Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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956 FXUS63 KDTX 210700 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 300 AM EDT Fri Jun 21 2024 .KEY MESSAGES... - Marginal risk of severe thunderstorms this afternoon and late Saturday afternoon/evening, with damaging winds being the main hazard. - Hot and humid through Saturday. High temperatures 85-90 today and 90-95 on Saturday, as heat indices peak out just under 100 degrees for Saturday. && .DISCUSSION... Moist airmass in place, as the 00z DTX raob indicated a PW value of 1.78 inches with a 700 MB dew pt of 5 C. Similar moisture profiles to hold through the day. Last vestiges some shortwave energy/PV tracking through southeast Michigan this morning (slight-low chance pops), with negative upper level PV advection in the 18-00z window. Despite the unfavorable environment/general subsidence late this afternoon, ill defined leftover frontal boundary and diurnal instability (MLcapes of 1500 J/kg) still will likely prove worthy to fire up convection (bulk of CAM solutions), but limited coverage (25-40%) expected. The normally bullish NAM is actually indicating instability parameters a bit lower compared to the past couple of days, but still potential for isolated downburst damaging wind gusts, despite little in the way of 0-6 MB bulk shear (under 25 knots for majority of the CWA). Locations south of I-69 stand the best chance with the greater cape build-up south of the front. 850 MB temps of 17-19 C suggest airmass potential in the upper 80s to lower 90s. But assuming clouds and scattered convection develops, likely looking at temps in the 85-90 degree range, in line with inherited forecast. Warm (10+ C at 700 MB) and dry mid level dry slot pushes into southern Lower Michigan this evening/around midnight, and hangs around through a good portion of Saturday, likely capping activity (south of I-69) and allowing for a warm and humid day with deep southwest flow ahead of an approaching cold front. High temperatures in the 90-95 degree range appear likely as 850 MB temps reach aoa 20 C, but mainly sub 70 degree dew pts expected to keep heat indices just under 100 degrees. Good 500 MB height falls (for summer standards) arrive around 00z Sunday, which will weaken the cap and and potentially allow storms to spread in late in the day or during Saturday evening. Increasing 0-6 KM bulk shear, reaching 30-40 knots by day`s end will bring the potential of isolated severe storms with MLcapes at least around 1000 J/kg. SPC day 2 outlook puts southeast Michigan in marginal risk. It should be pointed out, several model solutions (NAM/RAP) suggest shower and thunderstorm activity holds off mostly until Saturday night, which limits severe potential with leftover MUcapes mainly under 1000 J/kg. Despite the unfavorable timing, the large scale forcing is expected to support a broken to solid line of showers and thunderstorms. Modest cold advection to follow for Sunday, with 850 MB temps now only progged to lower into the lower teens by Monday morning per 00z Euro (vs 10 C indicated by 12z Euro). None-the-less, the 500 MB trough axis swinging through the Central Great Lakes may still touch off a few showers over the Thumb region as 500 MB cold pool (-15 C) tracks through Lake Huron. && .MARINE... High pressures to the north and south of the Great Lakes result in weak northerly flow across much of the region today. There remains a weak stalled boundary across the southern Lakes which may try to be a focus for strong storms once again today. Additional storms look to track out of WI and across Mid MI into Lake Huron later today. Mild air remains across the region resulting in stable conditions across the waters minimizing wave heights into the weekend. Though winds should remain generally light and out of the north, any location in the vicinity of a stronger storm will have higher gusts potential with it. A more organized low pressure system will pass through the northern Lakes Saturday night pulling a cold front through the region on Sunday likely resulting in more widespread convection and wind speeds then could reach or exceed 25 knots with waves building to around 4 feet. Small craft advisories may be needed. && .HYDROLOGY... A moist and moderately unstable airmass holds in place today. Isolated to scattered thunderstorms are expected to develop once again, capable of producing highly localized rainfall amounts in excess of 2 inches in less than 3 hours due to the slow movement. This amount of rain would result in urban/low lying flooding. The daytime hours of Saturday look to be mostly dry before a line of showers and thunderstorms track through southeast Michigan Saturday evening/night. This activity will have potential to produce half an inch to one inch of rain, especially if activity arrives in the evening. Stronger thunderstorms will bring the potential for locally higher amounts. && .PREV DISCUSSION... Issued at 1155 PM EDT Thu Jun 20 2024 AVIATION... Convective potential remains minimal overnight as greater nocturnal stability maintains control. Very moist near surface conditions and limited wind will provide favorable conditions for some shallow fog/haze development during the pre-dawn hours. The underlying moist and unstable environment will again bring potential for diurnal convective development Friday afternoon and evening. Similar to recent days, overall coverage and placement of possible development remains quite ill-defined at this stage. For DTW/D21 Convection...The overall environment will again be favorable for some degree of thunderstorm development Friday afternoon and evening, but with usual uncertainty at this stage on timing and coverage. DTW THRESHOLD PROBABILITIES... * Low in thunderstorms impacting the airspace Friday afternoon and evening. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...SF MARINE.......DK HYDROLOGY....SF AVIATION.....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.