070 FXUS63 KDTX 091924 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 324 PM EDT Tue Oct 9 2018 .DISCUSSION... Record warm and moist airmass in place (5 C dew pt at 700 MB), although the upper level ridge off the East Coast is starting to slowly weaken. Based off the low temperatures this morning (DTW 67, FNT 67, MBS 66), all 3 climate sites should set record high minimum temperature values for the Date (Oct 09), as temperatures likely only fall to around 70 degrees by Midnight. This is in addition to the record high temperatures set (MBS 85) or tied today (DTW 86 as of 3 PM). Diurnal instability (MLCAPES 1000-1500 J/kg per SPC mesoscale analysis) has been sufficient to generate scattered showers/isolated thunderstorms, most concentrated along/north of I- 69 with the strip of higher 850-700 Theta-E. A slow wane to the activity expected with the lose of the daytime heat, with mainly dry forecast for tonight. Highly amplified upper level pattern over north America has allowed for this record setting airmass, with trough encompassing the entire Rockies, and off course Hurricane Micheal in the Gulf of Mexico. Upper level energy/slightly negative tilted trough axis ejecting out of the Four Corners region will lead to cyclogensis taking place over the Midwest this evening, with a slowly deepening low over the Western Great Lakes tomorrow, and over the northern Great Lakes tomorrow night. One more renewed surge of deep moisture arriving late tomorrow ahead of the cold front, pushing PW Values to around 2 inches. Increasing wind fields through the day, with low level jet exceeding 40 knots by early evening will bring the potential for severe storms. However, instability looks to be on the low end, as the mid levels are warm in this departing tropical airmass (7 C at 700 MB). MLcapes under 800 J/kg suggests just a marginal risk at this time, but 0-1 KM bulk shear aoa 30 knots also allows for the possibility of a tornado, although not convinced the surface winds will be backed enough. Not to mention, widespread rain shower activity could possibly develop with the moisture advection/isentropic ascent during the early afternoon (see 12z Euro), which would squash what little instability develops by the time, before the better wind fields arrive. Cold frontal passage looks to be in the 8-11z Thursday time frame. Excellent drying/subsidence indicated, along with the impressive low level cold advection. Looks like enough moisture around at 925 MB level to support considerable cloud cover during the day. If skies do go partly cloudy for an extended period, the cold pool (negative 850 MB temps) crossing Lake Michigan should allow for low cloud development with steep low level lapse rates. Isolated showers are not even out of the question, especially across the northern Thumb region with Lake Superior-Michigan-Saginaw Bay connection/trajectory. Amount of clouds around Thursday night muddles the Frost/Freeze concerns, but mins at least down into the upper 30s are likely, with decent potential to go colder with clearing skies. Broad surface high pressure will begin to drift out of the northern plains and into the Midwest on Friday and Saturday. This will bring much colder and drier air over the region with 850 mb temperatures dropping to around -3C to -5C on Friday into Saturday morning. This will keep high temperatures on Friday in the upper 40s and low 50s and a fair amount of clouds coming off the lakes with cool west to northwesterly flow. Temperatures overnight Friday into Saturday morning will dip into the mid to lower 30s for much of the southeast Michigan resulting a good chance to see frost in the coldest locations. Southwesterly return flow on Sunday will kick in Sunday as surface high drifts further east while a southern stream wave is drawn northward and a trough across Ontario drives a cold front through Michigan. This will result in a return of rain chances Sunday, which will continue into Monday. && .MARINE... Southerly flow across the eastern lakes will prevail through the overnight as a strong cold front remains positioned to the west of the area. Only caveat to that would be across the northern Lake Huron basin where winds will flip to the northeast as a warm front sags south tonight. Front will lift back north on Wednesday as the low pressure system approaches. Pressure gradient will also increase as the low pulls the cold front closer. Stable conditions over the water will keep winds limited to around 20 to 25 knots through Wednesday evening but gusts will increase further while becoming southwesterly with the cold front late Wednesday night. The cold advection added to the tight gradient will likely lead to hazardous small craft conditions and possibly gales on Thursday. && .HYDROLOGY... Widespread showers and thunderstorms are expected late Wednesday afternoon into Wednesday night ahead of a cold front. Total rainfall amounts between a half of an inch and an inch appear likely. Locally higher amounts are possible, conditional upon the extent of thunderstorm activity. The lack of more widespread rainfall for a couple days prior to this frontal passage will allow river levels to continue to drop. So forecast rain amounts with this next system to not suggest river flooding concerns. && .PREV DISCUSSION... Issued at 122 PM EDT Tue Oct 9 2018 AVIATION... CU field popping up across the area as afternoon instability continues to rise. Hires models still indicate any shower or thunderstorm coverage to be fairly widespread thus will hold onto the vicinity mention this afternoon. Best chance of precipitation will be across MBS. VFR then through the overnight with only high clouds to speak of. CIGS will lower tomorrow as cloud field expands ahead of an approaching cold front. Winds will remain southerly through the taf period. For DTW...Hires models continue to suggest the best window of opportunity for convection to impact metro is between 20Z and 23Z, with the chances a little higher just to the north of metro (closer to PTK and points north). DTW THRESHOLD PROBABILITIES... * Moderate in ceilings at or below 5000 ft late this afternoon and evening. * Moderate in thunderstorms within the Detroit area late this afternoon and early this evening. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...SF/AA MARINE.......DRK HYDROLOGY....DRK AVIATION.....DRK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.