Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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703 FXUS63 KDTX 070710 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 310 AM EDT Sun Jul 7 2024 .KEY MESSAGES... - The holiday weekend closes out with dry weather today under partly sunny skies. - Warming up into Monday with highs in the mid to upper 80s. Shower and thunderstorm chances return Monday and Tuesday. - Remnants of Beryl may begin to impact parts of the area by Tuesday night and Wednesday. && .DISCUSSION... Upper level ridging will translate in the region today and provide mostly sunny conditions with temperatures warming back into the low 80s in most locations (upper 70s over the Thumb). The upper ridge axis will shift a bit east into Monday with strengthening south to southwest flow developing between this feature and an encroaching weak frontal boundary to the northwest. Temperatures will continue to warm within this regime with middle 80s common by afternoon (and upper 80s possible metro Detroit south). The chance for scattered showers and thunderstorms will increase into the afternoon and evening period as the aforementioned frontal boundary shifts into the forecast area late Monday. At this time, it appears convection will most likely be most prevalent over the north to northwest one quarter to one half of the forecast area where the best frontal forcing will reside along northwest edge of remaining upper level ridge. This forcing will act on an increasingly unstable airmass as surface dew points edge into the upper 60s to around 70. This should promote SBCAPES nearing 1500 J/kg locally. Stronger mid level flow will also translate into the area and increase deep layer shear from about 20 knots midday to 30-40 knots into the evening. So, the combination of these two modestly supportive parameters may lead to a few stronger storms. This frontal boundary will settle into the remainder of the forecast area Monday night into Tuesday, but stall over/near the area as the positive tilt upper level trough driving this front southeast minors out as it crosses the area Tuesday. This will maintain rain chances into Monday night and to some degree into Tuesday (although model differences are substantial in terms of active convection along/near this front by that time). The largest forecast challenge that appears to be emerging is how the remnants of Beryl will initially interact with this stationary frontal boundary by the middle of the week (Tuesday night into early Wednesday) as it is steered around the northwest periphery of the western extension of the Bermuda high centered over the Atlantic and then just where the remnant low ends up tracking as it rounds the top of this ridge over the southern Great Lakes/northern Ohio Valley later Wednesday into Wednesday night. This general idea having Beryl impact the area was basically "new" to the model suite at the 00z cycle Friday night and the 00z suite for Saturday remains notably divergent in the exact progression of events (although all models have the system over/near the area now). This will be a significant rain producer for a rather wide swath of the southern/eastern Great Lakes and/or northern Ohio Valley. While details remain elusive, it appears that increasing the chance of rainfall in this late Tuesday night to Wednesday night period seems prudent. && .MARINE... A ridge of high pressure centered over the Ohio Valley maintains dry conditions with light winds and low waves the rest of the weekend. Southerly wind of around 10 knots develops on Monday ahead of the next frontal system moving in from the Midwest. Scattered showers and storms arrive over northern Lake Huron Monday morning before expanding south and east into the evening. Additional showers and storms will be possible into Tuesday as the system slowly continues tracking through. The mid-week carries a considerable amount of uncertainty but the potential exists for a period of heavy rain and strong winds if the remnants of Tropical System Beryl track in the vicinity. && .HYDROLOGY... The remnants of Beryl may very well begin to interact with a stalled frontal boundary along the southern portion of the forecast area by Tuesday night with the remnant low then tracking into the vicinity Wednesday into Wednesday night. At this time, details on the track of this system are difficult to determine. Suffice it to say that an increased risk of heavy rainfall will exist as the system encroaches on the area. If impacted directly, rainfall will most likely reach or exceed 2 inches in some areas. Follow upcoming forecasts as the forecast track into this general part of the country is fine tuned. && .PREV DISCUSSION... Issued at 129 AM EDT Sun Jul 7 2024 AVIATION... For the rest of tonight, look for winds to become calm as high pressure off continues to slowly moves into the area. Expect another round of BR or HZ tonight, so do have mentions of vsbys falling to around 4-5SM. Sunday will feature light west-northwest winds, with the development of lake breeze boundaries that will bring wind shifts late in late Sunday and diurnal cumulus. This cumulus looks to be around 5-6kft, with the better potential for BKN ceilings near KFNT/KMBS. For DTW/D21 Convection...There is a very low chance (<10%) that we will see isolated convection along lake breeze boundaries on Sunday. Next chance for thunderstorm activity moves in from the west, late Monday. DTW THRESHOLD PROBABILITIES... * Low for ceilings at or below 5000 ft on Sunday. PREV DISCUSSION... Issued at 346 PM EDT Sat Jul 6 2024 Pop up showers remain a consideration through tonight. Temperatures have creeped up into the mid-to-upper-70s across the CWA today. Isolated showers have already begun to develop, and further development is expected throughout the evening. The best chances for showers remains north of I-69, where CAPE values of 500 J/kg are currently in place. 0-3km lapse rates of 7 C/km are the most favorable ingredient for shower development currently, and not much else supports anything more organized. CAPE values are not expected to increase through the evening, and low shear values are a problem for updrafts trying to organize further. PWAT values struggle to reach 1", and showers that do develop are not expected to bring more than a few hundreths of an inch. Warmer air at the 600mb level will advect in this evening and bring lapse rates of around 5 to 5.5 C/km, below the moist adiabatic lapse rate and as a result, cutting off convective access to the upper levels. With updraft potential limited to the lower levels of the atmosphere, thunder is not expected with these showers. However, an isolated rumble of thunder cannot be ruled out. High pressure ridge fills in briefly on Sunday keeping dry conditions and few to scattered clouds through the day. As a result temperatures will reach the 80s across the CWA tomorrow with urban areas likely to push 85 degrees or better. The next chance for rain comes Monday ahead of a weak front that will pass through. The combination of frontal forcing and daytime heating will produce decent chances for showers and storms. Hi-res models remain out of range at this time, but looks from global models resolve CAPE values between 1000-1500 J/kg. Trough axis will line up as well and place a jet streak over the lower peninsula, giving the area a shot at some decent speed shear of 30-40 knots. Beyond Monday, models struggle to convincingly resolve rain chances through the rest of the week. One of the main disagreements in the deterministic models is the evolution of the negatively tilted trough through the week. The ECMWF for example, keeps the trough axis slightly further to the northwest than models like the GFS. This is especially important when considering the potential for the remnants of Tropical Storm Beryl to be picked up and brought over the southern part of the CWA. Regardless of if Beryl makes its way over the area or stays to the southeast, the setup will allow for warm, moist air to advect in, pushing dew points into the upper 60s/low 70s and PWATs up to 2 inches. As a result, available moisture in combination with daytime heating still provide chances for showers to pop up in the mid-to-late week time frame even if the more robust system stays to the southeast. MARINE... Light winds and low waves accompany the weak pressure gradient in place through this weekend. Apart from a stray shower this afternoon or early evening, dry conditions will prevail through Sunday as an area of weak high pressure builds in over the Ohio Valley. Southerly wind of around 10 knots then develops on Monday ahead of the next frontal system moving in from the Midwest. This system will bring scattered showers and storms late Monday into Tuesday as it tracks through. Slightly cooler northerly flow follows for the mid-week. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...DG MARINE.......TF HYDROLOGY....DG AVIATION.....JA You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.