Quite the discussion from Mt.Holly ref late weekend/next week.
.LONG TERM /SUNDAY THROUGH FRIDAY/...
So it continues. A stormy period looks to be taking shape Sunday
through Friday. The Mid-Atlantic continues to be sandwiched in
between the mid-level high to our south and the mid-level low to our
north. In between, a somewhat zonal flow this week with a handful of
fast moving perturbations.
Latest model runs have consistently shown a front approaching the
Mid-Atlantic Sunday and Monday before stalling it near or in the
area for the rest of the week. The forecast problem comes down to
timing the best chances for convection in this regime, which is tied
to low-amplitude (and likely convectively-generated/maintained)
perturbations moving eastward in the quasi-zonal mid/upper flow
across the eastern U.S. throughout this period. Unfortunately, this
is of low predictability, with models once again exhibiting
variations run to run and model to model. Thus, the approach for the
medium-range forecast remains the same: higher-than-climatology PoPs
for most of the period and near to slightly above average
temperatures. In general, the updated forecast is quite close to
continuity.
The main changes are with the Sunday/Monday forecast, where models
are showing slow convergence on the convective evolution. The
aforementioned cold front will be approaching the lower Great Lakes
east-northeast to northern/central New England on Sunday, with
several weak perturbations moving west-to-east near the boundary.
Convection should readily develop along/downstream of the front by
afternoon, mainly to our north/west but probably also in our CWA as
well. The 00z GFS is depicting a stronger vort max approaching the
northern Mid-Atlantic during the evening, with a round of
strong/widespread convection in our area by this time. The 00z ECMWF
is fairly similar, which provided enough confidence to raise PoPs to
high-chance and even likely in northern portions of the CWA Sunday
afternoon/night. Precipitation will wane late Sunday night as
nocturnal stabilization takes over and the strongest large-scale
lift moves to our east.
The CAPE/shear parameter space would be sufficient for severe storms
Sunday afternoon/evening, and I am rather concerned the GFS is
underdoing instability in the pre-frontal warm sector given
increasingly warm/moist conditions. Moreover, BUFKIT
soundings/hodographs suggest a substantial amount of low-level
shear/helicity may exist. Will need to watch Sunday afternoon/night
closely for the severe-weather threat in the coming days.
After perhaps a brief reprieve late Sunday night into Monday
morning, chances of strong convection return Monday afternoon. Both
the 00z GFS and ECMWF depict another strong perturbation moving
through the northern Mid-Atlantic during the afternoon/evening. Once
again, the CAPE/shear parameter space is favorable for severe
storms, though shear may be somewhat weaker than the previous day.
However, the pre-frontal warm sector may be more unstable (using
model sounding comparisons Sunday versus Monday). Complications from
antecedent convection will exist (increasing the uncertainty in the
forecast by this point), not to mention the model volatility already
in place with the perturbations responsible for the larger-scale
lift associated with the convection. Nevertheless, I am becoming
quite concerned with the severe threat both of these days, and hydro
issues will be an increasing concern as well given the multiple
rounds of storms that may affect the area.
Speaking of, the forecast does not look much better Tuesday onward.
Models show little southward progress of the front and more low-
amplitude perturbations affecting the region the rest of the week.
Variability in timing/track of these vorticity maxima is quite high
during this period, but the pattern is certainly suggestive of a
stormy period...with hydrologic concerns only increasing if such a
pattern were to verify.
&&
Upton:
.LONG TERM /SUNDAY THROUGH FRIDAY/...
The main story of the long term will be with a frontal boundary that
approaches on Sunday and then likely stalls over the Tri-State on
Monday. This front may linger near the region through the rest of
the week. Confidence in the exact location of the front remains
uncertain later in the week, with the best consensus of model data
indicating the front remains near the region.
The 12z ensemble means continue to show an upper level low over
southeast Canada on Sunday becoming mostly locked in place through
the middle of next week. This is due to a blocking pattern at higher
latitudes. Ridging sets up over the western Atlantic through the
week. The surface frontal boundary will become nearly stationary
near the region next week between the upper low to the north and
western Atlantic ridging.
Chances for showers and thunderstorms increase Sunday afternoon and
evening as the front nears. Shortwave energy appears weak so have
capped PoPs off at 50 percent. A little better defined shortwave and
frontal wave is progged to move through late Monday afternoon and
Monday night. Have increased PoPs to likely based on some better
support aloft (shortwave energy) as well as some continuity among
the models with the frontal wave. With the front near the region on
Tuesday, the chance for showers and possible storms continues.
Guidance over the last several runs has hinted that the front may
try to sink south on Wednesday. Have not completely gone dry yet as
this may be too aggressive. Unsettled weather may continue for the
end of the week. A more well defined shortwave is currently
indicated by the GFS/ECMWF/CMC to act on the front to bring
precipitation late Thursday into Friday.
While the long term looks unsettled, there will be periods of dry
conditions and periods of precipitation. The exact timing remains
uncertain.
Temperatures through the long term will average near to slightly
above normal.
&&
