Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 191416 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1016 AM EDT Mon Apr 19 2021 .UPDATE... Based on the radar representation and considering the low to mid level frontogenetical forcing will increase as the front traverses the forecast area this afternoon, a forecast update was issued to increase precip chances. Also based on the latest observations and hi res guidance, there will be a little tighter thermal gradient along the front. Adequate daytime heating will boost highs well into the 60s across the eastern 1/3rd of the forecast area before temps plunge into the 40s by late afternoon. The earlier forecast update also made some minor adjustments to temperatures. && .PREV DISCUSSION... Issued at 631 AM EDT Mon Apr 19 2021 AVIATION... Predominately VFR conditions through this TAF period which will be maintained by a dry low level environment as a greater coverage of mid level clouds spread into southeast Michigan today. Winds pick up out of the west-southwest today in advance of a cold front that is expected to pass through southeast Michigan this afternoon. Gusts of 20 to 25 knots are expected during the early to mid afternoon period. Some lowering of cloud bases will accompany this front along with light rain showers. Winds shift more towards the west-northwest in the wake of the front for tonight. DTW THRESHOLD PROBABILITIES... * Low for ceiling at or below 5000 ft Monday afternoon through Monday night. PREV DISCUSSION... Issued at 338 AM EDT Mon Apr 19 2021 DISCUSSION... Warm air advection will persist within west-southwest flow this morning. A bit of elevated instability may even brief a brief sprinkle/shower early this morning as nose of WSW 35 knots low level jet works through southern Lower Michigan. Temperatures at the surface will quickly respond as boundary layer mixing ensues after sunrise. Expect temperatures to climb to near 60 by midday over the southern half to two-thirds of the forecast area, say I-69 south roughly. By midday, a strong cold front will begin pushing south through the area with temperatures never making it out of the 50s north and falling back into the 50s in the mid afternoon further south. Scattered light showers will accompany this front today and persist into tonight over southern portions of the area as the front stalls over the northern Ohio Valley. Temperatures will be much colder tonight to the north of the front with lows ranging in the lower 30s for the most part with some upper 20s possible over the Saginaw Valley. The colder temperatures will hold into Tuesday as highs struggle back towards 40 degree in most areas as rain/snow showers increase across the area with the approach of a strong shortwave. Overall model trends continue to shift the bulk of the strongest lift/forcing associated with FGEN induced by this shortwave south into far southern portions of the forecast area on into parts of the Ohio Valley. It is within this general area that periods of heavy snow will be most likely Tuesday evening/night. Modest lift will extend further north through the area as coupled jet structure leads to broad scale upper lift over the region. FGEN with also be forced northward up the frontal surface to some degree as the shortwave encroaches/reaches the area Tuesday night. Air temperatures will become plenty cold enough for accumulating snow as cold air will be pulled further south into the area and temperatures fall into the mid/upper 20s north to the upper 20s/around 30 metro Detroit south. Ground temperatures (generally in 45-50F range), on the other hand, will be more problematic for accumulating snow, especially if much of the higher snowfall rates remain south of the area. Generally expect to see a 2-4 inch swath of snow I-69 south (especially on grassy areas) with locally higher amounts possible, particularly over the higher elevations of the Irish Hills from the M-59 corridor south. This snow will occur from late Tuesday afternoon into the overnight hours before pulling east early Wednesday morning. A freeze warning will also likely be needed for much of the area Tuesday night as the early warmup so far this spring has the green up ahead of schedule by several weeks. Another cold night is also expect in the make of this system on Wednesday night with another period of hard freeze conditions expected as temperatures fall below 32F much of the night and bottom out in the middle 20s most areas. Temperatures will then moderate for the remainder of the forecast as highs return to the lower 50s on Thursday after another chilly day on Wednesday. From late this week on through the weekend, upper 50s to lower 60s will be common (which is rather average for late April). MARINE... Southwest flow to start the morning will back to the west following the passage of a cold frontal boundary, which will sweep across the Great Lakes from northwest to southeast through the better part of the day. Cold air advection behind the front will increase mixing depths and will tap into an energetic field field aloft, which will increase wind speeds and elevate wave heights late Monday into Tuesday. The highest wind speeds are expected across northern Lake Huron given the westerly fetch and better proximity to a passing low pressure system. Gusts to gales can be expected from this evening into the overnight hours and a Gale Warning has been issued for the northern portions of Lake Huron. Otherwise, locations south of this will also see an uptick in wind trends following the passage of the front. However, with gusts are expected to remain below headline thresholds. The passage of the cold front will bring about the chance of rain showers through the day across the Great Lakes region, with the likely chance for snow then entering late Tuesday into early Wednesday due to an approaching low pressure system. Southern Lake Huron and locations south will have the best chance to see persistent snow during the overnight hours. HYDROLOGY... Low pressure lifting northeastward along a cold front will drive heavy wet snow into portions of Southeast Michigan from Tuesday afternoon into late Tuesday night. There has been an overall southward trend in the axis of higher QPF. The latest model consensus generally carries a quarter to half an inch of moisture from the M-59 corridor south to the Michigan and Ohio state line. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Gale Warning from 8 PM this evening to 6 AM EDT Tuesday for LHZ361- 362. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ UPDATE.......SC AVIATION.....AA DISCUSSION...DG MARINE.......DG HYDROLOGY....DG You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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