Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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087 FXUS63 KDTX 061218 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 718 AM EST Tue Dec 6 2016 .AVIATION... A weak area of low pressure will lift northward today through the Ohio Valley. Upper level moisture is forecasted to shed off of this energy and lift due northward through southeastern Michigan before merging into the cyclonic circulation over the Minnesota. This enhanced moisture will lead to an area of rain across portions of southeastern Michigan this afternoon. Model consensus is aggressive in amount of low level moisture and saturation that will develop during the afternoon. As a result, maintained fairly heavy handed mention of mvfr with prevailing precipiation this afternoon. A cold front is still timed to push through southeastern Michigan at 3z. For DTW...Warm air advection seems to be doing the trick in disrupting the low level inversion in place. Still expecting some improvement to VFR this morning before moisture lifts northward into the terminal for the afternoon. Showers with MVFR conditions expected between 18-23Z time window. Cold front to end previaling shower mention although could see some drizzle linger into evening. Relatively fresh easterly winds today, to transition to gusty west winds this evening behind a cold front. //DTW Threshold Probabilities... * High for cigs below 5000 ft this afternoon and tonight. * High confidence precipitation Tuesday will be rain. && .PREV DISCUSSION... Issued at 346 AM EST Tue Dec 6 2016 DISCUSSION... Polar jet has taken a position across the northern tier of the US as a strong upper low over the northern Plains drifts northeast through the northern Great Lakes. A strong vort lobe wrapping tightly around the low will surge through the straits this evening and overnight. Accompanying cold front will work through southern MI later tonight. Meanwhile, an open wave in the subtropical jet will be lifting from the Gulf Coast to the mid Atlantic states. Deformation on the northern flank of this subtropical low has been flirting with SE MI for days now in the models. Not much has changed with the current model cycle. We remain sandwiched in between the two stronger areas of mid level lift, with only weak troughing connecting the two lifting across lower MI today. Thinking is that the weak deformation will lift into extreme southeastern MI this afternoon (15-18Z) and slowly expand northeast through the early evening. Any precipitation will come as light rain as the saturation layer fails to get colder than -5C and forcing is quite weak. As the deformation region tried to exit east, looks like there is some potential for the left exit region of the approaching jet to regenerate some light rain or drizzle over the thumb after 00Z. Drier air behind the cold front will quickly end the rain/drizzle by 06Z. This cold front will mark the beginning of a stretch of colder air that will affect the region through the weekend. 850mb temps will fall to around -5C on Wednesday and -10C by Thursday as the main trough axis passes to the east allowing the northwesterly flow aloft to advect much cooler air into the region. This airmass will knock high temperatures down into the 20s through Saturday before ridging over the central Plains starts building into the Midwest warming us back into the 30s. Main concern with the cold airmass will be the lake effect snow generated off Lake MI which will try to work into SE MI. Westerly flow at the surface with initial cold airmass will keep convective depths on the east side of Lake MI only around 6- 7kft so chances of the better snow bands reaching the east side of the state aren`t great. Flurries and light snow showers will be possible though Wednesday night into Thursday. Little better fetch Thursday may enhance the convergence band south of I-94 but not going to get too excited about that yet this far out. The next low pressure system won`t arrive til Sunday/Monday but model continuity has not been good with this one thus far stemming from potential amplification of the jet stream. Euro is keeping flow flatter resulting in cyclogenesis much further north while GFS deepens the wave and resultant surface low at lower latitudes. They have been consistent with timing so will keep pops enhanced for this period. MARINE... Surface Winds will transition this morning to the southeast and increase into the 20 to 30 knot range over the Lake Huron basin. Small craft advisories are in effect this afternoon for the nearshore waters of Lake Huron from Port Austin to Port Huron. Two separate low pressure systems are expected to slide eastward remaining to the north and south of southeastern Michigan. An organized cold front will push through the area this evening opening the door to an unmodified arctic push and stronger westerlies. Latest forecast information continues to suggest that west wind speeds will remain in the 30 to 34 knot range tonight and Wednesday. Unstable conditions over area waters and fresh westerly surface flow is likely to hang around through the end of the week. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Small Craft Advisory from 10 AM this morning to 10 PM EST Wednesday FOR LHZ441>443. Small Craft Advisory from 10 PM this evening to 10 PM EST Wednesday FOR LHZ421-422. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....CB DISCUSSION...DRK MARINE.......CB You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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