2/12/12 - 2/13/12 South Plains Winter Precipitation Event

A difficult forecast is on tap for the southern plains as a winter precipitation event is expected to unfold tomorrow evening into the morning hours on Monday.

A piece of energy in the southwest US will continue to move eastward and will lead to weak cyclogenesis and return flow across much of the southern plains. Moisture advection will begin in earnest by Sunday evening as a nocturnal low level jet on the order or 50+ kts gets going in full force.

5PM Sunday WRF Forecast - Norman, OK  - Note the dry air through the column

The atmosphere will quickly saturate with the low level jet returning moisture into the area Sunday evening. Lift associated with the upper level energy should aid in light precipitation developing across western Oklahoma and Texas by Sunday evening before overspreading much of Oklahoma and into areas of Arkansas and Missouri in the pre dawn hours Monday.

1AM Monday WRF Forecast - Norman, OK - Note the column now saturated with the model generating light to moderate snow.

SREF Forecast - Notice the spread in members

There is a rather wide spread in the SREF members, not only in the surface temperatures, but also the effect of the temperature advection in the low levels. The overall wind and jet structure (at least to me) seems rather anomalous to ordinary winter storms.

At this time it appears that the best potential for significant snowfall (significant with respect to 2011-2012 winter season) will lie across far northeast portions of Oklahoma, and portions of southwest Missouri. These ares will be under less influence of warm air advection and will likely see a longer period of snow accumulations than other areas.

12.00z NAM forecast showing Warm Air Advection taking place Monday in the early morning/pre dawn hours.

Although the event will ultimately come down to short term forecasting and analysis, the models are in a decent consensus at the moment about the overall setup and evolution, but very small differences in thermal profiles (totally inside the range of uncertainty in this model range) preclude greater certainty in the event.

Taking the NAM with a grain of salt, and using its forecast, I would expect precipitation to begin by late evening Sunday evening, likely starting in the form of sleet or snow before transitioning to all snow through the early hours Monday. By Monday morning, precip will switch to more of a mixed bag, which is where hazardous travel becomes an issue. The mid levels will continue to warm through the overnight hours, while the surface stays cool, possibly allowing for a few hours of a very light glazing of ice, mainly across central Oklahoma where the best conditions for such an occurence exist. Elsewhere, expect probably a 1-2 inch snowfall across much of Oklahoma west of I35 with 2-3 east of 35 and north of I40. Higher amounts of 3-5 inches may be found in portions of far northeast Oklahoma and southwest Missouri but these will likely be isolated.

NAM Snowfall Forecast

Well, we will see where this forecast leads us!