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 )!
A harsh period of winter weather is poised to strike the mountain region during the next 7-14 days. This has been well anticipated by large-scale changes amid the atmosphere across the Northern Hemisphere.
Temperatures above the North Pole at 10 MB have recently been at RECORD high ( warm ) levels for this time of year, having warmed dramatically from near record low ( cold ) values in late December and mid January.
Zonal Mean Temperatures in the 60-90 degree latitude range at 10 MB have also peaked at record high ( warm ) levels in recent days.
Record strong Wave 1 forcing has been responsible for the dramatically high stratospheric warming in upper levels.
Wave 1 forcing has been strong through the depth of the stratosphere ( near bottom level above ), but clearly has been strongest in upper levels of the stratosphere.
Wave 2 forcing has been weaker than average this winter.
A sense for what Wave 1 means can be gained by looking at the European Model’s 10 MB analysis ( above ) at 7 AM on February 7, with dramatic warming over Siberia associated with a single ridge and trough couplet ( High and Low at 10 MB in the Stratosphere ). Upward WAF ( Wave Activity Flux ) from extensive Siberian snow has helped to drive this event along with a favorable large-scale pattern that allows for co-location with the MEAN climatological standing wave pattern of the Northern Hemisphere winter-time, in addition to Torques driven by major mountain barriers.
For comparison, above, I have the 10 MB analysis at 7 AM on January 30. Note that the TEMP MAX is listed at -22 C verses the TEMP MAX of +18 C on the previous 10 MB analysis for February 7. That is a 72 degree F ( 40 C ) increase in temperature in 9 days.
Despite dramatic high stratospheric warming, this event has not been able to yet reverse winds at 60 degrees North and 10 MB to meet the technical criteria for a major SSW event ( Sudden Stratospheric Warming ).
There is considerable debate about whether this technical definition for a major SSW event needs to be defined in different terms and/or expanded to also include additional scenarios like this event which has clearly had an important impact upon the Polar Vortex and Northern Hemispheric weather pattern.
The European Model forecast is ever so close to meeting the technical definition, with easterly winds shown at 45 N and 10 MB as well as at 72-90 N and 10 MB but not at the defined 60 N and 10 MB required for the technical declaration of a MAJOR SSW event. So the debate continues.
The Arctic Oscillation ( AO ) which has recently been in a positive phase is forecast to trend back negative for a long period of time. Past climatology, following SSW events, show that -AO periods of 4-6 weeks are not uncommon.
Despite the +ENSO in the Pacific, temperatures this winter have been strongly correlated to the phase of the AO.
Note above how the AO was mostly in a positive phase from November to the start of January ( when we observed above average temperatures ), then shifted into a negative phase through most of January ( when it was cold ). Recently, the AO has been positive and temperatures have been mild. A very high temp correlation this winter to the AO phases.
The North Atlantic Oscillation ( NAO ) is also trending back toward a negative-neutral state on the GFS. The ECMWF Ensembles forecast a more negative NAO trend than the GFS ( I am not allowed to show the ECMWF due to rights established by the European Center For Medium Range Forecasting which require a very costly license ).
A positive Pacific North American ( +PNA ) oscillation phase is predicted to continue, and become very strong in the next few days as a big western North American ridge builds.
The Eastern Pacific Oscillation ( EPO ) is forecast to remain in a negative phase through most of this week, then become positive before dropping again later. Recall last winter that temperatures had a high correlation to the EPO phase.
*Temperatures in the eastern USA almost always tending to have correlation to the PNA phase of various degrees, with western USA ridging naturally correlating to downstream troughing ( and visa versa ), with variations in tilt and amplitude at any given time.
In basic summary, all teleconnection phases are coming into alignment for an arctic outbreak this week with a prolonged negative AO phase upcoming to suggest that colder than average conditions will continue.
**It is very important to again stress that teleconnections are not driving these changes, but instead are in response to large-scale changes and allow us to be able to more clearly predict what such changes may do in the near future to a given weather pattern.
The European Model 100 MB stratospheric forecast ( which I can show ) is supporting this via ridge building and blocking in the North Atlantic into Greenland, and a vortex split and orientation that is acting to drive cross-polar flow from Siberia through Canada into the eastern USA.
This vortex split being only visible up to around 50 MB at 10 day, with the big change in orientation of the Polar Vortex and the pronounced North Atlantic ridge near Greenland being most important and pronounced.
A pattern that is simply primed for delivery of bitterly cold air ( late season ) into the region during the next 7-10 days. Any snow on the ground will act to make this colder.
During the next 10 days the European Model snow forecast is predicting a general 6″ to 16″ to fall along the upslope side of the Appalachians ( with respect to W-NW flow ).
The problem, of course, this is based upon 10:1 snow densities and the upcoming cold will make snow density much lower. Amounts in such a setting could easily be 2-3 times as great. Climatology of past settings like this certainly supports such amounts, especially amid upper elevations in the High Knob Massif and other of the most favored sites such as Snowshoe Mountain in West Virginia, Mount LeConte in Tennessee & Mount Mitchell in North Carolina.
