Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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682 FXUS63 KDTX 210936 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 436 AM EST Sat Jan 21 2017 .AVIATION... VLIFR vsbys firmly in place north of a warm front positioned immediately to the south. High confidence in improving vsbys as the front lifts north. However, warm sector inversion combined with the potential for some added moisture flux off of Lakes Erie and Saint Clair casts doubt on cigs improving beyond IFR during peak heating, especially in the Detroit area. Allowed for some brief improvement in cigs to low MVFR in the wake of the warm front for KMBS/KFNT. Similar conditions redevelop tonight, thus the inclusion of 1/4SM FG at all locations. Stratus/FG encroaching off the lakes will warrant watching through the evening for potential timing adjustments. For DTW...Window for potential breakout in the afternoon is diminishing as confidence increases in SE flow off the water. IFR could easily plague the area through the day even if other locations clear out. Elected to retain BKN006 as a result. //DTW Threshold Probabilities... * High for cigs aob 5kft * High for cig/vsbys aob 200ft and 1/4SM tonight. && .PREV DISCUSSION... Issued at 353 AM EST Sat Jan 21 2017 DISCUSSION... Conditions remain favorable for widespread dense fog due to the exceptionally mild and moist air mass in place over the region. These conditions will only be reinforced during the morning as a warm from moves in with a mixture of drizzle and rain showers. The dense fog advisory remains in effect through 10 AM before some improvement is expected south to north through the region, possibly as early as mid morning near the Ohio border. This will be aided by temperatures making a run into the lower and mid 50s most locations during the afternoon, but given this mild and moist air mass, fog will likely develop and thicken again tonight. Early morning satellite imagery indicates an upper level circulation moving northward through the Midwest with a weak reflection in the broad surface trough through the Plains. This system is strengthening the warm front that extends eastward through northern Indiana and Ohio before sunrise and will pull it northward into Lower Michigan during the morning. The result will be a modest increase in the pressure gradient that will produce light southeast wind over the region and introduce an advective component to fog and drizzle maintenance through the diurnal minimum. Surface dewpoint ranges from the lower 30s in the Saginaw Valley to mid 40s near the Ohio border at press time which will develop northward with the front. Corresponding low level theta-e advection will also support scattered rain showers which will be just a cosmetic concern. The surface low is projected in model solutions to reach SE Minnesota by mid afternoon, far enough north to pull the warm front into central Lower Michigan. This may not be far enough north to scour the fog from the Tri Cities and northern Thumb and an extension of the advisory may be required there. The warm sector of the system should make it to the I-69 corridor by late in the day with enough of a mixed layer to produce broken low cloud coverage from there south and bring in the lower to mid 50s surface temps. The low pressure system is then shown to move north of Lake Superior tonight and leave a 1000-850 mb thickness gradient over Lower Michigan as the surface pressure gradient flattens out again between it and the next low pressure system moving through the southern Plains. Rich boundary layer moisture will be left behind judging by surface dewpoint in the upper 40s to possibly lower 50s indicated in some of the mesoscale model output. Modest coverage of mid and high clouds will expose the boundary layer to radiational cooling and open the door for redevelopment of fog during the evening through Sunday morning. That southern Plains system will be the remains of the current Pacific coast upper trough. It will be driven inland by a new round of long wave trough development over the eastern Pacific and will become take more of center stage in the forecast for the Great Lakes during Sunday. The 00Z model package still shows some spread in the position of the system but depicts a general northward trend Sunday into Sunday night, at least in terms of the northern fringe of the precipitation pattern. This appears reasonable as there will be an upper level trough connection to the northern stream that has potential to set up an energetic deformation pattern over the Great Lakes. The good news here is that the system will interact with the still mild thermal pattern over the region. It won`t be as warm as today with readings limited to the 40s by increasing easterly surface wind but will be warm enough to maintain an all liquid precipitation type through Sunday night and even into Monday. Not until Monday night does enough cold air get drawn in from eastern Canada for a rain/snow mix before the system exits eastward by Tuesday. The break in the action will be short as the next low pressure system is set to arrive in the Great Lakes by Wednesday. Global model solutions project a track through the central Great Lakes and another round of mixed precipitation for SE Michigan. Above normal temperatures through mid week then take a turn down to readings more typical for late January for the end of the week into next weekend. MARINE... Dense fog will impact the waters through at least Sunday morning, though clearing is possible for Lakes Saint Clair and the Michigan waters of Lake Erie during the daytime hours today. Dense fog advisories are now in effect for all marine zones. Winds and waves will remain quiet until late Sunday when strengthening low pressure well to the south will bring a period of fresh easterlies that will persist well into Monday. Onshore flow will build waves toward small craft advisory criteria during this time...conditional on ice cover as usual. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Dense Fog Advisory until 10 AM EST this morning FOR MIZ047>049- 053>055-060>063-068>070-075-076-082-083. Lake Huron...Dense Fog Advisory until 10 AM EST Sunday FOR LHZ421-422-441>443- 462>464. Dense Fog Advisory from 1 PM this afternoon to 10 AM EST Sunday FOR LHZ361>363. Lake St Clair...Dense Fog Advisory until 10 AM EST this morning FOR LCZ460. Michigan waters of Lake Erie...Dense Fog Advisory until 10 AM EST this morning FOR LEZ444. && $$ AVIATION.....JVC DISCUSSION...BT MARINE.......JVC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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