Area Forecast Discussion
Issued by NWS Marquette, MI

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000 FXUS63 KMQT 182037 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 437 PM EDT Sun Apr 18 2021 .SHORT TERM...(This evening through Monday) Issued at 437 PM EDT SUN APR 18 2021 The short term will bring another return back to winter. Water vapor imagery and RAP analysis show a shortwave trof extending from Hudson Bay to ND. Associated sfc cold front runs from James Bay across ne MN to SD. Shra are occurring along/just behind front with shra switching to shsn within about 3hrs of fropa. Closer to home, it`s been a warm/dry day and generally partly to mostly sunny skies. Temps in the interior are in the mid 50s to around 60F. Lake breezes are keeping lakeside locations cool in the low/mid 40s. With dwpts as low as the upper teens/lwr 20s F, RH has fallen to 20-30pct in the interior. Approaching shortwave will amplify as it swings se across the Upper Great Lakes. Much of the model guidance indicates a weakly closed mid-level low will form over the fcst area with the center passing across northern Lake Superior. With 12hr 500mb height falls around 100m tonight and a nice upper diffluence signature within left exit of upper jet surging into the western Great Lakes, stage should be set for a band of shra mixing with/changing to shsn moving across the fcst area tonight. Of concern is the lower level cyclonic flow that develops under postfrontal caa regime dropping 850mb temps around -11C and the amplifying trof/falling heights. Further aided by brisk upsloping NW winds, expect an upslope/lake enhanced snow scenario to develop overnight into Mon morning. High terrain of the w and nw fcst area will be favored for this event. DGZ ends up mostly above the best upward motion so SLRs will be on the low side, probably around 10 to 1. 12hr snow amounts over the high terrain from around KIWD ne up the spine of the Keweenaw overnight/Mon morning may push low SLR winter wx advy criteria of 3 or more inches. For now, given the greatest amounts pinned locally to the high terrain, will issue an SPS for the western counties to highlight the potential of hazardous travel conditions due to some roads likely becoming slushy/snow covered, at least in spots, for the Mon morning commute. Winds will also ramp up behind the front as sfc low pres wave develops on the front over Lake Superior and briefly deepens. Wind gusts of 25-35mph should be common, developing nw late tonight then spreading across the area thru Mon morning. Gusts up to around 45mph are expected at lakeside locations exposed to a nw wind from the Keweenaw eastward. So, a blustery, much colder day is on the way for Mon. During the day, expect temps generally in the upper 20s/lwr 30s F across the w and n. Temps may sneak up to 40F across the s central, but given the expectation of abundant cloud cover, that may be optimistic. Loss of deeper moisture/relaxing cyclonic curvature of the low-level winds will lead to diminishing snow over the w and nw fcst area during the aftn. To the e, conditions for lake enhanced snow never become nearly as favorable as over the w. Minor snow accumulations under 1 inch are expected. Limited daytime heating and moisture off the lake may support some development of isold -shsn/flurries well inland during the day. .LONG TERM...(Monday night through Sunday) Issued at 327 PM EDT SUN APR 18 2021 A active early long term period with the tail end of a lake effect snow event followed by a quiet period thanks to a 1027mb surface high shifting southeastward into the northern Plains. Expecting below normal temps initially before warming up Thursday and Friday, with a weekend finish near normal following the passage of a cold front this weekend. Starting off Monday night, lingering troughing over the region with the mid-level low just east of our forecast area will help maintain the unseasonable colder temperatures. Overnight 850mb temps are progged to remain about -12 to -14 over the region under northwesterly flow off Lake Superior. With Lake Superior hovering near +3C resulting in a delta T of 15 to 18, lake effect snow showers are expected across the northwest wind snow belts. While there is decent lift through the DGZ, model soundings show an inverted V at the lower levels, indicating any snow will have to overcome the dry air near the surface. If earlier showers are able to erode the dry