Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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316 FXUS63 KDTX 180729 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 329 AM EDT Tue Jun 18 2024 .KEY MESSAGES... - Hot and humid conditions will persist across most of the area through the week. - Chances of thunderstorms will continue each day of the week. Some of these storms may be strong to severe with locally heavy downpours. && .DISCUSSION... Amplification of the East Coast mid level ridge will be ongoing today into Wednesday, with the ridge becoming more elongated as it stretches across the Ohio Valley during the end of the week. Short wave energy rotating along the western periphery of this ridge will advance across western Lower Mi today. Hi res model solutions generally suggest this will set up a thermal/instability gradient across the western portions of the forecast area this afternoon. This and potential lake breeze convergence zones across the eastern portions of the area will provide enhanced boundary layer convergence to support additional rounds of convection, mainly this afternoon and evening. ML Cape values projected near 2k J/kg with model soundings showing respectable CAPE density within an uncapped environment will again be supportive of localized strong/severe convection despite relatively week deep layer shear profiles. The depth of the warm layer, with PWATs around 1.8 inches will support some locally high rain totals as well. Expectations are for temps to be a little cooler today compared to yesterday given high clouds and the chances for an earlier convective release. Forecast highs in the low 90s with dewpoints near 70 will still push heat indices well into the 90s. The humidity will sustain another warm night tonight as lows will likely hold in the 70s. Some building/expansion of the mid level ridge across the eastern lakes will sustain heat and humidity across Se Mi Wednesday. Timing and coverage of convective development within a moderately unstable and uncapped atmosphere will play heavily into forecast highs. Thermal profiles suggest low to mid 90s for highs Wed with heat indices well into the 90s to around 100. The potential for ML CAPE values to exceed 2k J/kg with little to no capping inversion will again support locally strong/severe convection. A little more elongation in the mid level ridge noted in the 00Z model suite increases the chances for a southward push of slightly cooler air from the north on Thursday as high pressure expands across the northenr lakes. Short wave impulses embedded within the westerly flow with a lingering instability gradient over southern Lower Mi also looks favorable for additional convection. Therefore, the heat headlines will extend only through Wednesday evening. A longer wavelength trough forecast in the northern stream over the weekend will attempt to drive the front back northward as a warm front. The potential for convection will however support a low confidence forecast on temps during the first half of the weekend. The passage of the mid level trough and associated cold front will then support cooler and less humid conditions by the end of the forecast. && .MARINE... Southwest winds will continue to advect hot and humid air into the Central Great Lakes through the mid week period. High degree of surface stability with the cooler waters should keep wind speeds under 25 knots through the rest of the work week. The exception will be in and near and strong thunderstorms which develop. Timing and location will be highly uncertain, but the typical peak heating of the day into early evening hours will be favored. Indications are the surface frontal boundary will be sinking south Thursday and Friday as seasonably strong high pressure tracks through Ontario. This will allow for light northeast/northerly flow (~15 knots) over Lake Huron. Airmass will remain warm, thus any wave build up with the longer fetch remains below 4 feet. && .HYDROLOGY... A moist and unstable airmass will be in place across the region through the end of the week. Scattered thunderstorms are expected each day this week. The most intense thunderstorms have the potential to produce rainfall amounts in excess of 2 inches over a short period of time, resulting in urban and low lying area flooding. Uncertainty in specifics for both timing and potential for flooding precludes issuance of a flood watch. && .PREV DISCUSSION... Issued at 1157 PM EDT Mon Jun 17 2024 AVIATION... Thunderstorms finished their evening run leading up to midnight leaving just a stray shower or rumble of thunder possible during the late night. There is little else of concern outside of convective trends under VFR clear to scattered sky condition until a brief period of fog or haze becomes possible with wet ground now combined with the already humid air mass. A couple of hours of MVFR restriction is likely around sunrise even with a 5 to 10 kt wind. The afternoon then brings more of the same hot, humid, and unstable conditions along with another pattern of showers and thunderstorms having even greater organization. Given larger scale mid level support moving in from the MS/TN valleys, mid afternoon storm initiation is likely with similar timing across the terminal corridor which then moves eastward toward Tuesday evening. For DTW/D21 Convection... A stray shower or rumble of thunder remain possible late tonight as warm and humid air is now rooted across Lower MI. A morning pause in convection is expected followed by another round of storms in the afternoon, likely with greater coverage across the bulk of D21. DTW THRESHOLD PROBABILITIES... * Moderate for thunderstorms mid to late afternoon into Tuesday evening. * Moderate for ceiling at or below 5000 ft, conditional with thunderstorms. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 8 PM EDT Thursday for MIZ048-049-054-055-062- 063. Excessive Heat Warning until 8 PM EDT Friday for MIZ061-069-070-076. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...SC MARINE.......SF HYDROLOGY....SC AVIATION.....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.