ALERT For Strong SSW To WSW Winds At Mid-Upper Elevations From Tuesday Through Wednesday
A strengthening pressure gradient will support strong and gusty SW winds into the Cumberland Mountains, especially at higher elevations, from Tuesday through Wednesday.
Downpours In Showers And Possible Thunderstorms Will Become Likely Wednesday Through Thursday, In A Pattern Conducive To Training And The Orographic Enhancement Of Rainfall Along And Westward From The Cumberland Mountains
Those living and driving along creeks and in low-lying, flood prone locations will need to be alert for the potential of strong water level rises, especially in locations along and west of the Cumberland Front where orographic rainfall enhancement will be favored over already wet ground.
*Thursday ( March 29 ) is looking like the day with best support for heavy rainfall. If rainfall amounts remain limited and west of the mountains into Thursday it will help but not eliminate the threat. Models currently disagree on how much rain will fall with this system, despite climatologically favored air flow trajectories.
Overnight Into Monday Morning
Mostly cloudy. Windy across mid-upper elevation ridges and exposed plateaus. SE winds 10-25 mph, with higher gusts. Temperatures varying from the upper 20s to the mid-upper 30s. Winds chill factors in the 20s to low 30s, except 10s in gusts at highest elevations.
Monday Afternoon
Mostly cloudy. Gusty. Winds SE-S at 5-15 mph with higher gusts. Temperatures varying from the mid 40s to the mid-upper 50s ( coolest upper elevations and warmest within downslope locations along & northwest-north of the High Knob Massif and Tennessee Valley Divide ). Wind chills in the 30s at the highest elevations.
Monday Night Into Tuesday Morning
Mostly cloudy. Chance of rain showers. Windy. SE-S winds at 10-20 mph, with higher gusts, along mountain ridges and plateaus below 2700 feet. SSE-SW winds 15-30 mph, with higher gusts, on mountain ridges above 2700 feet. Temps varying from the mid-upper 30s to mid-upper 40s. Wind chills in the 20s and 30s ( coldest at highest elevations ).
Tuesday Afternoon
Mostly cloudy. Chance of rain showers. Windy. S-SW winds 10 to 25 mph with higher gusts. Temperatures varying from the upper 40s to lower 50s in upper elevations to the upper 50s to lower-middle 60s ( warmest in downslope locations of northern Wise and Dickenson-Buchanan counties ).
Tuesday Night Into Wednesday Morning
Mostly cloudy. Rain showers becoming likely. Windy. SSW-SW winds 10-25 mph, with higher gusts, on mountain ridges and plateaus below 2700 feet. SW-WSW winds 20-30 mph with higher gusts on mountain ridges above 2700 feet. Temperatures in the 40s to lower 50s.
Wednesday Morning Through The Afternoon
Showers with a chance of thunderstorms. Downpours possible. SW winds 5-15 mph with higher gusts. Temps widespread in the 50s to lower 60s.
A colder than average pattern is being monitored for the first week of April, with the potential for more significant precipitation as winter-spring air masses continue to clash.
Weather Discussion ( Lion In & Out )
Monday Night Update
A flow pattern conducive to significant rainfall amounts is being highlighted during mid-late week. The good news is that the system will be progressive, the bad news being this type of flow is climatologically favored to generate rainfall amounts which are moderate-heavy over very wet ground.
Creeks are running strong and some snow is yet to melt at highest elevations, but mostly the February-March period has been very wet with locally more than 20.00″ of total precipitation.
NAM Model 925 MB Streamline-RH Forecast At 8 AM Wednesday – March 28, 2018
The forecast low-level streamline pattern fits annual climatology = inflow into the Cumberland Mountains from the Gulf of Mexico with orographically enhanced rainfall amounts on rising air flow trajectories. Here is where the pattern is forecast, not any given model prediction of rain amounts. Past climatology, a powerful tool, of similar type settings signals that significant rainfall amounts will be possible to likely from Wednesday through Thursday.
