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LCZ460 Lake St Clair- 946 Am Est Tue Nov 28 2023
.small craft advisory in effect until 4 pm est this afternoon...
Rest of today..West winds 15 to 20 knots. Mostly Sunny. Waves 1 to 3 feet.
Tonight..Southwest winds 15 to 20 knots. Partly cloudy. Waves 1 to 3 feet.
Wednesday..Southwest winds 20 to 25 knots with gusts to 30 knots becoming west 15 to 20 knots early in the afternoon. Partly Sunny. Waves 2 to 4 feet subsiding to 1 to 3 feet early in the afternoon.
Wednesday night..Southwest winds 15 to 20 knots. Partly cloudy. Waves 1 to 3 feet.
Thursday..Southwest winds 15 to 20 knots increasing to 20 to 25 knots with gusts to 30 knots in the evening. Partly Sunny becoming mostly cloudy. A chance of light showers in the evening. Waves 1 to 3 feet building to 2 to 4 feet in the afternoon and evening.
Friday..North winds 15 to 20 knots. Mostly cloudy with a chance of light showers. Waves 2 feet or less.
Saturday..East winds 5 to 10 knots. Partly cloudy. Waves 2 feet or less.

LCZ400
No data

FXUS63 KDTX 282101 AFDDTX

Area Forecast Discussion National Weather Service Detroit/Pontiac MI 401 PM EST Tue Nov 28 2023

DISCUSSION

An amplified upper level height field has continued to dominate the longwave pattern today across CONUS, with locations east of the Rockies still entrenched in broad cyclonic flow owing to a 496 dam H5 low over Hudson Bay. The core of this cold airmass is now downstream of the Great Lakes, sampled by the DTX sounding this morning with H8 temperatures of -14 to -16 C. Evening temperatures stay chilly and well below normal in the 20s with overnight lows dipping back into the teens.

Notable wind shift occurs through the evening, with winds becoming southwest as surface high pressure translates overhead. This will lift both diurnally-driven stratocumulus and the more substantial lake plume (South Bend-NW Ohio) northeast through the forecast area.
At the very least, a transient period of cloud cover is expected overnight, but flurries or even a few snow showers are plausible south of I-94 where the more robust moisture flux set up earlier today. This moisture stream, which is currently still south of the cwa, has been consistent in producing light snow showers throughout the day owing to the shallow moist layer sitting right within the DGZ (3.0-5.0 kft agl). If there are accumulations, they will be minor and favored near the Ohio border. Snow showers will quickly lose steam upon pivoting to the northeast as they lose their moisture source and mix with the much drier inland airmass tonight.

The Tri Cities and Thumb region will be another area to watch for snow potential beginning this evening and lingering through Wednesday. The first batch of snow comes with a round of cellular lake effect snow showers that are just reaching Saginaw Bay at issuance. The extra moisture boost from Saginaw Bay will be just enough to shield the updrafts from surrounding dry air along with deep convective depths that extend up to ~7.0 kft agl. Any accumulations will be highly localized due to the cellular nature of activity, with generally minor amounts less than a half inch.
Meanwhile, attention turns upstream to a low amplitude shortwave that is currently just east of Lake Winnipeg. This shortwave will glance across northern Michigan between about 09z-15z (4am-10am local time) on the heels of a period of warm advection/isentropic upglide that overspreads the lower portions of the state. The continental origins of the shortwave provide just a limited spatial footprint and duration of deep layer moisture, which is favored to clip just the northern portions of the cwa. This keeps QPF under a tenth of an inch through Wednesday evening and, given the warm advective processes and decreasing snow ratios, keeps total snowfall through Wednesday evening around a half inch to localized one inch.

As the system glides along the thermal trough, the resident temperature gradient will support a strong low level jet with H8 wind speeds around 40 knots. Improvement to boundary layer depths during afternoon heating will tap into this fleeting wind field, and result in gusts up to 30 mph. Meanwhile, background warm advection will begin a transition back to near-normal temperatures with daytime highs Wednesday in the mid-30s.

The longwave pattern flattens toward the end of the week, setting up a more zonally-oriented storm track that results in several Pacific disturbances being directed toward southeast Michigan heading into the weekend. A weak clipper system pivoting around the Hudson Bay low sends a cold front south into the Great Lakes, which eventually stalls over the Ohio Valley. Cyclogenesis initiates along the residual baroclinic zone and directs the low pressure system toward the Ohio Valley. There are still differences in the deterministic and ensemble guidance, with the EPS trending slightly south and the GFS trending more north. Regardless, southeast Michigan looks like it will be on the northern fringe of the QPF bullseye with a sharp gradient in precipitation amounts as a result. Precipitation-type associated with this system is still in question and will depend on how far south the front gets, with forecast soundings hovering right around the freezing mark, alongside diurnal and thermodynamic processes. Attm it looks like rain will be favored to the south with at least a rain-snow mix plausible with northward extent for Friday's system.



MARINE

Gusty winds continue through the evening as the boundary layer remains deeply mixed, with lake effect snow coverage tapering off briefly as winds shift to the southwest tonight. Small Craft Advisories continue for the Thumb and Saginaw Bay, although may need to be expanded further south with later issuances to account for another uptick in winds Wednesday morning. Will hold off for now to avoid confusion with the recently expired advisories. A clipper system is set to track across northern Michigan late tonight into Wednesday, bringing additional snow along with gusty southwest flow.
A strong low level jet accompanies this system and may support a brief period of gales, especially between Saginaw Bay and Georgian Bay where the fetch aligns with the wind direction. The window in which gale force gusts may occur continues to be brief, precluding the issuance of any additional headlines. Remainder of the week will be active as a cold front sweeps through on Thursday followed by another disturbance that will track across the Ohio Valley.

PREV DISCUSSION
Issued at 1223 PM EST Tue Nov 28 2023

AVIATION...

Clear skies early this afternoon give way to increasing strato-cu as northwest low level flow advects lake moisture into SE MI. High MVFR to borderline VFR ceilings are likely initially with this cloud cover before diurnal mixing is expected raise heights into low VFR territory. MVFR ceilings are possible again by late evening as deeper layer westerly flow establishes itself resulting in MVFR lake- induced cloud currently confined over west MI being dislodged east into the area. These clouds eventually vacate overnight with mid- cloud quickly filling in ahead of an approaching weak clipper system. Track of this system favors light snow shower chances mainly north of the region with best chances locally over mbS, though some limited potential as from south as FNT- have only included mention at mbS in current TAFs however. Main aviation impacts instead are another period over lowering ceilings toward (or into for the northern sites) MVFR and renewed breezy southwest winds gusting 20- 25kts Wednesday morning.

DTW THRESHOLD PROBABILITIES...

* Moderate confidence in cigs aob 5000 feet this afternoon and evening.



DTX WATCHES/WARNINGS/ADVISORIES
MI...None.
Lake Huron...Small Craft Advisory until 4 PM EST Wednesday for LHZ421-422-441.

Lake St Clair...None.
Michigan waters of Lake Erie...None.

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