Afternoon discussion from Sterling NWS summarizes the uncertainty with the end of the week outlook...
Plenty of uncertainty remains in the extended period in regards to
the placement and timing of a slow moving (nearly cutoff) upper
level trough from the west and an area of low pressure working along
the southeast U.S coast. These two features combined with the
interaction of broad wedging high pressure off the northern New
England coast/southern Canadian Maritimes will influence how much
deep tropical moisture is funneling into the region.
As of now, have went ahead and increased shower and thunderstorm
chances (PoPs 30-50 percent), especially during the afternoon and
evening hours Wednesday through Friday as onshore flow increases
with the low pressure system just off the NC coast and an inverted
trough nearby. Have backed off the rain chances for the upcoming
weekend to around 15 to 30 percent. The 12z GFS/GEFS favors low
pressure coming up along the coastal Carolinas and into eastern
VA/Delmarva Friday into Saturday leading to increased shower and
thunderstorm chances during this time. The 12z ECMWF/EPS favors more
of the Thursday through Friday timeframe for tropical moisture as a
strong baroclinic zone sets up over the region. The ECMWF/EPS is
also more aggressive with high pressure wedging itself back into the
area for the upcoming weekend allowing precipitation chances to
decrease. The 12z Canadian is a blend of the two aforementioned
solutions above along with central guidance. It still carries heavy
probability of precipitation Thursday into Friday while lingering it
into the weekend.
With all said, specifics surrounding rain chances, amounts, and wind
will continue to remain uncertain until models can get a better grip
on the features at play. Increased onshore flow will remain leading
to seasonably normal to slightly below normal temperatures and
increased cloudiness throughout the extended period. Expect highs in
the 70s and 80s with lows in the 50s and 60s.