Forecast Discussion
Summary
SYNOPSIS
... Dry high pressure will return to the western Carolinas and northeast Georgia today through Monday. Moisture will return atop another high pressure center ridging down from the north Tuesday into Wednesday, with cloudy, damp, and cool conditions lingering through late in the week.
NEAR TERM /THROUGH TONIGHT/... As of 3:15 AM EDT Sunday...Except for some bkn to sct stratocu still lingering over the I-77 corridor and some fairly dense stratus over the northern NC mtns within a N/NWLY upslope flow, we're mostly clear across the fcst area. Even though winds have gone calm at many locations, it's doubtful that we'll see much in the way of fog this morning (outside of the Little TN River Valley) as dewpoint depressions remain too great at most sites. Lows this morning should be near climatology, if not slightly below, over the higher terrain.
Otherwise, we can expect dry conditions thanks to a Canadian sfc high nudging into the region from the north. Mostly sunny skies are anticipated across the bulk of the fcst area today, although some broken cloud cover may linger across the far northern tier of the CWA well into the afternoon. Winds will remain light today and favor a SWLY direction outside of the mtns this aftn/evening. They will favor a NWLY direction over the higher terrain. Increased insolation should allow for warmer temps this aftn, with high temps expected to top out a few degrees above climatology.
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 245 am EDT Sunday: Looks like one more fair weather day for Monday with a short wave ridge moving through overhead and an otherwise non-descript sfc pattern. Model guidance suggests temps a category above normal for Monday afternoon. This will probably be the warmest day of the week. Changes will already be underway to the north late in the day as a large sfc high over Quebec will be nosing its way down the east side of the Appalachians, aided perhaps by diabatic cooling from light precip that develops over the Mid-Atlantic region late in the day. This development essentially drives a wedge boundary south-southwestward into the region Monday night and early Tuesday, such that by sunrise on Tuesday we may have a nascent cold air damming wedge east of the Blue Ridge. What remains to be seen is how quickly weak upglide can develop overnight/Tuesday which would provide diabatic cooling over the western Carolinas to lock-in the cool air mass. The fcst leans toward the new ECMWF in that regard with introducing precip chances that emanate/expand from the Blue Ridge Escarpment, but some of the guidance keeps much more dry thru Tuesday. Either way, high temps on Tuesday will be 5-10 degrees cooler than Monday, with a ten degree gradient S to N in the afternoon. Confidence is only average at best.
LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 152 am EDT Sunday: The main feature of interest through the medium range period continues to be the weak cold air damming wedge that persists across the region through the middle of the week in spite of a muddled and blocky upper pattern to our north, with variations in the location of upper low centers, between a relatively weak parent high over Quebec and our region well to its south. It is almost as if there is nothing else going on between us and it, so the high manages to ridge all the way down to the western Carolinas with nothing to prevent that from happening. The model guidance still develops some lower level forcing and isentropic lift during the middle of the week, but it is weaker than previous runs. Precip probs have been cut back in response over the east, but think enough weak low level upslope flow against the Blue Ridge Escarpment will warrant a chance through Wednesday and Thursday. Amounts should be light. Without a really strong wedge, temps will probably be kept only maybe 10 degrees below normal at coolest. Ironically, as the upper pattern becomes more coherent and high amplitude later in the week, with good model agreement as to a strong and positively-tilted mid/upper ridge axis to our west, the support for a parent high to the north improves but the pressure goes down. Isentropic lift/upslope also ends by Friday. So, we end up with a dry wedge for the weekend. Forecast confidence improves as the model signal looks clearer. Temps warm a bit without the threat of light precip, but remain about five degrees on the cool side of normal.