Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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315 FXUS63 KMQT 220845 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 445 AM EDT Sat Jun 22 2024 .KEY MESSAGES... - Wet pattern continues into early Sunday with some periods of patchy fog. - The heaviest rainfall should stay south of the UP, but there is still a slight chance (15% chance) for locally heavy rain resulting in minor flooding impacts across south central and southeast portions of Upper Michigan. - Another round of showers/thunderstorms is possible Sunday and Monday night into Tuesday. && .SHORT TERM /THROUGH TONIGHT/... Issued at 444 AM EDT Sat Jun 22 2024 More showers to move in today and tonight with the heaviest/steadiest rainfall central and east... Latest water vapor imagery and current RAP analysis currently show broad mid-level ridging over the Upper Great Lakes early this morning but this will give way to a couple of upstream shortwave troughs of interest, one over southern/central MN and another over western SD. The initial shortwave trough over MN is expected to move across the Upper Great Lakes today with the second trough from the Dakotas expected to move across the area tonight. Both these shortwaves along with an associated sfc low pressure system will support periods of rainfall across the U.P. today into tonight. Based upon the tracks of the shortwaves and the associated sfc low along with the most favorable fcst forcing from mid-level fgen and isentropic ascent would expect the heaviest and most prolonged rainfall to occur over south central and east half portions of the U.P. today through tonight. Weak elevated instability could support isolated t-storms as well, mainly south central and southeast. Currently, only isolated to scattered light rain showers are occurring over south central UP but expect this coverage to increase to numerous or widespread toward sunrise as it spreads slightly farther north and east in response to the shortwave trough moving in from MN. It is worth noting that WPC does have the southeast half of the U.P. (roughly along and east of a line from Iron Mountain to Harvey) in a slight risk for excessive rainfall today into tonight as PWATs range from 1.5 to 2 inches across much of the area or nearly 200% of normal. Would expect the most vulnerable areas for risk of flash flooding would be urban or poor drainage areas southeast if training of stronger showers/storms occurs over these areas. With the expected moist conditions will also continue to carry a mention of patchy fog in the grids through much of the period. Under mostly cloudy skies, temps today will generally be in the lower to mid 60s, although could be in the upper 50s along the Lake Superior shore. Lows tonight will be mostly in the 50s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Issued at 304 PM EDT Fri Jun 21 2024 Deterministic and ensemble guidance packages continue to highlight the potential for multiple rounds of showers and thunderstorms in the extended forecast period as Upper Michigan sits primarily under near-zonal to northwest flow aloft. During this period, daytime temperatures will start off cool, but trend back into the 70s and 80s for the first half of the work week. Beginning Saturday, surface low will lift northeast along a warm front into the Great Lakes as a shortwave presses east through Minnesota. This will support a deepening surface low Saturday afternoon into early Sunday as the low transits Wisconsin and lower Michigan. Precip along and north of the boundary will build into the region through the day as PWATS remain 1.75-2 inches. Recent NBM and LREF guidance suggests a high (>75%) chance of exceeding 1 inch of rain across the southern half of the forecast area, with 30-60 percent chance across the north half. While most deterministic guidance suggests a widespread 0.5-2 inches through Sunday morning, GEFS and EC ensemble means suggesting the same supports the higher confidence in a potential notable and widespread rainfall event. This generally matches the EC EFI and SOT, which paints much of the south half with 0.8-0.9 EFI and 2 for SOT, indicating a potential extreme rainfall event outside of climatology. It should be noted though, that even if widespread 1-2 inches of rain does occur, recent RFC flash flood guidance suggests 2+ inches of rain in 1-6 hours would be needed to raise flash flooding concerns. Given that this is not the case with this event, flash flooding is not a concern. With that being said though, given recent rainfall, I`d expect some ponding of water in low lying locations and some additional river rises through the next few days if we do experience this rainfall. Additionally, rainfall amounts will be dependent on where the low tracks and where the warm frontal boundary stalls across Wisconsin, which a general clustering analysis of the EC and GEFS ensembles still suggests a range of locations. Model soundings suggest a mostly capped atmosphere across the area, with some elevated instability noted across the south. With this in mind, some embedded thunderstorms can`t be completely ruled out, but strong or severe thunderstorms aren`t expected at the moment. Daytime highs Saturday should be in the 60s to near 70F while overnight lows dip into the 50s to upper 40s across the forecast area. Precip should end Sunday morning from west to east as the low pulls away and weak mid-level ridging transits the area. This break appears to be short-lived though, given the clipper-like shortwave pressing southeast across Ontario/Lake Superior in the afternoon/evening. The GFS and NAM suggest the morning rain should end early enough to enable small daytime destabilization through the day, which would support thunderstorms to accompany the afternoon/evening wave. At the moment, strong or severe weather aren`t anticipated. High pressure over the area Monday should keep the region dry while upstream, a ridge rolling impulse moves east through the Dakotas/Minnesota and a surface low tries to develop. By Monday night, precip chances increase for Upper Michigan as a cold front extending south of a low moving through Manitoba and the low moving through southern Minnesota press closer. These swing into the Great Lakes on Tuesday. Ahead of the front, daytime temps could warm into the 80s across much of the region Tuesday. High pressure and dry conditions builds in Wednesday into Thursday. Beyond this, guidance differs greatly on the timing and position of the next wave. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 140 AM EDT Sat Jun 22 2024 Next round of showers will move in overnight and will bring deteriorating conditions with them. IWD will be VFR overnight and then IFR Saturday with LLWS coming in late Sat afternoon into the evening. CMX will be VFR and then by late Saturday afternoon, rain moves in there with LLWS and MVFR conditions setting in by evening. SAW will be VFR until around 12Z Saturday morning when rain moves in and then drops to MVFR. By late Sat afternoon, heavier rain and IFR/LIFR conditions move in. LLWS sets up at SAW by Sat evening. && .MARINE... Issued at 304 PM EDT Fri Jun 21 2024 A deepening low pressure system will gradually lift into the region tonight and Saturday, before exiting into Ontario Sunday morning. As this transit occurs, expect winds to shift to northeasterly/easterly across Lake Superior tonight before becoming northerly Saturday night and northwesterly by Sunday morning. Light winds of 20kts or lower are mostly expected in this event, although northeast winds going down into the Duluth Harbor Saturday may climb to near 25 kts at times. Additionally, as winds shift to the north Saturday night, expecting an increasing to 25-30 knots across central and eastern Lake Superior as the peak pressure gradient force shifts through. Winds lighten to 20kts or less Sunday and predominately remain there until at least Tuesday. At this point, expecting southerly winds to increase to near 25 kts ahead of a transiting cold front. Thunderstorms will be possible, mainly Sunday afternoon/evening and then again on Tuesday. Winds may be erratic near these, but at the moment, strong or severe thunderstorms are not expected. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...JTP AVIATION...07 MARINE...JTP