Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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639 FXUS63 KMQT 230719 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 319 AM EDT Thu May 23 2024 .KEY MESSAGES... - Another shortwave and low pressure system will bring another round of showers and a slight chance (around 20% chance) for some thunder to Upper MI late Friday into early Saturday. - There will be more opportunities for rain next week although model uncertainty leads to low forecast confidence on timing/extent. && .SHORT TERM /THROUGH TONIGHT/... Issued at 318 AM EDT Thu May 23 2024 RAP analysis shows a stacked closed low north of Lake Superior with central surface pressure near 994 mb. While a tight pressure gradient and tapping into a LLJ caused windy conditions earlier, the weakening low departing the region is allowing winds to come down somewhat, though some gusts to 25 mph may linger throughout the morning. Despite weakening surface flow, diurnal heating will support cu development with a few CAMs suggesting some shower development in the south and interior west. Instability has trended lower with the last 24 hours of model runs, so confidence in showers of any strength is low, but left some 15-24% PoPs from 18Z to 02Z. Expect highs mainly in the mid 60s, close to the climatological normal for this time of year. The exceptions will be locations downwind of Lake Superior that will have highs near 60 and the south, which bias- corrected guidance suggests mid- to upper-70s may be observed between Menominee and Iron Mountain. Overnight, winds turn easterly and northeasterly in response to a 00Z GEFS-mean 997 mb low approaching Minnesota. Previous forecasts had rain arriving in Ironwood by 12Z Friday, but virtually all of the most recent model runs at varying resolutions have backed off on the initial line of precipitation, so PoPs have been largely removed from the overnight time period. Low temperatures will be in the 40s, near normal for this time of year. && .LONG TERM /THURSDAY THROUGH WEDNESDAY/... Issued at 401 PM EDT Wed May 22 2024 By Thursday morning, the deep surface low just north of Lake Superior this afternoon will have moved over James Bay while slowly weakening. A mid-level ridge building over the Northern Plains should lead to weak ridging/subsidence and mostly dry conditions across the area on Thursday. That said, will still hang on to some chance PoPs during the afternoon with a few of the models hinting at a subtle shortwave rotating thru the area in the afternoon from the storm system over James Bay. Any shower development from this weak wave should be sparse given dry low-levels depicted in fcst soundings. With some CAPE present in soundings, a few rumbles of thunder will not be ruled out - but there is some capping to overcome. Otherwise, expect sunny skies for the most part while temperatures climb into the 70s across most of the UP, and in the 60s near Lake Superior. Though winds will come in much lighter than today with a weakening pressure gradient, shallow daytime mixing could still bring down some 20mph gusts across much of the UP, potentially higher across the Keweenaw. By Friday, the focus shifts to the next shortwave emerging from the western CONUS mid-level trough . This shortwave lifts NE through the Plains and Upper Great Lakes, eventually swinging into Manitoba and phasing once more with the broader troughing over the western CONUS/Canadian Prairies. Increasing isentropic ascent, 850 mb theta advection and moderate q-vector convergence out ahead of the shortwave will lead to another quick round of showers across the area beginning late Friday afternoon in the western UP and spreading eastward during the evening. If showers can hold off until later in the afternoon, then we`ll stand a better chance at eroding a building cap which would allow for some rumbles of thunder. Otherwise, guidance continues to favor amounts largely around a 0.10- 0.25in, but ensembles are also showing around a 40% chance for more isolated amounts around and in excess of 0.50in. Rain showers move eastward out of the UP late Friday night, then for the most part, Saturday should be dry with ridging behind the exiting shortwave with much drier air working in. However, with another subtle wave emanating out from the parent low over Manitoba, a few additional sprinkles/light showers will not be ruled out; little to no rain accumulations are expected. Expect otherwise partly cloudy skies and seasonable temperatures for the rest of the day with highs mostly in the 60s with a few cooler mid 50s readings near Lake Superior. While models indicate weak ridging should hold on long enough to keep Sunday dry, there is plenty of model uncertainty with what will happen after that. Latest deterministic Canadian guidance continues to maintain mostly dry conditions through the first half of next week, suppressing a southern stream trough over the Lower Great Lakes/Ohio Valley and keeping the Upper Great Lakes mostly dry. This increasingly looks to be the outlier among the global models. The Euro, UKMET, and now the GFS are trending toward a phased, deeper and farther north system tracking somewhere between the central Lower Peninsula and the Straits of Mackinac. If a more northwestward solution verifies it will potentially be a much more impactful system for the Upper Great Lakes into early next week with much of the UP receiving significant soaking rainfall, and the eastern UP potentially seeing heavy rainfall Sunday night through Monday. Wraparound moisture in the deformation zone, comma head of the deepening system will lead to the potentially heavy rainfall Tuesday as well. The deep system would also lead to more wind impacts with gales likely over Lake Superior and windy conditions across much of the U.P. Needless to say, model trends will be watched closely in the coming so stay tuned to possible forecast changes into early next week. As of right now, given the uncertainty, this forecast reflects the latest NBM solution which does bring in an increase in wind speeds as well as better chances for rainfall early next week. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 123 AM EDT Thu May 23 2024 In the wake of low pres tracking ne across northern Ontario, drier air moving into the area will allow VFR to prevail at IWD/CMX/SAW thru this fcst period. W to NW winds will still be elevated into this aftn, especially at CMX/SAW. Expect w to nw winds of 15-20kt at CMX thru late aftn. Winds at SAW will increase to 15-20kt a few hrs after sunrise. Winds will become light, aob 5kt, at all terminals this evening. && .MARINE... Issued at 401 PM EDT Wed May 22 2024 Deep low pressure is centered just north of Lake Superior this afternoon, with a tight pressure gradient over the lake. SW gales of 35 knots are common across the western half of Lake Superior, but higher gusts to 40 knots are still possible through the evening especially closer to the shoreline of the Keweenaw. Winds are coming in comparatively lighter to the east, mainly up to 20-25 knots. As the low gradually lifts north through Ontario and weakens this evening, winds should fall below gale force by midnight. Internal probabilistic guidance indicates only around a 20% chance for gales the rest of the night. The winds continue to diminish through Thursday morning and afternoon, with light winds of 20 knots or less returning to the area by evening. The period of light winds doesn`t last long over the western lake as northeast winds will begin to ramp up to 30 knots late Thu night into Friday in advance of another low pressure lifting from the Northern Plains towards Lake Winnipeg. Guidance indicates around a 30-40% chance for gale force gusts Friday afternoon in far western Lake Superior. Winds diminish to 15 to 25 knots over the west half of the lake and becoming southwest behind the low and the passage of its cold front late Friday night into Saturday. Behind this system, expect light winds of 20 knots or less across Lake Superior for the rest of this weekend as high pressure ridging moves over the area. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... High Wind Watch from 6 AM EDT Wednesday through Wednesday evening for MIZ001-003. Wind Advisory from 9 AM EDT /8 AM CDT/ to 10 PM EDT /9 PM CDT/ Wednesday for MIZ002-009. Lake Superior... Gale Warning until 8 PM EDT /7 PM CDT/ Wednesday for LSZ162. Gale Warning from 7 AM EDT /6 AM CDT/ to 8 PM EDT /7 PM CDT/ Wednesday for LSZ240-241. Gale Warning from 10 PM this evening to 11 PM EDT Wednesday for LSZ242>244-263-264. Gale Warning from 2 AM to 11 AM EDT Wednesday for LSZ245>251- 265>267. Lake Michigan... None. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...GS LONG TERM...LC AVIATION...Rolfson MARINE...LC