In the short term, record warmth, rather than wintry precipitation, is the most important story to follow.
Early this morning, temperatures were already higher than average for this time of year.
This morning, strong south-southwest surface winds and classic turning to the southwesterly across the lower troposphere will reinforce the low-level WAA regime in situ.
Despite the presence of a significant amount of high clouds, particularly in the morning, and the possibility for some stratus over areas of southeast Missouri and southwest Illinois, the intensity of the WAA is excellent, and I anticipate the clouds to clear from late afternoon through early evening.
According to current forecasts, temperatures will reach record or near-record levels on Christmas Eve Day, with temperatures ranging from 25 to 35 degrees above average.
I believe the most substantial opportunities are in Columbia and Quincy, and I think we will be knocking on the door of St. Louis shortly.
The commencement of a more busy and progressively rainy weather regime will occur tonight and continue through the following day. A series of migrating low-amplitude short waves will pass across the area overnight and into the morning of Christmas Day.
The first of them is expected to arrive tonight and push a cold front into the area.
Large-scale forcing/height falls associated with this wave, combined with extreme mid-level frontogenetic forcing, is expected to produce a swath of rain from the late evening into the overnight hours, primarily across northeast Missouri and west-central Illinois, with potential as far south as the I-70 corridor, according to the National Weather Service.
With the passage of the first shortwave, I believe most of the rain will be east of the region by dawn Christmas morning, with the following shortwave assisting in advancing the cold front through the CWA.
It seems that both the frontal advancement and the total strength of the CAA are a little slower on Christmas Day, which is not surprising. Because of these characteristics, the far southern CWA will very certainly be warmer than it is now.
Furthermore, although temperatures throughout a vast portion of the CWA will be cooler due to the proper, the whole region will still suffer many above-average temperatures.
Christmas Eve seems to be a peaceful time. A weak and slowly departing high-pressure system will remain in command, with high clouds expected to rise before the next storm system arrives.
This should be done for as long as the minimum temperatures are above usual.