695 FXUS63 KMQT 210536 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 136 AM EDT Sat Aug 21 2021 .SHORT TERM...(This evening through Saturday) Issued at 327 PM EDT FRI AUG 20 2021 Currently, we are looking almost like a complete repeat of yesterday. Satellite imagery shows diurnal cu popping up in the U.P. this afternoon as a dry high pressure ridge slowly makes its way eastward. Some areas in the elevated terrain near Lake Superior (and near southern Houghton County) are already around 90F! The only saving graces right now is that RHs are around 40% in those areas this afternoon and there is a light south/southwesterly breeze across most of the area. Some light haze can still be seen across the area, particularly in the east (as seen in the vertically integrated smoke product in the HRRR smoke model). This haze should slowly leave the area tonight as a cold front approaches from the west. Tonight, expect temperatures to bottom out near the 60s across the area, as some cloud cover associated with the cold front should start rolling into the western CWA late. As the front approaches, expect southerly winds to pick up from west to east. These winds should bring some breezy conditions across the area ahead of the cold front tonight and Saturday. Not expecting the rainfall associated with the cold front to arrive in the far west until late tonight. Given that only the NAM12km was showing some CAPE along the frontal boundary during the overnight and early morning hours, decided to cap thunder chances to slight until late Saturday morning. As the front progs eastward throughout the day Saturday, expect cooler temperatures (mainly upper 70s) in the west behind the front, whereas the far east (near Newberry) could see still see temperatures approach the mid-80s. Could still see some pockets of low 80s along the downslope areas near Lake Superior, as the downslope of southerly winds could raise temperatures to get over 80. Also, could see the low-80s in the south central too Saturday, as the front isn't expected to arrive until the afternoon. Thunderstorm chances improve throughout the day Saturday, as some diurnal heating ahead of the cold front should increase instability in central and eastern Upper MI. Not expecting severe wx, as the front should be dying as it moves east; while MUCAPEs look modest (around 1000-1500 J/kg) and bulk shear looks marginal for severe wx (around 30 knots at most spots near the frontal boundary), because the front is dying, the forcing mechanism to produce convection should weaken with time. Therefore, while I think convection is a definite possibility, I'm doubtful that the modest instability and marginal bulk shear will be enough to overcome the loss of forcing in the cold front to produce severe wx. The better forcing for convection is expected north of us in northern Ontario, as the low associated with this cold front lifts northeast towards Hudson Bay. Thinking we will see more breezy conditions behind the cold front Saturday, particularly in the Keweenaw Peninsula, as significant height rises and temperature advection is expected; the Keweenaw could see some wind gusts over 35 mph late tomorrow afternoon! The wind direction behind the front is expected to be westerly. .LONG TERM...(Saturday night through Friday) Issued at 341 PM EDT FRI AUG 20 2021 Through the extended fcst period, models indicate mean troughing over western Canada, and at times over the western CONUS, as a series of shortwaves eject eastward across the northern CONUS and Upper Great Lakes region in a progressive flow through next week. Based on dynamics and available moisture, it looks like the more promising chances for widespread showers would not be until mid to late next week. Temperatures will fluctuate from near to above normal through much of the period. Beginning Saturday night into Sunday, models indicate any remaining showers ending in the evening over the eastern portion of the cwa, then dry, cooler and less humid conditions thereafter into Sunday as sfc high pressure builds in quickly from the west behind Saturday's shortwave/cold front. Min temps Sat night will fall back into the more comfortable 50s for most locations. Sunday's max temps will be closer to seasonal normals with highs in the 70s and dew points in the upper 40s to mid 50s. Waves generated from fairly gusty nw-n winds behind the front will likely warrant a high swim risk for Alger County on Sunday. The next shortwave moving across the Northern Plains on Sunday will weaken as it lifts into northern Ontario by Monday morning. Models show a weaker pcpn signal with this weakening wave compared to the wave on Saturday. Even though GFS soundings indicate MLCAPE values increasing to 500-1000j/kg Mon ahead of the front, warm nose of nearly 17C temps aloft and fairly significant CIN may prohibit convective development on Mon across much of the area. In the end, the better chc of pcpn with this wave looks to be late Sun night/early Mon over the w in association with an approaching, but weakening 30 kt low-level jet. Otherwise, nothing more than low chc/schc pops are warranted late Sun night/Mon. Max temps will rise back into the lower to mid 80s most locations on Monday and Tuesday. Latest models indicating perhaps a better signal for showers/t- storms with the next shortwave due in late Tue into Wed. Trends indicate better shortwave dynamics and stronger WAA/moisture transport ahead of the system. With MUCAPE values approaching 1000- 1500 j/kg and deep layer shear 40-50 knots there certainly could be some strong to marginally severe storms associated with this system. High pressure building in behind this system should result in dry and cooler conditions on Thursday. Models certainly differ on the timing/strength details but there does appear to be a pretty consistent signal that a broader, deeper trough will dig in from the Northern Plains late next week/weekend bringing more opportunities for rainfall. && .AVIATION...(For the 06Z TAFS through 06Z Saturday night) Issued at 135 AM EDT SAT AUG 21 2021 With the precip and its front inching closer to Upper Michigan, timing looks fairly on track to the previous TAF issuance. Lightning remains embedded, albeit has certainly dropped off after sunset. But, with enough instability lingering around, have left VCTS mention, but went with predominately rain at KIWD and KCMX. With it still a bit too far out timing wise for KSAW, have also left just VCTS mention, leaving time for the next TAF issuance to determine if TSRA or simply RA is warranted. Current indications for KSAW lean toward the former, particularly with a diurnally-driven assist possible. Winds remain a high-impact for aviation interests, especially overnight with LLWS expected. Gusty southerly winds overnight will yield to a more westerly component with the fropa, remaining elevated through the end of this TAF period, especially at KCMX. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 327 PM EDT FRI AUG 20 2021 Winds should remain 20 knots or less until this evening. As a cold front approaches the lake tonight, expect southerly winds to increase to 20 to 30 knots ahead of the cold front. As the cold front moves through Saturday, expect the southerly winds to weaken ahead of the front and for the westerly winds behind the front to strengthen to 20 to 30 knots. Some westerly gale force gusts up to 35 knots are possible behind the cold front in the western and central lake Saturday afternoon and evening. As the winds become northwesterly Saturday evening, expect wind speeds to diminish; by Sunday morning the winds should be 20 knots or less. The winds should remain around 20 knots or less for the remainder of next week. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...TAP LONG TERM...Voss AVIATION...lg MARINE...TAP