Rain & Snow Will Develop Today ( Jan 17 ) With Amounts Varying From Little To None Up to 1-3″
I have expanded my accumulations to now include more of the area, with snow accumulating at temperatures above freezing northward to Clintwood.
A fast moving weather system will spread a mix of rain and snow across the mountain area Thursday, with cooling on upslope winds expected to favor locations along and south of the High Knob Massif for greatest snowfall amounts.
A Major Weather Change Is Expected This Weekend With Strong Winds & Rain Saturday Giving Way To Plunging Temperatures & Wind Chills Sunday
Temperature are expected to fall through the 10s at lower-middle elevations, and through the single digits at upper elevations, during Sunday, with colder wind chills.
Former Alerts Ending Late Evening_January 16
ALERT For Low Cloud Bases On Northerly Upslope Flow With Dense Fog Changing To Freezing Fog At Middle-Upper Elevations Along & Northwest-North Of The High Knob Massif-Tennessee Valley Divide.
Drizzle to freezing drizzle & light snow will also be possible. Any snow accumulations are expected to be light.
Caution Is Advised For Low Visibility & Icing On Above Ground Objects. Icy Patches On Roadways, Especially Secondary Routes At Higher Elevations, Will Be Possible. Dense Fog Will Be Most Consistent And Widespread Above 2500-3000 Feet.
Low Cloud Bases On NW-N Flow_UVA-Wise_11:09 PM January 13, 2018
Rime deposition with freezing fog ( clouds ) began at the summit level of the High Knob Massif around 8:00 PM on January 13.
Freezing levels had dropped downward to higher portions of the Wise Plateau at 11:00 PM on Sunday, and will continue dropping into Monday AM.
Temperatures will remain below freezing at upper elevations through a prolonged period and will also struggle to rise above low-mid 30s, beneath an 875 MB centered inversion, to maintain raw, cold and damp conditions at middle to lower elevations.
Freezing Fog At 4:12 PM on January 14, 2019_UVA-Wise
Update – Monday Afternoon_January 14, 2019
My alert will continue tonight as freezing fog has become widespread at elevations above 2500 feet, locally dropping to around 2000 feet, in locations on upslope flow along and north of the High Knob Massif and Tennessee Valley Divide. Be safe and slow down.
Eagle Knob of High Knob Massif At 4:04 PM_January 14, 2019
Weather Headlines ( January 14-21 )
A short break, with partial mixing out of an inversion centered around 875 MB, on Tuesday PM gave way to more low clouds and renewed riming at the upper elevations where amounts were already significant.
Heavy Riming At Upper Elevations of High Knob Massif_January 16, 2019
So I left my alert for fog and low clouds through the daylight hours of Wednesday ( riming continues at highest elevations as of 1 AM Thursday ).
Following another nasty system today ( Jan 17 ) focus will shift to a major event this weekend which will bring the first of what likely will be numerous blasts of arctic air into the Appalachians.
Previous Headlines
Nasty conditions brought by a Miller B style winter storm during the weekend will finally improve on Tuesday as sunshine returns.
Conditions will begin to deteriorate later this week with strong winds and rain developing well in advance of a major arctic outbreak.
European 51-Member Ensemble Mean 500 MB Height Anomalies_Days 6-10
Rising heights with building High pressure at high latitudes and lowering heights at middle latitudes will begin driving bitterly cold, arctic air southward later this week into the January 20-21 weekend.
European Model Temp Anomalies & Wind Forecast_January 21, 2019
Although specific details remain to be worked out from this distance, and changes are certain to occur from current projections, a threat for severe winter conditions is great enough to begin highlighting it now ( given this could be life threatening for those caught unprepared for such conditions ).
Given a major Sudden Stratospheric Warming that already has occurred, this increases the odds for a major intrusion of bitterly cold air. This has now been on the table for weeks, so it should not be a surprise that middle latitude weather is poised to turn severe. In fact, timing is nearly ideal, based upon past climatology for such events.
Sudden Stratospheric Warming Became Official On New Year Day
This major mid-winter warming event ( SSW or Sudden Stratospheric Warming ) at high altitudes above the arctic became official at beginning of the new year on January 1.
Zonal Mean Wind Analysis At 7 AM on January 13, 2019
This resulted in a splitting of the Polar Vortex, with two major centers currently dominating the 10 MB flow field within the stratosphere.
Although temperatures are cooling again in the arctic stratosphere, winds continue to be reversed and are predicted to remain easterly through the next 10 days as the impacts of this major SSW are working downward into the troposphere.
Temperatures Cooling From Record Warmth Above North Pole
Major teleconnections on both the European and GFS ensembles are trending in the direction conducive for severe winter conditions in the eastern USA.
A small negative trend in the PNA being offset by a much larger negative trend in the EPO. A point of notable inflection in these indices, centered on the January 20-21 weekend, is often indicative of major cyclogenesis; otherwise, the longer-term tendencybeing toward bad-severe winter conditions with or without major cyclogenesis by this weekend.
Mean Zonal Winds Become Easterly At High Latitudes
Since I consider this upcoming pattern to be so important, I have inserted a preliminary look at my weekly weather column, to be officially published on January 16, for those interested in a more plainly worded description of what is expected ( * ).
It should be stressed that the most important aspect that I am trying to get across is not whether a major arctic blast hits exactly on January 20-21, but rather that a hemispheric pattern change forced by changes already observed in the stratosphere will be setting the stage for severe winter conditions during weeks encompassing the second half of winter and possibly into Spring 2019.
*This marks 26 years that I have written weather columns.
The core of this upcoming air mass will have temps at or below -25 degrees Celsius. Many factors yet to be determined will dictate if that type of air mass can reach the Mountain Empire, with snow cover, both locally and to our north, being critical to how cold temperatures ultimately get in the short-term.
A major winter storm, likely with more than one wave, will be impacting the eastern USA within the baroclinic zone ( temp contrast ) that forms and intensifies ahead of incoming bitter air.
