Expires:No;;149846 FXUS63 KDTX 040904 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 404 AM EST Wed Dec 4 2024 .KEY MESSAGES... - Light snow continues across the Tri-Cities and Thumb this morning, bringing a dusting to a half-inch of new accumulation. - An arctic cold front crosses the area this evening which is expected to support numerous snow showers. Snow squalls are likely within this activity. Gusts up to 35-40 mph will produce brief but rapid near-whiteout to whiteout conditions under snow squalls. - Temperatures plummet below freezing after the front passage this evening. A flash freeze will be possible on untreated roadways. - Snowfall accumulations of 1-2" possible by tomorrow morning. Highly localized totals of 3-4" possible with any repeated snow squall activity. - Wind chills in the single digits overnight. && .DISCUSSION... For this morning, mid and upper-level system relative isentropic ascent from roughly 700mb to 400mb will support light snow chances north of I-69, favored over the Thumb and Tri-Cities. Snow accumulations over a dusting will be most favorable over the Thumb, tied to the stronger forcing and better moisture depths, where a dusting up to a half-inch of new accumulation will be possible. Snow coverage dwindles between 9-11AM. Otherwise, a strong and expansive low-level wind field is now in place across the Great Lakes, south of a maturing low pressure system which now resides over western Ontario and northern Lake Superior. While mixing depths will not be particularly impressive with low-level inversion heights around 2.5kft, the shallow nature of the wind field and sustainment of a strong pressure gradient will bring an extended period of breezy conditions. This will initially result in sustained southwesterly flow of 15-20 mph with gusts up to 35-40 mph through the afternoon. Low pressure will continue to track southeast into Ontario and northern Lake Huron through the afternoon and evening hours. This will draw in a strong surge of polar air across the Midwest and Great Lakes on the backside of the system, driven by robust cold air advection. Initially, an elevated cold front will produce subtle lift from 825mb to 500mb, bringing the chance for light snow showers to initially develop and expand over the Tri-Cities during the early afternoon, with snow chances then expanding from west to east through the afternoon and early evening hours. Light accumulations of a dusting up to a half-inch will be possible with this first wave of potential snow, but minimal impacts are initially expected as surface temperatures hover around or slightly above freezing. A strong arctic cold front in conjunction with support from a strong upper-wave will then quickly move across SE MI from west to east from roughly 5 PM to 10 PM, which will bring numerous snow showers, including the likely chance to see snow squalls capable of producing brief but rapid reductions to visibilities down to near white out or white out conditions, along with quick snow accumulations of a half- inch to an inch and a half in a given 30-60 minute window. Upright forcing right along the arctic boundary will be capable of extending convective depths to or above 10kft through the dgz, while the expansion of cold air quickly boosts low-level potential instability. The NAM might be overzealous with surface cape values exceeding 100 J/kg across SE MI, but from a model climate perspective, this does highlight the potential for vigorous snow showers, especially with 100-200 J/kg CAPE coming off Lake Michigan which will contribute to very efficient moisture flux off the lake. Both type of snow squall modes will be possible this evening, with the more traditional linear mode along the strongest portion of the arctic boundary, and cellular modes along the weaker portion of the boundary, especially in the wake of the front, as 0- 1km bulk shear values increase. Additionally, hi-res models also suggest the possibility for mesovortex development, which can sustain elevated snow rates and highly localized snowfall totals well inland. A hint of this is seen in the coarse GFS and UKMET models which show elevated snow accumulations of 2+ inches right along the I-69 corridor. In additional to the aforementioned squall hazards, temperatures rapidly plummet behind the front, going from near freezing values into the low to mid 20s. Flash freezes on untreated roadways will be major concern under this setup. Snowfall totals will range between 1-2" with highly localized totals of 2-4" possible with any repeated snow squall or mesovortex