cold front moves south across the lake. At this time, waves should remain less than 3 feet. Waves will be highest north of Pentwater. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...None. && $$ DISCUSSION...Ceru/Thomas AVIATION...Thomas MARINE...Ceru