Winter Weather Discussion for December 8 – 12, 2007.
– Snow is possible for northwest Oklahoma and the panhandles of OK/TX Sunday into early Monday. Freezing rain is possible southeast of the snow area, generally in west-central through north-central Oklahoma.
– Additional frozen precipitation is expected Monday night through Wednesday.
Complex event shaping up for the weekend into next week. Models are similar regarding the mid-level pattern, which is described by a slow moving low over the southwest U.S. This system should develop Friday evening and stall for a few days as it attempts to close and potentially cutoff from the southern jet stream. The northern jet stream will be characterized by a large low over northeast Canada with a broad shortwave ridge over Alaska and western Canada.
Lots of discussion ongoing this morning regarding what is expected during the forecast period. I'm going to give it my best shot, owing mainly to model differences for uncertainty. Also knowing that closed lows can be quite difficulty to deal with.
As the southern stream closed low develops on Friday the mid-level flow will back to the southwest with a surface low developing in Colorado. Warm, moist air will start moving north from Texas with dewpoints in the low 60s per the 15z RUC. As this is occurring, a shortwave trof is progged to rotate around the base of the large low in northeast Canada and dislodge partial Arctic air. Said Arctic air is then progged to ooze southward into Oklahoma on Sunday. 12z NAM shows the main push occurring around 12z Sunday; the 00z GFS is quite similar on the temperature prog. However, this is the general description and does not account for local effects. So, the real impacts appears to start Sunday per both 12z NAM/GFS runs. Given that southwest closed lows usually evolve slower than initial progs, this is not a shocking development. This is shown in the 500mb map as a shortwave trof ejects out of the mean closed low position. Precipitation show begin in earnest late Sunday across the
northwest and panhandle. In the southeast, it appears that some shower activity will occur along the cold front.
Current indications are that snow will be the precipitation type in the panhandles and in to far northwest Oklahoma. Just southeast of that area mainly from west-central to north-central we'll see a mixed bag. The primary type in the mix bag area will likely be freezing rain. Current model QPF doesn't leave much to be worried about until late Sunday and primarily over north-central Oklahoma. Since that is still a ways out, I'm going to hold off and see how the models change.
Monday – Wednesday look ripe and will have to be closely monitored. A big problem for this time period will be the lifting out of the southwest U.S. upper system and intense warm air advection. At this time it appears that frozen precipitation is likely for the northwest 1/2 of Oklahoma, however this area will change.
Ground temperatures are in the mid-40s, so they may be a factor for freezing rain, but not for moderate/heavy snow.
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