A Hit-Miss Pattern Of Showers & Tropical Downpours In Thunderstorms Will Continue Through This Week
Although the heaviest widespread rainfall is expected along and north of the Ohio River, locally heavy to excessive rain will remain possible in places across the southern Appalachians and Tennessee Valley. A frontal boundary will get closer to the area by mid-late week, with significantly cooler air currently expected in the extended 5-10+ day period from August 19-23+.
Saturday Night Into Sunday Morning
Partly cloudy. Chance of an evening shower or local downpour. Areas of dense fog developing overnight. Winds SSW to SW 5-15 mph, with higher gusts, along middle-upper elevation mountain ridges-plateaus. Temperatures in the 60s to around 70 degrees.
Partly cloudy. Chance of hit-miss showers & tropical downpours. Thunder possible. Light & variable winds, except SSW-WSW at 5-10 mph, with higher gusts, along highest mountain ridges. Temperatures varying from the middle 70s at highest elevations to the mid-upper 80s.
Sunday Night Into Monday Morning
Partly cloudy & hazy. Chance of an evening shower or local downpour in a thunderstorm. Areas of dense valley fog. Winds SSW to SW 5-15 mph, with higher gusts, along middle-upper elevation mountain ridges. Humid with temperatures in the 60s to around 70 degrees.
Partly cloudy & hazy. Chance of hit-miss showers & tropical downpours. Thunder possible. SSW-SW winds at 5-10 mph. Temperatures varying from the lower-middle 70s at highest elevations to the low-mid 80s ( hotter south, as typical during this entire period, toward the Tri-Cities ).
Monday Night Into Tuesday Morning
Partly cloudy. Chance of hit-miss showers & downpours thunderstorm. Areas of dense fog. Winds SSE-SSW 5-15 mph, with higher gusts, on mid-upper elevation mountain ridges. Humid & hazy with temps in the 60s to lower 70s.
Weather Discussion ( Relief In Sight? )
The air temperature in Clintwood fell quickly from its PM MAX of 85.6 degrees into the 70s amid downpours in storms that developed over the area ( one of several showers during the day-light hours of August 14 ).
Areas of dense fog developed in mountain valleys into the evening and overnight with temperatures dropping into the upper 60s.
Places receiving rain during the weekend will begin the week with MAX temperatures a bit lower than locations that missed out ( via more insolation being used for evaporation than heating up surfaces ).
Continued high dewpoints making it difficult to really tell much difference in the way it feels, even though air temps will be a little lower in places with ground that got wet during the weekend.
Multiple runs of the 51-Member European Model Ensemble show that temperatures in the extended 6-10 day period will be dropping to near or a little below average in the region between the Rockies & Appalachians ( much cooler than average air centered over the Dakotas ).
Meanwhile, continued muggy air will support hit-miss showers and tropical downpours in thunderstorms during this week, with a better coverage expected by mid-late week.
Beautiful tropical skies have ruled the mountain landscape as a relentlessly long stretch of atypically humid air grips the region. This has produced a hit-miss pattern of showers and thunderstorms throughout the first half of August.
Take the atmosphere over the Gulf & Caribbean and shift it north into the southern Appalachians and these gorgeous tropical skies are the result ( minus the ocean + the mountains ). And with luck, for us, minus the flooding rains creating havoc over Louisiana.
While day-time temperatures have been plenty hot enough in the Cumberland Mountains, it’s night-time MINS which have actually been most anomalous versus climatology.
The August 1-13 MEAN Daily MAX in Clintwood has been 83.2 degrees, 2.2 degrees warmer than the 1981-2010 average.
The August 1-13 MEAN Daily MIN in Clintwood has been 65.9 degrees, which is 5.9 degrees warmer than the 1981-2010 average.
While the pattern has been warmer than average, nights have been MUCH warmer than average due to relentlessly high dewpoints.
While dewpoints have been in the lower-middle 70s in Clintwood by day, unlike flat terrain, this does not dictate night-time MINS given decoupling of boundary layer winds and development of nocturnal cool air drainage through mountain valleys.
This nice process allows night-time temperatures to drop below what the dewpoints might suggest. Still, despite the terrain driven feature, nights have been much warmer than average given a deep, vertical depth of humid air that limits how much radiation + drainage can cool the air.
The anomalously humid air is reflected by temperatures at night recorded above 4,000 feet ( above ), where the average August 1-12 MIN has been 64.2 degrees along the crestline of Black Mountain.
Note this LIMITS the diurnal temperature range along these high crestlines, with a August 1-12 MEAN MAX of 76.3 degrees falling only 12.1 degrees to the MEAN MIN of 64.2 degrees. High valleys amid the High Knob Massif consistently being the coolest during this pattern with general MINS in the 60-65 degree range ( away from any moderating influences of larger lakes ).
In honor of the Olympics, the current Gold Metal Count for 90 degree days continues to climb for the Tri-Cities in the Great Valley of the southern Appalachians.
*It is interesting to note that in the Tri-Cities the daily departures of both the MAX and MIN are running nearly identical from long-term averages, with the August 1-12 MEAN Daily MAX of 91.7 degrees being +6.6 degrees above average while the August 1-12 MEAN Daily MIN of 69.2 degrees is +6.7 degrees above the 1981-2010 average.
The 90 degree day count for this year remains at 1 for Wise and Clintwood, and at 0 for Nora 4 SSE and elevations above that level ( 2650 feet ). Meanwhile, Grundy has added one more day to make 10 for the Levisa Fork Valley this season.
Looking ahead there are finally signs of change showing up in the modeling, with a break down of the heat ridge that is controlling current conditions and keeping flooding rains to the south and west ( above ).
Deep moisture along the Gulf will eventually advect toward the north and northeast. While the heaviest flooding rains are currently forecast to fall mostly along and just north of the Ohio River, this will bear watching since the longer the main swirl lingers along the Gulf Coast the better the odds that it could get picked up and advected farther northeast with time ( by mid-late week into next weekend ) than is currently forecast by main models ( some ensembles do show such a scenario as being possible ). Something to watch through coming days in the modeling.
The NAM Model has been wanting to generate a subsidence zone of sinking air adjacent to the main rainfall corridor, keeping amounts very scant across much of central-eastern Tennessee & Kentucky versus the European Model which is allowing for more convection to fire over the region during the next 5 days ( a bigger and more important increase in rainfall does occur on the European during the 5-10 day forecast period as the upper ridge breaks down ).
The Bottom Line…More diversity looks to arise in weather conditions during the second half of August, with a continuation of tropical air and high humidity levels in the short-term ( next 3-5 days ) giving way to chances for more widespread rainfall and cooler air temperatures as upper ridging finally weakens in the 5-10+ day forecast period ( that is the current trend ).