... A warm front will lift northward from the Carolinas while a cold front approaches from the Great Lakes today. The warm front will lift northeast of the area by tonight, but the cold front will likely meander over the Mid-Atlantic much of the rest of the week. High pressure may return by the second half of the weekend.
NEAR TERM /THROUGH TONIGHT/... Large scale NW flow continues around troughing draped over the NE US. Embedded within this flow are multiple, largely convectively induced shortwaves. At the surface, a warm front was analyzed from the lower Great Lakes SE to near the VA/NC border, lifting NE.
A lead wave aloft moving from OH into SW PA will pivot across W MD through mid morning. This wave, coupled with an expansive cirrus shield ahead of convection over northern IN, will likely shroud the region in clouds to start the day. A few showers are possible over W MD as the wave crosses, but instability and forcing are pretty meager to start so coverage/intensity should be minimal.
Thereafter, brief clearing is possible mainly over the Shenandoah Valley area of VA into the E WV panhandle. It is in this area where the best heating and instability may develop as low-level moisture surges up the valley. An MCS extending from near Detroit to Chicago early this morning will push SE; it or its remnants are progged to reach the Allegheny Front by midday. Depending on how much strength this MCS has left, there may be an attendant localized damaging wind threat over the Alleghenies. Some training or backbuilding potential is evident, and any upslope into the west side of the mountains could elevate this risk resulting in a flood threat, though the MCS should largely be in a decaying state by this time.
Remnant outflow beneath the shortwave aloft likely impinges on increasing instability up the I-81 corridor resulting in renewed thunderstorm development by early to mid afternoon. Initial discrete cells may pose a risk for some hail, though the main threat is expected to be damaging wind gusts. Humidity will be rising and FFG is somewhat compromised over the Shenandoah Valley vicinity, but storm motions should be relatively swift (i.e. 25-30 kts). An isolated flood threat is evident, but confidence was too low for a watch as of early this morning.
Lingering clouds and lagging warm/moist advection east of US-15 and especially east of I-95 may temper instability further east, so the severe weather threat may be slightly tempered toward the metros relative to areas further west. Still, gusty to damaging winds and heavy downpours perhaps resulting in spotty flooding issues are possible through early evening before storms dwindle due to a loss of forcing and daytime heating.
The 05/00Z NAM12 in particular shows the potential for backbuilding thunderstorms from near the DC/Baltimore metro SW into northern and north-central VA this evening. FFG is very low over the metros given recent rain, but confidence in an organized enough cluster developing and maintaining itself into the metros, and then backbuilding or regenerating, is too low for a watch just yet.
Otherwise, temperatures should be near normal with increasing humidity through tonight on a steady southerly wind.
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... An unsettled pattern continues Wednesday through Thursday. Troughing will remain, placing the region beneath NW flow aloft. A surface front will oscillate over the Mid-Atlantic during this time.
Questions linger in finer scale details such as exact frontal placement, heating, and instability (as well as timing of individual waves passing by in NW flow aloft), but the overall pattern suggests a threat of severe weather at times given sufficient shear. Flooding may also become more of an issue as the week wears on due to repeated rounds of thunderstorms, and eventually more of an easterly component to the low-level flow.
It is prudent to stay tuned to later forecast updates given the potential for one or more clusters of storms which could bring damaging winds or flooding to parts of the region over the next several days.
LONG TERM /FRIDAY THROUGH MONDAY/... A trail of shortwaves will continue to influence the region by the end of the work week. Increasing moisture availability (PWATs 2" or greater in some areas) and instability coupled with decent shear may allow for some potentially strong to severe thunderstorms Friday afternoon and evening. Do think that the majority of the system will likely be further south for the weekend but some hazardous activity may be possible during this system for portions of central VA and southern MD. Influencing high pressure across portions of the northeast should allow for drier conditions for the weekend. This should continue into the early part of next week as the boundary is further south of the area along with the high pressure beginning to break down. Highs for the period will be in the 80s for most (70s for the higher elevations) with lows in the 60s and 70s throughout the long term period.