Grandfather Mountain / Linville

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Linville, NC

Forecast Discussion

Summary

SYNOPSIS

... A weak cold front approaches from the west today then crosses the area Monday. A hot and increasingly humid air mass moves in for the rest of the week.

NEAR TERM /THROUGH MONDAY/... As of 1045 AM EDT Sunday: Ongoing MCS has turned southward and is diving down into AL, so very little in the way of convection from it has a chance of making it into our area. It is spreading high and mid-level clouds eastward towards the forecast area, but progress has been slow and temperatures have warmed a bit faster than previously forecast. Still expect some cloud cover to reach at least the mountains over the next few hours, but enough surface heating has already occurred and will continue over the next couple hours that the forecast is trending towards the potential for a bit more destabilization by this afternoon.

The atmos becomes more dynamic this afternoon as a upper heights become difl and a stj crosses the region. The jet max will only be on the order of 60-70 kts, but some measure of added lift will be provided late evening as the RRQ entrance region swings over the FA. It will take a little while for the sfc high to be nudged east ahead of a pre-frontal trof and warm air in the mid levels will keep sbCAPE values in the low to moderate range thru the afternoon. The convec models have varying ideas with the amt of destabilization and formation of stg/svr storms, but believe by the later afternoon mtn top convection will be enhanced by enuf dyno lift to create decent storm coverage, which will then traverse east thru the evening ahead of an approaching frontal zone.

The SPC has most of the area in marginal risk of severe storms and this seems probable given the increased dynamics, yet deep shear levels will remain limited to arnd 20 kts, so highly organized lines of convection seem unlikely with a more linear multicell mode favored. The biggest threat will be damaging winds as freezing levels remain high and will temper a large hail threat somewhat. Convective activity will linger into the late evening and likely thru the overnight as the front pushes across the area. There is a less likely severe potential during this later period, yet not zero. Temps today will reach a few degrees abv normal in continuous sw/ly flow and mins will also remain abv normal within enhanced cloud cover.

SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 215 AM EDT Sunday: A short wave and associated weak cold front cross the area Monday. This keeps another day of scattered diurnal convection across the area, favoring the I-77 corridor. Highs will be a couple of degrees above normal. Dew points remain high ahead of the front leading to heat index values into the mid to upper 90s. The upper trough axis moves east of the area Tuesday with rising heights moving in from the west. Some of the guidance has slowed the movement of these systems. This has a result of slowing or even stalling the weak front near the Atlantic coast with a wave of low pressure forming along it. Easterly flow develops ahead of this low bringing low level moisture back into the area with scattered diurnal convection. The ECMWF moves the system far enough east to keep a dry forecast across our area. Would like to see a trend develop in the guidance before jumping on this change, especially with the ECMWF remaining dry. Therefore, have kept Tuesday dry for now. Highs should rise a couple of degrees on Tuesday. Dew points should be lower with the drier air mass moving in. This keeps heat index values from reaching the 100 degree range.

LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 325 AM EDT Sunday: The medium range forecast continues to feature a building upper anti-cyclone over much of the southern CONUS. The GFS is now weaker with this feature, along with the axis of highest heights farther south and the center farther west than the more consistent ECMWF. The GFS allows short waves moving over the top of the feature to move closer if not even over our CWFA through the period. As mentioned above, the ECMWF is more consistent showing a stronger, broader anti-cyclone with an axis that is farther north and a center farther east. Will trend toward the ECMWF given its consistency. The ECMWF keeps the initial short waves north of our area but does retrograde the center of the anti-cyclone by the end of the period. This allows instability to develop by the weekend with scattered diurnal convection. Temperatures remain above normal through the period, but do warm through Thursday then drop slightly through Saturday. Dew points will be in the increase as well, helping heat index values to flirt with triple digits each day.

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