Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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266 FXUS63 KMQT 010721 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 321 AM EDT Mon Jul 1 2024 .KEY MESSAGES... - There is a slight chance (<20%) for patchy frost across portions of the interior-western UP early this morning. - Dry weather continues through this evening. - Next rounds of showers and thunderstorms arrive Monday night, continuing into Wednesday. Gusty southerly winds up to 25-35 mph are also expected on Tuesday. - Low chance (~25%) of afternoon and low to medium chance (25-40%) of evening showers/storms across the western half of Upper Michigan on July 4th. Rain spreads over the region Thursday night and Friday. && .UPDATE... Issued at 922 PM EDT Sun Jun 30 2024 Main fcst concern overnight is how low temps will fall, and with that, the potential of frost for the first morning of July. Sfc high pres will be settling over the western Great Lakes during the night, allowing for calm/near calm conditions tonight across the fcst area. Skies are already clear, and the air mass is very dry. Precipitable water tonight will be running just 30-40 percent of normal to enhance what is already setting up to be a good radiational cooling night. Afternoon dwpts bottomed out in the mid 30s F at some sites across the fcst area, and that is likely a good indicator of where temps will be heading at the traditional interior cold spots. 12z MET guidance for KLNL had a min temp of 34F tonight, also a good indicator of where traditional interior cold spots across the w will end up. Fcst has been updated to knock a few degrees off of min temps. While fcst reflects mid/upper 30s F across a fairly large portion of the interior, would not be surprised at all to see the typical cold RAWS sites fall toward 30F. Expected coverage of possible frost across the interior w is still very low and spotty given the isolated nature of the lowest temps that are supportive of frost and also the short duration of the those lowest temps. && .SHORT TERM /THROUGH TONIGHT/... Issued at 231 PM EDT Sun Jun 30 2024 Robust upper ridging over the Plains is supporting a sprawling 1028mb surface high centered over MN this afternoon. With strong subsidence over the UP, there is hardly a cloud in the sky. In spite of this, temperatures remain quite cool; temperatures are only climbing into the lower 60s across much of the UP, while shoreline locations and the easternmost portions of our CWA are struggling even to break out of the upper 50s under chilly NW flow off of Lake Superior. NW winds are staying somewhat gusty across the eastern half of the UP, but gusts should fall back heading into the evening. Tonight, as the aforementioned high pressure becomes centered overhead, even stronger radiational cooling and calm winds will lead to widespread overnight lows in the upper 30s to lower 40s. The frost potential across the interior-western UP is still difficult to pin down, with most of the guidance staying just warm enough to preclude frost. Only about 10% of href ensemble members reach the mid 30s, while the NBM 10th percentile also only flirts with the mid 30s. Will note, however, that some spots in the western half of the UP fell farther into the 30s than expected, with the "winner" of the night (Watton) reaching as low as 34F. Therefore, have been just confident enough to come in a couple degrees under guidance, particularly across Iron and southern Baraga counties, where we may just get cool enough for patchy frost. This will continue to be monitored/adjusted as needed. In addition, dangerous swimming conditions for Marquette and Alger counties are expected through this afternoon. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Issued at 320 AM EDT Mon Jul 1 2024 Primary focus in the extended forecast period continues to be the broad mid-upper level trough shifting out of the northern Rockies beginning tonight. This system will amplify and support a surface low developing this afternoon over eastern Montana/western Dakotas. As the main trough axis/closed low aloft shifts east into Manitoba tonight, the surface low will lift to near Lake Winnipeg, and then to northeastern Manitoba/far northwestern Ontario by Tuesday afternoon. Its expected to continue lifting north Tuesday night. This progression will result in two waves of precip lifting through our forecast area, in addition to a strong low level jet and tightening pressure gradient resulting in gusty winds. The first wave of precip is expected to slide east late tonight and Tuesday as a surface trough rotates through. Models continue to highlight an environment lacking much in the way of instability, but the elevated MUCAPE of ~200j/kg means a thunderstorm can`t be ruled out. A lull is expected by afternoon in the west, which will shift east through the evening as the initial swath of precip exits into Ontario. As this initial wave moves through, a strengthening pressure gradient over the region will ensue as a strong 925-850mb 40-50kt low level jet presses overhead. Even with modest dinural