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Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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373 FXUS63 KMQT 132340 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 740 PM EDT Sat Jul 13 2024 .KEY MESSAGES... - Seasonably warm this afternoon with a 20-30% chance of showers/thunderstorms over the west. - 40-60% chance of showers and thunderstorms this evening into overnight hours. Marginal risk (category 1 out of 5) of severe thunderstorms for most of the UP. Slight risk (category 2 out of 5) for the far west. Main threats are large hail and damaging winds. - Chances (20-40%) for thunderstorms along lake breeze boundaries Sunday. - Marginal risk (category 1 out of 5) of severe thunderstorms Monday. - Cooling and drying trend into the midweek portion of next week with the arrival of high pressure. && .UPDATE... Issued at 739 PM EDT Sat Jul 13 2024 Ongoing showers and severe thunderstorms in central Wisconsin should continue pressing southeast through the evening. Some sprinkles/light rain may fall in and around Menominee, but otherwise, mostly dry conditions are now expected for the next few hours. Current satellite analysis shows what appears to be a stable strato layer of clouds over western Upper Michigan, implying a more stable atmosphere. East of this area, a north south boundary is apparent on radar through Marquette County. This boundary may be the focus for some late evening convection, but this is very uncertain. East of the boundary, SPC Mesoanalysis shows very little instability, and without any real shear to speak of, I`m skeptical about any organized development. With this being said, the HRRR, which has been the most consistent hourly CAM this afternoon/evening so far, is insistent on scattered showers and storms developing around 4-7z along and just east of this boundary. Will continue to maintain low POPs elsewhere in the western Upper Michigan given the continued uncertainty in this forecast. Upstream in northwest Minnesota, some convection has been observed. If upscale development continues as the HRRR implies, development would congeal into a bowing segment as it tracks southeast into western WI after midnight eastern time. If this development occurs as stated, main risk area for strong thunderstorms would be in areas bordering the Michigan/Wisconsin stateline. However, timing suggests even strong storms may be hard to realize. && .SHORT TERM /THROUGH TONIGHT/... Issued at 1235 PM EDT Sat Jul 13 2024 Upper air consists of an anticyclone centered around the Four Corners and a cutoff low over northern SK/MB. Belt of seasonably fast zonal flow between these two features is diffluent over the local area. Several small areas of convection are noted in this diffluent zone - one in far SW ON, one in northern MN, and one in northern WI. These are being fed by modest SW winds at 850 mb and are located in an area of steep midlevel lapse rates. These lapse rates weaken with eastward extent, and as a result, there is uncertainty whether the lead convective cluster over northern WI will make it into the western UP this afternoon. This cluster has outperformed CAM depictions of it so far, leading to greater than normal uncertainty in its evolution. Have expanded 20-40% PoPs over the far west for mid-afternoon to account for this. Severe risk appears low given paltry bulk shear if storms do indeed unfold this afternoon. Otherwise, a few showers are firing up along the lake breeze in northeast Alger/northern Luce County. Isolated ts possible here this afternoon. Similar low predictability exists in the overnight hours with any MCS activity due to wide variance in CAM output and tendency for better instability to be located SW of the local area. As a result, early afternoon forecast update went with a more broad-brush approach to PoPs in the 50-60% range for the overnight hours. Severe risk (large hail/damaging winds) does still exist mainly for the western half of the UP if an outflow-dominant MCS does develop given respectable convective parameters (1000-2500 J/kg MUCAPE), although deep shear is a bit lacking at less than 30 kt. Otherwise, the other concern is the heat with temps on track to reach the mid-80s to near 90 (warmest in downslope zones near Lake Superior), although dewpoints should mix out a bit in the warmest areas with humidity contribution to apparent temps negligible. && .LONG TERM /SUNDAY THROUGH SATURDAY/... Issued at 353 PM EDT Sat Jul 13 2024 Aloft, the path of most prominent troughs and ridges is well to the north over Canada, leaving the Upper Great Lakes in a primarily zonal pattern through this weekend. This will lead to the primary driver of sensible weather to be weak shortwave impulses in