Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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421 FXUS63 KDTX 211859 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 259 PM EDT FRI OCT 21 2016 .DISCUSSION... Overcast stratus is firmly in place over the area in response to the intrusion of a seasonably cool airmass today. Temperatures have responded relatively little, about 5 degrees or less, since this morning`s lows. Lake effect showers are underway beneath the upper trough which is currently directly overhead and will persist, along with the stratus, through the early evening. Deepening low pressure off the New England coast and high pressure being forced east downstream of a deepening Aleutian low will force winds to back to northwesterly prior to midnight. In addition to causing lake showers to pivot toward the eastern Thumb between about 21-03z, backing wind will disrupt the northerly fetch likely leading to some breakup of clouds during the latter half of the night. The gradient alone will be sufficient to prevent frost except on an isolated basis, but temperatures will still fall into the low to mid 30s in most areas per most guidance. Superior-Michigan stratocu may work into the area by early Saturday morning, but warm advection, backing flow, and increasingly anticyclonic flow through the boundary layer will ensure erosion of any lingering lake cloud through the morning hours. However, steep lapse rates in the presence of sufficient moisture will still support a partial coverage of diurnal component through the day. Increased insolation should support at least a 4-5 degree moderation of temps compared to today. Clipper is progged to sweep across the area on Sunday, the large upper low over Quebec acting as a wave guide. This compact feature will be subject to track adjustments, but it does appear that it will be impressive dynamically. Warm advection ahead of it will force double digit 850mb temps to lift into the area supportive of highs in the low 60s on Sunday. Specific humidity of 3-4 g/kg will be adequate in the presence of such forcing to support showers within a band of enhanced fgen and quick-hitting deformation on the back side. Confidence in track will likely increase after the rapid deepening of downstream low pressure gets underway. Highs fall back into the 50s in its wake. The start of the work week will be dry and cool as high pressure builds over the region through Tuesday. As a shortwave approaches the region midweek, expect milder conditions and increasing chances for precipitation. The best chance for precipitation will occur Wednesday night and Thursday as a warm front lifts slowly through southern Michigan followed by the trailing cold front on Thursday. After the passage of the shortwave, northwesterly flow will remain in place through the end of the period with cooler and unsettled conditions through the end of the week. && .MARINE... Marine observations indicate northerly winds gusting in the 25 to 30 knot range, supporting small craft advisory conditions across southern Lake Huron and Saginaw Bay. Low pressure off the East Coast is forecast to deepen as it lifts into New England tonight into Saturday. Winds will back toward the northwest tonight, but this strengthening of the New England low pressure system will support continued gusty winds across the lakes through Saturday night. Wind gusts across southern Lake Huron will reach 30 knots at times. Winds will decrease by Sunday as the gradient finally relaxes across the region. This will be brief however as another push of cold air will support a reintesification of the northwest winds by Monday. && .PREV DISCUSSION... Issued at 1250 PM EDT Fri OCT 21 2016 AVIATION... Ongoing low level cold air advection will sustain a deep low level inversion through the day. The flux of moisture off Lake Huron within the N-NE flow is supplying ample cloud cover to the region. Given slightly rising inversion heights, cloud bases will trend slightly upward during the afternoon and evening. There will however continue to be areas of MVFR based clouds within more organized lake bands, impacting mainly FNT and PTK. The low level flow will back slightly toward the N-NW this evening into the overnight. This will cut off the lake connection to Central Lower Mi and will allow an opportunity for clearing to overspread much of SE MI inland from Lake Huron. There is still uncertainty as to the extent and timing of this clearing. The ongoing expansion of clouds suggests perhaps a late evening clearing. For DTW...Recent observations have shown a trend toward a more northerly wind direction (350-360 deg). The well mixed boundary layer will support gusts up around the 20 knot range during the afternoon. The loss of daytime heating this evening (21-23Z) will result in a decrease in wind speed and a backing of the wind toward the NW. //DTW Threshold Probabilities... * Moderate in ceilings below 5000 ft this afternoon and evening. Low overnight and Sat morning. Moderate Saturday afternoon. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Small Craft Advisory until 4 AM EDT Sunday FOR LHZ441>443. Small Craft Advisory until 10 PM EDT Saturday FOR LHZ421-422. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...JVC/JD MARINE.......SC AVIATION.....SC You can obtain your latest National Weather Service forecasts online at is the U.S. government's official web portal to all federal, state and local government web resources and services.