Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 211057 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 557 AM EST Tue Feb 21 2017 .AVIATION... The band of light rain now moving toward Southeast Michigan is expected to decrease in coverage as it moves through the area late this morning and early this afternoon. This system will be weakening, leading to a decrease in the coverage and intensity of rain as it traverse Se Mi. Funneling in behind this rain will be an axis of low level moisture, resulting in lowering ceiling heights. This includes sfc dewpoints in the lower 50s. This degree of low moisture with a weakening gradient during the night as the associated sfc front washes out across the area will set the stage for very low stratus and/or dense fog tonight. For DTW...The slow eastward pace of the low level moisture and expected weakening of the upstream showers as they approach metro Detroit may not bring IFR conditions into Detroit until tonight. Until then, expect some sub 5k ft cloud development late this morning and afternoon with the approach of the remnant showers. //DTW THRESHOLD PROBABILITIES... * Moderate for ceilings at or below 5000 ft this afternoon. High tonight and Wednesday morning. * Low in ceilings/visibilities below 200 ft and/or 1/2 mile tonight through Wed morning. && .PREV DISCUSSION... Issued at 300 AM EST Tue Feb 21 2017 DISCUSSION... Band of showers stretches from the Gulf of Mexico to Northwest Ontario at press time, the northern branch of which is undergoing a steady weakening phase as forcing peels away to the northeast. Extrapolation puts light rain showers on the doorstep of the Saginaw valley at 12z. Diminishing trend is then forecast to accelerate through the morning as the northern branch wave currently over northern Wisconsin and Lake Superior peels away and the LLJ weakens and veers out. As a result, took another whack at the inherited pops as confidence in showers reaching the SE half of the CWA in any organized fashion is reduced since yesterday. High and mid-level overcast will dominate in the wake of any light rain. 925mb temps increasing to the high single digits over the SW portion of the CWA combined with reduced rain potential will make for a good opportunity for highs to reach the low 60s once again. The low-level moisture axis will remain in place tonight as the lead edge of energy presently coming onshore in the Pacific Northwest forces lee cyclogenesis over the northern Great Plains this evening. Steady southwest gradient at the surface will support dewpoints perhaps reaching the low 50s while strengthening westerly flow atop the strengthening inversion layer sets up a decent shear layer for enhanced forcing of drizzle development. With support from existing upstream obs this morning and the addition of better forcing tonight, added both fog and drizzle to the forecast for the latter half of tonight. Aforementioned lee cyclone will track well north of the area on Wednesday, the 00z EC indicating a slightly flatter solution as it grapples with energy offshore in the eastern Pacific. Strengthening southwest gradient as the low approaches the western Great Lakes may support some gusts upward of 20 mph. Meanwhile, late Feb insolation and low-level warming should help mix out low clouds/drizzle/fog by mid to late Wednesday morning. Mid 60s seem like a sure bet with warmer spots potentially making a run toward all-time February marks of... DTW...70 (1999) FNT...68 (1999) MBS...67 (1930) Weak height falls associated with the passing wave is modeled to force the cold front just south of the Michigan/Ohio border for Thursday allowing temps to fall back toward sub-record values. During this time, jet energy digging south along the West Coast will deepen the existing trough as it translates across the Rockies. Strong cyclogenesis will result. Weakly coupled jet structure will emerge as longwave pattern amplifies, dominated by the southern jet, allowing isentropic ascent to ramp up in full force immediately to the south. Baroclinic zone will lift back north bringing widespread stratiform rain Thursday night into early Friday with a few rumbles of thunder possible as h7-h5 lapse rates steepen coincident with strengthening LLJ nosing into the area. Consensus is essentially set on a warm track to the west of the CWA with the vast majority of variability attributable to different intensity outcomes. Several low amplitude features over Canada and the eastern Pac appear to be playing havoc with larger scale trough evolution. Thus, while confidence is sufficient for a high pop scenario, confidence in Friday afternoon high temperatures and Friday evening/night severe weather variables remains low. This is largely a result of uncertainty in surface warm front progress. Worth noting that the potential exists for another run all-time February highs will be possible given that Wednesday`s airmass will simply be re-surging back into the area. MARINE... The southeasterly gradient has been increasing overnight with the approach of a frontal boundary. Meanwhile, an influx of very warm low level air atop the shallow cool layer over the lake is greatly limiting stability. Nonetheless, south-southeasterly winds across Lake Huron will gust up to 25 to possibly 30 knots at times during the pre dawn hours given the strength of the gradient. The front is forecast to pass across Lake Huron this afternoon and into Lake Erie this evening. There will actually be a weakening of the gradient as the front passes through today before washing out over Lake Erie tonight. The result will be a marked weakening in the winds during the course of the day and evening. Modest south-southwest winds will then develop late tonight and persist into Wednesday night as a slow moving low pressure system and frontal boundary pushes into the northern Great Lakes. A strengthening low pressure system is forecast to lift into the Great Lakes region on Friday, potentially bringing gale force winds Friday through Saturday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Small Craft Advisory until noon EST today for LHZ441-442. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....SC DISCUSSION...JVC MARINE.......SC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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