the zonal flow. While the synoptic forcing may be weak and ambiguous, hot and muggy conditions this weekend will allow for instability to grow, allowing for the potential for strong to severe thunderstorms over the weekend and to begin next week, especially in the form of MCS`s. High pressure then settles over the region by Tuesday, allowing for a cooler dry period towards the middle and late week period next week. Sunday, clearing via subsidence following lingering convection from the day prior will allow for some clearing skies. This will lead to a pretty warm day, with highs around 80 except in the south central where highs could approach 90, though the 00Z LREF only gives about a 10% chance of exceeding 90. Moisture values increase as well, with the PWATs exceeding 1.5 inches representing the 90th percentile of climatology by GRB and APX sounding climatology. Dew points are forecast to be approaching 70 for at least some period of time for much of the UP, with the highest chances (30-70%) of exceeding a muggy 70 being the south-central and the east. Monday looks to be similarly warm, though lower chances of dew points being oppressively high. These hot and humid summertime conditions will be accompanied with westerly to west-northwesterly flow at 500mb, which will allow for some minor shortwaves to progress through the region. One of these shortwaves looks to pass just south of the MI/WI state line on Sunday. While mesoscale ridging will act to keep larger-scale thunderstorms away from the UP, the mid 60s+ dew points and 1000- 2000 J/kg of only weakly capped SBCAPE combine for a climatologically favorable setup for convection over the UP. With the southwesterly surface flow contrasting the west-northwest flow aloft, directional shear will be present, though speed shear will be somewhat lacking. Regardless, shear will be present enough to help maintain whatever thunderstorms do initiate, so if enough lake- breeze convergence zones can lift parcels enough to realize the instability, severe weather is still a possibility for Sunday primarily along the lake breeze in the east. Monday, another shortwave passes from west to east across the UP starting in the west in the early morning hours and progressing east throughout the day. Instability does not look as strong with this wave, with the 12Z GEFS mean around 1000 J/kg, but forcing is much better, so thunderstorms are expected with a few being potentially strong to severe, consistent with the SPC Marginal Risk (category 1 of 5). By Tuesday, broad troughing aloft shifts from northern Ontario towards the East Coast and ridging fills in behind. As a result of the advancing ridging, high pressure to around 1020mb will keep weather quiet through at least the end of the week. A cooling trend is also expected to accompany the arriving ridging as north and northwest flow will bring highs only in the upper 60s and low 70s Tuesday through Thursday. Temperatures rebound in the late week towards more seasonably summer temperatures. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 723 PM EDT Sat Jul 13 2024 Upstream convection continues to struggle as it approaches Upper Michigan. Recent satellite imagery suggests a mostly capped environment over western Upper Michigan, which suggests the main concern for convective development will be late evening over central Upper Michigan and then upstream in Minnesota. The former may support some thunderstorms in and around KSAW while the latter would be a concern overnight as it tracks southeast for KCMX/KIWD. This generally matches recent HRRR runs, but it should be stated that there is still a good bit of uncertainty in this. Outside of convection, VFR conditions are expected. && .MARINE... Issued at 353 PM EDT Sat Jul 13 2024 Southerly winds remain below 20 kts today as the pressure gradient stays light. South winds increase tonight over the east to near 20 kts with a 15-25% chance for gusts reaching 25 kts tonight ahead of the next disturbance. Some strong to severe storms are possible tonight, especially across western Lake Superior. The main threats are damaging winds, but large hail is also possible. Another round of storms is expected Monday into Monday night as a low pressure system moves through the area. Patchy dense fog is also a possibility in the wake of any precipitation. Following the Monday/Monday night low presusure`s cold front, west winds increase to around 20 kts across much of the lake Monday night and Tuesday. As high pressure begins to build in mid next week, winds look to fall back below 20 kts, remaining light through the remainder of the forecast period. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ UPDATE...JTP SHORT TERM...Thompson LONG TERM...GS AVIATION...JTP MARINE...GS