Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000 FXUS63 KDTX 231902 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 302 PM EDT Thu Mar 23 2017 .DISCUSSION...
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Upper ridge axis over Michigan will flatten tonight as shortwave energy arrives, first from MN/IA this evening and then as additional energy ejects out of the upper low over the Desert Southwest. Strong 60kt low-level jet will surge up into Michigan late as the Desert Southwest low moves towards the Plains. This will send a warm front up through Lower Michigan this evening and tonight. Min temps in the 30s should be reached in the evening and early overnight before beginning to rise. Band of isentropic ascent (290-300K) and strong theta-e advection, supported by upper diffluence, will bring a chance for rain showers after 10 PM. Will keep pops higher north of I-69, where the nose of the low-level jet will push in as the front lifts northward. Very dry air will initially allow for some cooling in the low-levels due to wet-bulb effects at precipitation onset. Quick arrival of warmer air and will make the chance for snow/sleet/freezing rain brief and low. Enough warm air will arrive with the low-level jet to increase elevated instability, and would not be surprised to hear a few rumbles of thunder, but potential is low overall. Frontal boundary will stall over the area late tonight, with convergence increasing along this boundary as the upper low moves through the Plains and as upper energy moves through Canada around another low over Hudson Bay. The front will only sink slightly south Friday and Friday night as both these features move east. Strong and moist southwest flow will meanwhile ride over the frontal boundary, and combined with right entrance region forcing from a strong upper jet streak, will yield a high chance for rain over Northern Lower Michigan Friday, and then across Central Michigan Friday night as the front sinks south. Well-mixed but shallow boundary layer in the warm sector combined with abundant cloud cover lends some uncertainty to the temperature forecast tomorrow. With 925-850mb temps only rising to 9-12C, kept max temps in the 50s over the northern Thumb and Saginaw Valley, and low to mid 60s elsewhere. The front, and rain along it, will sink into Southern Lower Michigan Saturday as strong high pressure develops over Ontario and Quebec. It will make little progress beyond that however as the upper low tracking into the Ohio Valley and Southern Great Lakes stalls the front or slides it back slightly northward Saturday night into Sunday. Max temperatures will vary widely across the area on Saturday, ranging from the low 40s north of Saginaw to around 60 near the Ohio border. Overall, the quasi-stationary frontal boundary is expected to remain over Southeast Michigan through the weekend, leading to a prolonged period of wet weather. As weakening low pressure approaches Southeast Michigan on Sunday rain will continue throughout the day as southerly flow advects mild, moist air into the region. Following the passage of the low across central Lower Michigan on Sunday night a brief interlude in rain will occur on Monday. Temperatures during this period will remain mild with highs in the mid 50s to low 60s both Sunday and Monday. Rain chances then return Monday night and Tuesday as another wave crosses the Great Lakes. High pressure builds in during the middle of next week bringing drier conditions with temperatures near normal for late March with highs in the lower 50s and lows in the 30s.
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&& .MARINE...
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Modest southeasterly flow will veer to southwesterly by Friday morning as a weak warm front lifts across the region. Highest speeds will be across west Lake Erie and Lake St Clair, where gusts will approach 25 kts. Given the offshore nature of the flow, waves are expected to remain in the 2-3 foot range. A stronger surface low will approach the Lakes region Saturday, flipping the flow to the northeast and freshening across Lake Huron. Winds will maintain a southerly component over Erie and St Clair early Saturday before slowly transitioning to easterly flow.
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&& .HYDROLOGY...
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Widespread rainfall is expected across Southeast Michigan for most of the upcoming weekend. Rainfall totals from Saturday through Sunday are expected to approach or exceed an inch across the region. Specifically totals in the 1-1.25 inch range are possible across the Saginaw Valley with slightly lesser amounts elsewhere. Runoff from the rainfall will increase flow rates and water levels in local streams and rivers. However, widespread flooding is not expected.
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&& .PREV DISCUSSION...
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Issued at 100 PM EDT Thu Mar 23 2017 AVIATION... Steady modest southeast flow will persist through the first half of the forecast period. As a warm front approaches from the southwest, expectations continue for a narrow region of showers to traverse just after midnight - might even be a lightning flash or two. The best coverage will be in the vicinity of FNT and MBS. Winds aloft will increase substantially overnight with speeds climbing into the 45-50 knot range below 2 kft. Therefore, will continue with the low-level wind shear mention into Friday morning. Winds will veer around to southwest in the wake of the warm front Friday morning. The southern terminals will be under the influence of a strengthening low-level pressure gradient. Speeds and gust potential should emerge by mid-morning with the potential for peak winds to touch 30 knots. The warm front is expected to stall out across the far north and the warm sector does not perform a clean sweep into Southeast Michigan. Therefore, with ample low-level moisture lingering in the frontal zone, opportunity for MVFR clouds appears respectable Friday. For DTW...ceilings are expected to drop below 5 kft in the 04-08z window with a few passing showers. Additional restricting ceilings around 2 kft are expected after 15z. Wind gusts will also emerge in this time window with values around 25 kts - occasionally reaching 30 kt. //DTW THRESHOLD PROBABILITIES... * Medium for cigs falling below 5000 ft 04-08z Thursday night. * Medium for cigs falling below 5000 ft after 15z Friday. * High for gusts exceeding 25 knots Friday.
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&& .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ DISCUSSION...HLO/JD MARINE.......Mann HYDROLOGY....Mann AVIATION.....Mann You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.

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