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Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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973 FXUS63 KMQT 200729 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 329 AM EDT Sat Jul 20 2024 .KEY MESSAGES... - 30-60% chance of showers and thunderstorms mainly over the southern half of the UP this afternoon/evening. Severe weather not expected. - Next chance of showers/storms Tuesday/Wednesday. && .SHORT TERM /THROUGH TONIGHT/... Issued at 328 AM EDT Sat Jul 20 2024 Morning water vapor and RAP analyses reveal an anomalously deep cutoff low moving into northern Quebec, remnants of an MCV spinning over the eastern Dakotas/western MN, and an elongated vort max moving east of Lake Superior. Ridging extends from the Desert Southwest into the Canadian Rockies. This is supporting surface high pressure over the Canadian Prairies, which is expanding east/southeast into Ontario in the wake of the exiting low. Altogether, this is pushing a weak surface cold front southward towards Lake Superior early this morning, indicated by some cooler cloud tops on satellite and weak radar returns over the far northern portions of the lake. The cold front continues to drop southward over the lake through the early morning hours, and may finally touch off some shower activity across the northern UP after sunrise. However, given the timing of the frontal passage (that is, before peak heating and destabilization), convection across the northern half of the UP should be spotty at best. Showers and storms look to increase in coverage as the front heads towards the WI border into the early afternoon, with simulated reflectivity favoring the south-central UP (spanning from Iron through Delta counties) for more numerous showers/storms. Per the HREF and model soundings, SBCAPE should increases to around 500-1000j/kg by then, though shear remains low and midlevel lapse rates unimpressive. Thus, strong convection is not expected. Still, with a narrow corridor of PWATS in the neighborhood of 1.5in and rather slowly-moving storms amid lighter wind fields, some heavier downpours would not be out of the question. Ensembles favor around a widespread 0.10-0.25in of rain, but some higher embedded amounts around and in excess of 0.50in are possible (50% chance among the hi-res ensemble members). Showers drop south of the UP closer to sunset. Otherwise, expect temperatures starting in the mid 50s-lower 60s this morning to climb into the lower to mid 70s by mid-morning in the northern half of the UP. Behind the front, temperatures should hold steady the rest of the day or even fall back slightly (especially closer to Superior); the southern half of the UP should be able to see highs ranging in the upper 70s to lower 80s before the front finally drops through later in the day. Into tonight, clearing skies, light winds, and a cooler airmass should yield lows several degrees cooler than early this morning. Expect lows in the lower to mid 50s across most of the area, while some portions of the interior-western UP potentially see temperatures dipping into the 40s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 247 PM EDT Fri Jul 19 2024 Low-level frontal boundary discussed in the short term section will continue progressing south through the UP on Saturday while losing upper level support as the parent low continues shifting eastward into Quebec. This may result in a few showers in the northern half during the morning and early afternoon, but should be no more than a nuisance if anything. Relatively more widespread coverage of showers and thunderstorms expected over the southern half (highest near the WI/MI border counties) where the arrival of the front will coincide with a modestly destabilizing diurnal boundary layer. SBCAPE progged by the HREF mean mainly in the 500-1000 J/kg range, but midlevel lapse rates are weak and winds through the column are very light, so any storms should be of the garden variety. There could be a few heavier downpours with likely slow moving storms and a narrow ribbon of 1.5-1.75" PWATs, but overall low impacts expected. Saturday night into Sunday, big bubble no trouble as the Ontario high continues to expand over Lake Superior and the UP. Highs both days fairly seasonable, a little cooler near the big lake due to onshore flow. Another tranquil day Monday under the influence of the high, but weak warm advection should boost temps a couple degrees to the seasonably warm side. Western NOAM ridging remains strong into next week, while shortwave energy dives south along its eastern flank. Deterministic guidance is showing some of this energy consolidating and possibly cutting off in the vicinity of the upper Great Lakes. This will bring our next chance at showers and thunderstorms in the Tuesday/Wednesday frame, along with cooling temps by Wednesday. Temps look to rebound with a drying trend for the end of next week as this low moves out. In fact, some summer warmth could return Friday into next weekend as there are indications that some of the western US ridging folds eastward into the upper Great Lakes. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 115 AM EDT Sat Jul 20 2024 VFR conditions will continue through the TAF period. The only forecast concerns are a northerly wind shift with an approaching cold front set to cross the UP in the daytime hours (12-18z) and some incoming cloud cover, though, not expecting any drop to MVFR or lower. Some spotty showers are possible along the boundary, however, more convective activity is possible in the southwest UP (potentially at IWD) along the MI/WI border as the cold front interacts with max diurnal destabilization. Confidence in shower or afternoon thunderstorm coverage is low, but I did include a VCSH at SAW Sat afternoon where shower coverage will probably be the best of all the TAF sites. && .MARINE... Issued at 517 PM EDT Fri Jul 19 2024 Southwest winds up to 20 knots over mainly the west half of Lake Superior will diminish below 20 knots tonight as a cold front moves through overnight into early Saturday. There is a slight (20%) chance for storms developing along this boundary to make it across the lake later tonight, but confidence is low. Winds stay light, mainly below 20 kts at least through Monday. Winds increase out of the NE across the western portions of the lake Tuesday with another shortwave trough moving through. Gusts around 20kts are possible. This is also our next decent window for showers/storms to move over the lake (20- 30% chance) before mainly dry weather returns midweek onward. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...LC LONG TERM...Thompson AVIATION...Voss MARINE...Voss