Winter Storm: Jan. 28-30 Update #2

Models continue to paint a winter storm over portions of the Southern/Central Plains, however the track and specifics on precipitation totals are still in question.  Both this mornings (12z) model runs and this afternoons (18z) continued to slow the systems progress and hence pull the system further north across parts of Kansas and Missouri.  At the same time, a strong arctic high will progress southward and situate itself over the Northern Plains for the same time frame as the upcoming winter storm.  This will lead to a very tight northern gradient of snowfall amounts, with a 50 mile north/south range of no snow to upwards of 6 inches likely.  The question that continues for most forecasters is where this line will be located at, will it be along/near I70 over Kansas and Missouri like the latest models anticipate, or will it be further south along Highway 54 as initial forecasts indicated?  With this northward progression of the snowfall totals this leads to a further north progression of the sleet and freezing rain totals as well.  Indicating that parts of extreme southern Missouri may see some initial precipitation fall as sleet rather than snow. Thus, a lot of questions remain in play for this system, especially with the system remaining out of reach by the upper air analysis for the forecast models.

We'll once again be waiting to see tomorrow mornings' model runs as they should finally begin to have data from at least portions of the system moving out of the Baja.  For now the previous forecasts are going to have a tendency to be pushed further north, leading the heaviest axis of snow to occur from the Texas Panhandle east/northeast into northern Oklahoma and into southern Missouri. The heaviest band of sleet/ice is expected to occur from central Oklahoma into northern Arkansas, which is especially a change for portion of northern Arkansas that previously were looking at upwards of 8" of snow and are now viewing 2-4" and ice amounts of greater than a 1/4".  Of greater concern is the northward extent of the snow, which as mentioned previously will come on a very sharp gradient.  What makes this situation even more difficult, or easy, depending on what you want to believe is the large amounts of dry air that are being brought down with the arctic high pressure over the Northern Plains.  RH values near 850hPa are going to be below 20% over much of Missouri and adjacent areas on Thursday evening! Now given the dynamics and good warm/moist air advection across southern Missouri and adjacent areas this shouldn't be much of a problem, although limiting the first couple hours of precipitation to saturate this dry layer. The problem arises further north where the winds are likely to stay northeast or easterly at best at 850hPa leading to only dry/neutral advection at best. Areas that cannot get winds turned to the southeast are not likely to overcome this dry air at 850hPa and thus will are not likely to see any accumulating precipitation.  I've included this nice image below to give you an example using the BUFKIT data at KMCI (Kansas City Intl), and a cross-section from northeast Nebraska into north-central Arkansas (thus including Omaha, Kansas City and Springfield). You can see on the BUFKIT overview (on the left) that through Thursday evening we are never able to completely saturate and theoretically allow precipitation to fall. The cross-section to the right shows a good reason why, valid at Thursday 6PM you can see the relative humidity given by the black contours, and frontogenesis in the colored image. The frontogenesis will aid in saturating the layer below, however if you were to watch the loop of the image you would see that it is only strong enough to overcome the area to the south of Kansas City. Leaving KC along the edge of near-saturation and still having RH values of less than 30% at/near 850hPa.

In the end, areas to the south of I70 appear to have the chance at accumulating snow, with areas along I70 at least having the chance of seeing snow occurring. Snowfall amounts near/along I70 will likely be less than an inch, with a rapid increase to the south where nearly 6" of accumulation may be seen 25 miles north of the Highway 54 axis of KS/MO. Exact values and locations still subject to change of course...  I may get an update in tomorrow morning, otherwise expect a quick update sometime tomorrow evening before this system really gets going over the Plains.