Marine Weather and Tide Forecast for West Peoria, IL

DISCUSSION
Issued at 254 AM CST Sat Dec 7 2024

*** THROUGH SUNDAY NIGHT ***

A 1030-mb sfc high pressure system sits over the lower MS River Valley early Sat AM, while a sfc low is over the Canadian Prairie.
Southwesterly winds will persist through the weekend, resulting in steadily warming temps, into the 40s today and then likely the 50s on Sunday. The probabilistic NBM indicates a 50-60% chance of highs exceeding 50 degrees along/north the I-74 corridor on Sunday, increasing to an 80%+ chance along/south of I-72. Those southwest winds are expected to become breezy today. While forecast soundings show shallow PBL mixing due to an inversion around 1000 feet AGL, winds at the top of the mixed layer are around 20-22 knots, suggesting gusts up to 25 mph this afternoon.

A closed upper low over currently evident in IR satellite imagery over the SW US will provide a rain chance Sun evening/night. There has not been much change in the track of this system or the forecast placement of the associated precip. Forecast models show that as this system approaches from the southwest Sun evening, a swath of higher PWAT air (values over 1") will move into SE IL. This is also the area where models have consistently focused the LLJ and associated WAA. Thus, all signs continue to point towards the best precip chances being SE of I-72, and the NBM PoPs seem to be slowly trending in that direction but still seem a bit too broad with the northern extent of the PoPs. The latest forecast now has PoPs of 30- 40% between the IL River and I-55, then PoPs gradually increase to 70-90% east of I-57. This should be a light rainfall, with areas north of I-70 likely (greater than 50% chance) to stay below 0.25", and south of I-70 there is just a 10-20% chance of amounts exceeding 1".

*** NEXT WEEK ***

Into the day Monday, forecast soundings from the GFS and NAM show lingering low-level saturation, and given guidance often dissipates cloud coverage too quickly in the cool season I'm concerned that the NBM sky cover (just 40-50% by Monday afternoon)
is too low. If that's the case, it could also impact Monday's high temp forecast, which currently calls for highs in the 50s again but could be a few degrees too warm if the skies are overcast as opposed to partly cloudy.

While the wave responsible for Sunday night's rainfall moves away, a deeper upper trough will sweep through the upper Midwest, and long wave troughing becomes established across the central CONUS by Tues night. This system is expected to push a cold front through the ILX CWA by Mon night. 850mb temps are progged to fall from around +5 degC on Monday to around -12 degC by Wed, when highs will are forecast to stay below freezing. Adding to the chill will be breezy northwest winds, and while I'm often concerned that wind speeds/gusts will overperform in CAA regimes, this system appears far less dynamic than the previous cold front which produced 50+ mph wind gusts. Instead, forecast soundings suggests NW wind gusts around 25 mph, which is supported by ensemble guidance showing a 60- 70% chance for 25 mph gusts, but a less than 20% chance of gusts exceeding 40 mph. This combination of winds/temps will result in wind chill values below 20 during the day on Wed, falling into the single digits into Thurs morning. This cool down will be short-lived though, with another (modest) warm-up anticipated into next weekend.

Regarding precip chances during the week, most of the week appears dry. I had previously noted the potential for some precip along the frontal zone during the Tues-Wed timeframe, but the GFS solution has trended towards the ECMWF in being more progressive with that front, such that any precip that does develop near it should be east of our area. Wednesday could offer a chance for flurries or isolated snow showers as the upper trough axis pivots through the area, providing some lift as well as cold temps aloft that result in steep lapse rates. GFS soundings look fairly dry at this range, although that is often the case and this is the kind of regime where we see flurries/scattered showery precip. Contemplated adding a mention of flurries to the grids on Wednesday but ultimately held off for now as there will be plenty of time to reevaluate in the coming days.

Erwin

AVIATION
(For the 12z TAFs through 12z Sunday Morning)
Issued at 439 AM CST Sat Dec 7 2024

VFR conditions should continue through the period, along with southwesterly winds with gusts around 20 knots during the afternoon. The main challenge is in regards to the LLWS tonight.
There is some uncertainty as to whether or not gusts subside during the overnight hours. Guidance suggests a 45-55 knot westerly LLJ developing around 1500 feet AGL, shifting across the terminals during the overnight hours. This jet will be weakening and departing towards the end of the period, so may be able to drop the LLWS prior to 12z Sun, but for now kept in at through 12z Sun at most terminals.

Erwin

ILX WATCHES/WARNINGS/ADVISORIES
None.