Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 252315 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 715 PM EDT Tue Apr 25 2017 .AVIATION... VFR will be firmly established over the region through most of the night. Fog/stratus toward sunrise remains a low predictability scenario with a wide range of development across model solutions. Formation of mid clouds is also in the picture which would be a limiting factor on fog/stratus. The mid clouds are more likely as moisture increases aloft in the southwest flow ahead of the Mississippi Valley low pressure system. The best approach is to maintain a brief mention around sunrise, slightly longer FNT to MBS, and monitor both model and observational trends for signs of greater coverage. The low level moisture axis/warm front will then move into Lower Michigan during Wednesday morning and continue to support low/mid cloud coverage. Model soundings remain weakly capped for convection along the boundary through the afternoon while daytime heating helps produce a gusty south to southeast wind. Showers and thunderstorms are then expected to move eastward from the associated cold front Wednesday evening possibly brushing the MBS area through midnight. //DTW THRESHOLD PROBABILITIES... * Low for ceiling 5000 ft or less Wednesday morning. && .PREV DISCUSSION... Issued at 319 PM EDT Tue Apr 25 2017 DISCUSSION... Upper level pv filament exiting east of the central Great Lakes this afternoon, taking morning light showers/sprinkles over the Thumb Region with it, along with the clouds. Developing afternoon sunshine has or will allow temperatures to climb to around 70 degrees across most locations once again. Active pattern/upper level energy over the Rockies of North America, leading to two distant mid level circulations around Tomorrow, one over Minnesota, with second wave/shortwave trough coming out of the southern Plains, becoming absorbed by stronger northern stream system, with the negative tilted trough axis lifting through southeast Michigan on Thursday. Warming low/mid levels is the weather story Tonight into Tomorrow, which should serve as a good CAP, as average 850-700 mb temps rise into the lower teens early Wednesday afternoon. 925 mb temps rising between 19-21 C supports highs around 80 degrees as warm front reaches at least Saginaw Bay. If warm front gets hung up over Tri- Cities region, enhanced low level convergence/forcing could be enough to overcome the weakening cap late in the day. If activity does materialize by early evening, 1000-850 MB Capes around 1000 J/kg with 0-6 km bulk shear up around 50 knots would support a marginal risk of severe storms as narrow moisture plume (PW values around 1.5 inches) reaches the doorstep of the CWA late in the day. Even better 0-6 KM bulk shear on Thursday, in the 60-70 knot range, but MLcapes expected to reside mainly below 1000 J/kg as showers and thunderstorms likely develop by early afternoon. Even so, with 50 knots at 850 mb, it will not take much to produce wind gusts up to 60 mph, and marginal risk of severe storms (last nights day 3 outlook) looks valid. If the front is even a bit slower, a better risk of strong to severe storms can be expected. Even without thunderstorms, should be a pretty good wind pop behind the front late in the day, with 6 hr rise/fall pressure couplet around 15 MB, with local probabilistic SREF weighted guidance indicating wind gusts in the 35 to 40 mph range. Low level cold advection looks good, as 850 mb temps crash at or slightly below zero toward early evening before leveling off Thursday Night. High pressure over the region on Friday will bring drier and cooler conditions with highs in the 60s. Shower chances return to the forecast late Friday as a warm frontal boundary becomes stationary south of Michigan. The weekend will feature a wet forecast as low pressure developing over the Southern Plains on Saturday moves northeastward towards the Great Lakes. The better chance for showers on Saturday will remain south along the Ohio border closer to the stationary frontal boundary as highs remain in the mid 50s across the Saginaw Valley and Thumb to low 60s near the Ohio border. As low pressure approaches the region, the frontal boundary will lift northward across Lower Michigan on Sunday with highs warming into the 60s to near 70 while rain and thunderstorms remain likely throughout the day into Sunday night. Cold frontal passage looks to occur on Monday as low pressure slowly exits the Great Lakes region keeping shower chances in the forecast. Following the frontal passage, a cooler air mass filters into the region for early next week with highs returning to the mid 50s to low 60s. MARINE... A long duration of moderate southeasterly flow will exist through Thursday with a gradually veering to the south by the end of that time frame. This flow will exist within modest pressure gradient between high pressure to the east and low pressure lifting into the Mid Mississippi Valley. Expect sustained wind of 15 to 20 knots over Lake Huron. While higher gusts will likely occur, rather stable low levels within this warming southerly flow will limit the highest gusts to around 25 knots on Wednesday and 25-30 knots on Thursday as the low pressure and attending cold front encroach on the area. Winds will turn southwesterly in the wake of this system from late Thursday into Thursday night with scattered showers or storms also accompanying the cold front. HYDROLOGY... Low pressure will track into northern lower Michigan on Thursday and drag a trailing cold front west to east from the region. Scattered showers and thunderstorms can be expected with this front. While the rainfall is not expected to be widespread, locally heavy downpours may bring one quarter to one half an inch of rain to some locations. With the basin average rainfall expected to remain low, there are no concerns for flooding at this time. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....BT DISCUSSION...SF/JD MARINE.......DG HYDROLOGY....DG You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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