Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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985 FXUS63 KMQT 212326 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 726 PM EDT Sat Sep 21 2024 .KEY MESSAGES... - The prolonged stretch of above normal temperatures ends today, with temperatures cooling near normal Sunday. - A round of showers and storms accompany a cold front tonight through Sunday. Severe weather is not anticipated, but some small hail are possible with stronger storms. - Showers end from west to east through Sunday as the cold front exits the UP. Gusty NW winds behind the front, with the highest gusts along the eastern shores of Lake Superior up to 30 mph. - Other than a slight chance (15-20%) of showers associated with a low pressure passing through Lower Michigan Tuesday, dry weather is expected this week. - Patchy frost potential (~20%) for typical cold spots of interior western Upper Michigan Monday and Tuesday morning. - Supportive setup for patchy fog (~20%) each morning next week. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 321 PM EDT Sat Sep 21 2024 Latest water vapor imagery shows a well-defined shortwave trough lifting northeast into northern Ontario and northern MN this afternoon. This shortwave trough will move into the Upper Great Lakes later tonight and Sunday, sending a sfc cold front across Upper Mi tonight into Sunday morning. WAA and a 40+ kt LLJ max ahead of the cold front have already supported showers and scattered t- storms early this afternoon into north central WI and portions of western Lake Superior. A few showers may have made it into far western Upper Mi but showers have generally dissipated moving into into ridging and the associated dry and stable air mass across Upper Mi. While it`s been more cloudy into western Upper Mi due the convection drifting into that area, ridging has supported more sunshine into central and eastern areas of the U.P. this afternoon. Afternoon temperatures have generally been in the 70s to lower 80s, warmest inland east and coolest west under the clouds. Heading into this evening and tonight, the vort max/shortwave will continue to lift northeast through northern Ontario which will send the mid-level trough axis across Upper Mi later tonight into Sunday. As the system`s associated cold front moves across Upper Mi tonight into Sunday morning, showers along the cold front will most likely move into far western Upper Mi early this evening and then spread into central Upper Mi late evening and eastern Upper Mi overnight. Instability along the front is not particularly impressive, generally 500 j/kg MUCAPE, with the best of that south along the WI border. Effective shear along the front when showers will be occurring also generally looks like it will be 30 knots or less, so not really expecting any severe storms, but maybe a stronger storm with some dime-sized hail could develop south central along the WI border where marginal instability and shear appear to be maximized. Look for min temps lowering into the 50s behind the cold front tonight. Northwest winds behind the front could gust near 30 mph late tonight/early Sunday along the tip of the Keweenaw. && .LONG TERM /SUNDAY THROUGH SATURDAY/... Issued at 404 PM EDT Sat Sep 21 2024 A cold front exiting the UP to the east Sunday will signal the departure of the best chances of precipitation for the next week ahead. A Colorado Low-style shortwave will phase with an Alberta Clipper-style shortwave over the southwestern extent of the Midwest Monday into Tuesday and the resulting surface low will pass through the Lower Peninsula of Michigan Tuesday, resulting in most of the UP staying high and dry. 500mb ridging then builds in behind the departing trough Wednesday into the weekend and while the details are uncertain (and could be complicated by any potential tropical development), another blocking pattern could bring up to 50% chances of an extended period of drier than normal weather into October. For Sunday, showers and thunderstorms will be ongoing in the morning hours across central to eastern Upper Michigan. Showers should exit the CWA by 02Z Monday, though not before bringing an additional quarter to half inch of rain to the eastern third of the UP. Despite meager surface instability, HREF reflectivity paintball plots still show some isolated to scattered thunderstorm potential with the showers, so slight chance to chance thunder (15-30%) has been kept in the forecast, though no severe weather is forecast. Winds look to be gusty behind the front especially over Lake Superior, with some shoreline locations seeing up to 30 mph gusts out of the NW, though the gusts will not penetrate too far inland with HREF mean gusts in the interior around 20 mph at most. Monday will be a dry day as 1019mb surface high pressure (12Z GEFS clusters) will reside overhead. Monday and Tuesday morning both have the potential (~20%) for morning patchy radiation fog. MOS guidance suggests lows in the upper to mid 30s in the interior west both mornings, which could lead to some patchy frost for elevated flat surfaces and typical cold spots. Will hold off on any products as the temperatures look borderline and there`s some disagreement between the NBM deterministic and its own ensemble 50th percentile that leads to decreased confidence. If the percentiles are to be believed, there is around a 25% chance of some sub-freezing lows around the Houghton/Baraga/Iron County triple point on Monday morning and across more interior locations on Tuesday. As the pair of troughs coalesces on Tuesday morning, the resulting surface low around 1010mb looks to pass through Indiana/southern Lower Michigan on Tuesday. PoPs have all but trended completely out of the UP now, though there is still ~15% chances for the farthest south and east portions of the UP to just get brushed by the precipitation shield of this system. Ridging behind the system will bring mainly clear skies and a slight warming trend of highs from around the mid 60s on Monday to the mid 70s by the weekend. The pattern gets a bit unclear by the weekend as the global deterministic models struggle to resolve whether a rex block sets up or if there is interference from a potential tropical system in the late week, but the CPC still has the UP in a up to 50% contour of lower than normal precipitation through the end of September regardless of exact solution. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 725 PM EDT Sat Sep 21 2024 Cold front will move through Upper Michigan overnight, supporting MVFR ceilings developing, mainly at KSAW. Recent model and observational trends of ongoing convection and prefrontal environment highlight stability and dry air winning out, which is reflected in this TAF with the drier trend at KCMX and KIWD. With that being said though, cloud bases will lower as the front approaches and MVFR ceilings may develop, most likely at KIWD. As the front continues eastward, guidance continues to highlight additional showers and some thunderstorms developing and potentially impacting KSAW overnight. Expect improving conditions at KSAW by morning as most shower activity presses east of the terminal. Post frontal winds will become north to northwest with some gust potential upwards of 20-25kts, mainly at KCMX and KSAW. && .MARINE... Issued at 404 PM EDT Sat Sep 21 2024 Winds will remain at 20 knots or below this afternoon and early evening. As a cold front sweeps across Lake Superior tonight, winds behind the front will gust to near 25 knots out of the west and northwest, first over the western portions of the lake around midnight and then over the east around 8 AM Sunday morning. Winds fall below 20 knots in the west through Sunday morning with winds relaxing in the east throughout the overnight period into Monday morning. Winds then look to remain below 20 knots as major low pressure systems remain far from Lake Superior. As the cold front passes tonight and Sunday, there is a chance (~30%) of thunderstorms, though severe weather is not expected. Waves behind the front will peak between 4 and 5 feet along the Keweenaw Peninsula shores Sunday morning and over the east half of the lake between 6 and 7 feet during the day Sunday, falling below 4 feet lakewide by Monday morning. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...GS AVIATION...JTP MARINE...GS