layer some, that could add to the snow accumulations. Generally, expecting an inch or two being possible, mainly across the Hurons and in the northwest wind belts east of Marquette. The northern half of the Keweenaw could also see another half inch or so on top of their daytime accumulations. Overnight lows are expected to bottom out in the low 20s, but if cloud cover breaks away from the lakeshores, particularly in the interior west, some mid to high teens can`t be ruled out. As the upstream high pressure sinks into southern Saskatchewan Tuesday, anticyclonic flow and increased subsidence should bring an end to any early lake effect snow showers. With temps hovering around -10C during the day Tuesday, expecting day time highs to remain largely in the 30s. Some low 40s across the south-central can`t be ruled out. A weak shortwave is expected to migrate south through the region late Tuesday night into Wednesday. This enhancement may help develop some flurries or light snow showers, but with drier low levels, notable accumulations are not expected. Daytime highs in the upper 30s across the north half and near 40 south half are expected. Height rises resulting from the upstream high building southeastward into the central and eastern Plains should help clear out the skies Wednesday night. With the colder air aloft lingering, winds becoming light and PWATS near 0.25", expecting an opportunity for some good radiational cooling. Lows right now look to be in the low 20s with mid teens in the colder interior west, but I wouldn`t be surprised if guidance trends colder, especially in the interior central and east. With the ridge persisting over the region Thursday and Friday, sunshine and WAA will help temps rebound back into the 50s. The next precip chances look to be Friday night or Saturday, but there are noticeable timing differences among the 12z guidance. The GFS looks to be the fastest solution with the cold front moving into the region Friday night. This contrasts well with the slower Canadian and Euro solutions, whom delay the system until Saturday afternoon or evening. Given there is still plenty of time for things to change and for the guidance to reach a better consensus, ran with NBM pops for now. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 143 PM EDT SUN APR 18 2021 VFR conditions will prevail thru the aftn at KIWD/KCMX/KSAW. A cold front just nw of Lake Superior will then sweep across the area tonight. Expect a period of -shra changing to -shsn as the front passes. While these -shsn will end at KSAW late tonight/early Mon morning, -shsn should continue thru Mon morning at KIWD/KCMX. With the pcpn, expect conditions at all terminals to fall to at least MVFR. Upsloping postfrontal winds at KIWD/KCMX may result in IFR conditions at times, especially at KIWD. Postfrontal nw winds will also be gusty to 20-30kt, strongest at KCMX where some gusts to 30- 35kt appear likely. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 437 PM EDT SUN APR 18 2021 Strong cold front will sweep across Lake Superior tonight. Along the front, a low pres wave will also develop and briefly deepen. Thus, after fropa, nw winds will ramp up, especially from central to eastern Lake Superior overnight thru Mon. Increasingly colder air and 3-4mb/3hr pres rises on the backside of the low pres wave will further boost winds. Thus, expect high end nw gales of 40-45kt to develop from central into eastern Lake Superior overnight thru Mon morning. Not out of the question that there could be an hr or two where wind gusts reach storm force in a corridor from n of the Keweenaw Peninsula se toward Grand Marais. Winds will diminish from w to e Mon aftn thru Mon night. While winds will fall blo 20kt over the w by sunrise Tue, winds may still be gusting to around 25kt over the e. Winds generally blo 20kt are then expected thru the midweek period. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... Gale Warning from 8 AM to 11 PM EDT Monday for LSZ251-267. Gale Warning from 5 AM to 11 PM EDT Monday for LSZ249-250-266. Gale Warning from 5 AM to 8 PM EDT Monday for LSZ265. Gale Warning from 2 AM to 8 PM EDT Monday for LSZ244-245-264. Gale Warning from 2 AM to 2 PM EDT Monday for LSZ243-263. Gale Warning from 8 AM to 8 PM EDT Monday for LSZ248. Lake Michigan... None. && $$ SHORT TERM...Rolfson LONG TERM...JP AVIATION...Rolfson MARINE...Rolfson

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