ALERT For The Potential Of More Heavy Rain With A Strong-Severe Thunderstorm Potential Saturday Afternoon Into Saturday Evening

*A upper-level low will spread waves of rain and thunderstorms across the mountains during Saturday afternoon into Saturday night.

Interactive 500 MB Flow Field_USA

*Strong rises will occur on streams in locations that receive heavy rainfall, especially in places impacted by a general 1.00″ to 2.00″ of rain during 23-24 April.

Interactive Doppler Radar

*Turning much colder Sunday with strong SW winds and wrap-around showers. Temperatures will fall into the 40s in locations along southwest to west of the High Knob Massif and Tennessee Valley Divide. Low cloud bases with dense fog at upper elevations, possibly dropping through middle into lower elevations.

Interactive 850 MB Flow Field_USA

*Expect cold air with low cloud bases late Sunday into early Monday. A chance of showers, with possible high elevation snow showers or mixed precipitation.

Conditions_Lonesome Pine Airport In Wise

A dense fog potential will need to be monitored for locations along and north-northwest of the High Knob Massif-Tennessee Valley Divide on upsloping northerly flow late Sunday into early Monday.

Another Double Digit Precipitation Month

It is very likely that precip totals for April will once again break the double digit barrier this weekend, marking the third consecutive month (if using a Midnight-Midnight format) to reach massive amounts in the High Knob Massif.

Mid-Spring 2020_High Knob Massif

Precipitation totals for 2020 are presently around 40.00″ in wetter portions of the High Knob Massif, and April is not complete yet.

Weather Headlines

*A wave of rain will overspread the mountain area Friday night into early Saturday. Rain may end as wet snow at highest elevations as conditions turn colder, with upper 20s to upper 30s along and north-northwest of the High Knob Massif and Tennessee Valley Divide by Saturday AM.

*Clearing and cold conditions will be observed by Saturday night as another hard freeze develops in colder mountain valleys, despite increasing high cloudiness into Sunday morning.

*Rain will spread across the mountain area late Sunday into early Monday with the next wave. Heaviest amounts are now expected to remain southeast of the Cumberland Mountains.

Totals could still be significant enough to monitor for rises on mountain streams and ponding in low-lying, flood prone locations given existing wet conditions.

Mid-Spring 2020_High Knob Massif

If counting Midnight-Midnight values, April has a good chance to become the third consecutive month with double-digit precipitation amounts at upper elevations in the High Knob Massif.

*The heaviest wave of rainfall, with possible thunderstorms, is now expected to develop late Thursday through Friday (24-25 April 2020).

An active but generally cooler than normal pattern is looking likely through most of the remainder of April 2020.

Cooler than average air across much of eastern North America occurs as the final warming over the Arctic marks transition from winter to spring.

ALERT For Flooding and High Water Levels Will Continue Through Monday Morning For Headwater Creeks – With Rises On Rivers Through Today

As of 5:00 AM Monday a general 2.00″ to 4.00″+ of rain have fallen across the area, with strong rises and local flooding ongoing. Extreme caution is advised.

Big Stony Creek was 2.2 feet above flood stage and rising as of 4:30 AM Monday. Rain totals up to 4.47″ have occurred at upper elevations in the High Knob Massif (as of 5:00 AM).

Thousands of residents are also without electricity due to damaging winds Sunday evening. The most concentrated damage occurred in northern Wise and Dickenson counties when the apparent phasing of a traveling atmospheric wave with stationary orographic waves produced a downward transfer of very strong winds to the surface.

*ALERT For Heavy Rainfall And The Potential Of Strong To Severe Thunderstorms From Sunday Evening Into Monday Morning (12-13 April)

Interactive Doppler Radar

An outbreak of severe thunderstorms across the Deep South will need to be closely monitored through Sunday into early Monday with respect to local impacts on the Mountain Empire.

Interactive 500 MB Streamline Flow Field

The GFS Model has been as consistent as any model can be regarding the development of a band of flooding rains from the Cumberland Mountains southwest across the Cumberland Plateau into middle Tennessee.

Note that the new mid-day Sunday update of the NAM 12 KM Model has now come more in line with a heavy-excessive rainfall corridor like the GFS, but shifted a little northwest of the new GFS axis.

The high resolution WRF Model is a compromise between the new runs of the NAM and GFS, with heavy rainfall across the Mountain Empire.

The European, ICON, and Canadian models also forecast heavy rainfall, but less excessive than the GFS with more run-to-run variations than shown by the GFS as well during the past several days.

