Marine Weather and Tide Forecast for St. Joseph, MI

DISCUSSION
Issued at 213 PM EST Sat Dec 7 2024

A split flow pattern across the United States with the jets connecting up in the western Atlantic/Mid Atlantic States starts the forecast period. With upper northwest flow, another clipper system moves across the northern Great Lakes this afternoon and vacates the area by Sunday morning. During this time, expect breezy winds as a 50 kt jet moves through the Great Lakes region. Still only expecting shallow mixing given cloudiness and warm advection, which should limit gusts to 15 to 25 kts. Dew points are on their way wetter given warm advection and this should provide a floor to our overnight lows keeping them at freezing or just slightly above and this should also help to raise highs on Sunday to the 40s, with a few spots south of US-30 flirting with 50 degrees. Additionally, models begin to bring snow-eating 35 degree dew points around midday morning after sunrise. Could begin to see lowered visibility in the area where a snowpack remains, mainly north of the Toll Road, as a result.

During the day Sunday, a Pacific trough moves into the West Coast of the US and kicks the stalled upper low originally in the southwestern US towards the area. The moisture plume arrives into areas south of US-30 around 1 am. It's a pretty quick moving plume and should be out of the area Monday morning as a mid level dry slot moves into the area behind this initial plume. The NAMNest is still suggesting some freezing rain/drizzle might be able to form at the rain's onset, especially north of the Toll Road and perhaps if it comes down light enough, but there are questions about if two 40 degree high temperature days before it could warm roads up enough to remove that chance. Those models do only create a trace of freezing accumulation. All told, QPF is expected to stay underneath 0.25" and could be more around 0.1" given the progressive nature of the system and that the storms in the south could rob moisture from it. We could also have a period of drizzle on the back side with the residual lift and lingering low level moisture Monday morning.

The GFS has trended away from bringing snow to the area Tuesday on a developing low pressure system's northern side. The GFS's low is still north of the rest of the deterministic model's placement at this time, but even the northern portion of the precipitation shield appears to have issues with saturating its DGZ, may include mixing with some rain at times, and dry air may cut into precipitation all together, all limiting snow accumulation.

As cold air wraps in on the back side of the system, a shortwave traverses the southern area of Lake MI Tuesday night and may be able to invigorate lake enhancement as lake induced inversions rise to between 5 and 6 kft with 20 to 25 degree delta T values. Also noted is weak low level wind convergence in saturation issues within the moisture column. Chances for lake effect snow are expected to continue through Wednesday and into at least Wednesday night. The trough looks to pivot through Wednesday night into Thursday AM.

High pressure dries the area out for Thursday, but uncertainty remains on Friday about the placement of the jets across the US. The ECMWF is slightly more southward with the jets and allows a little bit cooler airmass into the area ahead of a system, whereas the GFS brings a clipper system through the Central Great Lakes, north of the area allowing for a dry day.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/
Issued at 542 PM EST Sat Dec 7 2024

Little to no change with this TAF cycle. A low racing across the upper Great Lakes this evening will feature a strengthening low-level jet, thus LLWS remains. The LLJ eases prior to 12z as the aformentioned low departs. High confidence in VFR conditions through the TAF period amid poor moisture profiles.

IWX WATCHES/WARNINGS/ADVISORIES
IN...None.
OH...None.
MI...None.
MARINE...Small Craft Advisory until 4 AM EST Sunday for LMZ043-046.