A harsh winter pattern during the February 8-15 period has currently relaxed. This has been a repetitive pattern since mid-January and is illustrated well by build-up and melting of snowpacks amid the High Knob Massif.
Whitewater tends to gush when levels reach 2-3 feet, with increasing volume toward RED Alert level resulting in pounding whitewater that ROARS loudly as it plunges along the many steep creeks draining the border area of Wise, Scott, Lee counties.
A long period of enhanced run-off began during the period of January 24 to 26 and continued through the first week of February as snow melt combined with early February rain. Snow depths peaked at 1-2+ feet on January 23-25.
Melt of the current snowpack is ongoing with solid snow still across northern slopes, at upper elevations, late on February 20. Depths peaked between 10″ and 20″ during February 15 at elevations above 3000 feet in the massif.
A mean snow depth of 8″ was measured at the City of Norton Water Plant on February 15, at the northern base of the massif.
Reference Winter Majesty In The High Knob Massif to see actual precipitation totals recorded during this period from Big Cherry Lake Dam & heads of basins for High Knob Lake, Big Cherry, and the Dual Norton Reservoir system.
As noted in my last extended outlook, winter temperatures this season have been correlated to the Arctic Oscillation to a high degree, with negative phases associated with colder than average conditions and positive phases with milder than average temperatures.
Observe that much of January 2016 had a -AO and mean temps were colder than average in the mountain area. The harsh period of February 8-15 is also correlated to a dip back to -AO, with the snowpack melt downs in late January-early February and at the present time associated with +AO phases ( positive phases ).
Naturally, therefore, the future trend of the AO will be of great interest and will likely be associated with how the pattern in the eastern USA trends.
Both the GFS & GEM ( Canadian ) model ensembles predict that a negative trend in the AO will begin on February 21 and continue through the first week of March ( European Ensembles agree well with these forecasts ).
Note I use ensembles and look for the MEAN since they tend to be more accurate than any given model run. The indication is solid for a prolonged negative phase of the Arctic Oscillation to occur.
Another strong indicator of a cold pattern redeveloping is the continuation and increase in strength of a +PNA phase which tends to be highly correlated to western USA ridge and eastern USA trough formation.
Note that means of both model ensembles remain positive through the first week of March ( the European Ensembles again agree with this +PNA forecast ).
This western USA ridge and eastern USA trough pattern is very well developed on the European Ensembles by later this week ( Friday, February 26 above ). A cold signal.
In addition, a NW Upslope Flow setting in wake of a strong middle latitude cyclone is likely to result in significant snowfall along the upslope side of the southern-central Appalachians with largely open expanses of water across Lake Michigan & Lake Superior.
The 51-Member European Ensembles are, in fact, showing a very cold signal for late this week into the early weekend.
Note these temperatures are in degrees Celsius, such that the departure in degrees Fahrenheit is around 20 degrees below average for this time of year by Friday-Saturday ( Feb 26-27 ).
There is increased confidence in these forecasts since they are once again correlated to major stratospheric changes via a polar vortex split, with one lobe moving to between eastern Greenland & western European as the other lobe relocates toward western Siberia. This promotes ridging amid the upper air to reinforce the +PNA pattern.
The splitting of the Polar Vortex and ridge formation in between the two lobes is illustrated above by the DAY 10 forecast from the European Model ( note that stratospheric forecasts out to DAY 10 tend to be more stable and are often better predicted than a DAY 10 forecast in the troposphere ).
Impacts of this are seen in the Mean Zonal Temperatures with a forecast rise from -85+ degrees Celsius above the North Pole on February 19 to around -55 degrees Celsius above the North Pole by February 29 ( below ), with more warming predicted beyond this point.
This forecast is for a 50+ degree Fahrenheit rise in temperature.
Another graphic illustrating the impacts of this are the zonal mean zonal wind changes through the atmosphere.
Observe the lack of easterly flow above the North Pole and the mean Polar Frontal Zone JET Position ( above ) analyzed at 7 AM on February 19 ( around 38 degrees N latitude ).
While this may or may not again meet currently accepted technical criteria for a Major Sudden Stratospheric Warming Event ( i.e., reversal of winds at 60 N and 10 MB ), the impacts combine with the previous episode to continue Polar Vortex disturbance and suggests via past climatology that prolonged negative trends in the Arctic Oscillation can be expected for a period of approximately 4-6 weeks. This alone suggests that March will tend to be colder than average in the eastern USA.
In 10 days winds above the North Pole reverse to easterly in direction and the mean Polar Front JET Position has dipped southward to around 30 degrees North Latitude.
Although not a huge force this winter, it should be noted that the Madden-Julian Oscillation is also forecast to move into Phase 8 through the first week of March, which is a cold signal for the eastern USA.
The Madden-Julian Oscillation ( MJO ) is a synoptic-scale linkage between the atmosphere and tropical deep convection that unlike the standing wave pattern represented by ENSO takes the form of a traveling wave which propagates through equatorial regions on a 30-90 day period, forming intraseasonal variability with impacts beyond the immediate forcing region of the tropics.
Yet another signal for cold to dominate into early March.
The Bottom Line
A trend toward colder than average conditions is expected to redevelop this week with redevelopment of a strong western USA ridge and eastern USA trough couplet. A longer term negative trend in the Arctic Oscillation, in wake of continued disturbance of the Polar Vortex, suggests that colder than average weather conditions will likely dominate March.
More arctic outbreaks and snow is likely in coming weeks, set against rising sun angles and longer days, to extend Winter 2015-16 ( sorry Mr. Groundhog )!