Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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243 FXUS63 KMQT 290717 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 317 AM EDT Mon Apr 29 2024 .KEY MESSAGES... - Occasional showers and some drizzle and fog today. Fog may be locally dense at times in high terrain. - Active pattern continues as three low pressure systems track across the region over the next week. Above normal temps/precip are expected including thunderstorm chances. - Elevated fire weather conditions are possible over the west half of Upper Michigan on Wednesday, but will depend on the preceding precipitation. && .SHORT TERM /THROUGH THIS AFTERNOON/... Issued at 316 AM EDT Mon Apr 29 2024 Water vapor imagery and RAP analysis show shortwave/mid-level low over eastern SD. At the sfc, associated 1005mb low pres is over sw MN. The low has started to occlude, and from the occluded front, a warm front extends across northern IA to southern Lwr MI. Main push of isentropic ascent in advance of the wave supported a solid area of shra that has lifted n of Upper MI during the night, leaving behind mostly just areas of -dz and some fog. This break in shra extends into WI. More shra are developing closer to sfc low and aforementioned fronts. These shra extend from sw MN into southern WI. Current temps across the fcst area are in the mid 30s to lwr 40s F. Mid-level low will begin to open up today as it lifts toward western Lake Superior. At the sfc, the associated sfc low will track from sw MN to the vcnty of Ironwood by 00z. It does not look like the warm front will make it into the U.P. Instead, the occluded front will lift to near the MI/WI stateline by 00z. As a result, being ahead of the occluded front, expect a gloomy day for the most part with some areas of -dz and fog. Fog may be locally dense at times in higher terrain. There will be shra at times as well. Closer to axis of 850- 700mb moisture transport, eastern fcst area should generally be favored for more frequent shra this morning into early aftn. A subtle shortwave will also be lifting across that area. Shra will become more nmrs mid to late aftn across the w and central as opening mid-level low approaches. Approaching occluded front will also aid this shra development. There is a little cape avbl for parcels lifted from top of inversion, but cape profile is very thin, suggesting little potential of thunder. Fcst will not reflect any thunder mention today. With winds maintaining an easterly component thru the day, knocked high temps down from previous fcst. Expect highs around 40F across the Keweenaw, mid to upper 40s central and e, and low 50s F w. These highs will occur late in the day, closer to 00z. && .LONG TERM /MONDAY THROUGH SUNDAY/... Issued at 445 PM EDT Sun Apr 28 2024 With three different low pressure systems in the extended forecast, there is fairly good agreement in the medium range model guidance for plenty of precip chances. Uncertainty builds in the latter part of the week as guidance begins to diverge ahead of the third low pressure system. The first low pressure system will be ongoing at the beginning of the extended forecast. Starting on Monday, a negatively tilted mid level trough will be situated over the Dakotas/MN state line, extending south into IA with weak ridging over the east U.S. coast and a trough over the Pacific Northwest. The midwest trough pivots over the UP on Monday and the sfc low slowly follows northward behind it. Better q-vector convergence will be located over Lake Superior already Monday morning with a dry slot highlighted in PWATs dropping ~0.2" behind the warm front. This leads to diminishing showers over the west in the morning hours. With increasing PVA in the afternoon, showers are reinvigorated mainly over the west half of the UP. This may be enough forcing to provide some thunder and lightning, however severe weather is not expected. Lingering showers and cloud cover will limit instability with model guidance hinting at ~200-300 j/kg of MUCAPE and mid level lapse rates mainly below 6 C/km. Also, by the time the low level inversion is eroded, the very limited instability will have nearly diminished. The 4/28 0z ECMWF EFI still highlights this period under anomalous QPF with SoT>0 and shaded values to 0.7 to 0.9. Morning showers look to add 0.01" to 0.15" in the west with 0.15" to 0.5" in the Keweenaw and eastern UP. Showers in the afternoon could result in an additional 0.25" in heavier downpours. That said, hydro hazards are not expected. Showers lift north out of the UP Monday night as the trough and sfc low lift over Lake Superior, temporarily bringing dry weather back to