Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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119 FXUS63 KDTX 210355 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1155 PM EDT Thu Jun 20 2024 .KEY MESSAGES... - Additional chances for thunderstorms exist Friday and this weekend with organized thunderstorms possible Saturday night-Sunday along a cold front. - Hot and humid conditions persist through Saturday with heat indices in the low to mid 90s Friday and the mid 90s on Saturday. && .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. && .PREV DISCUSSION... Issued at 353 PM EDT Thu Jun 20 2024 DISCUSSION... Strong to severe thunderstorms are ongoing along a line from roughly Marine City to Dearborn with a slow eastward trajectory at around 25 mph. Deep reflectivity cores of 60+ dbz have prompted severe warnings already, with additional activity upstream in the presence of a theta-e pool and plentiful instability. Lack of deep layer shear has resulted in storm organization that is reliant on cold pool interactions, so while organized convection will not be widespread there is potential as we have already seen over Oakland/Macomb/St. Clair. The second concern with these storms is heavy rainfall and flooding, as hourly rates have exceeded one inch in these storms per MRMS with additional convective potential through the evening. Please refer to the Hydrology section for more information. Expectation is for storms to lose strength after 9pm- 10pm with the loss of daytime heating. Friday will once again be hot and humid, but heat indices in the low 90s preclude the issuance of any heat headlines. Otherwise, chances exist for pulse convection Friday afternoon-evening, even with temperatures/humidity slightly tempered in comparison to the past few days. Forcing mechanisms again remain in the form of shallow surface boundaries and/or weak shortwave impulses aloft. Similar hazards and timing as today are expected for tomorrow, with strong precipitation cores likely to develop and resulting in downburst potential with damaging winds up to 60 mph. Broad high pressure center will continue to retrograde toward central CONUS and flatten through the weekend, contributing to mid- level height falls over lower Michigan and transition to zonal flow aloft. The ridge has been effective at steering any stronger synoptic disturbances northwest of SE Michigan, but this will change over the weekend as a Pacific wave accelerates across northern CONUS. Locally, this will drive a cold front through the region on Sunday and draw in a cooler/drier airmass for early next week. Until then, hot and humid conditions will persist and even be reinforced on Saturday as theta-e advection wraps from the central Plains into the Great Lakes invof a ~40 knot low level jet. Strengthening mid-level flow and approaching upper level trough should result in more organized thunderstorm potential than what we have seen the past few days, although frontal timing overnight Saturday-early Sunday raises question as to if storms will be surface-based. Nonetheless, the late Saturday-Sunday system will be one to watch for strong-severe convective potential and additional heavy rainfall. Seasonably warm conditions may return briefly middle of next week, ahead of a strong low pressure system and cold front that looks to bring in a more permanent Canadian high pressure/cooler weather. MARINE... The southern Great Lakes becomes positioned between surface high pressure building across the northern Great Lakes and Ontario and the persistent ridge across much of the eastern conus for the end of the week. Hot and humid conditions will persist across much of the area south of Lake Huron keeping chances of pop up thunderstorms possible each day. The warm temperatures will also add stability over the waters helping keep wave heights minimized overall. 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 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 holds in place through the end of the week. Thunderstorms this afternoon have already resulted in rainfall totals in excess of 1 inch in a 30-60 minute period, prompting urban flood advisories. While there is not a strong signal for training storms, there is a chance for localized areas to see more than one thunderstorm which could result in highly localized rainfall amounts in excess of 2 inches by late evening. Additional thunderstorms are possible again Friday and this weekend with heavy downpours possible. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....MR DISCUSSION...MV MARINE.......DRK HYDROLOGY....MV You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.