Interesting Mt. Holly discussion for the mid/late week system.
An impactful system is expected to move through the region on
Wednesday and Thursday, with much colder and breezy conditions
expected to close the week.
Deterministic model solutions have noticeably converged
regarding the Wednesday/Thursday system evolution. However,
critical differences remain, particularly with the track of the
developing wave of low pressure along the advancing front in the
southeastern U.S. Tuesday into Wednesday morning. The 00z ECMWF
and CMC remain noticeably slower with the advancing trough and
continue to be preferred owing to the developing high-amplitude
ridging downstream. The 00z GFS has trended closer to the tracks
of the ECMWF/CMC with tonight`s output, increasing confidence
somewhat. Nevertheless, the GFS continues to be more
progressive and drier with the precipitation from the system
during this period, an important caveat to the discussion below.
As the low approaches the CWA Wednesday afternoon and evening,
considerable large-scale lift will be in place via right-
entrance region upper divergence from a favorably positioned
250-mb jet streak, strong differential cyclonic vorticity
advection downstream of the advancing, more neutrally-tilted
trough, and substantial warm/moist advection on the northern
periphery of a poleward-advancing warm sector. Models indicate
widespread precipitation developing in this regime, convectively
enhanced near the approaching front and in vicinity of the
intensifying surface low. Model soundings do indicate some
instability in the pre-frontal warm sector, especially if the
surface low tracks farther west. Have added thunder to the
forecast for much of the region Wednesday afternoon and evening.
Heavy rainfall is quite possible with this setup, especially
since upper-level flow will become oriented mostly parallel to
the approaching front (thanks in large part to the high-
amplitude ridging downstream). QPF of 1-2+ inches is depicted
with the CMC/ECMWF (50+ percent less in the GFS/ICON). Given the
potential convective enhancement of the precipitation and a
couple of antecedent soaking rain events, this seems like a
setup that favors some flooding potential. Will monitor this
closely as the event approaches.
In addition, very strong cold advection will occur on the
upstream side of the cold front, with temperatures dropping
10-20 degrees in a matter of a few hours after frontal passage.
The cold conveyor belt of the intensifying surface low, along
with favorable frontogenetical forcing/deformation, may produce
a band of precipitation on the west/northwest side of the low
that lingers for several hours. Thermal profiles would favor a
switchover to snow for the southern Poconos and far northwest
New Jersey, perhaps resulting in some accumulations Thursday
morning. (Much heavier snow may occur to our north/northwest,
notably.) Will be monitoring this potential as well in the
coming days.