Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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011 FXUS63 KDTX 210803 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 403 AM EDT Sun Jul 21 2024 .KEY MESSAGES... * Low coverage of showers and isolated thunderstorms each afternoon today through Tuesday. * Widespread showers and thunderstorms arrive Wednesday. && .DISCUSSION... A weak cold front will settle southward into central Lower Michigan by around sunrise this morning. There is enough moisture along this front supporting corridor of mid clouds that will move into northern portions of the forecast area during the early morning hours. A closed mid/upper low pressure will also be meandering over the mid Mississippi River Valley throughout today and be responsible for weak mid level vorticity advection into the central Great Lakes. Lower level flow will be weak as clear anticyclonic flow is depicted at 850 mb moving across lower Michigan this afternoon which will greatly limit deep layer shear across southeast Michigan. Dewpoints in the 60s dewpoints into central Lower Michigan will support increasing instability into the afternoon with models showing MLCAPE values to around 1000 J/kg closer to the the frontal zone north of I- 69. The weak lift with a weakly capped unstable environment will support isolated to scattered showers and thunderstorms during the mid to late afternoon period today. Convection will be of the weaker pop up variety given very limited shear. Most activity will be focused across the Tri-Cities and Thumb, but some isolated showers and thunderstorms will also be possible down to near the M-59 corridor. A chance for isolated to scattered showers and thunderstorms exists on Monday as the aforementioned trough lifts into southern Great Lakes providing some weak forcing. Diurnal instability builds again to 1000 J/kg or greater helping to support the isolated thunderstorm chances during the afternoon. Similar to today, there will be an lack of deep layer shear bringing a pulse type storm mode again. Models point towards the best instability and CAPE depth focused along the glacial ridge up towards the Tri-Cities. Monday`s shortwave trough eventually gets absorbed into the mean flow of the Canadian trough and southern stream jet by Tuesday as another round of height falls drops out of Ontario. Favorable timing of this shortwave with building diurnal instability will bring another chance of pop up showers and isolated thunderstorms Tuesday afternoon. Tuesday will have greater coverage of 20-30% PoPs across southeast Michigan. Wednesday will see a stronger trough swing into the Great Lakes and drive a cold front through southeast Michigan bringing likely widespread convection. Slight increase in overall flow will increase wind shear to 30-40 knots and instability will be sufficient with MLCAPE up to 1000-1500 J/kg. Cooler temperatures aloft will also increase mid level lapse rates to 6-6.5 C/km. All of this will be supportive of more organized convection. Lower end PoPs (20%) linger on Thursday afternoon, but a more progressive wave may bring and end to PoPs earlier. High pressure builds into the region Friday and Saturday resulting in dry conditions. && .MARINE... A weak cold frontal boundary gradually sags through the central Great Lakes today through Tuesday supporting scattered shower and thunderstorm chances focused in the afternoon-evening each day. Winds shift to N-NE behind this front though speeds remain light at or below 10kts. Wider spread shower/storm chances don`t arrive until midweek when a trough dives out of Canada into the Great Lakes. && .PREV DISCUSSION... Issued at 1139 PM EDT Sat Jul 20 2024 AVIATION... A weak cold front will drop into Se Mi from the north on Sunday. Low level moisture pooling along this boundary will be supportive of the development of a broken cu field 4-6k feet by Sun afternoon. Weak to moderate instability will develop Sunday afternoon within the moisture pooling along the front, primarily affecting locations from PTK northward. The overall weak forcing should keep convection changes late Sun afternoon to 30% or less. The probabilities for thunderstorms are highest at MBS and will warrant the introduction of a PROB30 group for late afternoon convection. For DTW/D21 Convection...Isolated to possibly scattered thunderstorms are forecast late Sunday afternoon. The chances are across the northern portions of the airspace in closer proximity to a frontal boundary. DTW THRESHOLD PROBABILITIES... * Low in ceilings aob 5000 feet Sunday afternoon. * Low in thunderstorms Sunday afternoon and evening. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...AA MARINE.......KDK AVIATION.....SC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.