Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
675 FXUS63 KDTX 201953 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 353 PM EDT Thu Jun 20 2024 .KEY MESSAGES... - Isolated strong to severe thunderstorms are possible through 10 PM this evening. Damaging wind gusts to 60 mph and highly localized storm total rainfall in excess of 2 inches will be possible. - 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. && .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. && .PREV DISCUSSION... Issued at 208 PM EDT Thu Jun 20 2024 AVIATION... Convergence along various shallow boundaries will bring scattered showers and thunderstorms across Southeast Michigan this afternoon. Storm motion is expected to be slow with cell movement perhaps at 20 knots or less. Main aviation concern will be obstructed visibilities due to brief heavy rainfall rates. The potential does exist for wind gusts to reach 50 knots in thunderstorm activity, but the likely of occurrence is too low to include in the TEMPO. A main synoptic dewpoint gradient augmented by outflow should push south of the Southeast Michigan between 00-06Z. Very weak flow and moist surface conditions will support br/hz at daybreak Friday morning. For DTW/D21 Convection...Scattered thunderstorm activity is expected to develop near DTW in the 18-21Z timeframe. Low confidence in when thunderstorms will push southward and storm motion may become variable and slow moving. DTW THRESHOLD PROBABILITIES... * Moderate in thunderstorms this afternoon and evening. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 10 PM EDT this evening for MIZ068>070-075-076- 082-083. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...MV MARINE.......DRK HYDROLOGY....MV AVIATION.....CB You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.