910 FXUS63 KDTX 062043 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 343 PM EST Sat Feb 6 2021 .DISCUSSION... Quiet and cool weather this afternoon with gentle isentropic downglide bringing a bubble of dry midlevel air across the region while suppressing low-level ascent. Surface high pressure sliding across Ohio has kept the breezy southwest wind in place today, but the gust component will drop off as the gradient weakens tonight. A midlevel circulation tracks over the CWA late this afternoon and evening and opens the door for moisture advection to fill in from the south and west ahead of the next wave dropping in from the upper midwest tonight. The isentropic ascent isn't initially impressive this evening with system-relative flow trajectories largely parallel to pressure surfaces. However, quality of forcing increases around midnight with flow directing a little more up the isentropes as the wave moves in from the west. The wave elicits two flareups of fgen tonight - the first centered between 700 and 800mb and the later centered around 600 to 675mb. Upper jet support is lackluster within the left entrance region of the jet streak over the Mid-Atlantic, but broad synoptic lift will commence in the divergence ahead of the inbound wave. Question remains regarding the quality of moisture moving in this evening as the main plume is shunted south of the border, but confidence is increasing in seeing a ribbon of 1+ g/kg 850-700mb specific humidity squeeze in. With the waves of forcing moving through, this should be sufficient for a short duration widespread light snow tonight. Model soundings show a deep (900-700mb) isothermal temp profile within the DGZ for most of the CWA with the Tri-Cities and northern Thumb having slightly colder profiles. With omega clipping at least the top of this layer, expect snow:liquid ratios north of 15:1 and a nice fluffy snow type. QPF comes in near or just shy of 0.10 inches, still looking at snowfall totals of 1 to 2 inches. Potential is there for some localized higher totals up to 3 inches with lower midlevel static stability in place for a brief period. Uncertainty remains regarding the lake moisture contribution via the southwest flow - this may locally enhance snow rates in the Tri-Cities/Flint earlier in the night. The snow looks to move into the Tri-Cities/Flint areas as early as 9pm and spread east into Metro Detroit by around midnight. Snow tapers off between about 3 and 5am. Strong deep-layer subsidence builds in on Sunday in the wake of the wave while a reinforcing shot of cold air sweeps in. This steepens low-level lapse rates through the DGZ which may touch off a few lake effect flurries, but enough dry air accompanies the arctic air mass and will prevent better potential for snow showers. Temperatures hold in the teens tomorrow with wind chills lingering below zero through the day. Modest warm air advection ahead of the next wave brings Monday temperatures to the upper teens - still some 10 to 15 degrees below normal highs for early-mid February. The next chance for light snow arrives on Monday evening into early Tuesday. A low amplitude wave dropping in from the Canadian Prairie helps pull the baroclinic zone back into lower Michigan on Monday and jet forcing moving overhead late in the day provides a better setup for ascent over the region. Thermal profiles again look favorable for a fluffy snow type and totals of about 1 to 3 inches by Tuesday morning. Early indications from the NAM currently suggest that the best forcing along the frontal slope occurs around 650mb which places the southern half of the CWA in a better spot to receive the higher end totals. Another glancing shot of arctic air moves in on Tuesday but will be relatively short lived. Mid range guidance keeps the baroclinic zone draped right across the Great Lakes through the balance of the week with the next wave tracking through on Thursday night. Another arctic air intrusion follows this bringing temperatures back well below normal by next weekend. && .MARINE... Gusts to gales have ceased across Lake Huron while waves have trended lower across most of the nearshore zones. Maintained the Small Craft Advisory for periods of gusts to 30 knots over Outer Bay and the tip of the Thumb until this evening. Winds barely veer westerly overnight with speeds diminishing into the 15-20 knot range. Gradient winds remain below criteria Sunday morning as the pressure field reorients from strengthening high pressure over the northern Plains. This will bring a reinforcing shot of cold air through the weekend with persistent and modest zonal flow. Winds back toward the southwest on Monday from diffuse high pressure off western Lake Erie providing a weaker wind field through the middle of next week. && .PREV DISCUSSION... Issued at 1209 PM EST Sat Feb 6 2021 AVIATION... The lake effect showers have diminished late this morning under large scale subsidence. The moist plume off the lake has however maintained a healthy MVFR based strato cu field. An upper level short wave impulse will advance across Lower Mi tonight. The increase in deep layer moisture preceding this system will reactivate the lake effect, with the southwest flow in the evening targeting mainly MBS and FNT for light snow. As the ascent overspreads the rest of Se Mi late this evening (after 03 or 04Z), light snow will move into the rest of the terminals. The ascent and thus region of snow will then depart to the east after 08Z. An aggressive push of mid level subsidence along with cold dry air advection under more west-northwest wind field will help scatter out the low level strato cu deck around daybreak Sunday. For DTW...The southwest flow is slowly driving the Lake Michigan moist plume north of metro. This has resulted in some slight improvement in ceiling heights and actually suggests some partial to perhaps full clearing of the low clouds by mid to late afternoon. The lead edge of the light snow is then forecast to arrive in metro between 05Z and 06Z. An inch or two of dry snow is possible tonight. DTW THRESHOLD PROBABILITIES... * Moderate in ceilings at or below 5000 feet today and tonight. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Small Craft Advisory until 7 PM EST this evening for LHZ421-441. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...TF MARINE.......KK AVIATION.....SC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.