... High pressure will remain in place over our region today into Sunday. Meanwhile, a low pressure system will develop over the lower Mississippi River Valley late in the weekend and move across the southeast early next week. A cold front associated with this system will cross the region Tuesday, and cooler air will spill into the area through mid-week.
NEAR TERM /THROUGH TONIGHT/... As of 615 AM EDT Saturday: Updated discussion for 12z taf issuance. As expected, patchy fog has developed nearby some of the area waterways, in addition to the Little TN River valley. Said fog will erode shortly after sunrise leading into a mostly sunny morning. As for the fcst, no sig changes needed/made with this update, however did tweak hourly t/td trends to align with recent obs.
As of 245 AM EDT Saturday: Currently conditions across the region are rather uneventful with only the usual mtn valley locales experiencing fog. Still woudln't be suprised if some additional patchy fog developed nearby any regional lakes, as well as along south of I85 were Tdds are lowest. Otherwise, an increasingly amplified pattern highlights the synoptic scale setup this morning as deep ridging continues to dominate across the extreme southeast states, while broad troffing and associated height falls approach from the west as the center of the trof axis swings into the plains. This pattern looks to keep the southern Appalachians dry and warm again today, however with moisture increasing through the period thanks to sly/swly veering flow. With that, think max temps today will once again be a few cats above normal, yet a degree/two cooler than yesterday as a bit more high based cirrus is expected to stream in aloft. Overnight tonight the llv flow should be veered sly allowing for improved moisture advection per latest sig level rh analysis on the GFS/NAM. Therefore high cirrus could eventually be obscured by intruding low stratocu from the south near periods end on Sunday morning. Min temps on Sunday morning will remain above normal levels as well thanks to reduced radiational cooling per the aforementioned sky cover.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 315 AM EDT Saturday: A trough axis over the central CONUS on Sunday will develop a split flow pattern as a southern stream low cuts off just west of the lower Mississippi River Valley through Sunday night. Developing low-level southeasterly flow ahead of this system will permit cloudiness to increase through the day on Sunday. With the surface high center to the north already well east of New England, and very limited precipitation potential through the day on Sunday, cold air damming conditions look less likely to set up and persist during the short-term period. Upslope moisture will allow PoPs to increase through Sunday night, with dewpoints quickly recovering around the region.
The southern tier system will gradually open and get re-absorbed over TN into a deepening low pressure system over the upper Midwest Monday through Monday night. Ahead of this phasing system, a period of deeper moisture, forcing, shear, and marginal instability will occur over the southeast. A slightly backed 40 to 45 kt low level jet will likely lift across the region, centered sometime around Monday evening, and coincident with the best period of forcing as a 90 kt upper jetlet rounds the southern stream trough. The lifting trough axis will likely cross the forecast area on Monday night, although the latest GFS/NAM solutions are a bit slower - with associated pre-frontal convection lingering into early Tuesday. The faster ECM/Canadian camp are preferred with the phasing system, which would bring the strongest convection through the area mainly Monday evening, with strong dry slotting occurring from the southwest early Tuesday morning. The models remain quite reserved on instability Monday afternoon and evening, with little more than a few hundred J/kg of sbCAPE during the best southerly jet and low level shear. It seems prudent to mention thunder for at least the southern/eastern halves, but the SPC Day 3 Outlook currently has only a general risk.
Regarding heavy rainfall, QPF will focus on the southeasterly upslope areas of the southern mountains Sunday night through Monday night, but with dry antecedent conditions making flooding rather unlikely.
LONG TERM /TUESDAY THROUGH FRIDAY/... As of 325 AM EDT Saturday: A prominent, full-latitude trough axis will get carved out from the Great Lakes to the Deep South Tuesday through Tuesday night. Westerly flow will develop over our region, along with less moisture, following the Tuesday cold frontal passage, however, scattered showers will remain possible under the trough due to very steep mid level lapse rates. Scattered northwest flow snow showers may start up in the highest terrain Tuesday night as the colder air spills in.
The trough will migrate east across the forecast area on Wednesday before deep layer NW flow sets up into the southern Appalachians behind the departing trough and reinforce the cooler air Wednesday night into Thursday. A brief uptick in moisture is expected as a shortwave rounds the trough axis Wednesday evening, mainly for the northern tier. Advective freezing temperatures will be possible across the northern mountains early Thursday morning. A shallow ridge will cross the region late Thursday into Friday, just as another deep trough develops over the plains.