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Forecast Discussion



... High pressure will remain across the region today, drifting east of the area Sunday. Partly sunny skies and seasonable temperatures will prevail today. Clouds will increase Sunday as a potent weather system begins to approach the area from the southwest Sunday. This strong weather system will move through the area Monday bringing a variety of inclement weather including heavy rain, gusty winds, mountain snow, and possibly even a few strong to severe thunderstorms to the southeast corner of the forecast area. In its wake, look for windy and the coldest temperatures of the season so far by Tuesday and Wednesday.

NEAR TERM /THROUGH TONIGHT/... As of 300 AM EST Saturday...

One more quiet day across the region today and tonight before a strong weather system moves into the area Sunday bringing a variety of inclement weather for the first part of the new week.

A weak short wave embedded within the westerlies aloft will traverse the region this morning. The strongest part of this disturbance will track across the southeastern states. Associated mid/high clouds will track across the region this morning. With better moisture and the stronger part of the disturbance to our south, a brief period of light rain falling mainly from the mid-level will skirt across central NC and could come as close as the I-40 corridor for a few hours this morning, but will not include mentionable (=> 15%) pops in our CWA at this time.

As winds shift to the west and increase in speed behind this disturbance, look for upslope low clouds to persist across eastern WV into far southwest VA and possibly even into northwest NC for a few hours, perhaps even into the early afternoon from LWB to BLF. The Piedmont will clear by midday and all areas should be clear by evening setting the stage for the last clear/cold night for a few days.

Temperatures will reflect a bit of cooling today and tonight as the upper disturbance passes to our east ushering in slightly cooler air from the Ohio Valley and Midwest. Nonetheless, temperatures will still be a bit above normal today with 50s west and 60s east. Low temperatures tonight will be near or below freezing in most areas, mainly upper 20s to lower 30s.

/Confidence Levels in Forecast Parameters/ Moderate to High Confidence in Temperatures, High Confidence in Probability of Precipitation Percentages, Moderate to High Confidence in Wind Direction and Speed.


Our earlier discussion for this portion of the forecast period will be repeated here given the gist of it still is holding strong. Comments will follow to reflect any additional details examined during this forecast shift.

Our earlier discussion...

Surface high pressure will jog across the region Saturday night into Sunday. The center of this ridge will move off the NC/VA coast Sunday night, leaving the western edge over the area. Overrunning moisture and rain from a southern stream complex across the southern states will then create and enhance an insitu wedge over the area Sunday night into part of the day Monday.

The southern stream complex will consist of an upper level low moving over the Red River Valley Saturday night, the Tennessee Valley Sunday and then into the Ohio Valley Sunday night into Monday. The surface low forms along the Texas coast then joins the upper level low when it is in the Tennessee Valley. This system becomes occluded over the Ohio Valley Sunday night into Monday. A northern stream upper level low over the Great Lakes will phase with the southern stream system on Monday to create a new colder closed lower over the Ohio Valley. This system will slowly move to the northeast Monday night into Tuesday.

This Sunday night into Tuesday system is not only complex but brings a multi-faceted range of weather features along with it.

1) Strong Dynamics and a negative-tilted trough will interact with an eroding wedge to possibly bring rotating storms and heavy rain to the area Sunday night into Monday morning. Models current have a triple point tracking in the vicinity of Southside VA which supports a strong convection case. Rainfall amounts could average 1-2 inches along and east of the Blue Ridge, under an inch along western slopes. On the other side of the coin, models have a habit of eroding the wedge too quick in our neck of the woods. If a line of convection across the southeastern states is strong enough, it may rob moisture coming into the area. If this does happen, heavy rain chances will be lower and the wedge may hang around a little longer.

2) A dry slot is expected over the area Monday afternoon. By this time the wedge should be gone with temperatures jumping into the 50s and 60s. These temperatures seem cool, but are warmer than normal for the end of November.

3) Phasing/Merging of the northern and southern stream lows will combine Gulf moisture with very cold air to have rain changing over to snow across the mountains Monday night. 850H temperatures drop below 0C through the afternoon. However 1000-850 MB thickness remains above 1300m into the early evening. This suggest the change- over to snow will start in the higher elevations first. Lower elevations may see snow starting to fall, but will melt on contact through most of the evening, some of that is due to a warm ground.

4) The closed low over the Ohio Valley will slowly move to the northeast Monday night into Tuesday night. With temperatures remaining at or below freezing, accumulating snow across the mountains will occur through the period. Being under the deformation zone and upslope longer than anyone else, western Greenbrier should see the highest snowfall totals for the Blacksburg CWA.

5) A 40kt low level westerly jet could bring gusty conditions to the area Monday night into Tuesday. However, extensive cloud cover should keep these gusts above 3000 ft. The stronger winds will occur Tuesday night as pressure rises behind the departing low. Models are also advertising a 50kt cross-barrier jet along the Blue Ridge.

Our new insight...

The temperature jump mentioned in 2) above likely will be short lived with high temperatures reached in the morning across the mountains, and around mid-day in the east. Perhaps, the Danville area and points east and south might have some resemblance of a normal diurnal temperature pattern. From these time references and onward, look for falling temperatures. The farther west you live, the lower your high temperature will be, and the quicker your temperatures will then fall. This decrease in temperature will allow some of the higher peaks in the west to have showers mix with, or change to snow showers during the afternoon hours as temperatures fall to the lower 30s or around 30. This is an adjustment from the earlier forecast which had this transition more during the early evening time period.

In referencing 1) above, we are expecting a region of very high shear, perhaps 0-3km SRH around 450-600m2/s2 off the latest SREF, with low, but probably not zero, MUCAPE. This is in concert with a lifting boundary across the region and a greater than 90% chance of LCL levels to be <= 750m. This scenario speaks to the potential for rotating low-topped showers, and a few rotating low-topped storms. This could result in the potential for some wind damage, and a non- zero chance of a tornado or two within the most favorable regime. The Storm Prediction Center has outlined the far eastern parts of the area for such a potential on Monday. In particular, the early morning through mid-day period looks to be the time period of greatest concern. Concerning point number four above, we are still looking at western Greenbrier County as the focus for the greatest amount of snow with transition of the system noted above. Our latest forecast will entertain two to three inches for the Quinwood, Duo, and Anjean region and points northeast along the mountain ridges. One to two inches is looking more probable in the southern half of western Greenbrier County, southwest into the Bluefield and Richlands region. The higher peaks of western parts of the Northern Mountains of North Carolina and the Grayson Highlands region of Grayson County also have snow forecast in the one to two inch range. Elsewhere, where measurable snow is forecast, amounts are expected to be under an inch. Local exceptions for higher amounts, as with most snowfall, are likely where any banded line of snow showers establishes itself for a lengthy period of time. LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 145 PM EST Friday... The upper level low will be moving to the northeast Tuesday night into Wednesday. Snow showers and windy conditions will eventually give way to sunshine and warming temperatures Thursday. However, rain returns to the region on Friday as warm air overruns another surface wedge. The coldest time in the period will be Wednesday morning with lows in the 20s, wind chills values in the teens. The wind will subside some on Wednesday but remain cold with highs in the 30s west of the Blue Ridge to the 40s east. Temperatures moderate a few degrees each day but remain colder than normal Thursday and Friday.