Marine Weather and Tide Forecast for Highland Park, IL

DISCUSSION
Issued at 224 AM CST Sat Dec 7 2024

Through Sunday:

It's certainly cool out there early this morning, but luckily not quite as bitter as yesterday morning with temperatures sitting in the lower and middle 20s. A large area of low level warm advection driven by storm system passing north of the region will overspread the Midwest during the day today. This will help pull temperatures back into the lower and middle 40s this afternoon. This will be the first day Chicago sees 40, and a warmer-than-normal high, since the day before Thanksgiving.

The big story today weather-wise will be some gusty southwesterly winds as a result of an impressive low level jet.
There is a notable amount of spread among wind guidance for today, but that's to be expected with a setup such as this one.
The warm advection will reinforce a strong, low-hanging temperature inversion overhead which will considerably limit boundary layer mixing during the day. Additionally, 925mb winds are expected to build to over 40 kt by this afternoon, likely increasing to 50+ kt during the evening. The very shallow mixing into an awfully tight low level vertical wind profile makes for a rather fragile wind forecast. We should see gusts start to build during the morning and reach 25 to 30 mph by early afternoon. The strongest gusts during the afternoon look to occur across our northern CWA and up near the IL/WI state line where the strongest low level winds will be right overhead. The LLJ will spread southward later in the day carrying 25 to 30 mph gusts well into the evening before the jet moves away and winds begin to subside late in the evening.

Continued warm advection ahead of an approaching storm system will keep temperatures relatively milder tonight and bring warmer conditions to the area on Sunday. There is uncertainty in afternoon temps on Sunday with discrepancies in the magnitude of the warm advection. At least upper 40s is likely area-wide, though much of the CWA will probably hit the 50 degree mark! No rain or snow is anticipated today and through the day on Sunday, although the aforementioned storm system will impact the area as early as Sunday evening. More on that in the long term discussion below.

Doom

Sunday Night through Friday:

Sunday night into early Monday, the cut-off low currently drifting along the Arizona/Sonora/New Mexico borders is expected to become reabsorbed into the northern stream flow and lift northeastward into the Ohio River Valley as a compact short-wavelength-trough. However, as a more pronounced upper-level long-wave trough with embedded shortwaves dives into the southwestern United States around the same time, height rises over the Great Lakes will effectively dampen the leading shortwave. The net result should be a weakening northeastward-moving shield of precipitation Sunday night into Monday, with a majority of rain expected to fall from western Kentucky to central Ohio along the nose of the shortwave (chances for rain locally range from 10% near Rockford to around 60% in Rensselaer).

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

AVIATION /12Z TAFS THROUGH 18Z SUNDAY/
Issued at 527 AM CST Sat Dec 7 2024

Relatively light south to southwest winds at press time are expected to increase in gusto a few hours after sunrise with frequent gusts of 25 to 30kt through early evening. In spite of the winds being driven by warm-air advection and upper-level clouds likely limiting mixing heights today, there is concern for a 2-3 hour window for southwesterly winds to gust 30 to 35kt given a tightening low-level pressure gradient (primarily from 19 to 22Z). Given relatively limited confidence (around 50 to 60% chance), did feel introducing TEMPO groups for southwesterly gusts above 30 kt at each terminal would be worthwhile.

At least sporadic gusts above 20 kt should continue after sunset as the low-level jet intensifies over the Great Lakes.
LLWS criteria may be met if surface decoupling is more efficient than currently expected, given flow at 2kft is expected to be 50 to 55kt from the southwest. For now, will withhold LLWS given limited (<50%) confidence in full surface decoupling.

Finally, broken upper-level clouds will stream overhead throughout the TAF period. NAM-based guidance is bullishly advertising the development of low clouds and fog at the end of the TAF period, though the remaining gradient flow in place should prove hostile to surface saturation.

Borchardt

LOT WATCHES/WARNINGS/ADVISORIES
IL...None.
IN...None.
LM...Small Craft Advisory from 10 AM this morning to 3 AM CST Sunday for the IL and IN nearshore waters.