... High pressure will build in from the Great Lakes and New England while low pressure meanders off the New England coast through tonight. A cold front will likely drop southward Tuesday. High pressure will gradually build in through the end of the week as another low spirals off the New England Coast.
NEAR TERM /THROUGH TONIGHT/... Dry conditions are expected today across the area as light northwest to north winds develop. Temperatures this afternoon are forecast to reach the mid to upper 70s for most, with upper 60s at the highest elevations. Prevailing cyclonic flow around a quasi-stationary upper low off the coast of Cape Cod is going to drag smoke from wildfires in Quebec south to our area this evening. This will make for hazy skies by sunset.
Winds become lighter into the night and shift over to westerly. Low temperatures will mainly be in the 50s with a few mid/upper 40s across the Allegheny and Blue Ridge mountain tops.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As the lead upper low remains caught in the broad negative height anomaly over the northeastern portion of the continent, additional shortwave energy dives down from Quebec. Ahead of these height falls, expect a marked warm up on Tuesday. Relative to the previous day, 24-hour 850-mb temperature rises run around 3 to 5C. Given ample boundary layer mixing, these increases should raise high temperatures by around 4 to 7 degrees from Monday. Consequently, the current forecast calls for highs in the mid 80s for locations east of the Blue Ridge. Given dew points are confined to the 40s, the dry nature of this air mass could easily allow afternoon temperatures to rise another degree or two. While the day is mostly dry, cannot rule out a high- based shower or thunderstorm during the afternoon hours as a cold front moves through. A few high-resolution models depict this scenario north of the D.C. metro. Any convective threat would wane with the loss of daytime heating. Northwesterly winds pick up through the day with gusts up to 15 to 20 mph. Heading into the overnight, low temperatures fall into the 50s again although the DC and Baltimore city centers may stay in the low 60s.
Cold advection behind this frontal passage will lower temperatures into the middle of the week. A return to the upper 70s to low 80s is likely which is slightly below early June climatology. Given some weak forcing aloft with the pivoting upper lows, have maintained a slight chance for afternoon showers and thunderstorms, especially south of U.S. 50. Northwesterly winds persist through the day with afternoon gusts around 15 to perhaps 20 mph. Expect a cooler night ahead as lows drop into the mid 40s west of I-81. Farther east, 50s will be more commonplace.
LONG TERM /THURSDAY THROUGH SUNDAY/... Upper level troughing will remain in place along the East Coast for both Thursday and Friday. Multiple shortwave disturbances will rotate through the area during this time as they pass through the broader longwave trough. The strongest of these shortwaves will pass through on Thursday, and could potentially lead to the development of a few showers, or even a thunderstorm or two Thursday afternoon. However, most model solutions still show the area remaining dry. A mix of sun and clouds is expected both days, with temperatures running near to slightly below normal (highs in the mid 70s to near 80 for most. Northwesterly winds will continue to transport unseasonably dry air into the forecast area, with dewpoints holding in the 40s.
The trough axis will pivot offshore on Saturday, allowing shortwave riding to briefly build overhead. This will result in mostly sunny skies, and a slight uptick in temperatures on Saturday (highs in the low-mid 80s for most). The shortwave ridging will be short-lived however, as the next trough approaches from the Great Lakes on Sunday. In response to the approaching trough, low-level winds will turn south to southwesterly, enabling warmer and slightly more humid air to be advected into the area. Highs may make it well into the 80s, or even approach 90 on Sunday. As large scale ascent starts to increase ahead of the approaching trough, there may be a few showers or thunderstorms late Sunday afternoon into Sunday night.