textproduct: Detroit/Pontiac

KEY MESSAGES

- Patchy fog, mist, drizzle, and spotty light rain will continue across the area today. There is potential for slick roads in the Saginaw Valley and Thumb this morning due to pockets of light freezing mist/drizzle.

- Light rain arrives late Friday, marking the start of a mild and rainy weekend with highs reaching the 50s on Saturday.

- Decreasing temperature trend brings temps closer to seasonal normals to start the new year.

AVIATION

An elevated warm front setting up over the region will maintain saturated low-level conditions much of today with low stratus, patchy mist/fog, and pockets of drizzle especially this morning. Early morning observations range from MVFR for terminals near/east of I-75, to LIFR along the M-59 corridor and across west and mid MI. Ceiling heights will trend lower early as additional moisture pools in, with prevailing lower MVFR to IFR/LIFR likely through the afternoon. Drier air will then work in from the south late this afternoon and evening causing ceilings to lift and trend toward VFR tonight into Friday morning. Light surface wind holds from the southeast through the period.

DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 feet today.

* High for any precip to fall as rain today.

* Low for ceilings at or below 200 feet and visibility at or below 1/2 SM this morning.

PREV DISCUSSION

Issued at 335 AM EST Thu Dec 26 2024

DISCUSSION...

A mid-level ridge is building directly overhead this morning with 500mb heights just north of the Great Lakes exceeding 2 standard deviations above the norm for this time of year. Beneath the ridge is a stable thermodynamic profile with abundant moisture in place from the surface up to the 700-850mb layer. A disorganized shortwave tracking just south of the IN/OH border within the base of the ridge is driving an elevated warm front north into the area with moisture depth increasing from south to north through the rest of the morning.

The warm/moist advection has been sufficient to lower the stratus base and result in some patches of sprinkles, drizzle, and fog early this morning. Air temps and dew points are sitting in the lower to mid 30s across the area with the Saginaw Valley and Thumb with readings right near freezing at press time. This will be a target for potential freezing drizzle early this morning before dew points rise above freezing. Rate of any precip is expected to stay light enough to keep ice accumulation minimal but a few slick spots on overpasses will be possible. This leads into another grungy late December day with overcast skies and continued patchy fog/mist/drizzle possible through the day into tonight as the elevated warm front begins to wash out over the area. Temperatures will reach the mid to upper 30s (Thumb/Saginaw Valley) to lower 40s (near the Ohio border) today before settling into the lower to mid 30s overnight.

A closed southern stream upper low will eject from the southern Plains into the Great Lakes on Friday, weakening through the day as it encounters the ridge still holding in place across eastern North America. The surface low lifts north across Wisconsin late Friday night, holding us within mild and drier southeast flow through the day. Confidence is increasing on later arrival of the main slug of moisture within the wing of isentropic ascent, with latest guidance holding the better chances after 21Z when the 40 kt LLJ arrives at the stateline. After another day of steady 1000-850mb thickness increases, surface temps will reside in the upper 30s to lower 40s ensuring an all-rain outcome. An arc of showers will track south to north across the area late Friday afternoon into the overnight, bringing rainfall totals on the order of 1 to 2 tenths of an inch. The dry slot may begin to cut into shower coverage after midnight but then a second shortwave quickly follows behind the first to bring additional shower chances through parts of Saturday. Very mild air builds in within the veering southerly flow with highs well into the 50s likely on Saturday.

Arrival of a strong Pacific jet streak over the PNW leads to consolidation of the upper air pattern by this weekend, with a longwave trough easing in from the Plains around Sunday. This will bring another chance of rain as a low or frontal wave tracks somewhere between the southern Great Lakes and Ohio Valley. Much of the ENS and GEPS ensemble membership favor a more amplified, slower trough that allows much of the moisture transport to become directed to our south and east. The GEFS members generally favor a lower amplitude trough that pulls the cold conveyor closer to the Great Lakes, offering a higher QPF scenario. Ensemble mean QPF data suggest another few tenths of an inch will be possible in this window. Cooler air arrives behind this system with high temperatures trending back into the 40s to start the week.

MARINE...

Western periphery of a high pressure system will continue to influence the Great Lakes today which will maintain lighter south to southeast flow. Low pressure derived from ArkLaTex will then travel north, impacting the Great Lakes area by late tomorrow into the early weekend. Arrival of the system will strengthen the pressure gradient, boosting wind gusts to around 20 to 25 knots across Lake Huron, while bringing increasing chances for rain showers. There will be additional chances for a second low pressure system to impact the Great Lakes again on Sunday, but confidence is lower regarding the final track of this system.

DTX WATCHES/WARNINGS/ADVISORIES

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