the UP for Tuesday. WAA during the day accompanied by clearing skies will bring above normal highs in the 50s near Lake Superior and in the east with 60s in the interior west and south central. Meanwhile, a shortwave will quickly ride east off the Northern Rockies toward the Upper Great Lakes during the day as it takes on a negative tilt and replacing the dry weather Tuesday night into Wednesday as it swings northeast over the UP. While there is some spread yet in the associated sfc low pressure, the general consensus is to take it northeast from MN into northern Ontario, but both GEFS and ECMWF ensembles have members that take the low further to the east over Lake Superior. The ECMWF also is a bit slower with the timing, which would drag precip longer into Wednesday. This means that timing and track still have some uncertainty yet, but a brief round of showers Tuesday night into Wednesday is expected, with better odds over the northwestern UP. Instability again is fairly low (MUCAPE below 100 j/kg), but the support of the cold front moving east across the UP may support a few rumbles of thunder near the WI/MI state line. Dry weather then returns on Wednesday, likely continuing through Wednesday night. Pressure rises behind the cold front and clearing skies will result deep mixing. This will yield warmer than normal temps in the 60s to low 70s and some breezy west winds during the day. Sounding analysis shows the interior west mixing up to around 800-850mb with up to 900mb in the east and the Keweenaw. The last two runs of ECMWF ensemble probabilities of wind gusts exceeding 34 kts were around 20-40% in the west with the 4/28 13Z NBM probabilities around a similar magnitude, except higher to 60% in the Keweenaw. This would also result in lower dew point temps in the west and thus RHs dropping near 25%. The combination of gusts and low RHs would increase fire weather concerns. The limiting factor here is the timing of the previous low pressure system. If the ECMWF solution is favored, precip will linger further into Wednesday resulting in delayed mixing, lower wind speeds, and higher RHs. Uncertainty continues to grow in the forecast Wednesday night onward, but chances for precip increase Thursday with 20-50% PoPs continuing into the weekend as we track out the third low pressure system. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 121 AM EDT Mon Apr 29 2024 Prolonged period of LIFR/VLIFR conditions will affect all sites this forecast period as fog and low clouds continue to move through along with some showers. At CMX, easterly winds overnight will be sustained at around 20kt with gusts up to 35kt possible. && .MARINE... Issued at 445 PM EDT Sun Apr 28 2024 Northeast gales to 35 kt are expected across the western third of the lake this afternoon increasing to easterly gales to 40 kts across most of the lake tonight, continuing into Monday morning. While a few gusts may exceed 40 kts late tonight into Monday, probabilities remain on the low end (25-50%). The strongest winds are expected in the far west as well as the north central portion of the lake between the Keweenaw and Isle Royale where there could be some channeling. The far eastern zone may see a few gale force gusts to 35 kts Monday morning, but confidence was not high enough to issue a Gale Warning for that zone. Gales quickly diminish Monday afternoon as the low pressure moves over western Lake Superior. Significant wave heights up to 14 ft are possible Monday morning between Duluth Harbor to the Bayfield Peninsula and near Isle Royale. Waves fall below 8 ft Monday evening. Winds fall below 20 kts in the west half of the lake Monday evening and after midnight in the east. Winds are then expected to remain mainly below 20 kts through Tuesday. East to south east winds increase to 20-30 kts Tuesday night, becoming west behind a cold front on Wednesday. With stronger pressure rises behind the cold front, west gales to 35 kts are possible on Wednesday over the west half of the lake. Highest probabilities of winds exceeding 33 kts are around 50-75% between the Keweenaw and Isle Royale. Winds quickly return below 20 kts Wednesday night. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... Gale Warning until 5 PM EDT /4 PM CDT/ this afternoon for LSZ162-242>246-263>266. Small Craft Advisory until 11 PM EDT /10 PM CDT/ this evening for LSZ240-241-247-248. Small Craft Advisory until 5 PM EDT this afternoon for LSZ249>251. Lake Michigan... Small Craft Advisory until 11 AM EDT this morning for LMZ221. Small Craft Advisory until 4 PM EDT this afternoon for LMZ248- 250. && $$ SHORT TERM...Rolfson LONG TERM...Jablonski AVIATION...07 MARINE...Jablonski