Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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549 FXUS63 KDTX 242259 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 659 PM EDT Fri Mar 24 2017 .AVIATION... Shallow front will settle south through area this evening. Modest low level instability within warm sector is helping to fire some convection along this boundary and hires models suggest this area of shras and perhaps a tsra will zipper up front into area from KPTK south. Cigs will generally remain MVFR/lower VFR with this activity. Broader area of rain/dz/fog will expand northwest to southeast across the area overnight as moisture continues to overrun the frontal boundary and large scale forcing increases as low pressure wobbles into the mid Mississippi Valley. These conditions more or less persist through Saturday (albeit with slight improvement in the afternoon) as the low only make very slow progresses into the Great Lakes. IFR/LIFR conditions will prevail overnight into Saturday. For DTW...Scattered showers should develop along front early in the forecast with an outside chance of a tsra. This activity will fester this evening and then be replaced by a broader area of -ra/br during the overnight hours as the front settles south of the terminal. Cigs should remain MVFR/lower VFR much of the evening and then steadily lower to the cusp of LIFR/IFR late tonight into Saturday morning. Vsbys will follow suite as well. //DTW THRESHOLD PROBABILITIES... * High for cigs aob 5000 FT this forecast. * Low confidence in cigs/vsby aob 200 FT or 1/4SM late tonight into early Saturday morning. * Low risk of a thunderstorm this evening. && .PREV DISCUSSION... Issued at 353 PM EDT Fri Mar 24 2017 DISCUSSION... Upper low centered over northern Texas and Oklahoma will slowly track east through the Plains tonight and Saturday, before beginning to lift northward towards the Great Lakes. The frontal boundary currently draped over central Lower Michigan will sink slowly southward tonight as high pressure builds through Ontario and Quebec. Main area of precipitation now over Northern Michigan and Wisconsin will settle southward as well, filling in some as the convergence along the front tightens in response to right entrance region forcing from a jet streak passing through the northern Great Lakes and eastern Canada. The FGEN forcing should provide a fairly steady rainfall along elevated portions of the frontal boundary tonight into Saturday, before the jet streak slides east. Main area of rainfall will sink into the northern portion of the forecast area this evening and tonight. Another area of rainfall is looking to develop this evening further south, however, and should affect the Detroit area. Forecast models, including all higher-res runs, continue to develop another area of showers ahead of the surface front this evening, as it reaches roughly near the M-59 corridor southward. The increase in activity looks to be in response to low-level convergence increasing as the front encounters strong southerly flow, and as a modest theta- e surge makes its way up into Michigan from Illinois/Indiana. Stability indices continue to hint that thunder may be a possibility, but forecast soundings show enough of a cap to justify leaving the mention of thunder out. Rain should then fill in over all of Southeast Michigan by early Saturday morning as the elevated portion of the front slides solidly over the area. High coverage/more steady rain should continue through about mid-day before it likely tapers to showers as upper jet support is lost. Showers will then continue through Saturday night and Sunday as the upper low lifts northward and pushes the front back northward into the area. Activity on Sunday should be more convective in nature, with a few thunderstorms even possible, as the upper low and associated cold pool work across. Clearing and mixing into very warm air aloft has pushed temperatures into the upper 60s to low 70s this afternoon on the south side of the warm front. Temperatures tonight will show wide variation as the front slowly slides through the area, dropping into the mid 30s for the northern portion of the area and the upper 40s near the Ohio border. Not much temperature recovery is expected during the day tomorrow as Southeast Michigan remains on the north side of the surface front, under clouds and rain, and we see stiff east to northeast winds off the colder lake waters (especially Lake Huron). A slight chance for spotty showers will exist throughout Monday as southwest winds continue to advect warm, moist air into the region. PoP values will steadily increase Monday night into Tuesday morning as low pressure pushes from Missouri, into the Ohio Valley. The chance for rain will gradually diminish throughout the day on Tuesday as high pressure moves in from the Northern Central Plains into the Great Lakes region late Tuesday into Thursday morning, keeping conditions relatively dry through that period. The next chance for precipitation will return Thursday into Friday, as the GEM and ECMWF 12Z suites pick up on low pressure moving from Texas/Oklahoma into Michigan. High uncertainty still exists regarding both the timing, track, and strength of the potential low. For comparison, the GFS long-range run keeps the system well to the south of Michigan, centering it across Kentucky Friday night and into West Virginia by Saturday morning. This feature will be something to keep an eye on as we approach next week. MARINE... Frontal boundary over Central Lake Huron his afternoon will sink south tonight as high pressure builds into Ontario, leading to northeast winds of 15 to 25 knots over Lake Huron tomorrow with gusts briefly up to 30 knots over the mid section of the Lake early tomorrow morning. This will lead to waves in excess of 4 feet impacting the nearshore waters over the northern Thumb region during the day, and small craft advisories have been issued. Winds will become a bit more East-Southeast for the second half of the Weekend as low pressure tracks through the western Ohio Valley and into Lower Michigan Sunday Night. The weak low then looks to slowly pass through Lake Huron on Monday, with generally light winds right into Tuesday, but from the north behind the low. HYDROLOGY... Periods of showers Tonight and right through the weekend as a frontal boundary meanders over southern Lower Michigan. Rainfall totals are expected to approach 1 inch across much of the area, but flooding is not expected due to the long duration and intermittent nature of the rainfall. Runoff from the rainfall will increase flow rates and water levels in local streams and rivers. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...Small Craft Advisory from 6 AM to 8 PM EDT Saturday for LHZ422. Small Craft Advisory from 6 AM Saturday to 4 AM EDT Sunday for LHZ421-441. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....DG DISCUSSION...HLO/AM MARINE.......SF HYDROLOGY....SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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