Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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723 FXUS63 KMQT 042321 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 721 PM EDT Thu Jul 4 2024 .KEY MESSAGES... -Low chance (15-30%) of showers/storms this afternoon roughly from Ironwood eastward to Newberry. -Good chance (~60%) of some areas getting an inch of rain Friday, though flooding rainfall is not currently forecast. -Mainly dry Saturday, but a rain shower cannot be entirely ruled out (20-30%) along the MI/WI state line in the afternoon. -Sunday through Wednesday, daily chances of showers and thunderstorms, highest chances in the afternoons. -Dry period begins Thursday, could be dry into next weekend. && .SHORT TERM /THROUGH TONIGHT/... Issued at 326 PM EDT Thu Jul 4 2024 This afternoon, weak high pressure ridging remains over Upper Michigan ahead of another shortwave that is analyzed over the Dakotas. A couple waves of convection associated with this are moving through MN and into northern WI, and cirrus continues to stream into the UP from this upstream convection. Meanwhile, closer to home, the Superior lake breeze is quite apparent on radar, already heading well inland into the UP. So far, just agitated cu with this sporadically apparent on satellite beneath the cirrus deck, but weak radar returns are finally popping on the Lake Michigan boundary in the eastern UP. Will not rule out spotty shower activity (and perhaps some rumbles of thunder) along the lake boundaries, mainly across the central and eastern UP. Heading into the late afternoon and evening, spotty showers and storms currently across northern WI may be able to make it into the southern UP, but better chances for rain hold off until later tonight (more on that later). By then, with several hundred j/kg of CAPE, some thunder will be possible. Any thunderstorm could put down some gusty winds and a brief heavy downpour. Otherwise, winds remain on the lighter side, but may shift suddenly with the passing lake boundaries. Temperatures inland have been able to climb well into the 70s and even around 80F, but where onshore flow is having an impact, temperatures are hovering in the lower to mid 70s, even falling back into the 60s. Overnight, the shortwave moves over MN and into WI with a surface low closing off over central WI. Expect showers (with some thunder) to increase in coverage after midnight, mainly across the western UP as the surface low continues its eastward trek. There is a chance for some decent rainfall amounts at times in the resulting deformation zone; href ensembles note a potential (20-30% chance) for rainfall rates rainfall rates of a quarter-inch per hour in the heaviest downpours overnight. So, while not a washout, we could expect a widespread quarter to half-inch of rain over the western half of the UP, with some isolated spots seeing even higher amounts closer to an inch. Temperatures, meanwhile, stay fairly mild overnight with lows generally in the mid 50s. && .LONG TERM /FRIDAY THROUGH THURSDAY/... Issued at 352 PM EDT Thu Jul 4 2024 After a very progressive pattern kicked off this summer, a more blocky pattern has now emerged as 500mb ridging over western North America will only very slowly progress eastward with time throughout this forecast period. The consequence of this for the UP will be dealing with the low-amplitude shortwaves that spill southeast from the ridge, and one such shortwave will be over the UP on Friday. The resultant surface feature is a 12Z GEFS-mean 1007mb low pressure over Wisconsin passing south of the UP through Friday. As the UP will be on the north side of the commahead, much of the UP is expected to be under the precipitation shield during Friday morning. The 12Z HREF does show precipitation becoming much more scattered in the afternoon hours though, particularly over the central UP. As the surface destabilizes somewhat during the afternoon hours, a few thunderstorms are expected as HREF mean SBCAPE climbs to near 500 J/kg, but these are mostly expected to be garden variety thunderstorms and not severe. With PWATs climbing above 1.25 inches, some heavy downpours are expected, with the HREF showing around a 60% chance that somewhere in the west-to-central UP sees an inch of rainfall in the morning and similar chances for the eastern UP in the evening hours. Chances of 2+ inches, where flooding might be a concern, is around 10-30% in the west early and in the south-central late. Given the strongest forcing (which is not incredibly strong to begin with) will be south of the UP and NAEFS indicates the PWATs and IVT are around normal for this time of year, flooding rainfall is not forecast, but it is still expected to be a wet end of the week for the UP. By Saturday morning, the low will be nearly completely departed from the area and showers will dry up, with the final showers being in the far eastern UP and upslope light rain showers in Alger County. Weak surface ridging is expected to take the place of the departing low, as the high pressure center is forecast to be near TN at 1015 mb. Because the high is so weak and far away from the UP, not enough subsidence will be present to completely preclude some diurnal showers along the MI/WI state line, but impacts should be low. A quiet night is expected Saturday night, but cloud cover begins to increase ahead of the next shortwave trough sliding southeast off the western ridge. Global deterministic models do begin to diverge here as to how this trough progresses, but the general outcome seems to be a mainly diurnal pattern of precipitation Sunday through Wednesday with lower PoPs in the overnight periods in between. Given how weak synoptic surface forcing is, the ability of diurnal forcing to help initiate showers will be key in determining PoPs as well as thunderstorm chances, though severe weather is unlikely because of said lack of forcing. Most deterministic guidance does have the trough beyond the UP by Wednesday, so PoPs are lower by a fair margin on Wednesday, but enough ensemble spread exists to keep at least 20-30% PoPs in the forecast for now. As the ridge aloft shifts over the Four Corners area from the Pacific Coast from where it was centered, high pressure does look to settle over the UP for Thursday, with the 12Z GEFS showing a ~1020mb high over the UP Thursday morning and building to the mid 1020s mb over the rest of the Great Lakes basin by the weekend. This will usher in a dry period to end next week, with the potential of a multiple-day period of no rain across the UP, something that has not been common this summer so far. && .AVIATION /00Z TAFS THROUGH 00Z SATURDAY/... Issued at 721 PM EDT Thu Jul 4 2024 VFR conditions in place to start the 00Z TAF cycle. A few light showers are possible at SAW early this evening, but are unlikely to impact flight conditions. Better surge of moisture and rain showers should impact at least IWD/SAW late tonight into Friday morning, with cigs falling to MVFR and IFR. CMX looks to be on the edge of the rainfall so VFR was maintained with this cycle, although confidence on placement of precipitation is fairly low. An embedded TS cannot be ruled out at IWD roughly 08-14Z and SAW 10-16Z, but coverage too low for inclusion in the TAFs. Gradual improvement in cigs expected through the day Friday, but IFR conditions may hang on at SAW until early afternoon. && .MARINE... Issued at 352 PM EDT Thu Jul 4 2024 As a ridge aloft over the western CONUS creates a blocking pattern, Lake Superior will see a particular lack of strong pressure systems passing overhead, and as a result, the slackened pressure gradient will keep wind gusts below 20 knots and waves at 3 feet or below for nearly the entire forecast period. That being said, there are still a few weak disturbances that will cause chances of thunderstorms periodically throughout the next week, mainly during the daytime and in the nearshore zones. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...LC LONG TERM...GS AVIATION...Thompson MARINE...GS