... A vigorous low pressure system will move from the Plains on Monday to the Ohio River valley Tuesday spreading moisture back across the Southeast. Conditions will remain unsettled through the middle of the week. Expect breezy conditions Wednesday into Thursday with below normal temperatures through the end of the week.
NEAR TERM /THROUGH TODAY/... As of 1245 AM...patchy rain is moving into NE GA and the western Upstate. Precip will remain limited to these areas early before rain spreads into the mountains by daybreak. Wet bulb temps are currently only cold enough for snow across the higher ridges. Have limited snow to those areas overnight and early Monday. Temps outside of those areas continue to run warmer than expected, so have adjusted temps in line with current conditions.
Otherwise, a low pressure system will continue to strengthen as it crosses the Southern Plains tonight, spreading moisture across the Southeast. Profiles show a moistening from the top down within deep- layer westerly to west-southwesterly flow. The evening should be seasonably mild under thickening mid clouds. Precip isn't expected to start entering the western NC mountains until after midnight, and should be light. Fcst soundings in the mountains do show an initial lack of warm nose, as dry sub-cloud air will help wet-bulb temps down. So a mix of sleet and snow will be possible above about 4000 ft at the onset, but strong WAA should turn everything to rain except above 5500-6000 ft, where an inch or so of snow accum will be possible before changing to rain late Monday morning. Min temps tonight will be held above normal (mainly upper 30s to lower 40s) thanks to the cloud cover and WAA.
Monday, guidance is in good agreement on a fairly large rain shield spreading across the entire area by midday, as low pressure occludes and enters the Mid-MS Valley. Deep-layer isent lift and upper divergence within the left exit region of the 300 mb jet should provide plenty of forcing for precip across the region. But rain rates should be limited somewhat by lack of instability. A weak in- situ wedge may develop, and hold temps in the mid to upper 40s, with lower 50s along the southeast edge of the fcst area.
SHORT TERM /TONIGHT THROUGH WEDNESDAY NIGHT/... As of 200 PM Sun: Surface low will move into the lower Ohio Valley Monday evening, with CAD entrenched across our CWA. Lift atop the wedge will peak overnight with LLJ, and wedge boundary is depicted as retreating. A nondiurnal temp trend is therefore fcst with continued warming thru the day Tuesday. After having trended downward, fcst QPF has ticked upward once again, though using PWAT as a metric, the event does not look especially remarkable, with values remaining less than 2 SD above climo, so flood risk appears localized to the nuisance spots, at worst. One trend to monitor is the instability now being depicted by both NAM and GFS Tuesday afternoon south of the wedge boundary, as the low approaches Lake Erie, still maintaining 0-3km shear as high as 30-35 kt during peak heating. This instability likely will taper off before cold front arrives Tuesday night, so at the present time the severe threat is not appreciable--not enough for SPC Day 3 outlook to highlight, at least. Above-normal temps will prevail during the wedge, but will fall back below normal behind the front as skies clear. Upslope forcing within the colder airmass will allow PoPs to linger near the Tenn border into early Thursday; falling temps should permit a change to snow, though the moisture is relatively shallow and is not expected to produce advisory-level accumulation at this time.
LONG TERM /THURSDAY THROUGH SUNDAY/... As of 220 PM Sun: Eastern CONUS trough will linger for the remainder of the fcst period, thru Saturday night. The airmass that arrives behind the midweek front will briefly modify to end the work week, but a reinforcing front late Friday will temper the rebound. A pair of embedded shortwaves will bring a small precip chance to parts of the area Friday night and Saturday, but it is questionable how much precip will make it east of the mountains. In light of recent experience, though, will go ahead and include a slight-chance PoP as suggested by model blend. Expect temps to remain well below normal overall, with the warmest part of the period being Thursday night and Friday when mins/maxes are "only" 5 to 10 degrees below normal.