Snowfall will be over a prolonged period of time, and not associated with a single dump. With that noted, the El Nino enhanced subtropical jet is not dead by any means. Merely suppressed to the south. So danger remains that a phasing event between the sub-tropical and polar jets will again occur as happened during January. It is very difficult to say when that might occur, with the most likely time currently being around and just after mid-February when arctic air begins to relax ( allowing the sub-tropical stream a potential entrance into more northern latitudes ).
The Bottom Line…Winter 2015-16 has a great amount of “gas” left in the tank, with a period of harsh winter conditions likely to develop this week into this next weekend. The strong +ENSO event of this winter has not been typical and nothing like that of 1997-98.
Snowfall during the next 1-2+ weeks could be significant, with total amounts that fall likely being greater than depths at any given time due to melting, sublimation, and settlement of snow on the ground over time ( if you want an accurate snowfall reading, then measure and sweep the snow every 6 hours to obtain 4 amounts to add up for each 24-hour total ).
As always, there are likely to be “wrinkles” and changes in this pattern that are not currently seen. The +ENSO jet adds complexity, with fluctuations in the timing of all embedded disturbances in arctic, polar, sub-tropical streams acting to play a role in the type of weather experienced on any given day. This extended is only a general guide to be used for the synoptic ( i.e., large-scale ) pattern, with details of any given day having to be worked out.
The cold January experienced is likely to be repeated during February ( perhaps March ) as the upcoming thaw period is merely a reloading interval for more wintry conditions ahead.
A stratospheric warming event is beginning and looks to become an important player in weather conditions for the remainder of Winter 2015-16 ( whether or not the warming becomes a major stratospheric event is yet to be seen ).
Observe how the change in phase of the AO from positive through December changed to negative at the beginning of January ( when colder weather overspread the eastern USA ).
Temperatures this winter have had a strong positive correlation to the phase of the Arctic Oscillation ( AO ) which is currently expected to trend positive to close January and open the month of February.
Given the previous trend in the AO it is not surprising to see a shift into above average temperature to close January and open up February. However, this positive trend in the AO is different from that observed during autumn-December and is now much more strongly linked to coupling between the stratosphere-troposphere than earlier in the season.
The latest 6-10 and 8-14 day outlooks are already reflecting the flip back to cold conditions as the AO trends negative.
Note how temperatures above the North Pole have been very cold, below climatology ( below ), but that the forecast now shows a sudden increase in temperatures over the North Pole at 10 MB heading into February. Note warming to near climatological mean levels occurred in early January but it was nothing compared to the magnitude of this predicted warming. Still even this warming is not yet shown to generate a technically Major SSW.
An upward flux of wave activity above extensive snowpack across Siberia initiated changes in the Polar Vortex which acted to drive the AO phase shift observed at the beginning of January.
Models predict new surges of WAF ( Wave Activity Flux ) during the next few weeks to greatly perturb the polar vortex & drive a Sudden Stratospheric Warming ( SSW ).
The European Model is predicting around 40 degrees F of warming at 10 MB in the stratosphere, over Siberia, by the end of the first week in February ( above ).
It is well understood that a Major SSW event does not technically occur until winds reverse direction at 60 degrees North & 10 MB.
There is some debate, perhaps well justified, that this type of strict definition needs to be modified.
That is why I term the above a stratospheric warming without reference to it being a Major SSW. That may or may not happen. Any technically Major SSW would tend to have large impacts on the Polar Vortex, but warming periods as observed earlier this month and which appear now do impact the vortex.
Very strong Wave 1 forcing is predicted to continue through this coming week, with new surges in WAF likely during the second week of February ( to further perturb the Polar Vortex ).
Observe that Wave 1 forcing ( below ) is currently near record levels with near surges in Wave 1 forcing ( above ) predicted during the next 10 days.
This initially tends to push the AO positive ( note above that a +AO spike occurred in December before the sharp negative phase developed into January ). The SSW event upcoming is expected to drive the AO negative again ( this time it will be long-lived in nature if past climatology is any indicator ) in its wake, or during a prolonged SSW period.
The polar vortex is like a great blob or amoeba and is constantly changing shape. It is forecast to change both shape and orientation during the next 10 days.
Current indications suggest building heights over the northwestern portion of North America and Alaska will combine with circulation around the PV to again develop cross-polar flow into central-eastern portions of North America beyond this upcoming thaw period.
A big western North American ridge and eastern USA trough pattern is looking likely by later next week into the week of February 7-13. Along with that may come the next MAJOR Winter Storm threat for the southern Appalachians.
The Bottom Line…The potential for more arctic air mass surges into the eastern USA is increasing for February ( even March ) as a sudden stratospheric warming ( perhaps a major event ) weakens the Polar Vortex and allows for development of cross-polar flow from Siberia through Canada into the USA ( +PNA ).
A continued active sub-tropical jet enhanced by the +ENSO is likely to generate more storms, with the next potentially major winter storm event for the eastern USA and southern Appalachians timed for the week of February 7-13 ( timing subject to change ).
February 3 Update – Odds of an important fall of snow is increasing for the February 8-9 period, especially along the upslope side of the mountains.