Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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813 FXUS63 KMQT 200738 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 338 AM EDT Fri Sep 20 2024 .KEY MESSAGES... - Extended stretch of well above normal temperatures continues through at least Saturday with highs mainly in the upper 70s and 80s. - A cold front continues scattered showers and thunderstorms over mainly the east half today and tonight. - Multiple rounds of precipitation possible through the first half of next week. Thunderstorms that do form are not expected to be severe at this time. - Temperatures around normal are expected to return next week. && .SHORT TERM /THROUGH TONIGHT/... Issued at 446 PM EDT Thu Sep 19 2024 Water vapor imagery and RAP analysis show troffing over the western U.S. with one well-defined mid-level low over southern Manitoba and a second just off of the central CA coast. Some elevated showers and a few storms have advanced into north central WI and western Upper Mi this afternoon ahead of the low over Manitoba. The mid-level ridge axis which was stationed over Upper Mi most of the week is getting pushed slightly se this afternoon although the attendant very dry air mass is still keeping the central and eastern U.P shower-free this afternoon. Afternoon temps thus far have reached into the mid 70s and lower 80s, coolest along the Lake Mi shore. Higher dew points in the 60s have resulted in a more unstable airmass south into north central WI where a cluster of elevated storms have formed at the nose of a theta-e ridge. Plenty of uncertainty regarding U.P weather for late this afternoon into tonight as the mid-level low over Manitoba lifts north and sends a mid-level trough and associated sfc cold front toward Upper Mi later tonight. High resolution models suggesting stronger convection and developing supercells now forming over southern MN in environment of SBCAPE values 1500-2000 j/kg will pose a severe risk into southern MN and western WI into early evening. These storms over southern MN and western WI are then expected to transition to a linear MCS tonight which moves east through WI. High effective shear of 40 kts or higher and CAPE values of 1000-2000 j/kg will favor the eastward movement of the MCS through WI tonight. Big question will be how this MCS affects moisture for supporting convection over the U.P tonight. A few of the CAMs suggest isolated to scattered showers and t-storms this evening over the west could potentially become more numerous in coverage into south central Upper Mi overnight if northern extent of MCS moving through WI clips this portion of the cwa. This will be something for the evening shift to keep an eye on. Increasing effective shear to 30 kts could support some stronger storms into the western U.P. this evening but severe threat will likely be limited by mostly elevated CAPE of 500-1000 j/kg. Look for min temps to stay around 60F tonight with increasing clouds and chance for showers. Patchy fog will be possible again tonight, especially central and east under moist southerly upslope flow. && .LONG TERM /TONIGHT THROUGH THURSDAY/... Issued at 337 AM EDT Fri Sep 20 2024 The last of the rain showers and thunderstorms associated with the cool front today ends over the east tonight as high pressure ridging builds in. As this occurs, the clearing skies will allow the temperatures to drop to around 50 in the interior west, whereas the interior east may only get down into the mid 50s due to the cloud cover earlier in the evening and patchy fog late tonight. Speaking of which, expect this fog to form over the central and east tonight given the clearing out and moisture from the recent rainfall; I wouldn`t be surprised if the fog was even dense in a few spots come early Saturday morning. The patchy fog looks to eventually burn off a couple of hours after sunrise Saturday morning. Expect Saturday to be another very warm and mostly sunny day via the weak high pressure ridging scooting over us. With warm air advection moving over us aloft late tonight through Saturday, expect high temperatures to get to around 80 in the east and the lower 80s in the west. Meanwhile, given the abundant sunshine and moisture, we could have some good mixing in the boundary layer by the afternoon hours, bringing min RHs down to possibly as low as the lower 30 percents in the interior west. If the mixing overachieves today, we could see some limited fire weather concerns via min RHs getting down to or below 30%. However, given the ridging overhead, winds are expected to be fairly light from the south across most of the area (the exceptions are the Keweenaw/near Lake Superior where some lake breeze action may come into play). Now as a low pressure over the Canadian Prairies lifts towards Hudson Bay Saturday into Sunday, a cold front associated with the low approaches us from the west by the afternoon hours. This cold front looks to bring additional rain showers and thunderstorms over us from Saturday evening into Sunday from west to east. Overall, don`t expect too much rainfall from this cold front either; most areas are looking to only get a tenth of an inch or less, although some spots may locally see more. That being said, the latest Canadian, NAM, and Euro deterministic runs are more generous with the rainfall; hopefully these newer runs are more accurate as we really need the rainfall, particularly over the south central and east where moderate drought (D1) conditions exist according to the latest drought monitor update. While there is an outside chance (2% or less) of seeing a strong storm or two Saturday night through Sunday along the front, with decreasing MUCAPE and increasing cloud cover ahead of the front with time, severe weather is currently not expected. A shortwave lifting from the Plains through the Great Lakes region Sunday through Sunday night may reinvigorate convection over the central and east, but the front may be too far to our south and east by that point for us to receive anything. Thus, the chance of rain from this shortwave over our central and east looks to be about 25% and 50%, respectively, late Sunday through Sunday night. Additional high pressure ridging is expected to return to our area by next Monday, although the warm temperatures are looking to be replaced by those more normal for this time of year. Expect Monday to be the coolest day of next week, with highs only getting into the low to mid 60s and lows possibly dipping into the upper 30s in the interior west Sunday and Monday nights. Moving to next Tuesday, a low originally from the Southern Rockies looks to move through the Great Lakes basin. While the south central and east could be skirted with some light rainfall from the low`s TROWAL Tuesday, with guidance honing in better on the low`s track moving through southern Lower Michigan, not much, if any, rainfall is expected. While near normal temperatures continue through the rest of next week, we may or may not see additional rainfall as the aforementioned low could retrograde back into the Upper Great Lakes. However, the more recent deterministic runs of the medium range guidance are suggesting that we remain under ridging for the last half of next week, with the low being too far to our south. Nevertheless, I feel that the NBM`s 20% pops for most of the area are pretty on point with the rain chances come late next week, just in case the low`s retrograde does move further north towards the Upper Great Lakes in later model runs. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 131 AM EDT Fri Sep 20 2024 VFR conditions should prevail thru the period at IWD. Shra and some tsra will spread across central Upper MI overnight. At SAW and CMX, shra should result in MVFR developing by late morning, then SAW and CMX will go VFR in the afternoon. SAW will have LLWS overnight. && .MARINE... Issued at 337 AM EDT Fri Sep 20 2024 The southerly 20 to 25 knot winds ahead of the cool front this morning over the north central lake decrease to 20 knots or less later this morning, but southwest winds of 20 to 25 knots do pick up behind the front over the west half of the lake by this afternoon and continue until this evening. Meanwhile, expect showers and thunderstorms to continue trudging eastward over the lake with the frontal boundary. As weak ridging builds in, expect the winds to die down to 20 knots or less again by around sunset, and the last of the showers and thunderstorms ending over the far eastern lake late tonight. Due to the recent rainfall and lighter winds late tonight, we could see some patchy marine fog develop over the eastern lake; some spots could see visibilities of 1 nautical mile or less, so make sure to have your lights on and to use your radar and compass if you are in a fog bank. The light winds continue until another cold front moves through late Saturday into Sunday. While showers and thunderstorms are expected to travel from west to east late Saturday into Sunday over Lake Superior, expect northwest winds of 20 to 25 knots behind the frontal boundary, mainly over the western half of the lake. As the front leaves our area later Sunday, expect the winds to die down to 20 knots or less again as more ridging moves over. The ridging and light winds look to remain over Lake Superior for the rest of next week. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...TAP AVIATION...07 MARINE...TAP