Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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911 FXUS63 KDTX 181221 CCA AFDDTX Area Forecast Discussion...CORRECTED National Weather Service Detroit/Pontiac MI 821 AM EDT Sat May 18 2024 .KEY MESSAGES... - Patchy fog, locally dense at times, rapidly improves after sunrise. - An Air Quality Adviosry is in effect for portions of Southeast Michigan, including Metro Detroit. - Warm and muggy conditions continue through early next week. Chance (35-40 percent) for showers and thunderstorms Sunday afternoon and evening. && .AVIATION... LIFR stratus and visibility restrictions that periodically range between 1/2 mile to 2 miles will lift and dissipate between 12Z-14Z, leading to VFR conditions thereafter. Winds will remain light under 10 knots from the southeast, veering more south to southwest later this afternoon and evening. For DTW/D21 Convection...Thunderstorms are not expected during this forecast period. DTW THRESHOLD PROBABILITIES... * High for ceilings aob 5kft this morning. * Low for ceilings and visibilities to drop below 200ft or 1/2SM through 14Z. && .PREV DISCUSSION... Issued at 333 AM EDT Sat May 18 2024 DISCUSSION... The culmination of the past 24 hours of precipitation accumulation coupled with a surge of very shallow low level moisture coming off the Great Lakes have resulted in extensive low-level stratus and areas of dense fog across portions of SE MI. Both fog and cloud coverage will quickly dissipate after sunrise once the mid-May sun angle works to lift cloud depths and mix out the moisture. Some scattered cu will likely re-form in the wake of the stratus, but clearing trends will allow temperature trends to or above the 80 degree mark, outside of the immediate nearshore locations. Cannot completely rule out a fleeting diurnally fueled shower, but very limited instability and weak kinematics support dry conditions for most locations. A series of upper-level waves will travel across the northern and central Plains through the weekend and into early next week while a secondary upper-level trough builds in through the Tennessee Valley by this afternoon. This will enhance ridging across the Great Lakes and will pool in warm air from the continental SW into Michigan, characterized by h850 values between 14-16C. This will support daytime highs in the 80s Sun - Tue, likely pushing into the mid-80s. Warm overnight lows will also accompany the warming trend given the constant stream of warm air advection. Overnight lows in the mid 60s are likely Tuesday morning and Wednesday morning. There will be multiple chances for showers and thunderstorms during this warm stretch, with PoPs increasing by the mid-week period. The notable change for the near-term will be increasing PoP chances for showers and thunderstorms for tomorrow afternoon and evening. Surface based instability will return on Sunday under the warm and moist airmass with CAPE building up to 1,500 J/kg. There will be a cold front that washes out across central Michigan by Sunday afternoon which will be one possible point of CI, mainly over the Tri-Cities, but the most probable focal point for initiation will be multiple lake breezes that push inland off of Huron/St.Clair/Erie accounting for the large surface deltaT. Surface convergence can capitalize on the building instability, bringing the chance (35-40%) for showers and thunderstorms. The limiting factor will be the meager deep layer shear values with 1-6 km shear holding aob 15 knots. Convective mode will be pulse thunderstorms. Strong 0-3 km lapse rates around 9 C/km, DCAPE aoa 1000 J/kg, and PW values above 1" will bring the chance to see heavy downpours with highly localized wind gusts up to 45-50 mph with the more vigorous activity. Weak mean boundary layer flow will be favorable for outflow boundaries, which can also support renewed neighboring t-storm development. Showers and storm chances wane after sunset with the loss of daytime heating. Upper-level waves riding within the longwave ridge will bring the additional chance for showers and storms Monday afternoon and evening and again for Tuesday, most favorable over the northern half of the cwa where the best moisture axis resides. The upper-level trough will amplify across pacific west early next week, while a potent mid-level wave derived around Baja California targets the Texas Panhandle, which will strengthen a weak surface low and drive it northeast into the western Midwest and up towards the northern Great Lakes. The EPS and NAEFS both show excellent agreement regarding cyclone centers holding northeast of the cwa which will push a cold front across SE MI likely on Wednesday. This will provide another chance for showers and storms, and pending the timing of the front, could bring strong to severe thunderstorm potential as 0-6 km shear values increase to 35-40 knots. A daytime passage would be more favorable for stronger storms. Cooler temperatures filter in behind the front, dropping temperatures back into the 70s by the late week period. MARINE... Showers in the area as a high pressure system briefly takes control today. Moist profile and southeasterly winds around 5-10 knots through the day today allow for areas of fog over Lake Huron to stick around into the early afternoon. A dense fog advisory is in effect for Lake Huron, and may need to be expanded into Lake St. Clair and western Lake Erie. Benign and predominantly southerly winds persist through the rest of the weekend into Sunday, where a shortwave brings the next low pressure system across to the north. The system will drag a cold front across the region Sunday with no inclement weather expected, before giving way to a second disturbance behind it. This second disturbance brings chances for showers and storms, but aside from inside any such storms, winds and waves are expected to remain below SCA criteria at this time. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Dense Fog Advisory until 4 PM EDT this afternoon for LHZ361>363- 441>443-462>464. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....AM DISCUSSION...AM MARINE.......BC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.