NAM Model 500 MB Vorticity Field Forecast At 11 AM Thursday – March 29, 2018
Upper air dynamics add to low-level orographics by Thursday to continue and enhance the threat for heavy rain with showers and moisture lifting northeast from storms to the southwest ( the local setting does not look favorable for strong-severe thunderstorms which is also good ). If it were not for so much antecedent precipitation during the past 8 weeks this system would not be as much of a concern.
*Although FFG ( Flash Flood Guidance ) is a useful tool, it must be recognized that input precipitation values are typically under-estimated for orographic locations; therefore, high water issues often arise quicker during such wet antecedent conditions than FFG values indicate. The terrain is three-dimensional, complex and is not fully resolved by models, which is where the human factor must come in to improve these model short-comings.
NAM Model 250 MB Jet Stream Forecast At 11 AM Thursday – March 29, 2018
This is not a prolonged flood threat, with the system now expected to clear the area Friday into Saturday, but is one that should not be taken for granted with orographics to be given their proper respect.
Black Mountain Mesonet At 1:40 AM Tuesday – March 27, 2018
Meanwhile, winds are already ROARING at elevations around and above 2800 feet, so caution is advised tonight through Wednesday as tree or tree limb damage may occur due to recent wetness and winter storms.
Flatwoods Mountain Mesonet At 1:55 AM Tuesday – March 27, 2018
Previous Discussion
Although weather conditions may improve by the final hours of March 2018, a setting favorable for more heavy precipitation could push monthly totals into ( or very close to ) double digits for the second consecutive month at the upper elevations in the High Knob Massif.
March 2018 precipitation totals of 6.00″ to 7.00″ have been observed at upper elevations in the High Knob high country in wake of this latest winter storm event that left significant ice accumulations and snow ( 3-5″ of new snow above 3000 feet ).
Wake of Ice Storm At 8:46 AM on Eagle Knob of High Knob Massif ( March 25 )
Snow depths decreased substantially in the high country into the morning hours of Sunday with freezing rain-rain, dropping from max depths ( including old snow ) that reached 3″ to 12″++ prior to the precipitation type change on Saturday afternoon.
Deepest depths of new snow occurred in the early afternoon of Saturday ( March 24 ) when a transition to rain & freezing rain occurred. A general 3″ to 5″ was widespread along and north of the High Knob Massif and Tennessee Valley Divide, with locally less ( to none ) where E-SE air flow downsloped off the high country into the Powell Valley-Big Stone Gap corridor of Wise County.
High Knob Massif Webcam – University Of Virginia’s College At Wise
Snow was so heavy that sticking began in Clintwood with air temperatures above freezing, as snow fell faster than it could melt ( with large flakes ). Roadways became covered at elevations below 1500 feet to the north of the Tennessee Valley Divide versus rain at similar elevations to the south.
GOES-16 Visible Image At 9:22 AM on March 25, 2018
Sunday morning GOES-16 imagery showed both the narrow nature of the system snow band, as well as a striking local contrast between sunshine atop the High Knob Massif and a deck of low clouds banked up along and north of the massif.
High Knob Massif Webcam – University Of Virginia’s College At Wise
The focus now shifts to a pattern favorable for heavy to excessive rainfall, especially in locations along and west of the Cumberland-Allegheny Front and Cumberland Plateau during the March 29-31 period with a tropical fetch of deep moisture from the Pacific Ocean and Gulf of Mexico ( along and in advance of a strong cold front ).
European 51-Member Ensemble Mean 500 MB Height Anomalies: Days 2-6
A return to a colder flow may arise by this weekend and the first week of April, following significant rains and possible thunderstorms.
European 51-Member Ensemble Mean 850 MB Temp Anomalies: Days 6-10
Since this is an evolving and changing pattern, stay tuned for updates as models better resolve the potential wetness of the atmospheric river of moist air expected to impact the region from the Appalachians to Mississippi River Valley.
GOES-16 Mid-level Water Vapor Image At 2:30 AM on March 26, 2018
Observe the long flow field across the Pacific Ocean into the United States, which is already beginning to be joined by a 850 MB flow from the Gulf of Mexico along the Mississippi River Valley.
