Weather Headlines
ALERT For The Potential Of Strong-Severe Thunderstorm Development With A Heavy Rainfall And Strong Wind Potential Through Thursday Night Into Early Hours Of Friday
*A chance of showers and thunderstorms Thursday PM will give way to likely activity Thursday night into the early hours of Friday. Some storms could be strong to locally severe, with downpours and strong winds.
Stay tuned to NOAA Weather Radio and your favorite media sources for the possibility of watches and/or warnings which may be needed.
A spring-time storm pattern is upcoming for the mountain region, with periodic waves moving through a developing longwave trough in the upper air that deepens over time.
Each shortwave passing through the longwave trough will tend to strengthen the mean trough and bring rain, with thunderstorms becoming increasingly likely as air turns unseasonably warm for mid-late March.
An increasing threat for heavy-excessive rainfall amounts will arise as time passes.
*Additional waves of rainfall are expected during late week into this weekend and next week. These waves are trending heavier in modeling, with a heavy to excessive rainfall potential being monitored once again. The exact placement of heaviest rain bands remains to be resolved, with the greatest threat region stretching from the lower Mississippi and Tennessee-Lower Ohio valleys across the southern Appalachians and northern Gulf Coast states.
Reference Persistence In Longer-Term of My 030520 Forecast
The ridge-trough-ridge pattern of February is rearing its ugly face once again, with a much more amplified pattern predicted by the 51-member European Model ensemble group by late this week into next week.
The current tilt of the mean trough favors heaviest rain amounts being along and west of the Appalachians, with orographic enhancement on westerly component flow into the western slopes of the mountain range as observed during February in 2020, 2019, and 2018.
Reference Huge Weather Swings In Early March for more details on the ridge-trough-ridge pattern that looks to become longer-lived again. Reference my 020620 Forecast for a review of past flooding and the repetitive nature of this wet 2020 pattern. In addition, please reference my 013020 Forecast for more information on the “big picture” of this pattern.
Deep moisture transport from both the Pacific Ocean and Gulf of Mexico will combine with unseasonable warmth for March to set the stage for heavy to excessive rainfall, including potential for strong-severe thunderstorms at times which could add convective downpours.
A pattern change across the Northern Hemisphere may (with emphasis on may) finally be upcoming as the final warming occurs with breakdown of an anomalously long-lived and strong polar vortex. This breakdown is typical and occurs every year over the arctic region.
Impacts from this may not be felt in the southeastern and eastern USA until the final days of March, and more likely impacts will be most pronounced during April 2020. Stay tuned for later updates as timing and impacts become better defined.
Diversity Of Nocturnal Temperatures
*A large vertical temperature spread develops tonight into Sunday morning as light winds and clear skies allow strong surface cooling to contrast with significant warm air advection across mid-upper elevation mountain ridges, generating a strong vertical temperature inversion that increases into early on 8 March.
A huge and seemingly always present (since beginning of time) problem in operational meteorology is the lack of recognition of diversity across complex terrain, with this aspect especially evident on nights featuring formation of nocturnal inversions which are more the norm than exception in complex terrain settings.
The vast majority of forecasters (including those in the NWS and Weather Channel) use much too narrow (tiny) nocturnal temp ranges to represent complex terrain.
Actual field research finds 15-30 degree (F) temp ranges to not be uncommon over short distances, and while official forecasters may be reluctant to use such large spreads their existence needs to be better represented in real-time forecasts for complex terrain.
This fact is becoming more evident to everyone as more and more people share personal weather data, and is no longer merely an aspect restricted largely to the research community. Here are merely a few examples.
Birchleaf of Russell Fork Basin
The Birchleaf weather station of Jonathan Owens, former broadcast meteorologist, lies 500 vertical feet above the Russell Fork River. This site is typically 3-5 degrees F or more milder than valley locations in the mid-upper basin through evening hours, but as the inversion inside Russell Fork Basin deepens to 500 vertical feet (152 meters) or so within the lower basin it tends to trend colder and become nearly as cold as Clintwood 1 W by morning. Clintwood 1 W is an official NWS Cooperative station within a lower elevation cold air drainage of the Russell Fork Basin (not currently listed with live data).
Flatwoods Mountain_KY_Dorton Near Pine Mountain
Contrasting mountain ridge sites for both Russell Fork Basin and Norton Valley stations, can be found by scrolling to Dorton in Pike County, KY and to Black Mountain in Harlan County, KY on nights featuring the development of nocturnal inversions (like tonight).
