Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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593 FXUS63 KDTX 191944 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 344 PM EDT Wed Jun 19 2024 .KEY MESSAGES... - Hot and humid conditions will persist across most of the area today as a Heat Advisory is in-place for all of Southeast Michigan. - Cooler temperatures arrive tomorrow, mainly confined across portions of the Tri-Cities and Thumb. - Chances of thunderstorms continue each day of the week, some of which may be strong to severe with locally heavy downpours and isolated damaging wind gusts. && .DISCUSSION... Retainment of the anomalously strong subtropical airmass characterized by ~594 dam h500 heights (99.5th percentile to outside of all climatological values wrt CFSR data set) continues through the day today. In terms of surface impacts, the return of temperatures highs back into the lower 90s with dew points in the upper 60s to lower 70s, have bolstered afternoon heat indices in the mid to upper 90s, where a heat advisory remains in effect. For the remainder of the afternoon and evening, attention will be focused on thunderstorms chances, specifically along land/lake differential heating boundaries and from inland locations, where an enhanced ribbon of h850-h700 theta-e will expand in from the Toledo area. differential heating along the demarcation of clouds, and/or the slight surface convergence along the glacial ridge can also be focal point for initiation. In subtropical conditions with h850 dew points aoa 10C, it will not take much for storm initiation, but confidence on the exact initiation point is lowered. The main hazard for any thunderstorm development will be precipitation loading that can result in wind gusts up to 60 mph. MUCAPE approaching 2,000 J/kg along with theta-a indices around 25 and PW values of 1.80 inches support heavy downpours with any thunderstorms. Strong 0-3 km lapse rates around 9C/km and a mini- inverted V sounding with DCAPE values aoa 1000 J/kg support strong downward momentum transfer with evaporative cooling potential. Hail to an inch would be a secondary concern, but as is common in humid airmass, high freezing levels and warm rain processes will contribute to melting. The overall kinematics are poor with bulk shear values around 20 knots with pulse to multicell clusters as the main storm mode. Last, LCL-EL (cloud layer) mean wind sits at around 15 knots. Slower storm motion with heavy downpour and thunderstorm training potential brings the risk for highly localized precipitation accumulation which may lead to localized flooding concerns. Please see the hydrology section for additional details. Any shower or storm development will taper off very late tonight. Warm overnight lows continue with temperatures only dropping into the mid to upper 60s overnight. Relief from hot temperatures will be felt across the Tri-Cities and Thumb, especially along the shorelines, as a backdoor cold front advects inland. Communities along the shoreline will likely not break the 80 degree mark, while locations more inland across the Tri-Cities and Thumb have high probabilities of staying capped below the 90 degree mark. There remain uncertainties with how far inland the cooler air will expand through, but the latest NBM output holds a 60% or higher probability to achieve 90 degrees for a daytime high along and south of M59, with increasing probabilities (near 100%) within urban Detroit and closer to the MI/OH border. Heat indices will peak in the mid 90s outside of the cold front. The heat advisory has been further trimmed to reflect the locations that have high confidence to be impacted by the cooler air. Renewed isolated to scattered thunderstorm development will also be likely tomorrow afternoon and evening. Surface convergence across the multiple boundaries (northeast flow from Huron, west-northwest flow off of southern Lake Michigan, southwest flow from northern Indiana) will provide multiple chances for initiation. Wet microbursts with wind gusts up to 60 mph and highly localized flooding will again be the main concerns for any stronger thunderstorm development. This pattern of above normal temperatures will continue to end the week. Friday will again have cooler temperatures along and in the vicinity of the lakes with the northeast flow in place along with renewed rain and shower chances in the afternoon. For Saturday, multiple shortwaves will ride along the periphery of the heat dome and will advect some of the hottest air across the western Midwest into the Great Lakes. This has the potential to support a boost back into the mid-90s for the southern portion of the cwa and will diminish the lake influence for the northern third as southwest flow returns. As of right now the increased stability looks to keep the greater portion of the cwa dry, but any slight modification of the shortwave path to the south with new model output would put us in the path of potential thunderstorms. Breakdown of this pattern looks to commence on Sunday once a prefrontal trough and eventual cold front swing over the state. Showers and storms will be likely along the prefrontal trough. && .MARINE... Hot and stable conditions across the waters maintain low wind and waves today outside of any thunderstorm activity. Timing and location will be highly uncertain, but the typical peak heating of the day into early evening hours will be favored. Some breakup in the pattern occurs Thursday as high pressure builds across Ontario which forces a cold front south through Lake Huron. This will flip winds around to the north but warm temperatures remain across region. A stronger cold front looks to be on track for the second half of the weekend however, 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 unstable airmass will remain in place through the end of the week. Isolated to scattered thunderstorm development are expected across portions of SE MI this afternoon and evening. The most intense thunderstorms will have the potential to produce highly localized rainfall amounts of 1-2 inches in a 30-60 min period. Thunderstorm training (repeated thunderstorms) can also provide the chance see highly localized totals of 1-2+ inches. Uncertainty in specifics of location and exact timing for any flooding precludes the issuance of an flood watches. Additional storms with highly localized flooding potential will again be possible on Thursday during the afternoon and evening. && .PREV DISCUSSION... Issued at 118 PM EDT Wed Jun 19 2024 AVIATION... A large lobe of 850-700mb thetae content is forecasted to lift northward and pivot into far Southeast Michigan after 21Z. Convergence along a secondary warm front feature within the northern flank of the thetae air mass is expected to provide enough forcing for shower and thunderstorm development this afternoon. Current cumulus development south of Toledo is lined out generally along the gradient. Additionally, model data does suggest some weak cyclonic circulation or mesolow feature is possible leading to a scattered coverage. Hires signal suggests the potential exists for thunderstorms to develop and track northward through DTW/YIP terminals. Less confidence exists with how far northward thunderstorm activity will persist this evening. For DTW/D21 Convection...The potential exists for thunderstorm activity between 20-24Z today. The shower and thunderstorm activity is expected to be scattered. DTW THRESHOLD PROBABILITIES... * Moderate in thunderstorms impacting the airspace this afternoon and evening. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 10 PM EDT this evening for MIZ047>049-053>055- 060>063. Heat Advisory until 10 PM EDT Thursday for MIZ068>070-075-076-082- 083. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...AM MARINE.......AM HYDROLOGY....AM AVIATION.....CB You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.