Reference Mid-Winter 2021_High Knob Massif for a recap of recent conditions, as well as a 2020 precipitation update.

Caution For High Water Levels On Streams Draining The Wise-Scott-Lee Border Area And Portions of Dickenson-Buchanan Counties Through Tuesday

A general 1.50″ to 2.00″+ of rain has combined with snow melt to cause elevated levels on creeks draining the High Knob Massif (which are ROARing).

Elevated stream levels may also be encountered locally within Dickenson and Buchanan counties (but with no snow melt contribution, levels are generally not as high as along the Wise-Scott border).

Big Stony Creek was only 12″ (1 foot) below flood stage (6.5 feet) at 4:00 AM on Tuesday (26 January 2021) and continuing to rise.

Caution is advised for swift, dangerous water through Tuesday (26 January 2021).

An ALERT for accumulating snow will likely be needed for Wednesday Night into Thursday.

ALERT For The Potential Of Strong Water Level Rises On Creeks, And Ponding Of Water In Low-lying and Poor Drainage Areas, From Monday Into Tuesday (25-26 January 2021)

While highest probabilities of strong water level rises will be across central-southern Wise, northern Scott, and adjoining areas within Lee, Harlan & Bell counties, the likely development of convection (thunderstorms) will increase the chance in all locations.

Terrain models are now trying to show the orographic couplets that I had anticipated.

Note the orographic wave clouds that are already present above the High Knob Massif as wind fields increase in advance of this system.

Convection could either enhance or diminish these terrain couplets depending upon how it develops.

Previous Discussion

Weather Headlines

The potential for heavy rainfall amounts are being monitored for Monday into Tuesday (25-26 January 2021), with local terrain enhancement becoming possible on strong S-SW low-level inflow.

I like the latest NAM Model idea of generating a secondary zone of enhanced rainfall amounts. This fits documented, past climatology of events with strong SW 850 MB inflow that acts to generate enhanced low-level terrain convergence across the High Knob Massif and Tennessee Valley Divide of the Cumberland Front.

It is not just orthogonal flow that must be recognized, with cross-contour ageostrophic flow developing locally due to terrain generated drag . With that noted, the backbone of the High Knob Massif also turns easterly from the Head of Powell Valley to generate a greater orthogonal component.

Models like the GFS are farther north, with less than 1.00″ of rainfall predicted locally, but it does have a bias of missing terrain convergence along the Cumberlands.

The European Model, and numerous ensemble members, also supports the idea of a secondary maximum in rainfall that is generally aligned with the Cumberland Front (locally) and Cumberland Plateau (farther southwest in Tennessee).

Enhanced Run-Off Potential (26-27 January 2021)

Although snow cover is limited regionally across the southern Appalachians, there is a significant amount of water being held locally in a snowpack at highest elevations in the High Knob Massif.

A good aspect, as I have noted many times in the past, is that watersheds such as those drained by Big Stony Creek, Little Stony Creek, Benges Branch, and South Fork of Powell River all contain lakes and wetlands that initially capture water from their snowiest basin heads. Although all lakes are currently overflowing, this will still slow run-off.

Rainfall will be absorbed by the snowpack, such that unless the worse case scenario develops (torrential rain amounts with rapid snow melt) run-off should be able to be handled.

It will likely push steep creeks to ROARING levels, and will thus need to be closely monitored by both local residents and official, EMS personnel.

Late Week Snowfall Potential

A second wave developing in wake of early week rainfall has the potential to generate significant snowfall by late Wednesday into Thursday (28 January 2021).

Although upper air dynamics appear favorable for heavy snow, the placement, timing, and intensity remain to be worked out for the Mountain Empire.

Stay tuned.