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Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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289 FXUS63 KMQT 131956 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 356 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. && .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 /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 109 PM EDT Sat Jul 13 2024 Main forecast challenge will be potential for thunderstorms this afternoon through the overnight period. Conditions should be VFR outside of any thunderstorms. A couple of thunderstorms will likely impact IWD at the start of the TAF period. Then, potential for another round of storms at all terminals this evening into the overnight hours. Low confidence on timing for any terminals, but included a prob30 for the most likely timeframe. Timing will be honed with future updates. Gusty winds and hail could occur in any thunderstorm, and damaging winds/large hail cannot be ruled out. Vsby could briefly be reduced to IFR/MVFR in any storm. LLWS will be a possibility at SAW overnight as well. && .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. && $$ SHORT TERM...Thompson LONG TERM...GS AVIATION...Thompson MARINE...GS