... An upper disturbance will cross the region overnight with a slight increase in moisture. Dry high pressure will then briefly return through Saturday night. A strong low pressure system approaching from the southwest may support a threat for heavy rainfall from late Sunday into early Monday. Northwest flow snow is expected to develop across the mountains in the storm's wake from late Monday through Tuesday. Another strong low may cross the region at the end of the week.
NEAR TERM /THROUGH SATURDAY/... As of 940 pm EST: Regional radars are showing showers holding together fairly well across northern Alabama and far northwest Georgia late this evening, and southern Appalachians PoPs will be raised slightly to account for the improved forcing arriving with the approaching shortwaves. Water vapor satellite imagery continues to depict this forcing in the form of a northern stream shortwave settling southeast of the Ohio Valley, while a southern stream wave lifts across the Deep/Mid south toward the region. Modest DVPA from the coupled forcing will combine with moisture advecting toward the base of the southern Appalachians to steadily thicken and lower clouds over our area through the overnight hours. Although any measurable precipitation will have to overcome the fairly dry surface based layer, the upstream presentation and improving forcing will warrant at least areas of sprinkles along with scattered showers. Brief evening fog developed near the Catawba river south of Charlotte this evening, but increasing clouds should limit any expansion of the foggy conditions beyond the extreme eastern Upstate of SC and visibility may improve as the cloud blanket lowers.
Precipitation will exit quickly Saturday morning with the eastward departure of the upper waves. Another sfc high will build in Saturday morning following the departure of the shortwave; cloud cover should diminish thru the late morning. Plentiful sunshine and downsloping will partially offset the cooler airmass. Max temps look only about a category below today's values.
SHORT TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 215 PM Friday...A well organized dynamic system is still on track to affect the area Sun thru Tue. The guidance is coming into better agreement with the overall evolution and timing of the sfc low, however, there are differences with QPF response btw the op models. The latest ECMWF has come more in line with the GFS and both models show more convection along the gulf coast and limited moisture adv into the FA Sun night. The NAM on the other hand has abt 1.5 times the amt of precip over many locales during this time. A look at GEFS mean values across the area show generally arnd an inch of rain btw 00z-12z Mon across the Upstate with 90 percentiles approaching 3 inches. With most ens members at or below the mean, will give more weight to the lower op model QPF output. Thus, the main threat for heavy rain (arnd 2.5 inches) looks to occur across the srn escarpment in a period upslope flow, then perhaps across the ern zones later as the sfc low pivots over the region. We're not out of the woods due to the continued uncertainty, but the overall trend is for less of a hydro threat.
Another hazard possibly in the works will be the potential for stg/svr thunderstorms. There will be a window in the early Mon morning before afternoon CAA kicks in for sbCAPE values to reach 200-300 J/kg, while 0-6 km bulk shear increases to 50+ kts. The SPC has a marginal risk for areas south of the I-85 corridor, which looks well placed given the latest guidance trends. So, will issue a briefing package this afternoon abt a possible svr threat given the "off season" timing of the event.
As far as snowfall is concerned...still anticipate rain changing over to all snow fairly quickly Mon afternoon across the higher NC mtn ridgetops. Snow levels will drop as mean thickness values lower thru Tue, but most of the snow shud be confined abv 3.5 Kft. Some of the higher valleys close to the TN line may see a half inch to an inch of snow by Tue morning. Expect the snow showers to begin tapering off during the afternoon Tue. For now, it loos like advisory level snow accums with the higher amts occurring along the TN spine and Smokies. During this same timeframe, the sfc p/grad will tighten to arnd 5 mb across the NC mtns. Soundings show mixing into 30-40 isotachs while CAA aides in downward forcing of momentum to the sfc. So, gusty conds, perhaps reaching adv level, are possible across the higher elevations Mon evening thru the overnight period.
Max temps will remain below normal, with the coldest day occurring Tue as highs are held in the m40s. Normal min temps Sat/Sun nights, but expect lows to drop into the 20s by Mon night.
LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/... As of 245 PM Friday...An ulvl ridge builds over the SE region Wed as another dynamic h5 low develops across the srn plains and pushes east. A modified broad area of hipres will build in and bring clearing skies, however, max temps will struggle to reach the m50s outside the mtns as morning lows begin the day in the u20s and l30s across the FA. Thursday looks to be a transition day as the wrn upper trof and sfc low approach the area. The models have varying solns with this system, yet moisture levels shud increase enuf to reintroduce PoPs late Thu the overnight. Expect cold temps in place ahead of of this system and there could a period of wintry precip, especially across the NC mtns thru Fri morning. Max temps on Thu will again be held below normal be a couple cats while mins are expected to remain the 20s and 30s.