The Sunday AM run of the GEM (Canadian) Model is most like the NAM and previous runs of the GFS.

The Bottom Line…Above average uncertainty exists in total rainfall amounts into Monday, but all models agree on the potential for heavy amounts. The final true solution will be in large part dependent upon the severe outbreak across the Deep South and how it unfolds to impact the southern Appalachians and adjacent foothills.

ALERT For Strong SSE-SSW Winds Sunday Night Into Monday…Especially At Higher Elevations And In Mountain Wave Zones

Wind gusts of 40-60+ mph will be likely at upper elevations and within local lower elevations within typical mountain wave breaking zones to the NW-NNE of higher mountains across southwestern Virginia and northeast Tennessee.

Interactive 850 MB Streamline Flow Field

Otherwise, gusty to strong winds will be likely across the entire area.

Wet Snowfall Potential?

A wave of low pressure moving along the boundary that stalls following this outbreak of severe spring weather will need to be closely monitored by late Tuesday into Wednesday (14-15 April) for the potential of a band of wet snowfall.

Weather Headlines

*An Enhanced Risk Of Strong To Severe Thunderstorm Development Will Exist From Late This Afternoon Into Morning Hours of Thursday (8-9 April 2020)

Interactive Doppler Radar

*The potential for strong-severe thunderstorms exists late this afternoon-early evening, along an outflow boundary, and again overnight-early Thursday AM ahead of a strong cold front.

Current 500 MB Streamline Flow Field

Potential for a Derecho-Type cluster of rapid, southeast moving thunderstorms exists for the overnight-early morning hours of Thursday.

What is a Derecho_About Derechos (SPC)

Wind damage, localized large hail, torrential rainfall and, of course, lightning will be the main severe modes (wind damage will be widespread across Kentucky toward the western front of the mountains if up-scale growth into a derecho system occurs).

Current GOES-16 Satellite Imagery

*Much colder air is expected late Thursday into Friday on WNW-NW upslope flow. Low clouds with a chance for snow showers and flurries is being monitored for the windward, upslope side of the Appalachians.

*Sub-freezing temperatures will be likely Thursday night into Friday morning at higher elevations, and in colder mountain valleys Friday night into Saturday morning.

Major Storm Potential Possible Into Next Week

The potential for major storm development is being highlighted in modeling, although timing and details remain to be resolved, for some point between this weekend and the middle of next week.

A huge temperature contrast, with much below average air moving south, will develop a baroclinic (clash) zone favorable for major storm development.

This will be part of a stormy pattern driven by a large northwest to southeast temperature gradient across the central-eastern USA into mid-April 2020.

A deep, positively-tilted upper trough implies, as well documented this year, wetness with the potential for heavy to excessive precipitation amounts (especially along and west of the Appalachians).

Please reference Mid-Spring_High Knob Massif for a recap of recently observed precipitation amounts.

ALERT For Heavy, Wet Snow Accumulations At Highest Elevations Tuesday Into Tuesday Night With A Chance For Heavy Snow And Mixed Precipitation Into Middle Elevations

A southern tracking storm system will spread significant precipitation across the mountain area on Tuesday. Rain and mixed precipitation is currently expected to rule the low-middle elevations, below 3000 feet, with increasing amounts of heavy, wet snow at elevations above 3000 ft.

Update_1:30 PM on Tuesday_31 March 2020

*Very heavy snow has fallen and accumulated at the summit level of the High Knob Massif, covering roadways despite recent above freezing conditions. Travel is being discouraged along Route 619 and adjoining roads toward the summit level.

Although not as classic as some well documented past events, the bright banding signature did take its position along the High Knob Massif with heaviest snowfall along and southeast of the edge of this zone.

Snow that falls next will be associated with the comma-head of the upper level low, with dropping snow levels this evening as temps fall (but generally remaining at upper elevations with respect to sticking).

The Potential Exists For A Crippling Fall Of Heavy, Wet Snow At High Elevations In The High Knob Massif (Fast & Furious Fall)

Temperatures in upper elevation basins fell sharply through Midnight, with dewpoints in the 20s at the summit level where mass convergence is expected.

Some routes currently expected to be impacted include State Routes 619, and Routes 237, 238, 704, among some others, due to rates of snowfall greater than melting on above freezing surfaces.

