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
131 FXUS63 KDTX 131920 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 320 PM EDT Mon May 13 2024 .KEY MESSAGES... - Scattered to numerous showers and thunderstorms are expected tonight. Severe weather is not expected, just some brief heavy rainfall and lightning. - There is a chance for additional showers on Tuesday. The higher chances are near the Ohio border. - Dry weather is expected Tuesday and Wednesday. && .DISCUSSION... The latest meso analysis shows SB Cape near 1k J/kg across the Saginaw Valley/thumb south of a sfc cold front where dewpoints are in the low to mid 50s and temps are near 80. Ongoing development of deep convection supports latest CAMS solutions which indicate convection persisting through the early evening across the north, aided by the influx of instability arriving from SW Lower MI. Despite the sfc front forecast to push south of metro Detroit late tonight, the loss in diurnal instability will limit nighttime coverage of convection as the front sinks south. This will warrant the better convective chances this evening along/north of the I-69 corridor, with decreasing chances to the south. With 0-1KM mixed layer CAPE still below 1k J/kg and limited deep layer shear (0-6km bulk shear values around 20 knots), strong to severe storm are not favored. The thumb region will be along the edge of stronger shear profiles and could see a marginal severe risk if late day instability overachieves a bit. Otherwise, warm and breezy conditions will last into the evening amidst robust late day mixing depths. The upper low and associated sfc reflection now over Kansas/Missouri will track across the northern Ohio Valley Tues/Tues night. This system will drive a plume of deep layer moisture into Se Mi Tues. Overall, the 12Z model suite suggest the stronger deformation forcing will remain closer to mid level circulation, generally south of the I-94 corridor. Lingering mid level frontal forcing, albeit weak, will remain over Se Mi into Tues night, which will at least support a chance of showers across most of the forecast area. Shallow post frontal cool air undercutting the moisture may also support some areas of drizzle Tues morning. The post frontal cold air advection and cloud cover will result in a notable cooler day Tues (highs in the 50s near Lake Huron to 60s elsewhere). Mid level ridging in the wake of the upper low will lead to a gradual departure of the deep layer moisture on Wednesday. The next chance of rain will be Friday resulting from deep layer moist isentropic ascent along a fast moving short wave. At this stage in the forecast, instability looks to be weak (under 1k J/kg) which should limit any severe weather risk. && .MARINE... Satellite imagery shows increasing cloud depths located across the Tri-Cities into the northern Thumb, pushing northeast into the Saginaw Bay to southern Lake Huron. This will be the focal point for shower and thunderstorm activity through the remainder of the afternoon and evening hours. The strongest thunderstorms will be capable of producing wind gusts to or just above 35 knots and small hail. Special Marine Warnings may be needed with any vigorous thunderstorms development. Showers and thunderstorms are expected to last through tonight along a stationary front, sagging slightly south into southern Lake Huron overnight into Tuesday morning. High pressure will build in across the upper Great Lakes which will end rain and thunderstorm chances through Tuesday afternoon and evening as a cold front clears the state. Wind direction will veer and hold from the north-northeast Tuesday and Wednesday in response to a low pressure system which will fill in across the Ohio Valley. This will increase wave heights into the Saginaw Bay and Lake Huron shorelines, where Small Craft Advisories will be likely. && .HYDROLOGY... Scattered to numerous showers and thunderstorms will occur this evening, primarily along and north of the Interstate 69 corridor. Locally intense rainfall rates are possible in some of these thunderstorms. Rainfall amount of a quarter to half inch are possible locally. Basin average rainfall is expected to remain below a half inch, so flooding (other than localized ponding of water on the roads) is not expected. && .PREV DISCUSSION... Issued at 1241 PM EDT Mon May 13 2024 AVIATION... Warm southwest flow and good mixing this afternoon, promoting wind gusts around 25 knots. Moisture/instability axis located over/close to Saginaw Bay, presenting MBS with the best chance of showers and a thunderstorm. Farther south, low clouds look to be hard to come by, even into the evening hours. The moisture axis/front will be sinking south this evening and tonight, but instability will be waning, thus low confidence in showers, much less any stray left over thunderstorm. With the cooling boundary layer tonight, the weak convergence along the front should provide a focus for low clouds and potentially even fog. High degree of uncertainty in just how low the clouds will end up being, as LIFR/IFR/MVFR are all in play, which should persist for a good portion of Tuesday morning. Ultimately, due to the frontal position, thinking PTK will see the lowest cigs, and will go with borderline LIFR/IFR. Upper level low tracking through Western Ohio Valley should allow for some showers to spread into the southern tafs, which should help improve ceilings, in addition to the surfacing heating during the day. For DTW/D21 Convection...Instability/moisture axis displaced north of M-59 this afternoon and evening, with instability then waning tonight as moisture axis/front sinks south. Thus no thunderstorms are anticipated at the terminal. DTW THRESHOLD PROBABILITIES... * Medium confidence in cigs aob 5000 feet late tonight and Tuesday. * Very low confidence in cigs/vsby aob 200 ft and/or 1/2sm 8-15z Tuesday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...SC MARINE.......AM HYDROLOGY....SC AVIATION.....SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.