|Wind||17mph from the NNE|
... Dry and chilly high pressure will build into the region through Wednesday. Winds become light tonight and Wednesday as the center of the high moves overhead. Moisture will return from the west late this week with unsettled weather occurring at times Friday through Sunday as waves of low pressure cross the Southeast.
NEAR TERM /THROUGH WEDNESDAY/... As of 615 PM EST Tuesday: Forecast remains on track with only a few tweaks to the temperatures, dewpoints, and winds based on current observations and latest model trends. Mostly clear skies will be in store through tonight as very cold air settles in over the area. Be sure to bring all pets inside and add a couple of blankets before going to bed tonight.
A broad longwave upper trough draped across the country east of the Rockies will lift northeast into New England by tomorrow. Several embedded shortwaves will swing across the Appalachians, but will be moisture starved as a very dry and cold airmass remains entrenched across the region. Cold/dry advection will continue this evening with dewpoints crashing into the low teens to single digits. Surface high pressure sliding across the Mississippi Valley will become centered across the Southern Appalachians tonight, which will allow winds to relax and become light to calm. Extremely efficient textbook radiational cooling will occur tonight as the boundary layer rapidly decouples within a cloud free and exceptionally dry airmass. Widespread teens are expected across the mountains as well as much of the North Carolina foothills and Piedmont with low 20s elsewhere. These will be the coldest temperatures so far this fall and possibly the coldest for the calendar year.
Cold advection will begin to wane tomorrow as the core of low-level cold air gradually pulls away from the area and winds shift to out of the west/southwest. Temperatures will remain cold, however, with highs topping out in the mid 40s to low 50s. This will result in large diurnal temperature swings with afternoon highs rebounding 30- 35 degrees from morning lows, which is common in well-mixed dry airmasses. Dewpoints will slowly recover tomorrow with surface winds out of the south/southwest and mixing won't be quite as deep as today owing to a strengthening subsidence inversion. This, combined with light winds, should generally preclude fire weather concerns with relative humidity values remaining just above critical thresholds. The one exception will be northeast Georgia where another fire danger statement may be needed.
SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 155 PM Tue: High pressure moves east Thursday as cyclogenesis takes place over the Southern Plains. Southerly flow and increasing thicknesses will lead to warmer highs, near normal, after a cold start with lows around 10 degrees below normal.
The upper low associated with the developing surface low opens up and moves northwest of the area Friday. The surface low tracks into the Ohio valley with the front weakening as it approaches the area. South to southwest low level flow will bring an increase in moisture along with the increase in forcing. Guidance now in agreement on warming H85 temps and partial thicknesses overnight given the southerly flow. The low levels do start out dry, but they moisten as well, with wet bulb temps near but above freezing in the coldest locations. Therefore, it appears that precip developing late Thursday night/ early Friday morning will be rain. Lows will be near normal and earlier than normal diurnal timing for many locations.
Isentropic lift will peak by midday Friday before the flow turns more southwesterly decreasing the forcing with diminishing PoP and QPF for the afternoon. Looks like some form of cold air damming develops with highs 5 to 10 degrees below normal.
LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 220 PM Tue: Guidance shows an unsettled pattern for most of the period with a series of short waves moving near the area in the general southwesterly flow aloft through Sunday. A couple of stronger short waves dig across the area in the Monday and Tuesday timeframe. Run-to-run inconsistency remains keeping the details uncertain.
A the weak cold front from Friday crosses the area Saturday with a wave moving along the front to our south Sunday. Precip chance will ramp back up Saturday into Saturday night then taper off again Sunday. Lows should be above normal even given the detail differences. Currently have highs above normal as well, but this is more uncertain as cold air damming could develop. Either way, any precip will remain liquid.
Monday and Tuesday is even more uncertain with the short waves possibly bringing a pair of clipper-type systems each day. The Canadian is dry while the GFS and ECWMF show varying light precip potential. Followed the guidance blend given the uncertainty. This gives us a chance PoP for Monday and slight chance for the mountains Tuesday. Monday temps are above normal keeping any precip liquid while Tuesday temps are near normal suggesting snow could mix in across the higher elevations. Of course, any accums are highly uncertain for now.