The most favorable location for heavy snow will be the upslope zones along the High Knob Massif where air flow trajectories and the forecast thermal profile is favorable for formation of a *TIM Circulation (with a rain-snow line setting up on the northwestern flank of the massif in a Doppler radar indicated bright-banding zone).

*The major difference is this is now mid-spring. If a setting like this had developed during the winter I would have been predicting a massive fall of snow. Up to 6″ or more could still occur if a TIM Circulation develops at the upper elevations, such that this is a situation worth watching.

Otherwise, highest peaks on the Blue Ridge southwest to the Great Smokies will be favored, mainly at elevations above 4000 feet.

Snow levels will drop Tuesday afternoon into Tuesday night and the early hours of Wednesday morning, but sticking is expected to mainly be restricted to elevations above 3000 feet [(+/-) 500 vertical feet of error potential].

Longer-Term Persistence

The longer-term pattern is wanting to trend right back into the same type of regime that has made this year so wet, with more heavy to potentially excessive rainfall if this indeed becomes the observed pattern.

Weather Headlines

*A weakening line of strong-severe thunderstorms across Kentucky & Tennessee will approach the mountains late Saturday into early hours of Sunday.

*Strong and gusty SSW-WSW winds Saturday night into Sunday will shift W-WNW with cooler air by late Sunday into Monday.

*Rain overspreads the mountain region during 31 March into 1 April (Tuesday-Wednesday) as air turns sharply colder (rain may end as snow at high elevations).

Colder Pattern Opens April 2020

A colder pattern will open April 2020 across the eastern USA as a negative North Atlantic Oscillation is joined by a negative Eastern Pacific Oscillation.

Note that this is opposite to these observed teleconnections during Winter 2019-20.

Cold weather across the eastern USA is favored during negative phases of the NAO & EPO oscillation patterns versus mild conditions during their positive phases.

Negative phases of the NAO and EPO should result in colder air during early April (in the mean).

As noted above, this would be nearly opposite to the observed winter pattern (below). The difference, with increasing sun angles-insolation and limited snow and ice coverage, air temperatures will be much below the average for this time of year but well above what they would have been during the same pattern in winter.

An ALERT For Elevated Stream Levels Will Continue Into Thursday (26 March 2020)

A general 1.63″ to 2.05″ of rainfall pushed steep creeks draining the High Knob Massif to near and above flood stage. High water levels will continue into Thursday. Extreme caution is advised.

Big Stony Creek crested 0.6 feet (7″) above flood stage at 2:15 AM on 25 March, with roaring water levels continuing along this creek, South Fork of Powell, Little Stony Creek, Clear Creek, Stock Creek, Cove Creek and many others that drain the border area of Wise-Scott-Lee-Harlan counties.

Main-stem rivers will also continue to be elevated into Thursday, at near flood stage, with falling levels through the end of this week. Caution Is Advised.

**An ALERT for strong SSW-WSW winds may be needed for mid-upper elevations during Thursday night into early Friday with strong warm air advection.

Former Statements

A Heavy To Locally Excessive Rainfall Potential Is Being Monitored Through Wednesday Morning (March 25)

Weather Headlines

*Another wave of significant rainfall, with thunderstorms possible, will impact the mountain region from afternoon hours of Tuesday into early Wednesday.

*Residents living and driving in low-lying, flood prone locations will need to closely monitor conditions. Stay tuned to NOAA Weather Radio and your favorite media sources for possible watches or warnings.

*A marginal risk of strong to severe thunderstorms has been shifted southward by SPC for Tuesday (24 March). This remains to be seen and could still be adjusted back northward. Regardless, embedded thunderstorms and another wave of significant rainfall remains likely.

**Tuesday presents concern for development of a squall line or scattered area containing strong-severe thunderstorms across southern Kentucky-Tennessee. An eastward movement needs to be monitored for the southern Appalachians into Tuesday night.

Precipitation Totals
1-23 (AM) March 2020

Black Mountain Summit
7.54″

*Big Cherry Lake Dam
7.41″

Eagle Knob Summit
7.32″

High Chaparral-Robinson Knob
7.08″

Clintwood 1 W
5.57″

*The 2008-2019 average for the entire month of March is 6.36″, such that month-to-date precipitation is currently running 2.69″ above this average.

Reference 2019-20 Precipitation Totals For More Values.

Looking Into April 2020

It is more of the same through this week, with intervals of rain-thunderstorms and up-down temperatures amid a general milder than average and, of course, wetter than average regime across the eastern USA.

