|5.99mph from the E
... Above-normal temperatures and an active weather pattern will persist through next week. A frontal system will bring showers and possibly a few thunderstorms to the area on Wednesday while another system will impact the area late next week.
NEAR TERM /THROUGH SUNDAY/... As of 430 PM EST Saturday: Went ahead and populated in the latest obs as temps were running a few degrees warmer than forecast thanks to great insolation this afternoon. Also lowered cloud cover based on the latest visible satellite loops. Otherwise, the CAD wedge over our area continues decaying with the parent high having moved well off the East Coast, but more due to drier westerly flow in the low levels and loss of higher cloud decks inhibiting insolation. The possibility thereof, and poor guidance handling of cloud trends so far today, are the main source of uncertainty in the forecast heading into tonight. As far as precip chances, more typical ridgetop cumulus are forming across the mountains and a few sprinkles can't be ruled out from those, but otherwise any redeveloping clouds should be too shallow for any PoP.
Later this afternoon and evening, 925-850mb flow will back to the SW again, as we lose influence of the East Coast shortwave and the one moving into the northern Plains becomes dominant. Thermal advection will go from weak CAA to weak WAA as a result, and a shallow moist layer will persist. This is expected to regenerate cloud cover. Where a surface cold pool does persist, this would translate to only a low ceiling developing, but many areas of the CWA probably will lose the cold pool and the WAA may permit saturation down to the surface. Surface RH should easily reach 100 percent. With light winds, there would seem little hindrance to development of fog, and likely dense across at least the foothills near the entire Blue Ridge Escarpment, but also in the NW NC Piedmont. A slight-chance PoP is also included near the Escarpment mainly for the off chance of the WAA kicking off shallow elevated convection. Min temps will be warmer than last night, mostly in the 40s, and any precip will be liquid.
For Sunday, given lack of higher cloud decks, insolation should promote some scattering of the morning clouds, although moist southerly flow will continue, so a mostly cloudy day is expected across most of the Piedmont. In turn, this flow will activate the stalled front to our south during the afternoon, which suggests light precip will not be entirely out of the question, but chances too small to warrant inclusion in the forecast. A few showers could get kicked off along the south-facing Escarpment, however. Despite clouds, max temps will rise 10-13 degrees above normal owing to a warm start and springlike thicknesses.
SHORT TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... As of 230 PM Saturday: Upper-level shortwave energy off the SC coast will deepen and possibly close off at the beginning of the period Monday morning, as a surface reflection develops on a stationary front just offshore. The surface low will move north towards the Outer Banks on Monday as weak ridging persists across the forecast area. Light northeasterly flow will result in ample low-level moisture but the overall airmass to the west of the coastal system will be subsident. Therefore, isolated light and shallow showers are possible within the moist flow especially through the morning hours, but they will not amount to much rainfall. Expect mostly cloudy skies Monday morning becoming partly cloudy Monday evening with a bit of mixing as rainfall chances minimize. The cloud cover and easterly flow will not significantly counter the abnormally high deep-layer thicknesses thanks to longwave ridging over the eastern CONUS; therefore, high temperatures will reach to near or just above 70 for the mountain valleys, the foothills, and the Piedmont.
On Tuesday, the coastal low will move into Delmarva as the next system approaches from the west. Weak but moist low-level flow will veer to the southeast as low-pressure develops along the central Gulf Coast and a cold front enters the Ohio Valley. Upslope flow and isentropic lift justifies slight chance PoPs returning to the western portions of the area late Monday night into Tuesday morning, with PoPs gradually increasing from west to east as the surface low and attendant warm front lift north and east into southern AL and GA Tuesday afternoon into Tuesday evening, increasing low-level flow and forcing. Through Tuesday however, total rainfall amounts will remain light in advance of the main system. Ample moisture and cloud cover will keep temperatures elevated overnight with lows Tuesday and Wednesday morning about 10-15 degrees above normal while the airmass and thicknesses support highs on Tuesday reaching the lower 70s east of the mountains or about 10-12 degrees above normal.
For now, guidance is in general agreement that the surface low will propagate to the south of I-85, generally along our southern zones or across central SC, during the day on Wednesday. Likely PoPs are forecasted overnight Tuesday through Wednesday afternoon as the system moves across the Carolinas; however, its exact track will largely determine how heavy our rainfall will be and whether or not the airmass, especially in our southern zones, will support at least a few thunderstorms. At the moment, forecasted instability is meager but enough to support a slight chance to chance of thunderstorms along and south of I-85.
Widespread 1-2 inch rainfall amounts are likely with isolated heavier totals possible, especially along and just north of the surface front/low pressure track. These amounts and rates are not significant enough to suggest a notable flood risk. Highs Wednesday will be slightly cooler than Tuesday given the widespread rainfall, but still 6-8 degrees above normal.
LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... As of 230 PM Saturday: PoPs fall to chance and then slight chance Wednesday evening into Thursday as the mid-week system quickly lifts north and east into the Mid-Atlantic and Northeast. Transient shortwave ridging dominates our weather Thursday into Thursday night resulting in partly to mostly sunny skies and high temperatures in the upper 60s to near 70 for the valleys and east of the mountains. PoPs once again start to increase overnight Thursday into Friday ahead of the next low-pressure system entering the Deep South in response to shortwave energy embedded in a longwave trough over the central U.S. Model guidance is in general agreement that surface low pressure will propagate along a quasi-stationary warm front anchored near the I-20 corridor from AL to SC. Ample forcing, modest instability, and an anomalous PW axis suggest an axis of thunderstorms, heavy rainfall, and possible flooding is likely with this system somewhere along or near the eventual low track and warm front. We have plenty of time to watch the guidance evolve as to where this is most likely to occur, but the general trend the past few runs keeps the most significant rainfall and thunderstorm chances to the south of our forecast area later Friday into Saturday. Regardless, the end of the week looks wet and unsettled. With the current forecast keeping the warm front south of the area, highs on Friday and Saturday have trended a few degrees cooler, but still 2-5 degrees above normal or generally the mid-60s east of the mountains. Nevertheless, overall forecast confidence is low.