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LMZ646 Wind Point Wi To Winthrop Harbor Il- 305 Pm Cst Sat Dec 2 2023
Through early evening..East wind 10 to 15 knots. Cloudy. Waves 1 to 3 feet.
Tonight..East wind 10 to 15 knots veering southeast early in the morning. Chance of rain late in the evening. Rain after midnight. Waves 1 to 3 feet building to 2 to 4 feet in the late evening and overnight.
Sunday..South wind 5 to 10 knots veering west late in the morning, then rising to 10 to 15 knots early in the afternoon veering northwest late in the afternoon. Rain in the morning, then chance of rain in the afternoon. Waves 1 to 2 feet.
Sunday night..Northwest wind 10 to 15 knots. Cloudy. Waves 1 to 2 feet.
Monday..Northwest wind 10 to 15 knots backing west late in the afternoon. Cloudy. Waves 1 to 2 feet.
wave heights are for ice free areas.

LMZ600
No data

FXUS63 KMKX 021638 AAA AFDMKX

Area Forecast Discussion...UPDATED National Weather Service Milwaukee/Sullivan WI 1038 AM CST Sat Dec 2 2023

UPDATE
(Issued 1038 AM CST Sat Dec 2 2023)

Watching QPF trends with the 12Z suite of models, as the 12Z NAM and models influenced by NAM initial conditions has come in higher with amounts across the area for later tonight into Sunday. There is good synoptic upward vertical motion from the negatively tilted 500 mb shortwave trough shifting through the region during this period, along with some upper divergence from the left front quadrant of a jet streak overnight. There is some modest frontogenesis response in the 700 to 500 mb layer overnight as well. The dendrite growth zone is tapped, but the best upward vertical motion is above it.

Forecast QPF is generally in the 25th to 50th percentile of Model Certainty away from the lake, and more towards the 75th percentile near it. Forecast snowfall amounts are between the 10th and 25th percentiles of Model Certainty, which is low. This all points to possible increases in QPF and subsequent snowfall accumulations away from Lake Michigan, once the 12Z models have come in and ensembles start to update.

Wood

SHORT TERM
(Issued 345 AM CST Sat Dec 2 2023)

Today through Sunday:

Some lingering snow showers mostly to the south of the CWA may sneak into far southern Wisconsin over the next few hours due to some lingering PVA with the passing system. But overall snow showers have largely ended as we will dry out into the daylight hours today with higher pressure likely keeping us dry through the day. However these drier conditions will be short-lived as the high quickly pushes out into the early evening with another low pressure system developing and lifting through the region.

This will largely be driven by a strong shortwave at 500mb barreling through the region, with plenty of midlevel moisture, a little bit of WAA, maybe some weak frontogenesis and possibly even a tiny bit of instability. Widespread precip across the area is expected but based on the CAMs you can definitely discern a bit of uncertainty in the timing of the system with respect to majority of precip. For example the HRRR and RAP are a bit quicker while the NAM 4km and ARW are a bit slower. This has largely washed out some of the QPF. Our forecast has favored the HRRR and RAP timing and progression.

As for snowfall, while amounts are not expected to be crazy by any means due to the near or above freezing temps we will still likely to see some snowfall accumulations. Similar to yesterday rates helped overcome some rather moderate temps and we could again see that, especially further northwest where temps will be a bit cooler with some better snow ratios. In addition, while the exact location is relatively uncertain it looks like there will be a relatively narrow corridor with better forcing in the DGZ that will lead to better dendrites and thus accumulation. Probabilistic information from ensembles and the HRRR are supportive of some accumulating snow up to around an inch largely across the western half of the CWA with most of this falling overnight into early Sunday morning. Sunday will be warming up becoming a bit too warm allow for much in the way of accumulations. There is around a 50-70% chance for much of the western parts of the CWA to see between a half inch and an inch, though some isolated higher amounts remain possible though not likely exceeding 2 inches anywhere. Eastern parts of the CWA are likely to see some snowfall but are unlikely to see accumulation given the warmer temperatures with more mixy precip expected overall.

During the day, warmer temps will shift precip over to largely a mix across the CWA with rain more likely closer to the lake.
Otherwise winds will turn from the east to the northwest as the low pressure system passes through the region during the day.

Kuroski

LONG TERM
(Issued 345 AM CST Sat Dec 2 2023)

Sunday Night through Friday:

Main focus in the extended period is on the potential for an accumulating snowfall on Monday night into Tuesday morning.

A mid level trough/system currently south of the Aleutian Islands will propagate across southwest Canada before ejecting southeastward through the upper Midwest Monday night into early Tuesday. In the lower levels, a surface/850mb low is forecast to track from the Dakotas through southwest Wisconsin over this period. The precipitation signal has become stronger out ahead of this low/trough due to the combination of low level WAA matching up with the leading shortwave associated with the mid level trough. Precipitation types will again be tricky since surface temps are hovering around freezing, but the rest of the lower level thermal profile looks colder/sub-freezing compared to what we've had recently, so we're expecting more of a snow situation than rain. Model-wise, the 02.00z NAM/GFS are the beefiest with QPF/lift while the 02.00z ECMWF doesn't look quite as hefty.
Ensemble guidance isn't looking too strong with low probabilities of hitting 1"+. GEFS is around 20-40% for 1"+ across central WI while the Euro Ens is down around 10-20% to hit 1". I think these are a bit underdone due to the potential rain/snow mix issue, but will monitor trends over the next few days to see how this goes.
As far as timing, it appears that the leading edge of the precipitation should be moving into western Wisconsin between 9pm-midnight Monday and exiting southern Wisconsin around daybreak...so a quick hitter.

After that, there's maybe another WAA period Wednesday night/Thursday morning that produces some light precipitation across far east central WI before some slightly warmer air moves in at the low levels to get temps back up toward normal by the end of the week.

Halbach

AVIATION
(Issued 1038 AM CST Sat Dec 2 2023)

Ceilings should remain in the 1000 to 2000 foot AGL range this afternoon, though there will be some breaks in northern parts of the area, and values down to around 500 feet AGL southwest of Madison. Light east northeast winds are expected this afternoon.

Light east winds tonight will gradually become north to northwest on Sunday, as low pressure passes by to the south. Light snow will spread into the area between 04Z and 08Z Sunday, then linger through Sunday morning. More of a mix of rain and snow, or all rain, is anticipated for the Milwaukee and Kenosha terminals. As temperatures warm into later Sunday morning, more of a rain/snow mix is expected across the remainder of the area. This activity should wind down by later Sunday afternoon.

Snowfall rates should be around one tenth of an inch per hour, with perhaps up to one quarter inch per hour rates overnight into early Sunday morning. It will be a wet snow with a good amount of liquid content in it. Ceilings should drop to less than 500 feet AGL overnight into Sunday morning with the precipitation, with visibility values down to around 1 mile. Ceilings should be in the 500 to 1000 foot AGL range Sunday afternoon, with improving visibility as the precipitation ends.

Wood

MARINE
(Issued 345 AM CST Sat Dec 2 2023)

Low pressure stretched along the southeastern Great Lakes in northern Ohio will continue to track to the east and weaken as a broad ridge of high pressure remains in place across southeast Canada. Another area of low pressure will develop over the mid- Mississippi Valley today and track toward the southeast portion of Lake Michigan by Sunday morning. A weak ridge of high pressure will track through on Monday before another low pressure system moves from the Dakotas on through southern Lake Michigan from Monday through early Tuesday.

Halbach

MKX WATCHES/WARNINGS/ADVISORIES
WI...None.
LM...None.

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