... High pressure will briefly build over the region today before shifting off the East Coast this evening. A frontal boundary will stall near the region Sunday through Tuesday and will combine with multiple upper-level disturbances to bring several chances of precipitation through Tuesday. High pressure will build back over the region during the latter part of next week.
NEAR TERM /THROUGH TONIGHT/... Clear skies are being reported throughout the region this morning with mainly calm conditions. The combination of clear and calm has allowed the surface to decouple from the boundary layer and good radiational cooling is occurring in most areas. Dewpoints in the upper 30s to low 40s have prevented overnight temperatures from dropping much below the low 40s.
A weak upper level low that was in place over our region on Friday will shift off-shore early this morning. High pressure that has been sitting over the eastern half of the US will slowly shift overhead today. Light winds should continue through this afternoon and be mainly out of the north. The mostly clear skies this morning will allow good mixing this afternoon as high temperatures are forecast to peak in the low to mid 70s. Looking at forecast soundings, the mixed layer is forecast to reach up to the 700mb level. Typically when you getting mixing to this height you would expect to get some winds to mix to the surface but the winds throughout the later remain relatively light. Isolated showers can't be ruled out this afternoon especially up towards the MD and PA border where a very weak shortwave is forecast to pass through the upper level flow. I believe the overall threat for any significant showers is minimal with sprinkles being the most likely outcome. A lack of good forcing and CAPE will prevent any thunderstorms from forming.
The high pressure overhead will start to shift of the east coast later this afternoon. As the the high shifts eastward, winds will become more southerly in nature. This lead will lead to weak warm air advection overnight and into Sunday. Overnight lows will be much milder in the 50s with skies slowly becoming overcast. Shortwave energy ahead an approaching trough will bring a chance for showers into our areas west of the Blue Ridge Mtns starting mainly after 6Z.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... A warm front will move into the Tennessee River Valley on Sunday and become situated just to the west of our region. A weak upper level trough axis will drop down into our region on Sunday. Weak warm air advection will combine with shortwave energy to bring a threat for area wide showers on Sunday. Warm air advection will lead to increasing moisture into our region which should allow for a few hundreds J/KG of CAPE. The combination of CAPE and lift from shortwave energy will lead to the threat for thunderstorms to develop Sunday afternoon. The main threat area for thunderstorms to develop will be focused along the Allegheny front will terrain will help storms to kick off. Overall, I only expect weak storms with scattered showers. Afternoon temperatures will be cooler in the lower 70s as skies will remain overcast. One thing to note about Sunday is that the GFS and NAM has precipitation while the Euro is relatively dry. So although I think someone will see some showers, there is potential for a good portion of our region to stay mainly dry or only see a few hundredths of an inch of precipitation.
The precipitation threat should taper off Sunday evening as the weak trough axis shifts eastward out of our region. High pressure will remain just of the coast through Monday. Overnight lows Sunday evening will be milder once again in the 50s. A front will remain stalled near our region to over KY and WV. The forecast for Monday has some uncertainty at this time as the GFS/NAM/ and Euro are disagreeing on the coverage and strength of precipitation. It seems the main difference between the models is the positioning of the high off the coast and the shortwave trough. GFS and NAM are further south with the shortwave energy and have a stronger high. The euro on the other hand is weaker with the high and has the shortwave moving through our region. I have kept at least chance pops throughout our region with likely pops in our SE areas where there is general agreement for the formation of precipitation. Increasing moisture along with the shortwave energy will likely lead to at least a slight chance for thunderstorms to form especially in areas west of the Blue Ridge Mtns. Showers will continue to be possible into Monday evening with overnight lows in 50s.
LONG TERM /TUESDAY THROUGH FRIDAY/... Long term guidance generally builds an upper-level ridge over the eastern US as we head through the remainder of next week. This will be accompanied by a surface high pressure as well. The stalled front which will be nearby Tuesday should dissipate as the high pressure builds overhead, with warmer air enveloping the region. Thus, the overall chance of precipitation will generally decrease Tuesday through Friday, but some chance of showers will linger Tuesday before the front dissipates and the ridge builds strongly overhead. Instability forcing from terrain features (mountains) will be the only remaining way showers and storms may develop as we head late in the week, so maintain some chance pops in our western zones through the period, but odds of rain further east are quite low after Monday. With the building ridge aloft and strengthening surface high, temperatures will also rise and should be 10-15 degrees above normal by the end of the week.