Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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202 FXUS63 KMQT 021832 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 232 PM EDT Tue Jul 2 2024 .KEY MESSAGES... -Two distinct rounds of precipitation today and tonight: one in the morning and one late at night. Thunderstorm chances are minimal with the first round and around 20%-30% with the second round. -Widespread southerly wind gusts of 25-30 mph and as high as 40 mph across downslope areas today. -Low chance (~25%) of afternoon and low to medium chance (25-40%) of evening showers/storms across Upper Michigan on Independence Day. Rain spreads over the region Thursday night and Friday. - Rain and thunderstorm chances continue this weekend. && .SHORT TERM /THROUGH TONIGHT/... Issued at 232 PM EDT Tue Jul 2 2024 Water vapor and RAP analysis continue to highlight an upper trough and surface low over Manitoba, and a couple of shortwaves ahead of this. The first, currently moving out of the Great Lakes, touched off our initial round of rain showers that is slowly tapering off across the eastern UP this afternoon. After a brief dry break, the next shortwave ejecting out of the Plains will bring in our next round of light showers after 00Z. Though some thunder is possible, confidence is low with rather limited instability (a few hundred j/kg of MUCAPE by the evening and capped soundings). Meanwhile, with plenty of lower cloud cover over the area, temperatures are on the cool side with most of hte area only peaking in the lower 60s. However, some spots in the western UP are struggling even to get out of the 50s. Southerly winds remain gusty, especially across the downsloping areas long Lake Superior, with a strong 40-50KT LLJ directed over the area. Gusts up to 20-30mph are common area-wide, but where downsloping becomes a factor, stronger gusts in excess of 35mph and even up to 40mph are not out of the question. Winds fall back into the evening while the jet shifts eastward out of the area. As the next shortwave moves in, rain showers become most likely across the eastern half of the UP with areas west of M-95 possibly staying dry the rest of the night. Another quarter to half an inch of rain is possible across the eastern UP. Otherwise, temperatures shouldn`t fall back too much with rain and lingering low cloud cover. Expect lows to range in the upper 50s to lower 60s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Issued at 333 AM EDT Tue Jul 2 2024 There continues to be fairly good agreement among the deterministic and ensemble packages in the extended period, supporting high confidence in the overall progression of the pattern and the features embedded within. Where confidence does shrink though, are the details that come with the minor spatial and temporal differences between these packages. Overall though, main item of interest will be the period from late July 4th through the coming weekend thanks to the eastward migration of negative height anomaly through the Central Plains and central Canada. Beginning Wednesday, mid-upper level closed low on the shores of Hudson Bay will continue northeast, dragging behind a cold front through the Upper Great Lakes. Most of the precip should clear the eastern portions of the forecast area in the morning with surface ridging and drier air building eastward into the region. A couple of weak surface troughs looks to swing through through the day after the main cold front exits. There`s a brief window where enough destabilization could result in showers and thunderstorms developing in the afternoon. MLCAPE among the various models generally averages 200-800j/kg with near 40kts of 0-6km deep layer shear. Models appear to have expanded this risk area from yesterday`s eastern UP only, to now isolated to scattered activity can`t be ruled out for a majority of the forecast area. Another item of note will be the winds in the west. While not incredibly strong, daytime mixing may support westerly wind gusts near 20-25 mph for many locations. Along the Spine and western lakeshores of the Keweenaw, wind gusts may approach 35 mph at times. Conditions improve by evening as we decouple. However, with a mild airmass overhead, overnight lows should only dip into the mid-upper 50s in the interior and near 60F by the lakeshores. Ridging shifts eastward through the forecast area Thursday while upstream, an amplifying shortwave/closed low exits the northern Rockies and shifts eastward through the north-central Plains. Guidance continues to suggest the system`s surface low will press east through Minnesota and Wisconsin Thursday night and Friday, then lift northeast through Upper Michigan Friday night into early Saturday. The main forecasting challenge with this progression will be the onset of