mixing, gusty southerly winds will develop, particularly near the Bay of Green Bay, Lake Michigan, and the downslope and higher terrain locations in the Gogebic Range, Michigamme Highlands, and lakeshore areas of Marquette and Alger counties. NBM appears certain of 25-30 mph wind gusts in these locations and eastern Upper Michigan and suggests ~25% chance of exceeding 35 mph. Model soundings that suggest effective mixing suggest potential upwards of 40 mph. The second wave will lift northeast into the U.P. Tuesday night ahead of the eastward migrating cold front. Between guidance available last night and tonight, there appears to be a better handle on when precip should end, with most now ending precip in the east Wednesday morning. A surface ridge extending northwest should help support a mostly dry day on Wednesday, although there is a brief period in the east that could destabilize enough for afternoon showers/storms to develop before the cold front clears. The 4th of July should start off dry thanks to the lingering effects of the surface ridge and a meso high developing over Lake Superior. Upstream though, another trough exits the northern Rockies and presses through the Plains. Guidance amplifies the shortwave and lifts a surface low through the eastern Dakotas and into Minnesota in the afternoon/evening. There`s good agreement among the guidance packages that this wave will shift east through Minnesota and Wisconsin through the day Friday, then lift northeast through Upper Michigan Friday night into early Saturday. Best chances for precip with this wave will be Thursday night and Friday. Its unclear if it will remain dry Thursday afternoon and evening in the western half of Upper Michigan. While probability is currently low (~25%), Thursday afternoon destabilization could result in convection developing. Additionally, increasing isentropic ascent may support showers lifting into the region during the evening hours (25-40%). Anyone with evening firework plans across the western half of Upper Michigan should continue monitoring the forecasts. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 125 AM EDT Mon Jul 1 2024 Very dry air mass associated with high pres settling over the Great Lakes overnight thru today will result in VFR continuing thru this fcst period at IWD/CMX/SAW. Winds will be light to calm at all terminals overnight, then during today, southerly increasing to around 10kt, except becoming ESE at CMX. LLWS is likely to develop at all terminals near the end of or just beyond this fcst period. && .MARINE... Issued at 320 AM EDT Mon Jul 1 2024 Light winds will persist over Lake Superior today with high pressure continuing to influence the region. A system will begin lifting from the Plains into Canada tonight, then continue lifting northward Tuesday into Wednesday. The passage of this system will result in at least 2 rounds of rain and storms and two periods of stronger winds. Expecting the first round of showers, maybe with a thunderstorm embedded within to shift through Lake Superior late tonight and Tuesday. These showers may support fog developing and periods of low visibility on the lake. As the system approaches tonight, tightening pressure gradient will develop while a strong 40-50kt 925-850mb low level jet moves over eastern Lake Superior. There`s still a great deal of uncertainty in how much of these stronger winds will mix to down to the surface given the increasing stability of the over lake environment. However, recent internal probabilistic tools are beginning to highlight nearshore areas downwind of the Michigan lakeshores and the stretch from Marquette northward into Canadian waters as those most likely to experience low end gales. This tool is only suggesting a 20-40% chance, which is in the middle of the road of probabilities when comparing to the HREF and the NBM. These ~40% values may also be somewhat representative downwind of the lakeshores east of Marquette and along the northern shores of the Keweenaw, where models struggle with the land/lake interface and localized terrain driven influences have been known to mix down stronger winds to the surface. At this point, given the uncertainty and the isolated nature of the stronger mixing downwind of the lakeshores, will hold off on a gale watch and allow the next shift to reexamine it again. Another round of moisture will lift through Tuesday night into Wednesday while the effects of the low level jet wane. The cold front presses through west to east Tuesday night into Wednesday morning, allowing winds to become westerly/southwesterly for Wednesday. Another period of stronger winds up to 20-30kts, looks possible between the Keweenaw and Isle Royale Wednesday in this southwesterly flow. High pressure returns briefly for Thursday with a weaker low pressure system expected to pass over the Upper Great Lakes late Friday and Saturday. Light winds below 20 kts returns Wednesday night, continuing likely into the weekend. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ UPDATE... SHORT TERM...LC LONG TERM...JTP AVIATION...Rolfson MARINE...JTP