Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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865 FXUS63 KDTX 171736 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 136 PM EDT Fri May 17 2024 .KEY MESSAGES... - There is a chance (40-45%) for renewed shower and thunderstorm development this afternoon and evening. Highly localized wind gusts around 45-50 mph will be possible with any stronger thunderstorms - Very warm this weekend through early next week. Increased chances for thunderstorms Tuesday into Wednesday next week. && .AVIATION... A stalled cold front over the region will excite a round of showers and thunderstorms this afternoon during peak heating. A lack of flow will result in scattered coverage with slow moving storms making it challenging to time out at any site this afternoon. Highest confidence is in the higher terrain where FNT and PTK reside with a line of showers already initiating. Lower confidence over the 3 Detroit area sites as the activity will only slowly drift toward them through the later afternoon. Opted to go with a tempo for each location though VCTS was considered for the Detroit sites. Storms have already initiated and chances will carry through 01Z Sat. Heavy downpours and/or a highly localized gust to or in excess of 40 knots will be possible with the strongest activity. Attention tonight turns to fog chances as light winds and clearing skies lead to good radiating conditions. For DTW/D21 Convection...DTW should reside on the eastern edge of much of the convection that is ongoing as of 17Z. Most of the activity is expected to stay to the west though there is a chance it could drift over the airspace later this afternoon. The best window for a thunderstorm or two will occur between 21Z-01Z. Locally heavy downpours, brief visibility restrictions, or a highly localized wind gust to or in excess of 40 knots will be possible with any stronger activity. DTW THRESHOLD PROBABILITIES... * Low for ceilings 5000 ft or less this afternoon outside of convection. * Low for thunderstorms this afternoon and evening, between 18Z - 01Z Sat. * Low for ceilings and visibilities to drop below 200ft or 1/2SM tonight. && .PREV DISCUSSION... Issued at 324 AM EDT Fri May 17 2024 DISCUSSION... A plume of enhanced deep layer moisture (PW values between 1.15 to 1.35") continues to build in across SE MI through the morning hours downstream of an upper-level trough, which will maintain scattered to numerous showers this morning, generally outside of the Tri- Cities. Some rumbles of thunder remain possible given the modest mid-level lapse rates and elevated instability. Surface instability will then quickly build in by the late morning hours in the wake of the trough, fueled by diurnally heating. A surface boundary is expected to stall out across SE MI this afternoon, extending from around Bad Axe to Adrian (or slightly east), which will capitalize on the building instability and will be the focal point for renewed showers and thunderstorm activity. The kinematics are extremely poor for sustained thunderstorm activity with weak 1- 3/1-6km shear, thus convective mode will be for pulse thunderstorms. However, very steep 0-3 km lapse rates near 9C/km and DCAPE values to 800 J/kg do support the potential for highly localized wind gusts up to 45-50 mph with thunderstorm development. This is further supported by the large amount of dry air located with the mid to upper-levels of the atmosphere which can be entrained to enhance evaporative cooling...But on the contrary, this can also be a negative factor which may inhibit convective cloud depths. Sub- severe hail will also be possible given the favorable dry mid- levels. Expansion of shower and thunderstorms east of the initial surface convergence boundary will be possible with the very slow meandering of the boundary and along outflows. Convective coverage and intensity will wane after sunset with the loss of instability. Timing for this shower and thunderstorm activity will be favored between 17Z to 01Z Sat (1 PM EDT - 9 PM EDT). Considering this morning`s activity and additional chances this afternoon, the very light boundary layer winds and clear cloud trends overnight could afford areas of fog through tomorrow morning. Multiple upper-level waves are expected to build in across the northern Plains through the weekend and into early next week while a secondary upper-level trough builds in through the Tennessee Valley. This will enhance shortwave ridging across the Great Lakes and will pool in warm air from the continental SW into Michigan, characterized by h850 values between 14-16C. This brings high confidence to see increasing temperature trends leading into early next week, with temperature highs firmly breaking 80 degrees by Sunday. This setup will also bring limited chances for precipitation through early next week given weak synoptic forcing. A slight chance (<15%) for diurnally fueled showers will hold for Saturday, but weak instability and poor shear makes this unlikely. An additional low end (15%) chance holds Sunday evening and again Monday afternoon and evening as shortwaves ripples through. The higher confidence rain/thunderstorm setup will enter within the Tuesday-Wednesday time frame once a stronger upper-level trough builds in across the pacific west, which will help usher in much better moisture downstream across the Midwest and Great Lakes. A potent mid-level wave derived around Baja California is also projected to path near the Texas Panhandle which will strengthen a weak surface low and drive it northeast into the western Midwest or up towards the northern Great Lakes. Still being out many days from this, there is uncertainty regarding potential phasing of these two systems, however, at this time there is excellent agreement between the EPS and NAEFS regarding cyclone location holding over or northwest of the cwa, bringing moderate confidence for a more active period by the midweek. The eventually passage of the low pressure system will draw a cold front across the state, bringing cooler temperatures by the mid to late week (most likely Wed-Thu period). MARINE... Scattered to numerous showers with embedded thunderstorms will cross the central Great Lakes this morning as a weakening frontal boundary works eastward through the region. Isolated showers/storms may persist into this evening but the bulk of the activity is likely to occur before noon. Winds will remain light, generally 10 knots or less, and predominantly from the south or southeast before backing to the east tonight as weak high pressure builds in. Fog, possibly dense at times, will be possible Saturday given the lighter winds and elevated surface moisture. Light winds and mainly dry conditions persist through the weekend with a weak cold front moving through on Sunday possibly bringing some more showers. Potential for more unsettled conditions Monday night into Tuesday as a stronger disturbance tracks into the vicinity. This system will likely bring slightly stronger southerly winds as well as showers and thunderstorms. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....DRK DISCUSSION...AM MARINE.......TF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.