activity. Given the lower end predictability of where the strongest banding/squalls/mesovortices will set up, will preclude the issuance of a Winter Weather Advisory (WWA), noting a possible upgrade to a WWA for the afternoon package, and/or leverage of the Snow Squall Warning product. Snow shower and squall potential will continue through the mid morning hours tomorrow until flow veers to the northwest, ushering in dry air. Will need to maintain a watch for the Tri-Cities and coastal Thumb as northwest flow may sustain snow showers chances into the late morning. Wind direction veers to the west-northwest in the wake of the front with continued gust potential up to 35-40 mph. Temperatures plummet into the upper teens overnight, with wind chills in the single digits. Wind chills only increase into the teens tomorrow afternoon as breezy conditions continue. Elevated mixing depths will support gust potential of around 35-40 mph. Flurries or light snow showers will be possible in the afternoon, with some lower end potential for cellular snow squalls brushing Washtenaw/Lenawee County and/or the Lake Huron shoreline under northwest flow. Cold again Friday morning with lows dipping into the teens and highs holding below freezing. Northern periphery of high pressure will fill in over Michigan on Friday, relaxing wind speeds and gust potential with mid-level flow exhibiting more zonality by the late weekend. This will end the below normal temperature trend by early next week, bringing highs in the 40s along with chances for rain showers. && .MARINE... The strong clipper is now over the northern Great Lakes and will drift southeast reaching Lake Ontario by Thursday morning. The tight gradient on the southern side of the low is resulting in the first round of Gales over Saginaw Bay and Central Lake Huron, with Small Craft Advisories for all other nearshore zones. The clipper will then pull a cold front across the region this evening. Very cold and unstable air in the wake of the front will produce widespread northwesterly Gales across all waters tonight through most of Thursday. Snow squalls will also be likely on tonight and Thursday. Cold air lingers into Friday but winds will back to the west while remaining around 20 to 25 knots across most of the region. && .PREV DISCUSSION... Issued at 1202 AM EST Wed Dec 4 2024 AVIATION... Extended period of warm air advection overnight and early Wednesday ahead of an intense low pressure system tracking across the northern great lakes will lead to some variability in low level moisture quality early in the period. Lower stratus tied to the advective process now lifting north across portions of Indiana. Potential remains for some degree of this cloud to enter southeast Michigan late tonight and particularly Wednesday morning, bringing a return of MVFR restrictions. Greater low level saturation will commence throughout Wednesday, supporting a more widespread expansion of MVFR stratus with some prospective flurries or brief snow showers plausible into the afternoon. A more focused window for intense snow showers/squalls centered on Wednesday evening, offering a rapid reduction in visibility and a quick accumulation of snow. Gusty southwest winds in excess of 25 knots through the afternoon, shifting to west-northwest and turning even gustier with the passage of an arctic front Wednesday night. For DTW...Potential for a period of intense snow showers/squalls Wednesday evening /00z-03z/. Gusty west-northwest will develop with the passage of a strong arctic front Wednesday, reaching in excess of 35 knots at times. DTW THRESHOLD PROBABILITIES... * Low for ceilings 5000 ft or less tonight. Medium Wednesday morning. High Wednesday afternoon and evening. * High precipitation type as snow Wednesday afternoon and evening. * High to reach crosswinds thresholds Wednesday night. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Small Craft Advisory until 10 PM EST this evening for LHZ441>443. Gale Warning from 10 PM this evening to 10 PM EST Thursday for LHZ361-362-441>443-462>464. Gale Warning until 10 PM EST Thursday for LHZ363-421-422. Lake St Clair...Small Craft Advisory until 10 PM EST this evening for LCZ460. Gale Warning from 10 PM this evening to 1 PM EST Thursday for LCZ460. Michigan waters of Lake Erie...Small Craft Advisory until 7 PM EST this evening for LEZ444. Low Water Advisory until 1 AM EST Thursday for LEZ444. Gale Warning from 7 PM this evening to 1 PM EST Thursday for LEZ444. && $$ DISCUSSION...AM MARINE.......DRK AVIATION.....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.