A -NAO pattern (above) is now showing up in the ensemble mean modeling for the end of March and first week of April 2020. This will generate a notably cooler weather pattern.

Changes are finally showing up in a more consistent manner within the modeling as an ongoing stratospheric warming continues above the North Pole with transition from winter to spring across the Northern Hemisphere.

Temperatures at 30 MB above the North Pole (above) have been much colder than average during most of the 2019-20 Winter Season (gray line = climatological mean).

A pattern featuring a colder trend, of some duration yet to be determined, is becoming more likely by the end of March into April 2020 as a powerful polar vortex that has dominated the Northern Hemisphere winter season finally weakens (releasing lingering arctic air)#.

#Weakening has been slow given the anomalously strong polar vortex. The magnitude of the final warming and impacts to middle latitudes remains to be seen, but changes of some form are likely across North America.

The European Ensemble and GFS Ensemble means are in general agreement with a negative trend developing in the North Atlantic Oscillation. This -NAO will favor colder temperatures across the eastern USA.

The PNA has been persistently negative during the 2019-20 winter, but a notable trend toward neutral (European Ensemble mean) and positive (GFS Ensemble, above) is now being predicted heading into early April 2020.

These trends will favor a period, at least of some duration, of colder conditions relative to average.

More accumulating snow may also occur, at least for the mid-upper elevations, which would fit April climatology.

Weather Headlines

ALERT For Dropping Cloud Bases And Dense Fog From Upper Elevations Into Middle Elevations On Northerly Upslope Flow And Cold Air During Saturday

*Dropping cloud bases on northerly upslope flow is expected to impact locations along and north to northwest of the High Knob Massif and Tennessee Valley Divide as air turns much colder through Saturday.

Saturday Update_2:00 PM: Low clouds are engulfing a wide area on upsloping northerly winds in wake of soaking rainfall. Afternoon air temperatures vary from 30s at upper elevations (gust wind chills in 20s) in the High Knob Massif to the middle 40s at lower elevations to the north.

Early afternoon temperatures are in the low-mid 50s toward the south in the Tennessee Valley, from TYS to TRI, with good visibility under downslope flow.

Caution for high stream levels through Saturday on headwater creeks draining the High Knob Massif-Black Mountain corridor in wake of significant rain.

Big Stony Creek crested 1.0 foot (12″) below flood stage this morning (21 March), in wake of soaking rainfall, to continue a trend of elevated stream levels throughout the month of March 2020.

Precipitation Totals
1-21 (AM) March 2020

Black Mountain Summit
7.01″

*Big Cherry Lake Dam
6.71″

Eagle Knob Summit
6.72″

*The 2008-2019 average for the entire month of March is 6.36″, such that month-to-date precipitation is currently running 2.40″ above this average.

Reference 2019-20 Precipitation Totals For More Values.

Previous Statements

*A chance of showers and thunderstorms Thursday, amid unseasonably mild air, will give way to likely activity on Friday in advance of a strong cold frontal boundary.

*Strong SW winds will develop Thursday night into Friday, beginning at upper elevations and mixing downward into middle and lower elevations.

Wind gusts of 30-40+ mph will begin Thursday night at upper elevations and mix downward into middle-lower elevations during Friday. Local wind gusts to 50+ mph will be possible.

*A heavy to excessive rainfall potential will exist Friday, with strong rises on streams more likely in locations that received up to 1.00″+ of rainfall into early Thursday.

Much like late Wednesday afternoon into early Thursday (19-20 March), SW flow will add orographic lift to help enhance totals along the Cumberland Mountains (1.11″ of rain was observed at Big Cherry Lake Dam into early Thursday, with 1.01″ on Black Mountain).

Wintry Feeling Conditions Expected Saturday With Cold Daytime Temps

*Much colder air surges into the mountain area Saturday on northerly upslope flow, with low cloud bases and the threat for more dense fog at middle to upper elevations (rime levels will drop from high summits downward into the 2500-3000 foot elevation zone over time).

A brief intrusion of drier air into early Sunday will allow coldest temps to develop in mountain valleys (coldest conditions Saturday will be at highest elevations) with potential for strong low-level inversion formation (coldest conditions in valleys with rising temps on high ridges into Sunday morning).

An exception may be in some lower elevation locations where clearing over wet ground may allow for dense fog formation. Stay tuned for later updates.

*Additional waves of significant precipitation will be likely from late in the weekend through next week. Interaction with colder air at times may need to be monitored for the potential of some frozen forms, especially to the north and northeast.