Norton Valley_Downtown Norton Virginia
This weather station in downtown Norton tends to be one of the coolest (on average) for any city in the Old Dominion on radiational cooling nights. The City of Norton lies on the divide between the Clinch and Powell river basins, nestled amid the northern base of the High Knob Massif, with cold air drainage from both the northeast end of Black Mountain (along Guest River) and the high country of the High Knob Massif. So while this site tends to be significantly milder at times than valleys embedded in the adjacent high country of the High Knob Massif, it still can have impressive cooling despite being under two-way drainage into both the larger-scale Clinch and Powell river basins.
Lonesome Pine Airport_Wise Plateau
A classic contrast to the Norton Valley on radiational nights with warm advection can be obtained by comparing the temperature observed on the exposed Wise Plateau at nearby Lonesome Pine Airport. It is a critical forecast mistake to confuse KLNP with Norton under these conditions (observed on many nights throughout a year). Amazingly, locations only a short distance from Lonesome Pine Airport can be much colder within depressions that are embedded within top of the plateau (such as the location of J.J. Kelly High School), with frost formation at times when air temperatures at KLNP are in the 40s and 50s.
Wise Plateau_Hurricane Road Cold Air Site
The Hurricane Road weather station appears to be an example of the above, and will be interesting to follow as a contrast to nearby Lonesome Pine Airport (as I have noted so many times in the past, the KLNP sensor appears to possess a +1 C (+1.8 F) degree error which should also be taken into account for greatest precision). Other sites listed may possess errors as well, but nocturnal temps are often more accurate than daytime temperatures when small solar radiation shields and other placements can increase temperature errors. In general, these sites are of high quality by night.
Mountain Lake Biological Station
The Mountain Lake Biological Station is located in an upper elevation sink featuring the only natural mountain lake in Virginia (even though it has mostly been dry in recent years due to seepage). During January 1985, when an official NWS Cooperative site was here, it recorded the lowest official temperature on record in Virginia with -30 F (-34 C). Colder, unofficial, temperatures have been documented in the High Knob Massif area.
Bald Knob of Salt Pond Mountain is the highest summit surrounding Mountain Lake and can exhibit significantly milder readings at times. It will be interesting to see if the upper elevation sink of the Biological Station can fully decouple into the overnight as warm air advection begins into the summit.
The Shady Valley Basin drains to the northeast, with this weather station located near its northeastern outlet. While the floor of Shady Valley is middle elevation, per my specific classification system, it is not far beneath the 3000 foot (914 meter) contour and like the Bark Camp Basin of the High Knob Massif can effectively be considered upper elevation given it is influenced predominately by elevations above 3000 feet on cold air drainage, outgoing longwave radiation (OLR) nights.
Northern Canaan Valley_WV_Frost Pocket
This central Appalachian site in the northern portion of the Canaan Valley Basin is within a classic cold air generating basin, and is part of ongoing research into frost pockets of the southern-central Appalachians. This upper elevation site, at 3150 feet (960 meters) has the potential to eventually break the state record MIN for West Virginia (-34 F or -36.7 C), along with other spots in Canaan Valley, where despite temperature recording since 1945 the lowest MIN ever documented reached “only” -27 F (-32.8 C). An aid to cooling here, other than its obvious elevation and latitude, is a large sky view factor (lack of trees).
A contrasting site for this study is the nearby weather station within Dolly Sods, on Cabin Mountain, located 885 feet (269.8 meters) higher than the northern Canaan Valley frost pocket. When wind speeds here are around 14 mph (6.3 m/s) or less the northern valley can typically decouple under clear conditions with strong radiative flux divergence.
Other classic sites not currently linked up with live data are found within Burkes Garden and the Big Cherry Lake Basin of the High Knob Massif. Cooling at all sites tends to be enhanced, of course, by snow cover which acts to block radiative heat flux from the ground that works to compensate for OLR that cools overlying air.
**The Big Cherry Lake Basin of the High Knob Massif will eventually break the all-time record MIN for Virginia and likely did so just prior to recording in February 2015 (temp recording began on a regular basis during 2016).
Unlike within the western USA, the most extreme temperature minima are even more restricted to fresh snow cover events in southern-central Appalachian cold air basins versus places like Peter Sinks, Utah where very dry air at high elevations can support extreme temperatures throughout the year (although, even there the coldest temps also occur most naturally above a snowpack).
Differences between central and southern Appalachian frost pocket sites are enhanced when snow is not present on the ground at all sites [being present to the north, like tonight (7 March), and limited to non-existent within the southern extent of the mountain range]. Many other factors are, of course, involved, and this is assuming ideal conditions at all locations which rarely occur.
It is very important to note that the above is not meant to criticize forecasters, but instead to push for an advancement of our knowledge and ability which is greater than being publicly displayed.
The extension of this existing knowledge possesses applicability beyond that to humans, with naturally occurring complex terrain differences acting to regulate essentially all aspects related to floral and faunal (flowering time, migration, breeding, etc.) activities across the natural world.