Grandfather Mountain / Linville

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Linville, NC

Forecast Discussion

Summary

SYNOPSIS

... Cool and very dry high pressure will build over the region through Saturday. A strong storm system with abundant moisture is expected to affect our region on Sunday and Monday before cool high pressure returns by the middle of next week.

NEAR TERM /THROUGH FRIDAY/... As of 255 PM EDT Thursday: A Red Flag Warning remains in effect for all SC counties in our FA through 8 PM EDT. A Wind Advisory remains in effect for portions of the NC mountains through 8 PM EDT as well. A Special Weather Statement remains in effect for portions of the NC Piedmont and northeast Georgia regarding the increased fire danger for this afternoon.

With temperatures well above normal and plenty of sunshine in most locations, conditions have been rain-free today with the exception of showers and thunderstorms that moved through the area early this morning ahead of a cold front. With the cold front continuing to push into the eastern Carolinas, the main story for today has been the gusty winds associated with this feature and the increased fire danger risk given these winds and the low relative humidity. As noted above, hazard products are in effect for these concerns.

For tonight, do anticipate quiet and dry conditions to prevail with higher gusts subsiding as upper troughing to the north begins to slowly drop southward, while shifting eastward as well. Latest guidance continues to suggest a tightening pressure gradient across the mountains before daybreak as the vort max drops into the area (around 09-12Z). As a result, around round of gusty winds may be in store for the mountains early on before expanding to the rest of the area (though higher gusts will remain confined to the mountains). As a result, a Wind Advisory may be needed. Min temperatures will be around normal. Will note, some of the CAMs continue to suggest light QPF across the extreme northern mountains late tonight, which with temperatures below freezing could allow for isolated snow showers (mainly Avery and Mitchell counties) before daybreak. Attm, confidence remains low and do not anticipate any snow accumulations.

On Friday, dry conditions will prevail as upper trough shifts eastward offshore and ridging begins to amplify to the west with sfc high pressure slowly building in from the west. With the increased NW winds and low relative humidity, do anticipate criteria to be near or met for fire weather concerns. Thus, additional fire weather hazard products may be needed for Friday. After a few days of temperatures above normal, max temperatures on Friday will actually remain below normal.

SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... As of 220 pm Thursday: The short term will be a tale of two halves, as the cool and dry weather of the late near term will extend into at least the first half of the weekend. In fact, within a strong radiational cooling regime, frost concerns will be on the plate for Sat morning, mainly along the I-40 corridor in the Piedmont and foothills. (The spring frost/freeze program is currently inactive for the mountains). Frost is certainly not a slam dunk, as dewpoints/RH will still be very much in recovery mode, but suspect a Frost Advisory will eventually become necessary for all or a portion of the northern NC Piedmont and foothills for Sat morning.

Otherwise, a split flow regime will be in place across the western half of the country through much of the period, with northern stream energy allowing a Four Corners upper low to kick out and open into a neg tilted trough across the Arklatx by Sunday evening. Partial phasing of the flow will yield deep S/SW flow/moisture return across the Southeast Sunday, with warm frontal/upslope precip likely developing across our forecast area during the afternoon. Potent cyclone developing across the Mid-Miss and western Ohio Valleys...tracking into the Great Lakes is expended to send a strongly forced frontal zone into the western Carolinas and northeast GA by Sunday evening, with plenty of model clues that a triple point/sub-synoptic scale low will likely track across the TN Valley/southern Appalachians. Considering that the Gulf of Mexico will be wide open...supporting unseasonably high levels of moisture, these factors would yield a heavy rainfall threat across the region late Sunday into Sunday night. However, the threat for excessive rainfall remains somewhat cloudy owing to recent dry conditions.

Perhaps of greater concern is the potential for high shear/low CAPE severe convection, as guidance is depicting very high values of low level shear (~50 kts 0-1 km) to go along with the strongly forced frontal zone. The GFS advects a ribbon of positive sbCAPE (250-500 J/kg) into the Piedmont after 00Z Monday, which is certainly adequate for severe/potentially tornadic convection in such a strongly forced/sheared regime. SPC's Day 4 Outlook depicting an area of 15% risk to coincide with this "ribbon" of sbCAPE therefore is entirely reasonable.

LONG TERM /MONDAY THROUGH THURSDAY/... As of 245 pm Thursday: After the fireworks of the late short term, much of the medium range looks to be quiet and cool, as a broad/low amplitude trough is forecast to become established across much of the eastern half of the country. In fact, temps are forecast to be around 5 degrees below climo through the period. The only potential disruption to this regime will be a potential for light rain during mid-week, when global models depict a Miller-A cyclone developing off the Southeast Coast. However, the ECMWF, which has been the wettest model with this scenario for a couple of cycles now, is trending drier with today's 12Z run. As such, only token small pops will be carried across primarily the Piedmont during the mid-week time frame.

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