ALERT For Strong S-SW winds Developing Monday Into New Year Eve_Beginning At Highest Elevations Early And Mixing Down into Middle-Low Elevations
An increasing pressure gradient will drive strong winds across the Cumberland Mountains during Monday into New Year Eve, with S-SW gusts of 30-40+ mph ( especially on mid-upper elevation mountain ridges-exposed plateaus ).
Sunday Night Into Monday Morning
Evening high cloudiness, then increasing clouds overnight with rain developing toward morning, especially along and west-northwest of the High Knob Massif and Tennessee Valley Divide. Areas of fog-low clouds developing. Winds SSW-WSW at 5-15 mph with higher gusts along mid-upper elevation mountain ridges. Temperatures varying from 30s in colder mountain valleys during the evening ( then rising overnight ) to the 40s to around 50 degrees.
Monday Morning Into New Year Eve
Morning rain & showers giving way to partly-mostly cloudy skies ( mostly cloudy in upslope areas of the High Knob Massif to partly sunny in downslope sites of northern Wise, Dickenson-Buchanan counties ). Windy and unseasonably warm. S to SW winds increasing to 15-25 mph, with higher gusts, below 2700 feet. Winds SSW-WSW at 20-35 mph, with higher gusts, on mountain ridges above 2700-3000 feet. Temperatures varying from low 50s at high elevations to the mid-upper 60s.
The Storm Prediction Center has issued a marginal risk of severe thunderstorms along and west of the Cumberland Mountains & Cumberland Plateau for December 31.
New Year Eve Into New Year Morning
Cloudy & windy. Rain developing. Downpours with a chance of thunder during the evening giving way to partly cloudy skies overnight-toward morning. Fog possible in valleys sheltered from wind. SW winds shifting W-WNW and decreasing to 5-15 mph with higher gusts by morning. Temperatures falling into the 40s to around 50 degrees.
New Year Day
Partly-mostly cloudy. Breezy & cooler. Winds WNW-N at 5-15 mph with higher gusts. Temperatures nearly steady to slowly falling in the 40s at middle to lower elevations along and north of the High Knob Massif-Tennessee Valley Divide ( falling into 30s at highest elevations ). Wind chills in the 30s to lower 40s, except 20s at highest elevations in gusts.
Possible development of dense fog is being monitored for late New Year Day into New Year Night-Wednesday AM as cloud bases lower on upsloping N winds and cool advection in places along-north of the High Knob Massif-Tennessee Valley Divide. Stay tuned for a possible alert.
The track of an upper-level low and cold pocket aloft is being monitored for possible accumulating snow by the January 4-5 period.
Weather Discussion ( A New Year )
An active but unseasonably mild weather pattern is closing out the soggy year of 2018, as a Major Sudden Stratospheric Warming ( SSW ) event is underway at high altitudes in the stratosphere.
High Knob Massif Webcam_University of Virginia’s College At Wise
Conditions in the troposphere and stratophere are not unrelated. Waves originating within the troposphere have rippled upward into the stratosphere where their breaking has resulted in releases of energy and momentum ( raising air temps ).
Wave 1 Height Amplitude At 60 North And 10 MB
Waves from the troposphere began reaching well into the stratosphere during Autumn 2018, with a recent record high amplitude achieved in December ( above ) and a subsequent elevation in temperature as waves lift the air aloft to cause warming.
The lapse rate in the stratosphere tends to be negative or directly opposite to that in the troposphere, such that rising air warms instead of cooling with increasing height. Waves that lift air in the stratosphere cause warming ( below ).
Mean Temperature Above The North Pole At 10 MB
Breaking of tropospheric waves in the stratosphere also releases momentum, slowing and even changing the speed and direction of flow ( below ).
Zonal Mean Westerly Winds Decrease In Speed And Become Easterly
The Bottom Line…
The beginning of January 2019 will be a highly transitional period and models will tend to struggle, as recently observed, more than usual given that changes occurring both horizontally and vertically, from the stratosphere to troposphere, will now have to be resolved in order to make accurate forecasts.
I expect more dependable and clear forecasts into the medium range to emerge as this troposphere-stratosphere-troposphere coupling continues to cycle and changes now underway within the stratosphere work down into the troposphere during the next couple of weeks.
European Model MJO Forecast_December 30 to January 13
As this major SSW event continues, a changing MJO or Madden-Julian Oscillation will be moving through phases 5-6 into phases 7-8-1 during January 3-13.
MJO Climatological Temperature Impacts During December-February
The progression of the MJO from the warm phases of 5-6 into the colder phases of 7-8-1 will be occurring during the January 3-13 period.
If the European Model is correct this suggests that cooling will intensify after January 5-7, so time will tell how all these factors interact with a Modoki El Nino ( central Pacific based warm anomalies ).
Sea Surface Temperature Anomalies At 1 AM December 30, 2018
Model differences into mid-January are currently exemplified by the 51-members of the European group which predict snow amounts varying from nearly nothing to excessive depths.
