Marine Weather and Tide Forecast for Waukegan, IL

UPDATE
Issued at 913 PM CST Sat Dec 7 2024

Gusty southwest winds have held temps up this evening, currently in the mid 40s over most of the CWA Winds will ease some overnight as clipper system passing well to our north scoots off to the east and a narrow weak ridge/axis of dilatation moves east into Wisconsin by 12z Sunday. This should allow temps to drop off more later tonight, but given how warm they are now, will be nudging low temps up a degree or two with forthcoming evening grid update.

Friday evening's guidance struggled mightily with high temps across the Midwest Saturday, exhibiting a significant cold bias (5F+). Interestingly, the 00z guidance this evening has come with 925mb 1-3C warmer than guidance had earlier today for Sunday. Given the unseasonably mild start to the day and probably more sunshine tomorrow than what we saw today (albeit the very low sun angle), planning on bumping up high temps Sunday with this evening update as well. Highs across most of the CWA should climb well into the 50s with even some areas potentially tagging 60 degrees (mainly south of I-80). These updated highs will be more in line with the 00z RAP/HRRR, but worth noting that both of those models were around 5F too cool last evening, so in theory temps could be even warmer than this evening's update.

One possible fly in the ointment temp-wise Sunday could be a lake breeze (yes, in December) along the IL shore, mainly north shore. Developing warm front over southern WI looks to result in a weaker pressure gradient over far northern IL, which could allow for a lake breeze to form as marine boundary layer temps are in the 40s vs air temps over land well into the 50s Sunday afternoon. Lake breeze threat will increase the closer you get to the WI/IL state line where gradient flow will be weakest.
Anywhere a lake breeze sneaks inland would likely see temperatures drop into the 40s tomorrow.

Should have updated grids and temps products before 930 PM CST.

- Izzi

DISCUSSION
Issued at 301 PM CST Sat Dec 7 2024

Through Sunday night:

Temperatures have over performed across the area this afternoon within the strong warm air advection pattern currently in place across the Great Lakes region. Accordingly, temperatures will now top out around (or a degree so warmer) the current readings, which generally range from the mid to upper 40s. High-level cloud cover continues to stream southeastward into the area late this afternoon. This will thus continue to result in partly to mostly cloudy skies for most locations into this evening.

Strong pressure falls in advance of a rather stout and fast moving clipper system tracking across extreme southern Ontario into this evening will keep our breezy southwest winds (gusting 25 to 30 mph) going for a few hours this evening. Winds will really be ripping within a couple thousand feet of the surface, however, as a low-level jet featuring westerly winds up around 50 kt continues overhead this evening. Fortunately, we will not be mixing into these strong westerly winds, so surface wind gusts will remain in check. Wind speeds will then abate overnight into Sunday morning following the quick eastward exit of the clipper system into New England.

Dry and unseasonably mild weather persists Sunday. Lighter southern surface winds are expected during the day in advance of a northern stream low pressure system shifting eastward across the northern Plains to the north of a notable southern stream impulse shifting from the Desert Southwest out across the TX Panhandle. With dry and mostly sunny continues expected in our area on Sunday, we continue to anticipate afternoon highs peaking around, or just above 50.

As we head into Sunday evening, the southern stream impulse is forecast to track eastward into the Ozarks. As it does, an increasing downstream southerly mass response will induce a pretty decent northward surge of low-level (dew points in the 40s) moisture into our area. This will result in the rapid northward development of a low-level stratus deck across much of the area after sunset Sunday evening, but not necessarily a lot of precipitation. Instead, it appears that the track of this southern stream impulse to our south Sunday night will steer the better deep mid and upper-level moisture and forcing (supportive of more substantial rain) to the southeast of much of the area. With this in mind, we continue to carry the highest rain chances in our area southeast of I-57. Farther to the northwest into much of far northern IL, I opted to maintain some slight chance pops Sunday night, mainly to account for the potential of drizzle from the low-level stratus deck overhead.
Model forecast soundings suggest these lower clouds will be around (or a bit more than) 3,000 feet deep, and thus may support some instances of drizzle northwest of the better precipitation shield shifting into the Ohio Valley late Sunday night. Eighter way, any light precipitation/drizzle threat will end into early Monday morning as a northern stream cold front, begins to shift eastward into the area.

KJB

Monday through Saturday:

Forecast thinking during the long term period has not changed from the previous thinking highlighted below.

On Monday, aggregate upper- level troughing across the western US will shift eastward anchored by a low pressure system lifting into central Ontario. Around the same time, an associated cold front should sweep eastward across the Great Lakes. While highs ahead of the front on Monday should still reach the upper 40s to lower 50s, temperatures will tumble Monday night with lows expected to fall into the mid to upper 20s. Tuesday into Wednesday, a sharp upper-level wave originating out of central Nunavut is expected to race southward and merge with the upper- level trough across the Great Lakes, effectively forcing the trough to contract and rapidly lift toward the northeastern United States. Such will set the stage for a lobe of arctic air to swing through the Great Lakes. Highs in the 30s on Tuesday will fall toward the 20s on Wednesday and Thursday (wind chills some 10 to 15 degrees lower). Finally, would have to think there should be a period or two of flurries or snow showers in the general area as the contracting upper- level trough whips overhead (perhaps on Wednesday).

Ensemble model guidance appears to be in agreement that the period of cold temperatures next week will be short lived as somewhat zonal flow becomes reestablished across the northern US. Indeed, multi- model ensemble meteograms of temperatures support highs returning to the 40s by next weekend.
Interestingly, both EPS and GEFS show a signal for wetter weather in the general region in the December 14th to 17th timeframe as well, which aligns well with the forecast for above-average precipitation by mid-month advertised by the CPC.

Borchardt/KJB

AVIATION /06Z TAFS THROUGH 12Z MONDAY/
Issued at 1130 PM CST Sat Dec 7 2024

VFR conditions will prevail through today with potential for MVFR increasing Sunday evening with some potential for IFR, particularly after midnight tonight.

Winds should be lighter today and closer to due south, which should allow for a lake breeze to develop during the afternoon.
Given the very short days, the lake breeze probably won't have time to make it to ORD or MDW prior to it dissipating at sunset, but something to keep an eye on.

Low level moisture and likely some MVFR CIGS should stream northward into the terminals this evening with the potential for some scattered showers as well. Seeing a pretty good signal in guidance supporting CIGS building down to IFR late tonight along with potential for some drizzle. Confidence isn't terribly high but still introduced this into the final hours of the ORD and MDW TAFS.

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Small Craft Advisory until 3 AM CST Sunday for the IL and IN nearshore waters.