Marine Weather and Tide Forecast for Palmyra, IL

SHORT TERM
(Through Late Saturday Afternoon)
Issued at 231 AM CST Fri Jan 24 2025

Our persistent cold weather pattern is finally beginning to change.
The last of the cold core upper trough is moving east and out of our area today. Behind it we'll see rising mid level heights and warming temperatures aloft. Surface high pressure over the Southern Plains also shifts eastward toward the Lower Mississippi Valley today, opening us up to a southwesterly low level flow. So despite a very cold start, we'll see a strong rebound in temperatures today, especially across much of Missouri where warm advection will be strongest. Very dry air in place will enable a strong warm up as incoming solar energy more efficiently warms a dry air mass.
Southwest low level flow will promote downsloping off the Ozarks especially across central and eastern Missouri, further aiding in mixing of those warmer temperatures from aloft down toward the surface. These first days emerging from a cold air mass typically warm more strongly than guidance would suggest, and we have increased forecast temperatures today by about 5 degrees over the NBM and prior forecast values. With full mixing this may not be warm enough, as projected 850MB temperatures around midday suggest low to mid 40s are possible. Further east across Illinois the cold air mass will be slower to leave, so we have stuck closer to NBM guidance which holds temperatures near or below freezing for one more day.

The high continues to move east tonight into Saturday, with southwest flow persisting ahead of the next cold front being driven by a trough moving east through the Great Lakes. With winds likely to remain somewhat elevated through the night, temperatures won't cool as well tonight. We've leaned the forecast more toward the NBM 90th percentile (the warm side) in this time period to account for that continued low level mixing. The cold front will be entering the northern part of the forecast area during the day on Saturday, with the colder air behind the front stalling further warming. But ahead of the front we'll see a mild day with southwest to westerly flow maintaining a well mixed low level environment and temperatures in the 40s to low 50s. Increased cloud cover ahead of the front could reduce the high end potential for temperatures as we won't have as strong of sunshine to work with. However, the pressure gradient ahead of the front is likely enough to ensure good mixing ahead of the front with temperatures reaching the upper 40s to low 50s. If clouds are less extensive, we could warm more solidly into the 50s before that front arrives.

Kimble

LONG TERM
(Saturday Night through Thursday)
Issued at 231 AM CST Fri Jan 24 2025

The upper level flow pattern across North America is beginning to change. While the cold trough over the central US moves east, another trough digs south along the West Coast this weekend, becoming cut off over California. To the north of this, ridging becomes established over British Columbia. This high amplitude ridge sets up northwest flow in the northern stream continuing the flow of continental air into the central US. While northwest flow often sends cold air masses southward, the air circulating around the ridge is more of a modified North Pacific air mass, so after a brief cool down behind Saturday's front, we'll actually see some mild air for a while. Surface high pressure pushes southward through the area on Sunday with temperatures some 10 to 15 degrees cooler than Saturday. But once that high moves south a westerly low level flow begins across the Central Plains and mild air quickly returns. High pressure pushing southward also has the effect of blocking Gulf moisture, so we'll stay largely dry for a while.

The cut off low will wobble over the Southwest US for several days.
Current guidance suggests an initial shortwave ejects out of that low and eastward across the southern tier of the country Tuesday into Wednesday. This should stay largely south of our area, and with moisture return being blocked precipitation chances with this remain low. A northern stream trough also digs into the Great Lakes around the same time frame, this time accompanied by a much colder Arctic air mass behind it. Guidance is still variable on where this cold air mass heads. A majority of the guidance sends the core of this cold further east toward New England with us getting more of a glancing blow, but some guidance sends a significant portion southward toward our area. This results in greater uncertainty in the temperature forecast in the middle to later part of the week.
This uncertainty is shown in part by the NBM interquartile range for high temperatures rising to 10 degrees or higher from Wednesday onward. While the forecast at this point represents somewhat of a middle ground, it's possible that we drop back below normal later in the week, in the 30s for highs, or we stay more mild in the mid 40s to low 50s.

The core of the Southwest US upper low doesn't move out into the Plains until late in the week, but when it does so it will serve as our next best chance for precipitation. As is typical with ejecting cut off lows, there's considerable uncertainty on the timing of when this occurs. Some guidance (as represented by the 00Z ECMWF) move this through our region Thursday into Friday, while others (as represented by the 00Z GFS) don't bring it through until Saturday.
When it does move through there will likely be a better Gulf moisture connection, supporting the idea of at least some precipitation. What type will depend on how much cold air lingers in advance of it. Given the setup, all types of wintry precipitation will be possible if enough cold air lingers in the low levels. If that cold air is less intense or more easily shoved aside, then precipitation will be mostly rain. Precipitation chances at the tail end of this 7-Day forecast remain somewhat low primarily due to that rather large timing uncertainty. It's likely we get precipitation out of this, it's just a matter of when, and it could be just outside our current 7-Day forecast.

Kimble

AVIATION
(For the 06z TAFs through 06z Friday Night)
Issued at 1035 PM CST Thu Jan 23 2025

VFR conditions will prevail through the TAF period. Light and variable winds will increase from the southwest late Friday morning and remain steadily around 10 kts through the rest of the period. LLWS may be a concern Friday night, especially in mid- Missouri through west-central Illinois where a nocturnal ~45 kt LLJ is forecast to strengthen. However, confidence in impacts is too low to include in the TAFs during this package.

Jaja

LSX WATCHES/WARNINGS/ADVISORIES
MO...None.
IL...None.