precip on July 4th. Guidance continues to suggest some afternoon destabilization alongside a weak inverted surface trough could spark afternoon/evening convection. However, there is the question of model run to run consistency and there are timing and spatial differences in the parent low and thus, this inverted trough. Overall though, it continues to look as those there is the potential for afternoon and evening showers and thunderstorms across the western half of Upper Michigan, and even as far east as Manistique. Will opt to maintain NBM pops for this forecast cycle given its representation of the low-end pop coverage increase and overall 30-40 peak percentages across the west half of Upper Michigan. If this does materialize, severe weather is not expected. Regardless, anyone with evening outdoor/firework plans across the western half of Upper Michigan should continue monitoring the forecasts. As the low presses closer overnight and into Friday, the timing and spatial differences become more apparent, although 0z runs do appear more aligned. A look at the GEFS and EC ensemble surface low clustering highlights this well. But as the system shifts through the region, any dry areas should fill in by Friday evening. The low will exit into Ontario Saturday while another shortwave dips down through Manitoba and western Ontario. At this point, its unclear if this will result in another round of showers/storms to finish out the weekend. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 129 PM EDT Tue Jul 2 2024 A brief dry period is expected the rest of the afternoon as rain showers work east of SAW, but plenty of lower cloud cover remains over the area. MVFR prevails at IWD and SAW, but brief drops to IFR are not out of the question at times as well. Meanwhile, CMX should continue to see mainly IFR ceilings through the rest of the day. Overnight, another round of showers moves through, mainly impacting SAW. There, expect IFR ceilings to settle in while IWD and CMX come in mainly at MVFR. A slow improvement to VFR is expected during the early morning hours of Wednesday as drier air works in and skies begin to clear out. Otherwise, southerly winds remain elevated this afternoon with 30kt gusts common, but winds fall back this evening. && .MARINE... Issued at 333 AM EDT Tue Jul 2 2024 Guidance continues to suggest strong southerly winds developing today across eastern Lake Superior. The forcing for this is the strengthening pressure gradient alongside a strong 40-50kt 925-850mb low level jet moving along a mid-level shortwave lifting through the region. Under the anticipated stable low level atmosphere, the strongest winds should have difficulty mixing to the surface. With this being said though, the pressure gradient, expected daytime mixing over Upper Michigan, and terrain influences along Upper Michigan`s lakeshore should be able to support areas where some mixing should occur. Ensemble probabilities presented by the HREF, NBM, and our internal probabilistic tools suggest the main risk area for some low end gales will be along the lakeshores east of Marquette, near Keweenaw Point, and north of Stannard Rock. Probabilities among these are widely mixed though, presenting a range of near 0 to 50% chance of 34kt winds at 10m, suggesting the overall stable synoptic environment will have difficulty mixing. I suspect higher observing platforms, such as Stannard Rock, will observe these stronger winds this afternoon, but 10m observations may only see the occasional gust. Given these persistent run to run signals, the elevated nature of where the strongest winds will be, and the localized nature of these stronger winds reaching the surface, decided not to issue a gale warning. Rain associated with this wave today may support some fog, mainly across western Lake Superior where winds are expected to be lighter. Winds should lighten this evening to 20kts or less as another round of rain builds. The rain should persist into early Wednesday morning as the system`s cold front presses west to east. Post frontal southwesterly winds should be able to climb to 25-30kts across the western half of Lake Superior, mainly between the Keweenaw and Isle Royale by Wednesday afternoon. Winds lighten Wednesday evening, and then are expected at or below 20kts going into the weekend. An exception to this could be Friday if a surface low moving through Wisconsin and Upper Michigan tracks a little further north than current thinking. If this does occur, northeast winds in the western half of Lake Superior may climb to near 25kts during the day. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... Beach Hazards Statement until 11 PM EDT this evening for MIZ014. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...LC LONG TERM...JTP AVIATION...LC MARINE...JTP