FXUS63 KMQT 062324 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 724 PM EDT Sat Jul 6 2024 .KEY MESSAGES... - Slight chance (~20%) for late afternoon showers and thunderstorms across interior western Upper MI late afternoon/early evening. -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 300 PM EDT Sat Jul 6 2024 Not much to talk about in the short term through tonight. Surface ridge axis extends from the Upper Midwest up into the Upper Great Lakes. Diurnally driven cu field has developed across the interior of the U.P. with light onshore flow along the Lakes shorelines. Fog per visible imagery over eastern Lake Superior has been shifting slowly eastward with time with the Luce county shorelines over to Whitefish point the only remaining areas experiencing fog/stratus. 12Z models have been consistent with previous runs showing enough destabilization by late afternoon/early evening for isolated shra/tsra activity mainly in the WI bordering counties. Will maintain slight chance pops until about 2-3Z there but most everybody will remain dry this evening. By late in the night, convection initiating this evening over MN along next shortwave moving into the Upper Mississippi Valley will be approaching northwest WI and far western Lake Superior. The U.P. will remain dry through 12Z with just an increase in mid/upper level clouds towards morning. Expect seasonable overnight lows mainly in the 50s. && .LONG TERM /SUNDAY THROUGH SATURDAY/... Issued at 324 PM EDT Sat Jul 6 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 1005mb per the 12Z GEFS, with the help of diurnal heating, chances of showers and thunderstorms will increase each afternoon. 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. Sunday morning, the next shortwave in line will be centered over Minnesota and approaching the UP from the west. Without much of a surface feature resolved in global ensembles, forcing will be fairly broad and unfocused, but HREF does show notable destabilization throughout the morning hours, with mean SBCAPE values climbing to near 750 J/kg by noon. Shear will not necessarily be abundant, and with the forcing being weaker and broad, severe thunderstorms are not expected, though a few stronger thunderstorms could bring frequent lightning and locally heavy rain to interrupt those wrapping up their weekend plans. Timing-wise, the HREF shows a line of showers approaching Ironwood perhaps as soon as 9AM Central but more likely closer to 11AM. Showers overspread the rest of the western half of the UP throughout the early afternoon with Alger/Delta counties and east not seeing much rainfall until around sunset. Monday's PoPs look to be a similar pattern to Sunday's, though for different reasons. The residual cloud cover from the previous day's showers will keep SBCAPE closer to 500 than the 750 of the previous day per the 00Z LREF, but the 12Z GEFS shows a cluster of low pressure centers around 1005 mb, which is a bit stronger of a low pressure than the guidance of 24 hours ago. Stronger forcing but weaker instability should lead to a similar level of impacts as a few stronger thunderstorms are possible but should remain sub-severe. Tuesday and Wednesday, uncertainty begins to grow as global ensemble and deterministic models diverge in the handling of shortwave propagation as the 500mb ridge axis finally shifts out of British Columbia. Once showers cease Wednesday, the northern arm of the ridge will shift towards the Great Lakes and high pressure looks likely to keep precipitation out of the forecast Thursday into the weekend for what would be the longest dry period UP-wide since the beginning of the summer. One interesting thing to note will be the progression of Beryl as it makes landfall and turns northeast. The 06Z GEFS has a 20% chance of the remnants of Beryl coming within 200km of the UP, which depending on how much strength Beryl maintains, could introduce showers into the forecast again late in the week. The more likely impact would be in how long the high pressure resides over the UP and at what strength, so it will be worth keeping an eye on Beryl as it becomes better sampled by the upper air network. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 724 PM EDT Sat Jul 6 2024 VFR conditions will prevail at all TAF sites through the period. Spotty showers and thunderstorms are starting to develop along the far MI/WI border near IWD, but will be rather short lived and taper off with the setting sun. Calm conditions are expected overnight before a weak surface low moves into northern Minnesota on Sunday, sending a wave of light showers across the west half of the U.P. in the early afternoon. More convective showers and thunderstorms look to develop across the west towards the end of the period, however, there is low confidence in the coverage and timing and have therefore been left out of the TAFs at CMX and SAW. && .MARINE... Issued at 324 PM EDT Sat Jul 6 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, namely over the western portions of the lake Sunday and over the east overnight into Monday, and in the nearshore waters Monday afternoon and evening. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...MZ LONG TERM...GS AVIATION...BW/Thompson MARINE...GS