FXUS63 KDTX 040502 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1202 AM EST Wed Dec 4 2024 .KEY MESSAGES... - Snow showers are possible over the Thumb Wednesday morning with these chances expanding over the rest of the area by the latter half of the day. - An arctic cold front crosses the area during the evening which is expected to support convective snow showers. Snow squalls are likely within this activity with gusts up to around 40-45mph producing near whiteout conditions. With arctic air quickly following overnight, any melting that occurs on untreated roadways will quickly freeze. - West to northwest wind gusts of 35 to 45 MPH are expected Wednesday night and Thursday. - Wind chill readings will plunge into the teens and single digits Wednesday night and Thursday as arctic air advances across the region. - A slight warming trend is forecast this weekend. && .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. && .PREV DISCUSSION... Issued at 324 PM EST Tue Dec 3 2024 DISCUSSION... Southwest flow is developing this afternoon in advance of a clipper system dropping out of northern Canada towards the upper Great Lakes. WAA that accompanies this flow lags by a couple hours offering a brief window where remnant lake effect snow showers from SW lower MI could creep into the Shiawassee/Tri-Cities/western Thumb area this early this evening. Activity will be decaying by this point as lake effect is being cut off by warming lower levels so expectation is only for some flurries or spotty light snow showers. Lead vorticity/height falls reach the area by Wednesday morning coinciding with steepening mid-level lapse rates, particularly the Thumb. Soundings show deeper saturation compared to yesterday's runs supporting better ice nuclei to support spotty flurries within this steepening lapse rate environment (rather than spotty freezing drizzle that was looking favored from prior model cycles). Soundings over the Thumb show the greatest moisture depth which given its better placement to lead height falls, likely supports light snow showers and minor accumulations through the morning. Maturing low reaches the northern Lake Huron shore latter half of the day Wednesday as its parent mid-level trough drives directly over southern lower MI. Strong jet streak along the base of the trough sinks south into northern IN/OH providing additional upper divergence as its left exit region sets up over SE MI. Following a midday lull, lead cold front is set to cross the region during the afternoon bringing the next chances for snow showers. Models are varying to what degree activity is able to develop along it owing to it preceding the main mid-level trough and subsequent strongest lift. Moisture quality within this system isn't anything remarkable with the strength of ascent being the driving factor for both coverage and intensities. Given the better saturation depths over the northern CWA from the morning, thinking is these areas would have the best chance to see light snow showers develop along this front- only minor accumulations possible. Focus is on Wednesday evening into the early overnight period with the arrival of the arctic cold front and mid-upper trough. Clipper reaches peak strength during this timeframe as it matures into a closed low near the Georgian Bay shoreline. Local gradient tightens in response with 35-45kt flow likely within the lowest 10kft. Due to the passage of the prior cold front, strengthening CAA results in the development of convective instability (>30 J/kg) and increasing convective depths which are further magnified along/immediately behind the arctic front- convective depths spike to at or above 10kft feet. Given the strength of frontal forcing and upper synoptic support, numerous convective snow showers are likely with the passage of the arctic front. Additionally, snow squalls are extremely favorable in this environment with snow squall parameters well in excess of 1 due to the potential for brief but intense snow rates and strong wind field as gusts reach the 40-45mph range. Rates under these convective snow showers could easily be over 0.5"/hr especially if a mesovortex develops which some of the hi-res solutions show signal for. The speed of the frontal progression is the limiting factor for accumulations as snow showers/squalls only linger over locales for an hour or two. Prior forecast of 1-2" still looks most reasonable at this time, however locally higher totals not out of the realm of possibility for the reasons above. Core of the arctic airmass settles across the Great Lakes Wednesday night as the mid-upper trough shifts over the eastern Great Lakes. Northwest wind gusts strengthen through the night as low level lapse rates steepen and mixing depths still hold around 4-5kft. Forecast soundings still are marginal for gusts reaching wind advisory criteria (45mph) with the 45-50kt flow residing just above forecast mixing heights. Running forecast will still hold sub-advisory with Thursday morning gusts up around 40mph. Regardless, wind chills crater, falling into the single digits. Breezy conditions linger through the day Thursday keeping feels like temps only in the teens. High pressure gradually builds into the region late this week with warming trends possible by this weekend. MARINE... The deepening mid week low is now over Manitoba and still strengthening. The strong high to our south is now centered over TN/KY and the combination of the two system will act to strengthen the pressure gradient through this evening and overnight. This will result in the first round of Gales over Saginaw Bay and Central Lake Huron. The clipper then tracks across the northern Great Lakes Wednesday and Wednesday night, while pulling a cold front across the region Wednesday evening. This will flip the winds around to the northwest with quick intrusion of cold unstable air. We'll hold onto the Gale Watch Wednesday night and Thursday across all of Lake Huron and Lake St Clair through Thursday evening. Already issued Gale Warning for Lake Erie after coordinating with our neighboring office. Snow squalls will also be likely on Thursday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...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. Small Craft Advisory until 10 PM EST this evening for LHZ441>443. 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. && $$ AVIATION.....MR DISCUSSION...KDK MARINE.......DRK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.