418 FXUS63 KDTX 070807 CCA AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 327 AM EDT Tue May 7 2019 .DISCUSSION... Widespread showers centered along/around the M-59 corridor with the 850 MB FGEN will slowly wane toward noon as subtle 500 MB trough axis slides east after 12z Tuesday and westerly upper level confluent flow results in anti-cyclonic flow/large surface high (1028+ MB) to build into the Central Great Lake through this evening. This will set the stage for a cold night as temperatures fall from the daytime highs in the 50s, with locations north of M-59 dipping into the 30s, while clouds south of M-59 due to the close proximity of the frontal boundary over the northern Ohio Valley should hold temps in the lower 40s. In fact, with increasing 850 MB southerly flow south of the border and pocket of instability/negative showalter indices across the northern Ohio Valley, will be carrying chance pops along/south of I-94 for possible weakening convection bleeding over. Upper level wave just south of Las Vegas this morning with the upper level jet energy diving south through the northern Rockies will help direct the southern wave off to the northeast through the Midwest Wednesday night, becoming absorbed within the large scale positive tilted northern stream trough tracking through central Canada/Plains on Thursday. Max height fall center tracking through the western Great Lakes with corresponding stellar 850-700 MB FGEN displaced to the northwest of southeast Michigan during the Wednesday-Thursday time frame, and thus bulk of heavy rain expected to miss southeast Michigan. None-the-less, PW values increasing to around 1.5 inches Thursday morning will lead to heavy downpours with any convection which develops. GFS-FV3 and Euro both showing low pressure tracking through central Lake Michigan and into northern Lower Michigan toward Thursday evening. Southeast Michigan will attempt to get into the warm sector, with cold front then tracking through during the evening hours. It looks like it will be a messy/uncapped warm sector, with clouds and likely showers persisting through the day on Thursday, limiting instability. It also appears 1000-850 MB capes of 250-500 J/kg will be possible. Close proximity of low/warm front will offer up 0-1 KM bulk shear on the order of 25+ knots which could support rotation, mainly north of I-69. Otherwise there looks to be healthy 35 knot flow at 850 MB and 50+ knots at 500 MB. However, with limited instability, a marginal/isolated severe threat will likely be the greatest extent of it, as moisture axis should get pinched off as convection erupts across the Mid-Southern Mississippi River Valley during Thursday. SPC day 3 outlook offering up just general thunder based on the limited instability making it into the state of Michigan. Good shot of cold air to follow the low pressure system for Friday, as 850 MB temps lower to zero or slightly below (per Euro), capping maxes in the 55-60 degree range with breezy conditions. Winds die off Friday night as surface high arrives, setting the stage for areas of frost as temps drop into the 30s. && .MARINE... There will be a gradual weakening of the post frontal north- northeast winds today as high pressure expands into the area from the north. As the high pressure drifts off to the east tonight into Wednesday and a warm front over the Ohio Valley begins to lift north, there will be a steady increase in the east-southeast gradient across the Great Lakes, especially the southern Great Lakes. By Wednesday afternoon, there is high probabilities that the easterly wind gusts will exceed 25 knots. This will support hazardous conditions to small craft. Low pressure is forecast to traverse Lower Mi on Thursday. This will result in strengthening easterly winds across northern Lake Huron, with gusts possibly topping 30 knots. The forecast track of the low suggests winds on Lake St Clair and Erie will veer to the south on Thursday. The low will exit to the northeast Thursday night, with a weakening gradient in its wake allowing winds and waves to decrease by Friday. && .HYDROLOGY... Showers will prevail through the first half of today generally south of the I-69 corridor. These showers are occurring within an elevated frontal boundary draped across srn Lower Mi. Total rainfall amounts from these showers will remain below a quarter inch, which will have little overall hydrologic impacts across Se Mi. This frontal boundary will slowly push south of the area during the course of the day, briefly resulting in drier conditions to Se Mi. The approach of a low pressure system will drive the front back north on Wednesday. This and the influx of deep moisture will allow for numerous showers to develop in the Wednesday to Thursday morning time frame. Low pressure will then lift into the region on Thursday. The instability associated with this system will trigger showers and a few thunderstorms. Overall, there is high a probability that two day rainfall totals will be around an inch. Given the potential for heavier convective rainfall, locally higher totals are certainly possible. This will pose the risk of some flooding along area rivers. The approach of the low pressure system and associated warm front Wednesday into Wednesday night will lead to strengthening east- southeast winds along the Great Lakes. This and the very high lake levels suggests lakeshore flooding is likely, especially along the shoreline of Lakes St Clair and Erie. && .PREV DISCUSSION... Issued at 1205 AM EDT Tue May 7 2019 AVIATION... A band of MVFR ceiling trailing the surface front begins to expand toward the Ohio border while clearing the MBS area during the night. The expansion is part of the southward drift of the front and also enhanced by showers increasing coverage and supplying moisture to the nocturnally cooled boundary layer. This results in MVFR lasting through the morning over the DTW corridor before improvement begins as showers decrease in coverage. Improvement is helped by dry air as it gains traction on NE low level wind which moves MVFR south of DTW during the afternoon and brings a clearing trend southward from MBS into Tuesday evening. For DTW... Ceiling continues a transition to VFR as showers increase coverage from the west and last through Tuesday morning. The best chance of thunderstorms is along toward the Ohio border, along and just north of the cold front. There will be some elevated potential north of the front across the DTW corridor however coverage and duration appear too limited for inclusion in the TAF. This will be monitored for later updates. DTW THRESHOLD PROBABILITIES... * High for ceiling below 5000 ft late tonight through mid afternoon. * Low for thunderstorms tonight. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...SF MARINE.......SC HYDROLOGY....SC AVIATION.....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.