431 FXUS63 KDTX 111955 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 255 PM EST Fri Jan 11 2019 .DISCUSSION... Despite partly sunny skies for a good part of the day and lack of snow cover, max temperatures look to be only topping out in the upper 20s to around 30 degrees this afternoon, slightly below normal. Noted 700 MB FGEN/Isentropic ascent over northern Great Lakes with virga even showing up downstream over southern Lower Michigan, but not expected to reach the ground with dry low level levels and with upper level ridge sliding over southeast Michigan tonight. Dew pts presently in the upper single number to lower teens makes for a difficult min temp forecast, as opaqueness and extent of clouds hanging around will determine lows. MAV/MET guidance suggests low/mid teens vs around 20/lower 20s per euro mos. Went with compromised blend (mid teens to lower 20s) based on the expectations a few breaks in overcast will occur. Upper level wave being booted out of the Four Corners region this morning, and weakening max 500 MB height fall center progged to track pretty close the Ohio River on Saturday, with just some modest height falls extending past the Michigan border. The deep upper level trough over Eastern Canada looks to be the driving force for our weather as head into the weekend, as good subsidence/drying/anticyclone tracks through Ontario. 700 MB shear axis to get close to the southern Michigan border, with 2.25 g/kg to perhaps 2.5 g/kg of specific humidity reaching Lenawee/Monroe counties toward 00z Sunday, otherwise 850-700 MB Theta-E min/troughing to hold over Washtenaw/Wayne counties. Ultimately, with persistent/cold easterly flow coming off Lake Erie (-7 C to -8C at 925 MB) during Saturday, and despite the basically dry NAM/HRRR solutions, should see the low levels moisten up enough to support light snow south of I-94. Low level winds backing to the northeast during Saturday evening, limiting duration at any given point, coupled with what looks to be weak forcing, expecting accumulations to generally remain under 1 inch, despite the aggressive Regional GEM, FV3-GFS, and now 12z Euro solutions pumping out a tenth or more of QPF for Lenawee/Monroe counties vs the much drier hires models (ARW/NMM) and our local SREF weighted probabilistic guidance. Low level northeast flow and cold advection coming off Lake Huron will present an opportunity for light snow showers across Tri- Cities and northern Thumb Region Saturday night, but the amount of dry air (PW values around 0.10 inches) and very low inversion heights suggest it will be difficult, as cloud depths will be shallow, about 1 kft deep from 2500-3500 ft per NAM soundings, but close/right in the DGZ with supersaturation with respect to ice indicated. Expecting a few flurries at the very least, but will still allow for an isolated light snow shower, as the fetch coming from Georgian Bay- Central Lake Huron through Saginaw Bay is long and may be sufficient. Granted, the airmass looks just marginally cold enough to generate activity. As such, 12z NAM indicating just modest 925 MB lift downstream of Saginaw Bay Sunday morning. Although modest 850 MB warming will occur during Sunday, temps reaching -4 C, we should be set up for a cold night Sunday night. As dry airmass remains in place and surface high/ridge settles overhead, expecting low temps in the teens. Return flow around departing high will continue to advect slightly warmer air into the region, especially across the Tri-Cities into the Thumb, allowing highs to peak in the mid-30s on Monday. These slightly above normal temps will continue through the midweek period. A cold front will then swing through the state Wednesday afternoon and will bring seasonal temperatures for the remainder of the extended period -- Thursday and Friday. Flurries to light snow will be possible with the passage of the cold front, however, opted to hold the inherited slight PoP values as forcing mechanisms remain week during the passage of the front. Last ECMWF model run advertised a dynamic low pressure system pushing across SE MI next Saturday, however, latest 12Z suite now has that system holding south of MI, traveling across southern IN/OH. Will continue to monitor any potential translation of the low pressure system with future runs, but at this time no significant precipitation chances exists in the extended period. && .MARINE... High pressure drifting from the central to the eastern Great Lakes will lead to continued light and variable winds over the region tonight. Low pressure developing tonight over the southern Plains will track into the Ohio Valley by late Saturday. This, paired with high pressure building south of James Bay will lead to increased northeasterly winds Saturday into Sunday morning, gusting to 20 knots over Lake Huron and 25 knots over Lake St. Clair and western Lake Erie where the gradient will be slightly stronger. High pressure will then expand over the region Sunday into Monday. Light to moderate southwest flow will develop during the early week before more active marine weather returns for the midweek period. Low pressure will swing through the northern Great Lakes and drag a cold front across the region on Wednesday. && .PREV DISCUSSION... Issued at 1226 PM EST Fri Jan 11 2019 AVIATION... Surface high pressure positioned over the region due to confluent flow aloft will drift into the eastern Great Lakes this afternoon and VFR conditions will continue. SCT to BKN coverage of mid to high clouds will be the only item of note into tonight as winds remain light - variable in direction this afternoon before gradually becoming more organized as easterly tonight as low pressure develops over the southern Plains. DTW THRESHOLD PROBABILITIES... * None. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...SF/AM MARINE.......TF AVIATION.....TF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.