FXUS63 KDTX 221043 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 543 AM EST Mon Jan 22 2018 .AVIATION... Favorable positioning north of a warm front will sustain the existing widespread low stratus and fog throughout the SE Michigan airspace during the late morning period. Recent observations indicate that pockets of rain now entering the region will bring some improvement to visibility, limiting the potential for additional dense fog where visibility drops below 1 mile. LIFR ceilings will remain common through this time. Improvement in conditions from south to north by early afternoon as the warm front lifts across the region. Upstream trends and recent model guidance continue to support a complete removal of low level moisture at least as far north as FNT. This will provide a window for VFR conditions as a mid level dry slot dictates conditions late today into early tonight. Greater potential for MBS to retain LIFR conditions throughout the daylight period, with the warm front struggle to reach this far north. Low level moisture will increase all locations upon the arrival of a cold front by early Tuesday morning. This will bring a corresponding reduction in ceiling height and a renewed increase in precipitation potential. For DTW...Existing LIFR conditions in low ceiling and dense fog will see slow improvement during the late morning period as intermittent rainfall lifts through. Much greater improvement then expected this afternoon in the wake of warm frontal passage. Window for cigs to lift above 5000 ft for the latter half of the day. /DTW THRESHOLD PROBABILITIES... * High for ceiling 5000 ft or less this morning. Low this afternoon. * High for rain as precipitation type today and tonight. && .PREV DISCUSSION... Issued at 347 AM EST Mon Jan 22 2018 DISCUSSION... Early morning fog will persist several more hours until a warm front lifts north and showers fill in across the area. Overall visibilities have improved over the last few hours with only sporadic 1/4SM observations being noted across SE MI. Though fog will remain across the area for several hours, only locally dense fog is expected here on out, thus the headline will expire at 4am and we'll handle any brief pockets of dense fog with SPSs. Active stretch of weather to start the new work week as a dynamic and very mature low/mid level low over the plains continues it's march toward the Great Lakes. Models in good agreement with the center of the low tracking through mid MI late tonight into Tuesday morning. Several rounds of rain showers will pass through the region associated with this low and the several fronts connected to it. Timing these periods of showers and possible dry slots seems to be one of the biggest forecast challenges early on. Model soundings show temperatures above freezing across all of SE MI up through about 700mb keeping ptype all liquid through Tuesday morning. In advance of the low, the lead wings of isentropic ascent along a warm front, current draped just south of the MI border, will provide the first round of rain showers this morning. The band of showers has already come together as seen on regional radar mosaic and should lift into the state by about 09Z. Strong low level jet starting to nose into SW lower MI should keep this band progressive lifting it north of the M59 corridor by 17Z as the warm front itself pushes north. Good moisture and forcing should allow a quick quarter inch of qpf with this band as it lifts through. Models vary with handling the pops during the daytime hours as it appears there is 2 distinct dry slots rotating about the low. First one is lifting northward just ahead of the first cold front and could clip the metro Detroit area this afternoon from about 17-20Z. Coverage of showers will decrease but still could see some scattered light showers. The cold front them moves through and is losing its definition due to occluding processes and distance from the low. Still should see a second batch of showers pass east through the area after 20Z. Meanwhile, with the warm front stalling over mid MI the east west oriented isentropic band could stall across the Saginaw Valley and Thumb leading to rain through most of the day. The next dry slot then looks to lift up and through southern MI between about 00-06Z Tuesday ahead of the secondary cold front located much closer to the low. Water vapor imagery shows this dry slot very well so the only question is do showers start bubbling up and filling back into the dry slot as its sliding though? In terms of the forecast, will recognize the dry slots with chance pops and highlight the frontal bands with likely or categorical pops. The center of the low and mid level PV max will keep at least scattered showers around through the rest of the night. Northwesterly winds on the backside of the low will usher in a colder airmass but still plenty of moisture to work with as the deformation band passes through on Tuesday. We will be dealing with a cooling boundary layer which could bring about a mix of rain and snow later in the day. At this point still expecting any snow accumulations to be on the light side as change over won't occur til waning hours of the event late Tuesday evening. Event total rainfall amounts should range from around a half inch near the Ohio border to around 1 inch north of I69. This much rainfall over frozen ground with recent snow melt could cause some flooding concerns. Look for area rivers to rise with runoff and ponding in low lying areas also seems quite probable. Quiet weather returns through the mid/late week as ridging builds into the region. Temps will fall back to late January normals with highs around freezing and lows in the 20s. Models advertising the next system to arrive over the weekend. Model consensus currently points toward another warm event across lower MI as the surface low is north of the area pulling warm air back up through the region. MARINE... Low pressure will track toward the central Great Lakes today and tonight, reaching the central Lake Huron waters by Tuesday morning. Easterly winds will strengthen today as this system approaching, leading to a period of gales over the north half of Lake Huron this afternoon and evening. The system will also produce widespread coverage of precipitation, primarily rain from Saginaw Bay southward and a wintry mix to the north. Wind will diminish as the low moves through central Lake Huron overnight and Tuesday. Northwest wind trailing the system could approach gales briefly Tuesday afternoon and evening. Winds will ease by Wednesday as weak high pressure builds into the region. HYDROLOGY... Mild and moist conditions across the region will result in periodic bouts of rainfall through the daylight period. This environment will also work to to melt any remaining snow cover while the ground remains mostly frozen. Efficient runoff from both the melting snow and rainfall could result in ponding of water on roads and other prone areas. Rivers, creeks and streams around the region could also become elevated due to runoff. Total rainfall is expected to be around 1 inch through Monday night, with most falling during the day. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Gale Warning from 10 AM this morning to 10 PM EST this evening for LHZ361>363. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....MR DISCUSSION...DRK MARINE.......MR HYDROLOGY....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.