Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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369 FXUS63 KDTX 170407 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1207 AM EDT Mon Jun 17 2024 .KEY MESSAGES... - An excessive heat watch remains in effect Monday afternoon through Friday evening. Several days of highs in the 90s are expected this week, with afternoon heat indices of 95 to 100. - Nighttime lows will only drop into the 70s over most of the area this week. - Scattered to numerous showers and thunderstorms tonight/Monday and Tuesday afternoon will bring potential of localized torrential rainfall. && .AVIATION... A large cluster of thunderstorms now represents both earlier surface based activity plus new development farther west fed more by nocturnal mechanisms. The parent MCV still makes storms possible farther north toward MBS although radar trends at forecast issuance clearly favor PTK and the DTW corridor for several hours of borderline MVFR/IFR conditions depending on rainfall intensity. Other observational trends will be monitored for signs of greater coverage of ceiling or visibility restriction within the frontal zone. The shower/storm pattern then moves eastward by late morning and VFR cumulus follows within the inbound heat and humidity for the afternoon. A stray pop-up shower or storm is possible in this air mass but with predictability too low for a mention at this point in the forecast. For DTW/D21 Convection... The leading edge of thunderstorms inbound from LAN to JXN weaken to lighter showers in favor of new storms farther west. It is possible the later activity holds together for scattered storm coverage across D21 and at DTW after 08Z until about 12Z. Localized heavy rainfall is the primary hazard with this activity until moving east of D21 by late morning. DTW THRESHOLD PROBABILITIES... * Moderate for thunderstorms at the terminal late tonight into early morning. * Moderate for ceiling 5000 ft or less mainly with convection late tonight and early morning. && .PREV DISCUSSION... Issued at 943 PM EDT Sun Jun 16 2024 UPDATE... Trends of showers and thunderstorms are highlights of the forecast for SE MI as scattered to numerous coverage is on track late tonight, mainly after 2 AM through the morning. Ongoing activity over SW Lower MI has upstream MCS/MCV origins and is still surface based and outflow driven. It begins to weaken and decrease coverage while running out of instability, a trend strongly suggested by the surface based CAPE gradient shown in hourly mesoanalysis. The ongoing storms could also spur a transition to elevated convection as the parent MCV and larger scale background low level jet become the primary drivers of new convection after midnight. Confidence is higher on an elevated transition or new development as HREF provides a favorable look of near zero surface based CAPE by 09Z/5AM while MUCAPE rises to around 1500 J/kg 09Z-12Z. Predictability is lower on identification of favored areas of SE MI with just scattered to numerous coverage expected areawide as mid level theta-e is fully ridged ahead of the NW to SE extending surface warm front. Locally heavy rainfall is the primary hazard as model sounding and HREF mean PW reach the 1.5 to 2.0 inch range after 06Z. A precip loaded 40 mph wind gust is also possible while high freezing level and low CAPE density limit hail potential. The parent MCV and any remaining nocturnal activity exit into Ontario by late morning leaving heat and humidity to gain traction through Monday afternoon. PREV DISCUSSION... Issued at 250 PM EDT Sun Jun 16 2024 DISCUSSION... No changes to excessive heat watch issued last night, but this certainly looks like just heat advisory criteria for Monday/Tuesday. Considerable uncertainty with just how hot we get and if dew pts can reach and exceed 70 degrees for any sustained period to support excessive heat warning criteria, although the cumulative days/effect of heat indices near 100 degrees still may be enough for future shifts to possibly issue a a excessive heat warning for urban areas vs heat advisory. Another uncertainty of the forecast is with the showers and thunderstorm chances this evening through Tuesday, as there is a lot of upper level PV filaments riding up through the Mississippi River Valley, which will be tracking through southeast Michigan, as the upper level ridge builds over the northern Appalachians early next week. Upward revisions for pops have been made for tonight and Monday, as cams are in pretty good agreement with the upper level disturbance/MCV which came out of the Kansas City area slowly tracking through southern Lower Michigan tonight, with the instability/cape gradient making inroads as moisture advection ramps up. Mid level lapse rates start out steep, 7.5 C/KM, but would then weaken as the batch of showers and thunderstorms and convective latent heat release tracks through southeast Michigan. Still, will carry just high chance pops due to exact location/coverage uncertainty, with torrential rainfall and even hail possible (MUcapes increasing to 1500-2000 J/kg), with another limited convective flare-up possible Monday afternoon as well. Trajectories then show a shortwave coming out of the eastern Gulf of Mexico on track to move into southeast Michigan late Tuesday. With a respectable 0-6KM bulk shear of 30+ knots tracking into/near western Lake Erie, which, coupled with the potential moderate instability/cape would be supportive of strong to isolated marginally severe storms, if activity is able to initiate. Low level convergence near the Land/Marine interface the likely locations within the backdrop of the low level southwest flow. Slow movement of storms/potential back building with PW values aoa 1.75 inches will draw concern for urban flooding, but at least airmass is not true tropical, with 700 MB dew pts only progged to be near 3 C. With said ingredients, Tuesday afternoon looks to be another good shot for scattered coverage of showers and thunderstorms (25-50%). As usual with these unstable air-masses, once the first cell goes, an outflow boundary is then usually sufficient to get additional activity to fire up during the peak heating of the day. Bottom-line, the prospects for convection to start the work week is decent, which should have some impact on max temperatures, likely capping maxes in the low to mid 90s. 500 MB heights building for Wednesday-Thursday as the upper level ridge center over southern New England retrogrades to the west makes for a higher confidence forecast in temperatures rising solidly into the 90s. However, even then, still some convective schemes getting triggered in this generally uncapped environment as the jet stream/strong westerlies hang around the northern Great Lakes. So, certainly a lot of more weather elements to focus in on over the coming days than just the heat. MARINE... A warm and humid airmass will set up over the Great Lakes through early tomorrow morning and will last through the end of the week. This will produce relatively stable near surface lake conditions. The passage of a warm front will produce isolated to scattered showers and thunderstorms this afternoon and evening for portions of Lake Huron and the Saginaw Bay. Some strong thunderstorm induced wind gusts aoa 30 knots and/or hail cannot be ruled out with today`s late day activity, favored across northern Lake Huron. Wind direction will veer from the southeast to the southwest after the passage of the front. Additional isolated to scattered shower and storm chances will exist tomorrow morning over the Great Lakes as an upper-level disturbance moves over the region and again in the afternoon, with additional chances returning Tuesday. HYDROLOGY... A moist and unstable airmass arriving tonight and continuing through Tuesday will bring the potential of a few rounds of showers and thunderstorms. The coverage is expected to remain mainly scattered, but locations which experience strong thunderstorms will have the potential for rainfall amounts to exceed 2 inches in a short period of time, leading to urban/low lying flooding. There is this low flooding potential late tonight into Monday, and then again Tuesday afternoon. Otherwise, most locations remain dry or will be lucky to see a quick half an inch of rain. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Excessive Heat Watch from Monday afternoon through Friday evening for MIZ047>049-053>055-060>063-068>070-075-076-082-083. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....BT UPDATE.......BT DISCUSSION...SF MARINE.......AM HYDROLOGY....SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.