ALERT For The Potential Of Torrential Local Rainfall Monday Into Monday Evening. Some Storms Could Be Strong To Locally Severe.
The Storm Prediction Center Has Issued A Marginal Risk For Severe Thunderstorms Across The Mountain Area For The Period Between 8 AM Monday and 8 AM Tuesday ( June 27-28 ).
Overnight Into Sunday Morning
Mostly clear. SE winds becoming SSW-SW at 5-10 mph, with higher gusts, along upper elevation mountain ridges. Mild with temperatures from mid-upper 50s in cooler mountain valleys to the mid-upper 60s.
Sunday Afternoon & Early Evening
Partly cloudy. More humid and hazier. Chance of afternoon and evening showers or thunderstorms. Local downpours. Light S-SW winds generally less than 10 mph outside of any storms. Temperatures varying from 70s in upper elevations to the lower-middle 80s.
Late Sunday Night Into Monday Morning
Partly to mostly cloudy. Hazy & humid with areas of fog. Chance of a hit-miss shower or thunderstorm. Winds SSW to WSW at 5-15 mph, with higher gusts, along mid-upper elevation mountain ridges & plateaus. Warm. Temps widespread in the 60s to around 70 degrees.
Showers & downpours in thunderstorms likely. Some storms could be strong to locally severe. Light & variable winds outside of storms. Temperatures varying from the mid-upper 60s to the mid-upper 70s ( coolest at highest elevations ).
Monday Night Into Tuesday Morning
Hazy & humid with a chance of showers & thunderstorms. Winds becoming WNW to NW at 5-15 mph along mid-upper elevation mountain ridges. Temps widespread in the 60s.
Weather Discussion ( June 22-28 )
Thoughts, Prayers, and Condolences to families and friends losing loved ones are given to those impacted last week.
A preliminary signal for this larger event was observed in extreme SE Kentucky when flash flooding damaged 75-100 homes in Harlan County during June 21-22. Rainfall totals up to 6.02″ were hand-measured 3 miles north of Harlan versus only 0.84″ atop Kentucky’s highest peak on Black Mountain ( Harlan 24 E ).
This skewed ( from climatology ) gradient of rainfall ( with less atop Kentucky’s highest and wettest terrain ) was again played out during the second and much larger event during June 23 when rain totals in the Greenbrier Valley ( for example ) were much greater than amid West Virginia’s wettest and highest terrain ( from the Pickens-Kumbrabow State Forest to Snowshoe-Canaan Mountain ).
While the pattern leading up to both of these episodes was well forecast, and I was both concerned and very aggressive with the forecasting, it must be understood that a pinpoint of where flash flooding or wind damage will occur is not typically possible in a convective pattern until after the thunderstorms actually develop on radar.
The high-resolution NAM 4 KM Model run at 8 PM on Wednesday, June 22, did the best job of forecasting rainfall with a MAX of up 10.00″+ over West Virginia ( just not over the counties where such amounts actually fell ). It did have the heaviest rainfall zone, in general, properly placed on this particular model run. By contrast, the HRRR Model in hours leading up to the main disaster had the heaviest rain forecast over northern West Virginia ( north of the Greenbrier ). The centroid of actual convection building more to the southwest and south with the initial Mesoscale Convective Complex ( producing high winds ) than the HRRR predicted during hours after the 00z June 23 ( 8 PM June 22 ) initialization.
The 1981-2010 Annual Precipitation MEAN is listed as 39.30″ for White Sulphur Springs ( the above being for 1971-2000 ).
An excellent example of how convection skews settings is that the Covington, Virginia to White Sulphur Springs, West Virginia corridor is typically among the driest in both states over the long-term mean ( average annual precipitation in the 37.20″ to 40.40″ range ).
During the January to May period of 2016 just over 15.00″ of total precipitation had been measured in Covington, with around 16.51″ in White Sulphur Springs ( only around half as much as in wetter portions of the High Knob Massif ).
During this event, around 3 times as much rain fell on White Sulphur Springs in just 12 to 24 hours as typically falls during an entire June ( 3.51″ ) at that location.
The 1981-2010 Annual Precipitation MEAN is listed as 37.80″ for Covington Filter Plant ( the above is for the 1971-2000 period ).
During the convective ( thunderstorm ) season it becomes important to understand that places which are the wettest ( climatologically over the longer term ) may not receive the most rainfall, especially during any particular event when any place ( even those typically among the driest ) becomes a potential target for heavy to excessive rain.
An interesting, perhaps ironic, twist to these terrible events being that this excessive rainfall fell amid a large region of developing drought in the eastern USA ( particularly along much of the Appalachian chain ).
A drier air mass and welcomed break from the stormy pattern was observed Friday-Saturday ( June 24-25 ).
Focus now shifts toward the next weather systems which will be impacting the mountain region from late Sunday into the upcoming work week and first week of July.
The Storm Prediction Center has issued a marginal risk for severe thunderstorm development across the mountain region for Monday into early Tuesday.
A threat for heavy rainfall, which may be implicit but not an actual factor in severe thunderstorm criteria, may end up being the most important concern given that another high precipitable water air mass will be in place during Monday-Tuesday ( June 27-28 ).
I may issue an ALERT for this Sunday Night if I think this will be a significant concern for June 27-28 ( with another pre-signal being how convection may or may not form by later Sunday into Sunday evening as a litmus test ).
I will say that the pattern ahead remains a concern, with persistence of a WNW flow across the region and a gradual amplification once again.
This causes a cooling trend across much of the northern half of the nation and a shift to heat dome cores over Texas and the Pacific Northwest and West Coast of the USA.
This once again strengthens a north to south temperature gradient across the eastern USA.
The pattern upcoming, therefore, will feature hot and very humid air to the south and unseasonably cool, drier air to the north with a battle zone in between featuring an array of showers and downpours in thunderstorms.
The job for regional forecasters in days ahead, especially during the extended 5-10+ day period, will be to determine where this battle zone sets up shop ( likely with waxs and wanes in precise positioning ) since it will be the zone that could again feature heavy to excessive rainfall amounts.