This morning's forecast focus continues to be on the likelihood of a significant winter storm affecting parts of the region late this week and into the weekend, with less eventful, if not totally quiet, weather preceding it. Details on the situation will come later in this discussion, but the bottom line is the medium range models continue to support the potential for a prolonged period of freezing rain affecting at least a portion of eastern Oklahoma beginning Friday, as well as heavy rain and flooding from southeast Oklahoma into western Arkansas.
Today, low level moisture will continue to increase as southerly flow strengthens ahead of an approaching front set to move through the region tomorrow. Cloud cover will be on the increase by this afternoon in response, with some patchy drizzle southeast of Interstate 44 also possible. Low temperatures tonight will likely occur during the evening in most spots due to the moisture return.
Low level winds will increase quite a bit tonight as a strong southwesterly low level jet develops, and it is possible that some parts of northeast Oklahoma and northwest Arkansas may reach advisory criteria. Will hold off on that for now, but will pass along concerns to the day shift.
The aforementioned front will move through a portion of eastern Oklahoma and western Arkansas tomorrow, with little associated decrease in temperature expected. South winds will make a quick return Wednesday, leading to even warmer temperatures than those expected tomorrow.
A stronger front will move through Wednesday night and early Thursday, likely becoming hung up in the higher terrain of southeast Oklahoma and northwest Arkansas. Showers and perhaps an isolated thunderstorm will be possible along the boundary, as deep layer moisture increases with the development of southwesterly upper level flow resulting from the approaching strong upper level trough.
Speaking of the strong upper level trough, this slow moving feature will be responsible for the significant weather event, both of the winter and flooding variety, that may affect eastern Oklahoma and western Arkansas from Friday into the weekend.
Moisture will continue to pour into the region ahead of the trough, with well above normal (+2 to 3 standard deviations above normal) precipitable water values expected. Due to the quasi- stationary nature of the front, heavy and repeated episodes of rainfall are likely near the boundary, which would lead to a considerable flooding risk, despite the ongoing severe drought conditions across a large portion of the region.
This moisture will also affect parts of the area located in the cold air, which continues to look very shallow. The 00Z model suite continued the westward trend contained in their 08/12Z counterparts, and as such, the potential for sleet and certainly, snow is drastically diminished in this scenario. Once again using a 50/50 blend of the GFS and ECMWF yields a 6-10C warm layer aloft, and in the presence of the aforementioned shallow cold air, supports freezing rain as a dominant winter type. The best chance for significant ice accumulations and the potential for prolonged power outages continues to be to the northwest of Interstate 44 in the latest data, with total amounts at least approaching, if not exceeding, an inch through Sunday. Expect the location of the freezing line to be refined with later datasets, which would, of course, affect the areas affected by the ice accumulations.
The effects of the upper low could linger into at least the early part of next week, although the medium range data differ on when the low will actually exit our area.
We continue to stress that although some details in this forecast exhibit less uncertainty than others, uncertainty nevertheless remains. There will continue to be refinement in all the details as additional data, closer to the event in question, are received and analyzed. Continue to monitor trusted weather forecasts through this week.