302 FXUS63 KDTX 061709 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 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. && .PREV DISCUSSION... Issued at 320 AM EST Sat Feb 6 2021 DISCUSSION... Moisture/heat flux/clouds from Lake Michigan helping to keep temperatures in the lower teens across much of southeast Michigan at press time, not very far off from normal low temperature values for early February. Next strong upper level wave digging into the upper Mississippi River Valley today. Shortwave ridging out ahead of this feature will lower inversion heights and help taper off the southwest flow Lake effect which has been focused in and around the I-69 corridor for much of the evening and night, leading to a few inches of snow in spots. Clouds holding through the day should help mute any attempt by modest warm advection pattern, and highs near 20 degrees for highs will probably be the best we can expect with snow pack now well established over southeast Michigan and extending south into northern Indiana/Ohio. Still looking at large scale forcing arriving this evening to support widespread snow development. However, a second upper level wave tracking through the southern Plains will help divert the moisture transport to the north. Looking at a narrow 850-700 MB specific humidity moisture axis around 1.25 g/kg tracking through around midnight (3-6z). Thus, forcing looks to be rather short lived, but will still favor a solid 1 to 2 inches of fluffy/dry snow as a brief boost of moisture off Lake Michigan should also help the cause. One can see that in the NAM 925 MB omega at 3z, which breaks off to the northeast. An isolated 3 inch total is not out of the question. Overwhelming subsidence and dry air taking hold on Sunday, as 30 C dew pt depressions at 850 MB over the northern Ohio River Valley arch across the state border. With such a cold airmass, even shallow saturated layer in the 925 MB layer, where temps look to be around -20 C, could be sufficient to touch of a few flurries, despite the more more unfavorable west-northwest wind direction. Energetic upper level flow/jet tracking through the Rockies and through the Central Plains by Monday will lead to increasing FGEN as surface low/wave tracks near the Ohio River. Tight baroclinic zone and overall favorable thermal profiles, but tough call on how much the flow will buckle over the northern Plains, and most medium range models continues to argue for a fairly flat wave tracking close to the Ohio River. Thus, going to be tough for any appreciable snow to make it this far north as pronounced surface ridge attempts to hold Monday night. In any event, 00z GFS/NAM solutions would argue for a couple inches. The Euro continues to bounce around from run to run, but now is a bit more amplified, but suggests light snow accumulation are delayed until late Monday night/Tuesday morning. Did take a glance at the 50 member Euro ensembles, and not surprising, there is a lot of variability noted in the Monday-Tuesday time frame. Thus, will not deviate from just chance pops. Speaking of trends, the massive upper level PV Anomaly for the mid week period over Central Canada is even farther west, which probably prevents the extreme cold air from returning to the Central Great Lakes in the Thursday/Friday time frame (Outgoing forecast is probably too cold for highs). However, this could open us up for a potential snow storm toward the end of the work week as a system comes out of the southern Plains. MARINE... Gusts to gales are diminishing this morning, confined to central Lake Huron under modest westerly flow. A few gusts to gales remain possible for the northern and southern portions of the basin, but the Gale Warning has been cancelled due to infrequent occurrences. Small Craft Advisories are in affect across the nearshore waters as winds generally hold in the 15-25 knot range with a few gusts near 30 knots until this evening. Due to the combination of arctic air and strong winds, moderate to heavy freezing spray is ongoing across the open waters of Lake Huron until this afternoon. Winds will further weaken on Sunday and Monday, backing toward the southwest. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Heavy Freezing Spray Warning until 4 PM EST this afternoon for LHZ361>363-462. Gale Warning until 4 PM EST this afternoon for LHZ361>363-462. Small Craft Advisory until 7 PM EST this evening for LHZ421-441>443. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....SC DISCUSSION...SF MARINE.......KK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.