024 FXUS63 KDTX 121655 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1155 AM EST Sun Jan 12 2025 .KEY MESSAGES... - Light snow is expected today, with minor accumulations expected. There is a chance of freezing drizzle this evening. - Another surge of arctic air is expected late Monday into mid week. - Lake effect snow showers redevelop with the arctic airmass. Greatest coverage looking to be Monday night through daytime Tuesday. && .UPDATE... For this afternoon... Positive theta-e advection downstream of a prefrontal trough will continue to fill in and produce widespread light snow across SE MI through the early evening. Moisture content will be relatively uniform across SE MI with enhanced mid-level forcing aligning over the Tri-Cities and Thumb. Elevated DGZ heights to and above 10kft with surface temperatures ranging between 28-32F will keep snow ratios in check, around normal values of 10:1 - 12:1. Snowfall totals around a half-inch... Up to an inch... are expected across the Metro region. Snow total potential gradually increases the farther north one goes, tied to the better forcing. This will result in totals around an inch...up to two inches... across the Tri-Cities to Thumb by late tonight. && .PREV DISCUSSION... Issued at 1145 AM EST Sun Jan 12 2025 AVIATION... Snow showers will increase in coverage again during the afternoon as an upper level disturbance tracks through SE lower MI. Snow will be most concentrated from KMBS to KFNT and to a lesser degree into KPTK but will still impact KYIP/KDTW/KDET from mid/late afternoon into evening. IFR cigs/vsbys will be more likely KPTK north at times with 1-2" of snow possible. MVFR conditions will be the rule further to the south where accumulations will remain under an inch. As the deep moisture associated with the snow shifts east, there may still be a brief period of light freezing drizzle/mist this evening although the probability for this is shifting lower (10-15%). MVFR moisture plume off of Lake Michigan will then set up overnight into Monday as flow veers to the west and ushers in the next batch of arctic air. Lake effect snow showers will become more prevalent beyond this forecast period into Monday night. For DTW... A period of 5000+ ft ceilings will be possible early this afternoon before MVFR cigs return with snow showers by the middle of the afternoon. MVFR/IFR vsbys can be expected with this activity into early evening. Total accumulations less than an inch still most favored outcome. Period of light freezing drizzle possible (10-15% chance) this evening. DTW THRESHOLD PROBABILITIES... * Moderate for ceiling 5000 feet or less by mid afternoon, high this evening into the overnight, medium to high through Monday. * High for snow as precipitation type this afternoon/evening. Low for patchy freezing drizzle this evening. PREV DISCUSSION... Issued at 315 AM EST Sun Jan 12 2025 DISCUSSION... It will be a dry albeit cloudy start to the day as upstream observations indicate ceilings are still quite high. A fast moving mid level short wave will advance across Iowa this morning, before quickly translating across Se Mi late this afternoon/evening. Mid level positive PV advection and divergence within the left exit of a 150 kt upper jet streak will result in a period of respectable dyanmics this afternoon. Per model soundings, deep layer moisture will not be entirely present through the duration of better dynamics. Deep layer system relative ascent is shown to be relatively brief, focused during the mid to late afternoon hours. This will be the time period when moisture depth will be most favorable for ice nucleation and a precip type of entirely snow. Per upstream observations, the degree of low level moistening later this morning within low level theta e advection may be a bit overdone on latest model solutions, suggesting precip chances will be better after noon. Ensemble mean QPF ranges from just under a tenth of an inch in the south to around 15 inches across the Tri Cities where moisture quality will be a little better. Considering cloud microphysics may not entirely be ideal for good dendrites through the afternoon, accumulations of an inch or two north to less than an inch south remains reasonable. Low level southerly flow will push afternoon temps into the 30s. So even with some periods where ice nucleation may be lacking, air temps may be warm enough to mitigate icing concerns. The passage of the mid level moisture to the east with the departure of the short wave around 00Z may however strip ice nuclei from the clouds. Given ample low level moisture and good shear atop the moist layer, a chance for some freezing drizzle during the evening hours seems warranted. Inversion heights will lift during the day Monday as a result of cold air advection under westerly flow. There will be limited moisture across Se Mi. However, model soundings suggest enough supersaturation near the dendrite layer Mon afternoon to warrant scattered flurries and/or light snow showers. The cold air advection (which will result in steady or slowly falling temps in the 20s) is associated with the circulation around an upper low forecast to drop south into Minnesota/Wisconsin on Monday. This upper low is forecast to transition to an open wave as it crosses Lower Michigan late Mon night/Tuesday. The resulting large scale ascent and increasing depth of the cold air will support an increase in the response off Lake Michigan. West-northwest flow will drive the snow showers across Se Mi. The potential for much if any accumulations looks low due to the very dry ambient airmass and the fact the airmass will be so cold that the ascent will be above the dendrite layer, keep flake size small. The passage of the wave will support a reinforcing shot of arctic air through the mid week period. The next chance for snow will be Wed night into Thursday with model solutions in relative agreement in showing a short wave feature along the nose of the upper jet supporting an increase in mid level frontal forcing across Lower Michigan. MARINE... Low pressure tracks toward Lake Superior this afternoon, with widespread snow filling in across the local waters throughout the day. Dry air initially will limit snowfall rates, but rates pick up this afternoon and evening and may drop visibility below 2 miles at times. Light southerly flow persists today and tonight, but shifts to the southwest by early Monday morning as the low`s cold front drags across the region. Arctic air fills in behind this front, generating over-lake instability that will be conducive for gusty winds and lake effect snow showers Monday and Tuesday. SW winds gusting around 25-30 knots are anticipated early week, with funneling along/downwind of Saginaw Bay possibly producing a few gale force gusts. Flow veers to the northwest Tuesday as the low finally releases into Ontario and drives a secondary trough axis down Lake Huron. A burst of heavier lake effect snow showers accompanies this trough axis. A brief axis of high pressure builds in on Wednesday before the active period continues to end the week. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ UPDATE.......AM AVIATION.....DG DISCUSSION...SC MARINE.......MV You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.