042516 Forecast

My Weekend Forecast ( April 23-25 )

*Frost Formation Will Be Possible Into Sunday Morning In Colder Mountain Valleys, Especially At Elevations Above 2500-3000 feet.  
Fog Formation Will Be Possible In Other Locations At Low-Middle Elevations In the Clinch, Powell, Russell Fork-Levisa Fork, Holston and Cumberland River basins.

Overnight Into Saturday Morning

Mostly cloudy and turning cooler.  Winds NW-NNE at 5-15 mph, with higher gusts.  Temperatures dropping into the lower 40s to lower 50s ( coolest at the highest elevations ).  Wind chills in the 30s along upper elevation ridges.

Saturday Afternoon

Decreasing clouds by mid to late afternoon into the early evening.  Cool.  NNW-NNE winds at 5-15 mph, with higher gusts.  Temperatures varying from upper 40s-lower 50s at highest elevations in the High Knob Massif to the lower to middle 60s ( milder south toward the Tri-Cities ).

Partly cloudy skies will continue along and south-southwest of the High Knob Massif into this evening, with mostly cloudy skies along and north-northeast of the massif.  Highest elevations will remain obscured in orographic clouds ( i.e., dense fog ).

Saturday Night Into Sunday Morning

Becoming mostly clear.  Seasonably cold.  Frost possible in high valleys with fog formation in many other locations.  Winds light and variable.  Temperatures varying from the upper 20s & 30s in colder valleys ( 28-34 in coldest valleys above 2500 feet ) to the middle-upper 40s.

Sunday Afternoon

Mostly sunny.  Warmer.  Winds becoming SSW to SW at generally less than 10 mph.  Temperatures varying from 60s at highest elevations to the mid-upper 70s.

Sunday Night Into Monday Morning

Partly to mostly clear.  Milder.  Winds SSW-SW at 5-15 mph on middle elevation ridges & plateaus below 2700 feet.  SW-WSW winds 10-20 mph, with higher gusts, along mountain ridges above 2700 feet.  Temperatures varying from mid 30s to lower 40s in colder mountain valleys to the 50s on middle to upper elevation mountain ridges-plateaus.

Monday Afternoon

Partly to mostly sunny ( high clouds ).  Warm.  SSW-SW winds 5-15 mph, with higher gusts.  Temperatures varying from mid 60s to lower 70s in upper elevations to the lower to middle 80s ( warmest at lower elevations of the Russell & Levisa Fork basins ).

Monday Night Into Tuesday Morning

Partly to mostly clear.  Winds SSW-SW 5-15 mph, with higher gusts, along middle elevation ridges-plateaus at elevations below 2700 feet.  Winds SW-WSW 10-20 mph, with higher gusts, along mountain ridges above 2700 ft.  Mild with temperatures varying from the 50s to lower 60s on exposed mountain ridges-plateaus to the 40s to lower 50s within mountain valleys.

Showers & thunderstorms will become likely by late Tuesday into Wednesday & Thursday.  Locally heavy rainfall and strong-severe thunderstorms will become possible, especially west and north of the mountains ( however, this will need to be closely followed ).  Please stay tuned for updates.


Weather Discussion ( April 22-24 )

Saturday Afternoon Update

A large difference in conditions has been observed today, with partly cloudy skies south-southwest of the High Knob Massif-Black Mountain area verses low clouds along and to the north-northeast of this high terrain.  Highest elevations have remained obscured in dense fog of orographic clouds.

High Knob Massif Webcam
High Knob Massif Webcam – University Of Virginia’s College At Wise

Cloud bases are higher, and skies are brightening at times, with drier air upstream of the mountains moving south.

NASA Visible Satellite Image
NASA Visible Satellite Image At 8:30 AM Saturday – April 23, 2016
Differences between this morning and this afternoon can be seen on NASA visible imagery, with increasing dry air along and north to northwest of the mountains on northerly air flow.
Observe the same pattern, with lee-side cloud breaks, has been present all day for many places across Scott, Lee and adjoining counties resting along and downstream of the windward slopes of the High Knob Massif & Black Mountain.  This has been in contrast to a persistent low cloud deck along and north of the High Knob Massif & Tennessee Valley Divide.
NASA Visible Satellite Image
NASA Visible Satellite Image At 3:30 PM Saturday – April 23, 2016
Temperatures in the 40s to middle 50s have been felt all day along and north of the High Knob Massif verses 60s to near 70 degrees in the Great Valley of eastern Tennessee and in lower sections of the Powell River Basin toward Cumberland Gap.
NASA Visible Image With Airport TEMPS Overlaid
NASA Visible Image With TEMPS Overlaid At 3:30 PM – April 23, 2016

No real changes in my previous forecast other than to stress these differences more for the remainder of this afternoon into early evening until drier air overspreads the area.

One change for tonight is to increase the potential coverage of fog to include much of the area outside of places having valley floors above 2500-3000 feet where drier air will be favorable for frost formation.


My Previous Discussion

Much needed, welcomed showers and local downpours in thunderstorms soaked the mountain landscape during the Thursday Night-Friday period of April 21-22.

Spring Moisture On The Trail of The Lonesome Pine
Spring Moisture On The Trail of The Lonesome Pine – Powell Valley ( April 22 )
Some of the heaviest rain fell over the High Knob Massif with general 1.00″ to 1.50″+ amounts.  The greatest rain gauge tally reached 1.69″ at the Upper Norton Reservoir.
Looking South To South Fork of Powell River Gorge
Looking South To South Fork of Powell River Gorge – April 22, 2016

A seasonably cool to chilly air mass will be felt Saturday into Saturday Night-Sunday Morning, with abundant clouds that eventually give way to clearing via the advection, or transport, of much drier low-level air back into the area.

This will set the stage for frost formation into Sunday Morning in mountain valleys with drainage from upper elevations where the 850-875 MB dewpoints will be tanking overnight Saturday into the morning hours of Sunday.  With light winds, and dry air, strong radiation cooling and development of cold air drainage flows will help fill mid-upper elevation valleys with cooling air.

A simply gorgeous, much warmer Sunday is on tap following the morning chill with large mountain valley temperature rises into the afternoon.

A more active pattern returns next week with rounds or waves of showers and thunderstorms expected.  Some of these may become strong to locally severe if a NW flow pattern develops.  Stay tuned for later updates.

Have a great weekend.