956 FXUS63 KDTX 311715 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 115 PM EDT Sat Jul 31 2021 .AVIATION... VFR conditions will continue to hold well into the evening as high pressure pushes away from the region. Southwest flow has developed with winds generally 10 kts or less. Diurnal cumulus will mainly be scattered over the Detroit area TAF sites. Otherwise, several bands of mid cloud (12k ft or higher) will rotate across Lower Michigan this afternoon and evening. A cold front will move through Southeast Lower MI late tonight and early Sunday morning. Will have tempo thunderstorms for MBS to PTK with PROB30 shower chances for Detroit as the convection will be weakening. In the wake of the front, the rest of Sunday morning will be characterized by a broken MVFR cumulus deck with a NNW wind around 10-15 kts. .DTW THRESHOLD PROBABILITIES... * Low for ceiling at or below 5000 ft this afternoon and evening...medium by early Sunday morning. * Low for thunderstorms from 10z to 15z Sunday. && .PREV DISCUSSION... Issued at 322 AM EDT Sat Jul 31 2021 DISCUSSION... High pressure over the southern Great Lakes continues to slide to the southeast today ahead of an approaching shortwave dropping out of northern Ontario. For the southern half of the CWA, forecast remains the same of dry weather holding through daytime today. For the northern half (north of I-69), its now looking that the region will stay dry through the evening, with the possible exception of the very tip of the Thumb who could get clipped by showers and storms around/after 00Z. There is good consensus across models (GFS, NAM, Euro, RAP, Canadian) of the Ontario shortwave taking longer to advance into the central Great Lakes as well as its track being further to the north and east keeping the vast majority of precip out over Lake Huron. Aside from the delay in PoPs moving into SE MI, the slower track also delays the ribbon of higher theta-e getting folded into the region from northern Michigan until the late evening/overnight period. The primary cold front swings across southern MI late tonight into Sunday morning bringing scattered to widespread showers and storms for all of southeastern Michigan. A secondary cold front accompanied by a PV packet rounding the upper trough then swings through the area the second half of the day Sunday maintaining lingering scattered showers. Low pressure and supporting jet streak pushes further into the eastern Great Lakes early Sunday night resulting in increasing upper-level confluence locally, due to left entrance region dynamics, which quickly brings precip chances to an end. A large weak surface high over the upper Midwest then builds into southern MI Sunday night into Monday. This high drifts east settling over lower MI by Tuesday and stays overhead through the midweek period. Upper flow pattern over the east-central portions of the US is dominated by a large amplitude trough that digs all the way into the southern Tennessee Valley. As a result, there is no major changes in the resident airmass with 850mb temps holding around 11- 13C for the first half of the week. High temps for this period stay slightly below average in the upper 70s to low 80s. Longer range solutions begin to break down/deamplify troughing by the end of the work week leading to a gradual increase in temperatures back to normal as well as a dewpoints creeping back into the 60s. MARINE... High pressure will slide further southeast towards the Mid-Atlantic region today as a northern stream disturbance moves into the northern Great Lakes along with an attendant surface cold front. These features will bring an increasing chance for showers and thunderstorms, especially to the northern half of the local waters during the day Saturday, and eventually the southern half of the local waters Saturday night into early Sunday morning as the front sags south through the region. Winds will also flip to the southwest ahead of the front and strengthen, but gusts will generally remain under 25 knots. Colder air aloft will increase the temperature difference between the warm lake waters leading to a potential for waterspouts as well Sunday morning into Sunday afternoon, especially across the southern half of the Lake Huron waters. Drier weather accompanying building high pressure across the upper Midwest and Great Lakes will then prevail for early next week with light to moderate northerly flow Monday turning southwesterly by the middle of next week. HYDROLOGY... Dry weather persists through this evening for most of the area before a compact low slides across the northern Great Lakes. Heavier rain potential is focused over areas north of I-69 where scattered showers and storms will be possible from late this evening into Sunday morning. Track of the low has trended further north and east which keeps the bulk of heaviest rain to the north over Lake Huron leading to forecast areawide rainfall amounts up to around 0.5 inches north of I-69 (best chances for these higher totals still looking to be over the Thumb). Locally higher amounts between 1-2 inches will be possible in those areas, dependent on track and speed of any thunderstorms. This could lead to minor flooding in creeks or poor drainage areas but overall flooding concerns have trended down. Additional scattered showers are possible over SE MI through daytime Sunday however accumulations are expected to be light (less than 0.25"). && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....RBP DISCUSSION...KDK MARINE.......IRL HYDROLOGY....KDK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.