|Wind||12.66mph from the SSW|
... A weak disturbance will brush by the area today. High pressure will build over the region through Friday, then move offshore this weekend. A strong frontal system will likely impact the region on Sunday. High pressure will return Monday.
NEAR TERM /THROUGH TONIGHT/... As of 11am, a band of snow showers was exiting northeastern Maryland. Skies will continue to clear this afternoon from southwest to northeast. As a result, the Shenandoah Valley will see the warmest temperatures of the day, reaching into the low 50s, while the rest of the area will see highs in the 40s (upper 30s in the mountains).
Tonight won't be quite as cold with most of the area dropping into the low 30s (into the upper 20s at locations where winds are light enough to decouple).
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Dry conditions are expected for most of the short term as an upper level ridge passes overhead both Friday and Saturday. Surface high pressure to our south is quietly setting the scene for the extended, exiting stage left with southerly flow behind it advecting moisture and above normal temperatures into the region. High temperatures around 10 degrees above average are expected, in the 50s for most of the area on Friday, and even reaching into the 60s on Saturday.
As low pressure approaches from the west, clouds and PoPs increase along our western periphery late Saturday night.
LONG TERM /SUNDAY THROUGH WEDNESDAY/... Latest guidance continues to show a potent upper-level trough with northern and southern stream energy digging over the Great Lakes through the Gulf Coast States Sunday. High pressure will remain well offshore and the cold front associated with the trough axis will slowly approach from the west. Most guidance indicates that the northern and southern stream systems will not completely phase, and this combined with more energy moving into the Pacific Northwest should allow this system to be more progressive. Having that been said, it is still a potent system and this can be seen by the strong meridional component to the upper-level trough axis. Therefore, warm and moisture advection will be deep ahead of the cold front, allowing plenty of moisture from the Gulf of Mexico and Atlantic Ocean to advect into the area. Also, the thermal gradient will be quite strong with subtropical air being pulled into the area ahead of the cold front and a Canadian airmass on the other side of the boundary. A strong low-level jet will also aid in moisture advection as well. Latest NAEFS indicates pwats to be about 2-3 standard deviations above climo which is pretty significant.
Therefore, widespread rain is expected across the area Sunday into Sunday evening. A line of heavier showers and perhaps a thunderstorm will most likely accompany the frontal passage Sunday afternoon/evening. Given the strong winds aloft, this has the potential to mix down gusty to perhaps even locally damaging wind gusts. One mitigating factor will be the lack of instability that is progged in the models. It will be difficult to get instability rooted within the boundary layer. Therefore, certainty for damaging wind gusts is low at this time. A soaking rain is expected given the dynamics and moisture associated with this system. Latest NBM indicates around 1-3" most likely. Given the recently dry conditions this may minimize the flood threat. However, localized flooding cannot be ruled out given the higher rainfall amounts and the fact that rainfall rates may be heavy at times with the frontal passage.
Colder air will move in behind the front, first later Sunday afternoon in the Allegheny Highlands and then Sunday night from northwest to southeast across the rest of the area. With the upper- level trough axis lagging behind the frontal passage by a few hours or so, this suggests that there will be some anafrontal characteristics to the boundary. Therefore, there may be a few hour period of rain or rain changing to snow behind the cold front before drier air eventually works its way in overnight. The best chance for accumulating snow will be along the ridge tops of the Blue Ridge and Allegheny/Potomac Highlands where cold air will move in sooner. For locations along and west of the Allegheny Front, an upslope component to the low-level flow will cause additional snow showers to last longer behind the cold front, enhancing potential for accumulating snow.
Gusty northwest winds are expected behind the cold front Monday ahead of approaching high pressure and it will turn out sharply colder. More snow showers are possible along/west of the Allegheny Front, but mainly dry conditions are expected elsewhere (could be a few flurries that spill east of the mountains). High pressure will build overhead Monday night, bringing dry and cold conditions.
High pressure will remain nearby for the middle portion of next week, bringing dry and chilly conditions.