... Low pressure will track into the Midwest tonight before moving into the Ohio Valley Tuesday. The warm front associated with the low will stall out over our area Tuesday into Wednesday. Stronger low pressure and its associated cold front will pass through Wednesday night and Canadian high pressure will build overhead for the end of the week.
NEAR TERM /THROUGH TONIGHT/... Low pressure will track into the Midwest through this evening while surface high remains offshore. A longwave upper-level trough will remain over the central CONUS while a weak upper- level ridge axis continues to shift off the coast.
A southerly flow ahead of the low and behind the high will continue to usher in mild conditions. Max temps will be in the mid to upper 50s/near 60 for most areas.
A southwest flow throughout all levels of the atmosphere continue to cause clouds to lower and thicken through tonight. Low-level dry air should hang on through this evening, keeping most places dry. However, a few sprinkles are possible this afternoon/evening. This is due to a weak shortwave at the mid- levels of the atmosphere passing through behind the departing ridge axis.
Isentropic lift will increase overnight and low-level moisture will also increase. This will allow for rain to overspread the area. Rainfall amounts should be on the light side (around a tenth to a quarter inch) due to weak forcing since the low and the mid and upper-level dynamics will remain west of the Appalachians.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... The warm front associated with the low over the Ohio Valley will stall out overhead Tuesday while a dry slot aloft moves overhead. Rain should taper off by mid to late morning for most areas, but low clouds along with areas of fog and drizzle will hang around on the cool side of the boundary. The boundary is most likely to stall out near the Potomac Highlands into central Virginia.
The boundary will also separate mild conditions to the south and west vs chillier marine air to the north and east. Max temps will range from the 40s and lower 50s northeast of the boundary to the upper 50s/60s southwest of the boundary. The temperature forecast remains uncertain due to the tight gradient in temperatures that will be directly overhead.
There may be a few popup showers Tuesday afternoon due to limited instability underneath the subsidence inversion from the dry slot. The subsidence inversion should be low enough causing any convection that develops to be low topped. Have added the slight chance/chance for showers Tuesday afternoon and evening, but if the convection were to be a bit deeper, then small hail and lightning would be possible (especially near the Allegheny and Potomac Highlands).
The boundary will remain nearly stationary for Tuesday night through midday Wednesday, with cool marine air leading to low clouds and areas of fog/drizzle. Fog may be locally dense Tuesday night into Wednesday morning.
Stronger low pressure and its associated cold front will approach the area Wednesday afternoon before passing through Wednesday evening. Showers are expected along and ahead of the boundary during this time. The upper-level trough associated with this system will swing negatively tilted while a potent jetmax passes through the area. Strong directional convergence along the cold front along with strengthening wind at all levels of the atmosphere suggests that isolated thunderstorms with gusty to perhaps damaging winds are possible. Shear profiles and dynamic forcing are strong, but confidence for severe thunderstorms remains low due to limited instability. With low pressure passing directly overhead, an isolated spin up cannot be ruled out either if instability can get rooted within the boundary layer.
Blustery and noticeably colder conditions are expected behind the boundary late Wednesday night along with upslope snow showers or locations along and west of the Allegheny Front.
LONG TERM /THURSDAY THROUGH MONDAY/... Low pressure will continue to move into Northern New England on Thursday, as its associated cold front moves offshore. Any lingering precipitation should cease by daybreak Thursday, with clouds decreasing through the morning as dry air aloft begins working its way into the region under a NW flow. As the low continues to deepen over Southern Canada, gusty NW winds will develop and will also enhance some upslope snow showers along the Allegheny Front. Weak high pressure returns on Friday delivering drier conditions. However, as the parent H5 cut-off low continues to retrograde over Southern Canada, a few weak shortwaves will move through the region late Friday night into Saturday. While guidance has been persistent with keeping most of the PVA offshore, cannot fully rule out a few passing rain and/or showers around, especially over the Allegheny Front and higher terrain areas.
The strong upper level ridge over the Atlantic will begin to break down on Saturday, allowing the eastern CONUS trough to slowly shift offshore. Stronger high pressure returns on Sunday as the trough axis shifts eastward, allowing subsidence to return for Sunday and Monday. While temperatures will remain below normal through Sunday, a warming trend will ensue early next week.