Weather Headlines

Caution for low cloud bases and dense fog will continue through tonight into Monday at middle-upper elevations along and north to northeast of the High Knob Massif and Tennessee Valley Divide.

Orographic lifting of northerly low-level flow will continue producing low cloud bases into Monday, with a shift toward more ESE to SSE flow potentially lifting bases at middle elevations while upper elevations at highest elevations continue to be engulfed.

*Rain into early Sunday will cause rises on mountain streams, as a wet early Spring 2020 pattern continues.

Caution is advised for ponding of water in low-lying locations and for rises on already elevated streams draining the High Knob Massif.

Recent elevated stream levels resulted from a general 1.49″ to 1.91″ of rainfall across upper elevations during 12 March into early on 13 March 2020.

*Waves of rainfall will continue through the upcoming week to next ten days, with potential for 3.00″ or more from western slopes of the Appalachians westward.

The spread on 90 different ensemble members across the European, GFS, and Canadian (GEM) model groups varies generally between 3.00″ to 8.00″ .

Pattern Change_Late March-April?

A Northern Hemispheric pattern change of some form is likely to occur by late March into April as a major change in the Polar Vortex above the arctic and North Pole marks the climatological final warming which occurs during the annual transition from winter to spring.

The 2019-20 winter season has been dominated by much below average air temperatures above the arctic region, a signature of a powerful, strong polar vortex, which has enhanced warming across middle latitudes (i.e., it has been a major player in the mild winter observed).

This resulted in a very strong polar night jet, centered above 65-70 degrees North, along the perimeter of the stratospheric polar vortex [note 60+ meter per second (134 mph) westerly jet core above].

Major warming aloft above the arctic region is forecast to weaken the polar night jet and to change stratospheric winds to easterly (above) during the next 1-2 weeks.

Although still cold (-28 Celsius at core), a 50 degree Celsius temperature rise is expected to occur above the North Pole as part of the final warming and break-up of the polar vortex with transition from winter into spring.

A release of lingering cold air may help to change the pattern at mid latitudes, with a colder trend developing during late March into April. It is possible that a 2-3 week period of colder conditions will develop, although, both the length and focus of colder conditions remain to be resolved in the modeling.

This does not produce a great amount of change in the wet, milder than average pattern through this coming week, but begins to by final days of March.

That more cold air is coming would certainly be in line with climatology, and more snow (especially at mid to upper elevations) will also be possible IF the pattern actually changes.

The lowest temperatures observed so far during March in classic Appalachian cold air collecting basins have varied from 4.5 degrees in Canaan Valley to 5.9 degrees in Big Cherry Lake Basin (12 degrees in Shady Valley and 17 degrees in Burkes Garden).

The 5.9 degree MIN on the morning of 1 March was the coldest reported along the length of the central-southern Appalachians as fresh snow cover allowed enhanced cooling within the high basin. Even lower temps would have occurred if some high clouds had not been streaming across the area aloft.

The 4.5 degree MIN in the northern Canaan Valley frost pocket occurred on the morning of 8 March when conditions in the Big Cherry Basin were much less favorable for extreme minima.

Cold March temperatures are nothing atypical, of course, with 0 degrees (F) being reached in Big Cherry Basin on 16 March 2017. Temps again dropped to near 0 degrees last March, during 2019, but fell only to 12 degrees in March 2018 (a heat wave).

The coldest March temperatures on record occurred during March 1960, with -10 degrees F below zero in Burkes Garden and -19 degrees in Canaan Valley.

My records do not extend back to 1960, but I recorded a -15 degree below zero MIN over 8″ of fresh snow on the morning of 3 March 1980 at Clintwood 1 W (**).

**This suggested that the MIN would have likely been colder than -20 (F) below zero in Big Cherry Basin during March 1980 (based upon typically observed differences between Clintwood and Big Cherry during recent years).

***It is interesting to note that the all-time coldest March temperature in the Tri-Cities, TN occurred during March 1980 with -2 degrees (F) below zero. That is the only March temperature in the record period to reach 0 degrees or below at TRI (1938-Present).

Recent March MINS at TRI reached 15 degrees in 2017, 24 degrees in 2018, and 19 degrees during both 2019 and 2020.