Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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602 FXUS63 KMQT 311125 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 725 AM EDT Fri May 31 2024 .KEY MESSAGES... - Scattered showers and isolated thunderstorms possible today for western Upper Michigan, then frequent opportunities for showers and thunderstorms over the next 7 days. - Above normal temperatures through the first half of next week, then turning cooler, potentially much cooler. && .SHORT TERM /THROUGH TODAY/... Issued at 355 AM EDT Fri May 31 2024 Southerly flow with increasing moisture, in addition to high clouds building into western Upper Michigan has produced a mild night across the forecast area, except interior portions of the east where dry air and light winds have supported effective radiational cooling. So far interior temps have fallen into the upper 30s while the lakeshores have remain in the 40s or 50s. Across the west, min temps in the 50s and even some low 60s have been observed so far. Upstream, a line of showers with some preceding isolated showers has been observed moving through northern Minnesota, pressing northeast as a weakening cold front advances. Some lighting has been observed, but activity has waned in the past couple of hours. As we move through the remainder of the morning hours and into today, showers and storms across central Minnesota will lift northeast as the boundary presses eastward into the Arrowhead and western Lake Superior. Some rumbles of thunder can`t be ruled out. The weak boundary will continue pressing east while upper level support shifts northeast, bringing with it increasing pops for the west. Onset is a little tricky given the anticipated dwindling line as it approaches, but the overall consensus is for light rain to move into the west by late morning. While the boundary inches across the Arrowhead, continued convergence with growing weak instability out in front will result in continued shower chances through the afternoon for the west half. Thunderstorms can`t be ruled out, but severe weather is not expected. In the east, dry air will win out, likely resulting in clear to partly cloudy skies. This, coupled with dinural heating, will support mixing and enable drier air aloft to mix down to the surface. Model soundings suggest mixing only to around 2k feet, which would support RH percentages dipping down into the mid 20s. If we are able to warm more and mix higher then expected though, lower RH near 20% will be possible. Daytime highs across the region should climb into the 70s, except remain in the 60s by Lake Michigan. && .LONG TERM /TONIGHT THROUGH THURSDAY/... Issued at 500 AM EDT Fri May 31 2024 A progressive flow regime will prevail thru about the middle of next week as a series of shortwaves track off of the N Pacific, then eastward roughly along the vcnty of the U.S./Canada border. As a result, frequent opportunities of pcpn are in the offing for Upper MI with the first already arriving over western Upper MI today/tonight. That pcpn will slowly spread eastward thru the first half of the weekend. The second wave and pcpn chc will be centered on late Sun night/Mon, and the third during Tue night/Wed, but this third round of pcpn may end up lingering for a few days due to potential mid-level low development over the Great Lakes region, resulting from a significant pattern change over and around N America late next week thru much of the week of June 9. Medium range ensembles are depicting development of a positive height anomaly across the Arctic Ocean, amplified ridge development across western N America, extending to the Arctic Ocean, and positive height anomalies/ridge development in the Labrador Sea area. If it was Jan, this type of pattern that would support a harsh arctic outbreak into the Great Lakes region. However, it`s June, so we`ll be looking at a mostly seasonably cool stretch of weather beginning late next week and continuing thru the week of June 9. Given the pattern though, a couple of unseasonably cool days (max temps upwards of 20 degrees blo normal) would not be unexpected during that time. It is noted that the EPS has been and continues to be more amplified with the pattern than the GEFS/GEPS. Its max ensemble mean 500mb height anomaly now reaches 195m over the Great Lakes region on June 7, suggesting coolest weather in the June 7-9 period. Prior to the cool down beginning late next week, temps will likely run above normal. Beginning tonight/Sat, an anomalously deep mid-level low will be centered over northern Saskatchewan/northern Manitoba. Main shortwave associated with this feature will swing thru northern Ontario to Hudson Bay today. A weakening cold front tied to this wave will stall out over western Lake Superior or western Upper MI tonight, but it does become quite difficult to track the sfc front with time. This boundary combined with the development of upper diffluence from right entrance of a sw-ne oriented 110kt upper jet streak across northern Ontario will support shra over about the western third to half of Upper MI tonight. CAPE up to 200-300j/kg may be avbl for parcels lifted from around top of sfc based stable layer. So, some rumbles of thunder are possible. Around the mid- level low, a shortwave will swing along the International Border tonight and then ene into northern Ontario Sat. This will give the subtle boundary and associated shra/tsra an eastward push into central Upper MI during Sat. Then, diminishing shra/tsra should spread across the eastern fcst area Sat evening. HREF shows probability of rainfall exceeding 1 inch up to 30-40pct over western Upper MI as that area will be affected by frequent sw-ne moving shra thru Sat morning before the weak sfc boundary shifts e. Should be able to slip in a dry day on Sun with sfc high pres ridge moving across the western Great Lakes. Expect highs in the 70s F. Temps will be in the 60s lakeside of the Great Lakes or will fall back to the 60s in the aftn as lake breezes develop. The next shortwave moving onshore over the Pacific NW on Sat will reach the Upper Mississippi Valley late Sun night and the western Great Lakes by Mon aftn. Along/ahead of the associated cold front, developing/organizing shra/tsra across the Dakotas into MN Sun aftn/evening will move e Sun night thru Mon. For now, it appears that the arrival of these shra/tsra late Sun night into western Upper MI will work against a svr storm risk as instability diminishes with time and eastward extent, but with a 40-45kt low- level jet translating over western Upper MI by 12z Mon, it will be worth monitoring in the coming days. Coverage/persistence of shra/tsra moving across the area Mon morning and whether any clearing occurs before cold front clears the area will determine if any stronger storms then develop along the cold front Mon aftn. That won`t be known until we get closer to Mon. In the wake of the cold front, passing sfc high pres ridge on Tue should support a dry day. A vigorous wave will then move out across the Northern Plains on Tue. The fate of this wave is tied to the aforementioned late week pattern amplification over and around N America. As would be expected at this time range and with the start of significant pattern amplification, there is considerable uncertainty in the evolution and progression of this vigorous wave. For now, it appears that shra will enter the picture at some point Tue night/Wed with shra chc probably continuing Thu/Fri and maybe into or thru the weekend if a large mid-level low sets up over the Great Lakes region. Cool conditions will set in during this time as well. && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 725 AM EDT Fri May 31 2024 A weakening and slow moving cold front will move into Upper Michigan from west to east in this forecast period. This will result in VFR conditions interspersed with scattered showers and potentially some thunderstorms today at KIWD and KCMX, while KSAW remains VFR. Tonight and into Saturday, shower coverage mixed with thunderstorms becomes more widespread. VFR conditions are primarily expected in this period; however, increasing low level moisture late tonight may result in MVFR ceilings at KCMX and KIWD by the end of this forecast period. && .MARINE... Issued at 500 AM EDT Fri May 31 2024 Under a relatively weak pres gradient and stable conditions over the lake, expect winds mostly under 20kt today thru Sun. An approaching cold front Sun night will bring an increase in southerly winds, especially across the e half of Lake Superior which is typically favored for stronger winds this type of situation. By sunrise Mon, s to se winds up to 25kt are expected, though given the stability over the cold lake waters, these winds up to around 25kt will mostly be observed at high obs platforms. That said, 25kt winds may observed locally in the nearshore waters where flow off of the terrain affects the wind. Cold front will pass later Mon/Mon night with winds under 20kt following on Tue. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...JTP LONG TERM...Rolfson AVIATION...JTP MARINE...Rolfson