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Scientific Forecaster Discussion
Area forecast discussion National Weather Service Detroit/Pontiac Michigan 1151 PM EDT Sat Apr 18 2015 Aviation... Departing surface high pressure to the northeast will sustain a strong east-northeast gradient over Southeast Michigan through the rest of the night. While nighttime cooling will suppress the degree of gustiness...sustained speeds of 8 to 12 knots should persist through daybreak. Low pressure will approach from the south on Sunday...leading to a strengthening of the easterly winds after daybreak. An influx of Gulf moisture with the arrival of this low pressure system will cause rain and lowering ceilings to overspread the Southeast Michigan terminals late Sun afternoon into the evening. For dtw...the onset of daytime heating will strengthen winds around 14z /with gusts possibly topping 20 knots/. The push of higher low level moisture should advance into metropolitan in the 20 to 22z time frame. This will mark the arrival of rain and onset of lowering ceiling heights. //Dtw threshold probabilities... * high in ceilings dropping below 5000 feet after 21z Sunday. && Previous discussion...issued 1002 PM EDT Sat Apr 18 2015 Update... An update will be issued to increase cloud cover a little across the southern half of the forecast area where high clouds have been rather thick. As a result of this...forecast overnight min temperatures from metropolitan Detroit/Ann Arbor and points south will also be increased slightly. Previous discussion...issued 327 PM EDT Sat Apr 18 2015 Short term... Rising mslp in the wake of this mornings backdoor cold and increased influence of a burgeoning stable lake aggregate has led to surface winds to decidely respond out of the northeast today. Low near surface Theta-E content has been steadily building into southeastern Michigan and has offset diurnal heating to cap the temperature response this afternoon. Theta-E forecasts suggest that conditions will cool rapidly between 22-00z with help from the nocturnal release of the marine layer. Message to communicate is temperatures falling into the 40s and 50s by 8 or 9pm. Strong low tropospheric ridging will keep the main frontal zone bottled up south of the state tonight. Expect quiet but cool conditions for the duration of the overnight. Long term... Conditions are expected to slowly deteriorate on Sunday as a deepening low pressure system approaches the area from the south and forces a warm front northward through the Ohio Valley. Did have to adjust the timing of rain as models have back off notably with the initial arrival of quantitative precipitation forecast...which is understandable given the amount of dry air in place over central Great Lakes...reference kdtx and kapx 12z radiosonde observations. Sunday morning will likely be dry with just an increase in middle and high level clouds. A decent area of rain will then progress from south to north across the area from early to middle afternoon into the evening as the warm front lifts through lower Michigan. While the instability with this system is quite limited...will maintain a slight chance of thunder given the decent dynamics expected with this deepening system. At most...though...expect just a rumble or two of thunder within a more general rain. A trailing shortwave will wrap around this main system late Sunday night into Monday as the main low pressure center lifts through Ontario. This wave will help focus additional showers along a cold front that will be surging east to northeast around this initial low. With drier air working into the area within the increasing southwesterly flow on Monday...activity will become more scattered with time...particularly over the southern half of the County Warning Area. Any leftover activity during the evening will end by around midnight. With the slower arrival of rain...temperatures will most likely warm a couple extra degrees...especially from around Flint into the Saginaw Valley where downsloping east southeast flow will aid in warming to some extent. Temperatures will remain fairly mild Sunday night into the first part of Monday as major cooling waits until the aforementioned cold front is pulled east across the area during the day Monday. Lows of 45 to 50 will be common Sunday night with highs back to 60 or so on Monday before stronger cold air advection leads to a notable cool down late afternoon/evening with temperatures then falling into the 30s Monday night. Overall story for the extended period next week is below normal temperatures along with some unsettled weather. A longwave trough will have a hold over the Great Lakes region Tuesday through the end of the week. This will allow for continued precipitation chances as multiple shortwaves move through the trough. Cooler temperatures...with highs only reaching into the 50s and lows dropping to around the freezing mark...will also be persistent during this time. Marine... Northeast flow will gradually become east and diminish this evening as high pressure builds past the area through Ontario. This will in turn allow waves to subside. The east winds will begin to increase late tonight into Sunday as a strengthening low pressure system approaches from the south. Small craft advisories may be needed once again by Sunday and Sunday night as this system lifts through the area. While gusts may approach gale force...generally stable low level conditions over Lake Huron will limit this potential greatly. Winds will veer from southeast to south and southwest Sunday night into Monday as this low pressure lifts to near James Bay. Gusty conditions will gradually subside during this time frame. && DTX watches/warnings/advisories... Michigan...none. Lake Huron...Small Craft Advisory from 4 PM Sunday to 2 PM EDT Monday for lhz441>443. Small Craft Advisory from 10 PM Sunday to 2 PM EDT Monday for lhz421-422. Lake St Clair...Small Craft Advisory from 8 am Sunday to 8 am EDT Monday for lcz460. Michigan waters of Lake Erie...Small Craft Advisory until 4 am EDT Monday for lez444. && $$ Aviation.....SC update.......SC short term...cumulonimbus long term....dg/ss marine.......dg You can obtain your latest National Weather Service forecasts online at www.Weather.Gov/Detroit (all lower case).
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