Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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006 FXUS63 KDTX 211734 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 134 PM 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. && .AVIATION... Early morning showers clear out, but isolated popup thunderstorms are still expected across the CWA this afternoon and evening as a stationary front remains overhead. Front migrates northward this afternoon which in combination with daytime instability, creates the environment for aforementioned storms to pop up. Have gone with a TEMPO over PROB30 due to the imminent timing of the storms, but confidence is low on the full extent of the event. Any storms that do move overhead will produce MVFR to IFR conditions, based on the strength of the downpour. All storms look to be clear of the area by 02Z tonight at the latest, shifting instead to the northern Lower Peninsula and Lake Huron. Some light fog is possible overnight, mainly at MBS where light winds off the lake produce favorable conditions for sustained fog. The next chances for showers and storms come on Saturday afternoon and evening. MBS and FNT see the greatest chances for development with the stationary front maintaining north/south position. Low pressure center moves into the area on Sunday, dragging a cold front across the region and bringing with it additional chances for showers and storms. After frontal passage, the pattern of daily isolated popup showers looks to be broken, with high pressure and clearer weather filling in behind to start next week. For DTW/D21 Convection... Conditions remain favorable for thunderstorms with mid afternoon to evening timing. The combination of Erie/St. Clair lake breeze and stationary front near the MI/OH border provide the best chances for storm development until the front moves north of DTW later tonight. DTW THRESHOLD PROBABILITIES... * Moderate for thunderstorms impacting the airspace this afternoon and evening. && .PREV DISCUSSION... Issued at 1040 AM EDT Fri Jun 21 2024 UPDATE... Forecast message still largely unchanged from prior discussion with only some minor adjustments this morning owing to the SPC update expanding marginal risk north into the Saginaw Valley area. Humid airmass remains firmly in place with 12Z KDTX RAOB showing 1.72" of PW as well as ~900 J/kg of MUCAPE residing above the near-surface nocturnal inversion. CAM guidance continues to advertise surface based capes increasing to between 1000-1800 J/kg by this afternoon supporting scattered convective development across the bulk of the CWA. Shear is lacking (aob 25kts) limiting potential organization though given the moisture availability, isolated strong downbursts similar to the past few days will again be possible. Activity wanes into the late evening period (by roughly 03Z) with the loss of diurnal heating/instability in addition to remnant shortwave energy finally fully pushing east of the area. PREV DISCUSSION... Issued at 300 AM EDT Fri Jun 21 2024 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. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....BC UPDATE.......KDK DISCUSSION...SF MARINE.......DK HYDROLOGY....SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.