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Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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244 FXUS63 KMQT 060538 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 138 AM EDT Sat Jul 6 2024 .KEY MESSAGES... -Mainly dry Saturday, but a rain shower cannot be entirely ruled out (~20%) along the MI/WI state line in the afternoon. -Sunday through Wednesday, daily chances of showers and thunderstorms, highest chances in the afternoons. -Dry period begins Thursday, could be dry into next weekend. && .SHORT TERM /THROUGH TONIGHT/... Issued at 232 PM EDT Fri Jul 5 2024 Water vapor imagery showing shortwave/mid-level low moving out of WI into Lake Michigan. Dry slotting over the central U.P. has kept the precipitation to mainly isolated shras there but with some recent breaks in the clouds across baraga and Iron counties additional shras are beginning to pop up. Better forcing has been over the eastern U.P. where the rain has been more persistent. As forcing continue to wane this afternoon, precipitation coverage will become less and less from west to east. Skies will then clear from west to east tonight as the low moves across lower Michigan into Ontario by Saturday morning. Still can`t rule out some patchy fog later tonight especially where rain as been more persistent. Temperatures tonight will fall into the 50s, perhaps a few upper 40s in the typically interior west cooler locations. && .LONG TERM /SATURDAY THROUGH FRIDAY/... Issued at 327 PM EDT Fri Jul 5 2024 After a very progressive pattern kicked off this summer, a more blocky pattern has now emerged as 500mb ridging over western North America will only very slowly progress eastward with time throughout this forecast period. The consequence of this for the UP will be dealing with the low-amplitude shortwaves that spill southeast from the ridge. While none of these shortwaves on their own are going to be strong enough to force any surface low pressures deeper than about 1010mb per the 12Z GEFS, with the help of diurnal heating, chances of rain will increase each afternoon with 20-35% chances of thunder with each round. As the the northern arm of the ridging slowly moves off of the Canadian Rockies, signal is strong for high pressure to usher in a period of dry weather Wednesday night into the weekend for the longest dry stretch of the summer for the UP so far. By Saturday morning, with the previous low pressure over the Lower Great Lakes, the final showers will end in the far eastern UP. Weak surface ridging is expected to take the place of the departing low, as the high pressure center is forecast to be near TN at 1015 mb. Because the high is so weak and far away from the UP, not enough subsidence will be present to completely preclude some low-impact diurnal showers along the MI/WI state line, with the HREF showing only scattered 20% PoPs by 00Z. A quiet night is expected Saturday night, but cloud cover begins to increase ahead of the next shortwave trough sliding southeast off the western ridge. Global deterministic models do begin to diverge here as to how the series of minor shortwaves progresses, but the general outcome seems to be a mainly diurnal pattern of precipitation Sunday through Wednesday with lower PoPs in the overnight periods in between. Given how weak synoptic surface forcing is, the ability of diurnal forcing to help initiate showers will be key in determining PoPs as well as thunderstorm chances, though severe weather is unlikely because of said lack of forcing and wind shear. Most deterministic guidance does have the trough beyond the UP by Wednesday, so PoPs are lower by a fair margin on Wednesday, but enough ensemble spread exists to keep at least 20-40% PoPs in the forecast for now. As the northern portions of the ridge shift off of the Canadian Rockies over the Prairie and towards the Upper Great Lakes, high pressure looks to settle over the UP for Thursday and beyond, with the 12Z GEFS showing a ~1020mb high over the UP Thursday morning and building to the mid 1020s mb over the rest of the Great Lakes basin by the weekend. This will usher in a dry period to end next week, with the potential of a multiple-day period of no rain across the UP, something that has not been common this summer so far. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 137 AM EDT Sat Jul 6 2024 Patch of LIFR/IFR cigs/vsby originating from Lake Superior continues to blow into SAW. They are near the edge of this cloud patch, so conditions may fluctuate between VFR/LIFR through around 12Z before any remaining low cigs/vsby mixes out, with VFR expected for the remainder of the day. Shallow MVFR/IFR fog patches will probably plague IWD up until shortly after sunrise. VFR should prevail there for the upcoming day, but a few showers and perhaps an isolated thunderstorm will be possible during the 21-03Z timeframe. VFR expected to continue through the TAF period at CMX, but will be watching for fog/stratus patches over the lake to upslope to the terminal under WNW winds. Included SCT clouds at 400ft for now, but there is potential for a few hrs of LIFR conditions until shortly after sunrise. && .MARINE... Issued at 327 PM EDT Fri Jul 5 2024 Light winds of 20 knots or less will continue across Lake Superior this weekend through next week as a cycle of weak shortwave lows followed by weak ridging continues across the Upper Great Lakes as high pressure continues to build over the western CONUS. That being said, a few of the disturbances will be strong enough to produce some thunderstorms across the lake from time-to-time over the next several days, mainly along the nearshores today into this evening and again each day during the daylight hours Sunday through next Wednesday. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...MZ LONG TERM...GS AVIATION...Thompson/Rolfson MARINE...GS/TAP