Forecast Discussion
Summary
SYNOPSIS
... Wind gusts will relax today as an area of high pressure sets up shop over the region. An unsettled pattern returns to the area starting on Monday, with multiple days of showers and thunderstorms possible throughout the week.
NEAR TERM /THROUGH TONIGHT/... As of 625 AM Sunday: Winds continue to relax across the region at this early hour. Other than some low clouds banked up against the nrn mountains on the TN border, sky was clear and should stay that way. Temp trends are in good shape.
Looks like a more quiet 24 hours than what we have had lately. A flat upper ridge will move in from the west today, which will push a sfc high center quickly past to the north, and then off the Mid-Atlantic coast tonight as the upper ridge axis moves overhead. Expect plenty of sun as a result, with high temps right around normal. The air mass will still be dry, but the RH is not expected to drop as low as yesterday. Fortunately, the wind will be light. As for tonight, a short wave will approach from the west after midnight, but it appears the precip should not reach the fcst area until right around daybreak Monday. Low temps will be a few degrees on the warm side of normal.
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 230 AM EDT Sunday: Quasi-zonal flow aloft will be draped over the region at the start of the new work week as an embedded shortwave slides within this regime from the west and enters the CFWA. Low-level ridge will be offshore by this point, providing a return flow into the area out ahead of the alluded feature. Upper divergence aloft from a jet couplet and mid- to low-level isentropic ascent will help spread clouds, and eventually precip across the CFWA by mid-morning Monday through the afternoon hours. Expect the precip to linger into the evening hours as the shortwave departs, but moist upglide remains in place. Dry entrainment will follow gradually behind the shortwave as it shifts offshore by Monday night. Temperatures on Monday will be at or a few ticks below normal due to extensive cloud cover and precip. Expect low clouds to stick around Monday night for most locations as thicknesses recover, but low-level moisture becomes trapped underneath a developing subsidence inversion. As a result, temperatures overnight Monday will be 5-10 degrees above normal with drier conditions expected after midnight from west-to-east.
Low clouds will slowly scatter Tuesday morning as vertical profiles dry out as an upper ridge noses into the Southeast. Tuesday looks drier than previous forecasts as the upper ridge axis has shifted further west compared to recent model trends. A digging upper low will traverse across the Great Basin and eventually into the Northern Great Plains by the end of the period. In response, deep layer south-southwesterly flow will settle over the region later Tuesday and beyond. In this case, vertical profiles will saturate from the top-down at a slow pace by Tuesday night. Otherwise, mostly dry conditions will be in store for much of the CFWA Tuesday with highs ~10 degrees above normal as height rises and deeper insolation settles over the region. Tuesday night will be 10-15+ degrees above normal due to elevated dewpoints under the WAA regime.
LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 315 AM EDT Sunday: Sensible weather becomes unsettled during the medium range as the upper ridge axis shifts offshore and the entire CFWA becomes engulfed within a deep layer southwesterly flow regime. A vertically stacked low over the Northern Great Plains will send a trailing cold front into the region from the west Wednesday night into Thursday. Deep WAA return flow ahead of this boundary and anomalously high heights will allow for temperatures to soar into at least the mid-80s outside of the mountains on Wednesday. Pre-frontal activity could commence Wednesday afternoon/evening and allow for showers and thunderstorms to develop across the area. Shear parameters are modest at best, so the setup should be similar to what we typically see during the summertime. As the main frontal axis enters the CFWA on Thursday, 0-6km bulk shear (30-40 kts) becomes better established over the area. Global models indicate good instability (SBCAPE 1000+ J/kg) in locations outside of the mountains Thursday afternoon. If there is a severe threat, the best day would be Thursday as the thermodynamics in place overlap the best, along with the overall forcing provided by the encroaching frontal boundary. In this case, another round of showers and thunderstorms will be in store on Thursday, allowing for ongoing slight chance to chance PoPs to linger in the forecast during the middle part of the week. Temperatures on Thursday will be a few ticks lower than Wednesday due to more extensive cloud cover and precip coverage, but will remain 10-15 degrees above normal.
More changes will be underway by Friday as the alluded frontal boundary will sag into our southern zones or just south of the CFWA, near the I-20 corridor. A stout surface high (1030+ mb) will travel across the Midwest and OH Valley late Thursday into Friday morning and eventually set up shop across the Mid-Atlantic/Northeast Friday afternoon/evening. Model guidance are in good consensus with developing a hybrid CAD into the CFWA during this timeframe, with the wedge boundary located in the vicinity of our southern tier. With a saturated mid- to upper-level profile and very dry sub-cloud layer, expect the CAD to become locked in Friday into Saturday as the low-level profiles eventually moisten and upglide allows continuous chance PoPs and cloud cover to remain in the forecast very late in the work week into the upcoming weekend. Model guidance shift the surface high offshore in the latest run and keeps an in-situ wedge over the CFWA through the end of the period. Global models and ensembles don't handle the placement precip coverage well D6 and beyond, but most agree on the overall synoptic setup. Either way, temperatures will do a complete turnaround compared to the middle part of the week as values should drop 6-12+ degrees below normal for highs by Friday and into the weekend, while low temperatures hover near-normal due to extensive cloud cover.