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Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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857 FXUS63 KDTX 121057 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 657 AM EDT Fri Jul 12 2024 .KEY MESSAGES... - Isolated showers and storms will expand across Southeastern Michigan through the day. These storms are not expected to be severe. - There will be a few chances for thunderstorms later this weekend and into next week. Severe weather will be possible with the systems on Sunday and again Monday evening. - A period of hot and humid conditions are forecasted for Sunday and Monday with temperatures reaching near 90. - Cooler weather will move in Tuesday through the rest of the week. && .AVIATION... Late night/early morning satellite and radar trends indicate a healthy expansion of clouds with a few pockets of showers/isolated thunderstorms within the mid level circulation traversing Lower MI. Ceiling is generally above 5000 ft even where showers occur and the showers are light enough to hold VFR visibility. An isolated borderline shower/thunderstorm with brief MVFR is possible throughout the day although with a better early morning time window for ongoing activity. A mid to late afternoon time window is also favored based on daytime peak instability interacting with light lake breeze augmented surface wind. VFR continues tonight as scattered evening shower/storm coverage wanes during the evening. Weak surface high pressure regains control with a mixed ground fog to MVFR/IFR fog signal late tonight into Saturday morning. For DTW/D21 Convection... Scattered showers and thunderstorms remain possible across the D21 airspace today. Confidence in location, coverage, and timing remains low even this morning due to limited duration. Otherwise, the mid to late afternoon is favored as daytime instability peaks in support of storms near DTW into early evening. DTW THRESHOLD PROBABILITIES... * Low for thunderstorms today and this evening. * Low for ceiling 5000 ft or less today and tonight. && .PREV DISCUSSION... Issued at 352 AM EDT Fri Jul 12 2024 DISCUSSION... Chances of showers and thunderstorms exist nearly daily today through early next week as a hot and humid airmass builds over the region. Forcing will be fairly weak most days with no significant frontal passages til about Tuesday, but several mid level waves will pass through a weak westerly/pseudo zonal flow pattern through the weekend. There will be a couple chances for strong/severe storms Sunday and Tuesday which we`ll get into below. Surface high pressure will hold across the region today while a mid level shortwave passes overhead. This wave is currently over southern Lake MI but will drift across lower MI through the day and into Ontario by tonight. There will be some mid level support for showers and thunderstorms as lobes of vorticity and slightly cooler mid level temps escort the wave eastward. Being on the west side of the surface high will really put a damper on any organized storms today with very little flow up to 600 mb and warm advection occuring through the day. So most guidance advertises tall skinny cape with 20-30 knots with better cape (around 1000 J/kg) to the north by MBS closer to the low center and around 500 J/kg south of PTK. This morning the first lobe of vorticity will lift through the Detroit area giving the first chance of showers and storms. With light winds and high pressure at the surface, lake breezes will likely generate which will offer continued activity into the afternoon along the eastern counties. Second vort lobe will then swing through Mid MI later in the afternoon. In addition, dewpoints will be in the mid 60s with over 1 inch of PWAT so with diurnal heating getting highs into the 80s so we could generate some pop up diurnally forced showers as well. With lack of stronger forcing, will keep a general chance/scattered pop going today as cells could pop up anywhere. Saturday looks pretty dry as mid level ridging slides overhead to go along with the lingering surface ridge. Temperatures increase into the mid/upper 80s as southwesterly winds at the surface and westerly winds aloft both offer warm air advection. Dewpoints still holding in the mid/upper 60s will make for a muggy day with heat indices around 90 degrees. Sunday through Tuesday brings several chances for thunderstorms as strong ridge over the southwest conus hold firmly against several northern stream troughs as jet level flow tops out only around 50 knots so no waves strong enough to dig into and displace the ridge. This helps set up a low amplitude west-northwesterly flow pattern across the Plains and into the Great Lakes. As this is setting up though, a shortwave will lift northeast across the state line bringing a chance of showers to the metro Detroit area Sunday morning. Attention then turns to the potential for an MCS to develop over MN and track E-SE across WI and into the Great Lakes. Many models (GFS, NAM) keep it tracking more easterly across northern MI clipping portions of Mid MI and the Thumb as a warm front sets up across that area helping to steer it. The Euro and RRFS both offer a more southern track with the RGEM somewhere in between. Will have to wait and see where the MCS originates to see how far south it can track with the westerly steering flow but we`ll keep a mention of thunderstorms and potential for severe weather Sunday for this feature. Heat ridge folds into the region Sunday and Monday with 850mb temps possibly exceeding 20C so highs of 90F will be possible both days. Will need to watch cloud trends to see if we can reach these temps as this pattern with all the moisture and upstream convective systems may keep temps down. Strongest synoptic feature will arrive Monday night into Tuesday as a trough finally gets some jet level support with a strengthening cyclonically driven jet max helping to push a cold front down through lower MI. After the storms clear, Canadian high pressure will bring cooler temperatures into the region for the rest of the week. 850mb temps look to hover around 10C keeping highs in the upper 70s to near 80. MARINE... A disorganized ridge of high pressure provides light winds out of the south-southeast today as the diffuse system drifts toward the Eastern Lakes. Winds/waves generally hold below criteria today and through the weekend in the absence of stronger flow. One caveat exists for marginal Small Craft Advisory gust potential amidst southwest flow over Saginaw Bay as peak winds approach 25 knots Sunday afternoon. A chance for isolated showers/storms exists this afternoon before storms return with broader coverage Sunday and Monday upon arrival of a warm front and approaching low pressure from the west. Some stronger storms are possible both days which could pose a heightened risk for locally higher winds/waves and hail. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....BT DISCUSSION...DRK MARINE.......KGK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.