Sugar Mountain

Forecast Discussion

Summary

SYNOPSIS

... Cold high pressure will move from the Great Lakes today to the mid Atlantic early Tuesday. Expect the weather to become milder into mid week in advance of the next rain chances which will arrive on Wednesday and Thursday. Expect very chilly weather next weekend.

NEAR TERM /THROUGH TONIGHT/... As of 930 AM: Temperatures have bottomed out and winds are beginning to really start to diminish. While a few locations in the NC mountains are experiencing wind chills below -5 F, they should improve quickly over the next couple of hours. So will allow wind chill advisory to expire at 10 AM.

The remainder of the near term looks uneventful with virtually clear skies and winds becoming light, as center of arctic high pressure continues to build in. Despite sunshine and a slight rebound in partial thicknesses under shortwave ridging, max temps will remain about 15 degrees below climo on the whole. With good radiation tonight, mins will be similar to this morning's for most of the Piedmont. Low to mid-level warm advection on the upstream side of the ridge however will allow mins to trend somewhat warmer over the high terrain.

SHORT TERM /TUESDAY THROUGH THURSDAY/... As of 230 AM EST Monday: Chilly and dry surface high pressure will stretch from Pennsylvania southward through the western Carolinas and into northeast Georgia early Tuesday. Despite good insolation, maximum temperatures will run about 10 degrees below climatology Tuesday afternoon. Conditions will then change rapidly Tuesday night. The surface high will move off the east coast, but leave behind a shallow ridge axis in place over the western Carolinas to support in situ cold air damming Tuesday night through Wednesday. Meanwhile, low level southerly flow will strengthen well east of a trough moving out of the plains states, with an associated Atlantic and Gulf moisture tap returning to our forecast area. This developing moist upglide into a cold and dry airmass could well pose some precipitation type problems for a good chunk of the forecast area at onset Tuesday night. At first blush, model profiles appear to indicate mainly rain versus freezing rain ptypes during the early morning hours Tuesday. However, the models might be underdoing the dry air, so cannot rule out some brief, frozen ptypes (sleet/snow) across western NC for a couple of hours at onset. Once profiles wet bulb down and warm advection kicks in, freezing rain does appear to the be the predominant ptype for a few hours across western NC early Wednesday, particularly east of the Blue Ridge and out along the Interstate 40 corridor. A few hundredths of an inch of freezing rain appear possible in these areas and a mention will be added to the HWO. Temperatures should warm just enough from the south through Wednesday for all liquid ptypes from mid-morning onward.

The peak period of upper forcing and deepest moisture should cross the region ahead of an approaching upstream trough axis Wednesday night. The southerly 850 mb jet should ramp up to 50 to 60 kt, deep layer DPVA will arrive, and right entrance region upper jet support will peak during this period. In addition, a series of surface waves could move up the approaching cold front to further focus heavy QPF atop our area Wednesday night. Fortunately, the best QPF will be associated with warmer profiles and all rain. Unfortunately, this could give rise to some hydrology issues - particularly in the southern mountains. QPF totals may reach in excess of two inches in the southerly upslope areas from the GA mountains to Transylvania and Henderson Counties. An HWO mention of heavy rainfall and flooding potential will be added. Drying should wrap in quickly from the southwest on Thursday with a cold fropa. However, a brief period of northwest flow moisture could permit upslope snow showers to develop and persist on Thursday. Any western NC mountain accumulations should be rather light.

LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/... As of 130 AM EST Monday: Starting at 00Z Friday with the 500mb pattern showing a broad trough from the Rockies to the East Coast with a series of clipper type systems moving SE from NW Canada toward our region. Weak high pressure will keep us dry for Thursday night then the first clipper system arrives Friday morning. The current run of the EC has a brief shot of snow only affecting the northern NC mountains around 12Z Friday. The EC has this feature lifting out quickly. The GFS has a more robust front reaching the length of the TN and NC border in mid day Friday with some spill over east for late day Friday across the foothills and piedmont. Some light NW Flow snow lingers along the TN border into early Friday night on the GFS. Medium range models have cold high pressure passing over our area Friday night into Saturday. The next shortwave and front increases moisture Saturday night into Sunday with a low forming near the Gulf coast then moving across Florida. The GFS fades out the frontal moisture as it crosses the mountains in mid day Sunday keeping us dry through Sunday night. The EC has a much more robust low pressure crossing northern Florida Sunday and moving up the Carolina coast Sunday night dropping a few inches of snow on the Piedmont Sunday night. Obviously, with varying solutions as to what may happen next weekend we cannot place any great certainty on any one scenario. Temperatures will be 5 to 10 degrees below normal Friday through Sunday.