... A vigorous low pressure system will move across the Ohio River valley Tuesday into Wednesday while keeping our weather unsettled through the middle of the week. Expect breezy conditions from late Wednesday into Thursday with below normal temperatures through the weekend.
NEAR TERM /THROUGH TUESDAY/... 630 PM Update...The fcst is in good shape as widespread rainfall continues across area and obs have become rather steady state. Generated an updated storm total QPF grid, which gives around another inch or so of rainfall thru Tue over most areas except the precip shadow regions of the NC mtns. Thus, sigfnt hydro issues are still not expected, yet localized poor drainage areas and some roadways will experience ponding conds.
As of 230 PM: A deep occluded low pressure system will slowly track into the Ohio Valley tonight, spreading plenty of moisture atop the forecast area. The widespread light to moderate rain will lock in a weak in-situ wedge overnight, keeping temps mainly in the 40s. The latest guidance has trended down a bit on total QPF, but the SW- facing slopes of the western and southern NC mountains along with the western Upstate and NE GA should see 1-2" of rain thru Tuesday morning. Isolated flooding cannot be ruled out in these areas. Forecast soundings show a little elevated CAPE developing tonight, so a rumble of thunder or two will be possible; but no severe weather is expected.
Tuesday, a dry slot associated with the Ohio valley low will punch into the forecast area by late morning, helping cut off precip and allow for a gradual breaking of the low overcast. By early aftn, the wedge will be eroded and temps will warm to well above normal. Highs will be in the 60s across all of the lower elevations. The steep mid- lvl lapse rates associated with the dry slot will overlap enough with lingering low-level moisture to produce some sbCAPE of about 300-500 J/kg along the southeast fringe of the forecast area. But only isolated showers are expected at this time.
SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... As of 140 PM Mon: Occluding low pressure system will continue to progress through the Ohio Valley Tuesday night and Wednesday. Some low-level cold advection will occur behind the cold front Tuesday night, along with the arrival of the dry slot. Precip will taper off across the area for a few hours, and the wedge will begin to erode. Temps will remain above normal until a secondary cold front later on Wednesday. Precip chances ramp up again as this front, and DPVA within upper trough, move into the area. Destabilization will occur Wednesday afternoon as the front pushes across the eastern third of the area. Strong flow aloft surrounding the trough will maintain strong shear parameters. Currently the more alarming overlap between the instability and shear is progged to our east, across the NC Sandhills and SC Midlands. However the Canadian GDPS, for one, depicts a later arrival of the front and therefore more CAPE in our CWA. We'll have to monitor model trends for a possible severe risk. Most of the area will be dry Wednesday night in the front's wake. The arrival of substantially colder air Wednesday night, and lingering moisture on the upslope side of the Appalachians, suggests precip will continue near the Tenn border into early Thursday. Temps at the top of the moist upslope layer will be cold enough to expect some pretty good SLRs, so even the modest QPF could result in accums approaching 2 inches in the most favored spots. Can't totally rule out a Winter Wx Advisory based on current fcst.
LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 205 PM Mon: Deep trough will persist across the eastern CONUS from Thursday night thru the weekend. An embedded shortwave will bring back some cloud cover mainly Friday, but moisture is only sufficient for a PoP near the Tennessee border, aided by NW flow. A second, deeper shortwave comes quickly on the heels of that first wave, which along with another shot of moisture, will keep the NW flow precip going into Saturday, possibly resulting in light accums in those higher elevations. With model consensus supporting the idea of a deeper shortwave, the better forcing and lapse rates appear more likely to miss us to the southwest than they once had. Thus, PoPs are now mostly too small to mention for the Piedmont, though a slight chance still is forecast for the southern Escarpment area along with parts of the upper Savannah river valley. Wet-bulb temps from the global models hint that some flurries could mix in, at the very least, in lower elevations. The rest of the story will be the cold temps. Max temps likely won't make it out of the 40s in the Piedmont, and 30s higher elevations, on Friday and Saturday. Slightly warmer temps are expected Sunday, but still several degrees below normal. Records currently don't look to be in jeopardy.