907 FXUS63 KDTX 172001 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 301 PM EST Thu Nov 17 2022 .DISCUSSION... The east-northeast release of the Lake Michigan moisture plume well underway this afternoon, as low level flow solidifies from the southwest with the passage of a lead weaker shortwave. The accompanying uptick in both forced ascent and moisture quality/depth effectively capitalizing on a steeper lapse rate environment, maintaining a higher coverage of lake enhanced snow showers within a favored ENE trajectory largely along/north of M-59 at this stage. Minor accums prior to sunset as this process unfolds, mainly confined to grassy/elevated surfaces given ongoing diurnal influence to encourage melting. Attention into the late evening period turns to the stronger inbound shortwave now crossing lake Michigan. The underlying moisture and thermal profile established today only improves with time as associated mid level cold air advection commences, supporting a convective depth in excess of 7000 ft. This combined with the noted strengthening of mid level forcing with the passage of the wave itself points to maintenance of a scattered to numerous coverage of lake effect snow showers throughout the night. The degree of column instability lends concern for periods of higher snowfall rates within the more organized bands, lending to the possibility for brief squalls with rapid reduction in visibility and quick accumulation on pavement. No clear convergence signal to properly pinpoint a more specific trajectory, but a standard response in this scenario often shows initial activity lifting into I-69 corridor before gradually veering flow in the wake of the wave reorients convergence into the M-59/I-96 tier and possible down toward I-94. Outgoing forecast maintains a broader distribution for potential accumulation of a dusting to an inch within these aforementioned areas, while acknowledging the possible upper bound for accumulation within a more localized footprint could exceed a couple of inches given the underlying environment. Existing lower height anomaly will continue to govern conditions through the weekend. Associated well below average temperatures effectively reinforced overnight, leaving a thermal profile characterized by 850 mb temps of -12c Friday. Ongoing downstream lake Michigan moisture flux within prevailing deep layer westerly flow maintains a higher probability for continued lake effect snow shower production, with the more organized structures migrating across prone locations bound generally by I-94 and I-69. Recent guidance suggests greater ascent/convergence may tend to align across southern sections of this corridor /Metro Detroit/ early, before trending northward with time as flow backs once again. Accumulation potential again sensitive to latitudinal positioning, overall scale and duration of activity, with localized amounts in excess of an inch plausible. Daytime highs parked in the vicinity of freezing, with wind chill upper teens/lower 20s. One final mid level wave digging into the mean trough arrives late Saturday. Maintenance of cold southwest flow in advance of this feature offers a lingering chance of light lake effect snow Friday night into Saturday morning, trajectory favoring Flint northward. Another window of modest cold air advection this period will edge temperatures down another notch - highs in many locations Saturday holding in the 20s. A pronounced, but narrow corridor of forced ascent emerges along the advancing arctic cold front and associated height falls within the 21z-02z Saturday evening period. This process will effectively draw the lingering lake Michigan moisture plume back across the area. Steepening lapse rates with a cooler mid level profile will provide a solid increase in convective depth, with a saturated profile upwards of 7-8k ft deep firmly planted within the dendritic growth zone. Favorable setup for a band(s) of heavier snow showers or squalls to materialize during this time. Trailing cold cyclonic flow under strengthening thermal advection maintains light snow shower potential overnight into Sunday morning, before moisture depth gradually diminishes to finish the weekend. The reinforcing shot of arctic air ensures temperatures remain near 20 degrees below average through the remainder of the weekend. Overnight wind chill dipping into the single digits. Warming trend with a stretch of benign weather expected early next week. && .MARINE... Cold southwest flow underway today with strengthening low-level wind field which increases the likelihood of +25 knot gusts this evening and overnight. Portions of western Lake Erie and St. Clair have already logged gusts in excess of 25 knots, associated with a well- mixed marine boundary layer under cold advection. Added those zones to the Small Craft Advisory in spite of the lower wave heights. For the Huron nearshores, a period of occasional waves in the 5-7 foot range arises overnight and through most of the day Friday. Elevated waves likely continue into the weekend with an uptick in gusts warranting an eventual extension of Small Craft Advisories as a northern stream trough continues to encompass the Great Lakes before merging with the southern jet. As for the open waters, gusts to gales are possible Saturday and Sunday as 35-40 knot flow at 925 mb fixates overhead. && .PREV DISCUSSION... Issued at 1258 PM EST Thu Nov 17 2022 AVIATION... Periodic bursts of lake effect snow showers will continue impacting the airspace through the bulk of the TAF period, as low-level west/southwest flow and cold air aloft continue to promote a favorable release of Lake Michigan moisture downstream into the region. Earlier morning burst of fairly widespread region of lake effect snow showers that produced little to no accumulations, but IFR/MVFR flying conditions, will continue exiting east of the TAF sites through the remainder of the afternoon hours. Secondary release of moisture is ongoing east of KGRR and may brush KFNT and KMBS through 21z. More robust lake effect response looks to potentially occur in the 00z-04z timeframe as a potent midlevel wave tracks through, focusing bands of activity across much of the region, even brushing as far south as the Detroit terminals although highest concentration of activity will be KPTK north. This activity will have potential for LIFR and accumulations. Otherwise, additional periodic snow showers through the remainder of the night and into Friday with generally MVFR ceilings in place with prevailing gusty southwest flow up to 20-25 knots at times. For DTW...Morning round of snow showers will continue exiting east through 19z. Potential will exist for another round of lake effect snow showers between 01z-04z as northern activity attempts to drift south towards the terminal. This activity will have the potential to lead to up to half of an inch of accumulation if more robust activity can drift southward. DTW THRESHOLD PROBABILITIES... * High for ceiling 5000 ft or less through much of the period. * High for snow precipitation type through the entire period. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Small Craft Advisory from 6 PM this evening to 10 PM EST Friday for LHZ421-441-442. Lake St Clair...Small Craft Advisory until 10 PM EST Friday for LCZ460. Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EST Friday for LEZ444. && $$ DISCUSSION...MR MARINE.......KK AVIATION.....IRL You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.