As another example of how mild this winter has been so far, we have yet to have a day in which the temperature failed to get above freezing. That will change today as afternoon temperatures will struggle to get into the mid 20s and gusty northerly winds will keep wind chill values in the teens or single digits for much of the day. For example, the map on the right shows the wind chill values first thing this morning.
Obviously, this is the coldest we have been all season and as Mike Grogan pointed out in his excellent discussion on Friday, these shallow, cold, arctic air masses are usually reluctant to move out very quickly. That is going to result in some real forecast challenges for Sunday night and Monday as a disturbance aloft will be moving across the state by then.
Until then, the morning clouds and gusty northerly winds this morning will be giving way to clearing skies this afternoon and we should have light winds and clear skies for the overnight hours. That will allow temperatures to plummet and the colder valley locations could see single digits with lower teens elsewhere to start the day on Sunday.
That cold, arctic high pressure ridge will then be shifting on eastward during the day Sunday and for Monday. That will result in our surface winds becoming more SE Sunday and southerly surface winds for Sunday night and Monday. Meanwhile, an upper level disturbance which is now approaching the coast of California will be coming this way and moving across the state on Monday. This system will bring moisture and warmer temperatures aloft and really complicates the forecast.
The problem is this is not a classic setup for a winter weather event here in Oklahoma. It is very rare for us to have wintry precipitation and have a southerly surface wind. Typically, the surface winds will remain more from the E to NE gradually veering around to the NW as the storm system passes by to the south of us. That is not going to happen this time around which creates some real question marks regarding the vertical profile of temperature as we will have southerly winds at the surface and aloft which will eventually bring warmer air in. Initially, those southerly winds will just be re circulating the very cold air from the arctic ridge, but eventually warmer air will be entrained into the circulation and the timing and location of the warmer air will have a lot to do with the precipitation types and amounts.
The latest and greatest data available as of early this morning suggests the vertical temperature profile will stay below freezing till mid-day Monday. If so, that would mean snow which should be starting around midnight Sunday night. As the temperatures warm at the surface and aloft, a gradual transition to a more mixed bag of sleet, rain, or perhaps even some freezing rain can be expected during the day Monday. Bottom line - there will likely be some travel issues for late Sunday night through the day Monday.
Fortunately, amounts are not expected to be very great. If it were to remain all snow, then total accumulations of 2-4" will be possible. That is not likely to happen though as there should be a mix of precipitation types. Total liquid equivalent now looks to be on the order of about ¼" or so. Obviously, if that were to be all ice, then we would have some real problems, but that does not appear likely either.
After that, the rest of the week looks to be mild with another chance of rain on Wednesday.
Of course, this is all subject to change so stay tuned and check back for updates.
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