Mt. Holly and Upton Ref: tomorrow.
It also looks like the very warm weather will continue and even get hotter over the next several days.
Mt.Holly:
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
An active period of weather is expected Thursday and Thursday night.
Starting on the synoptic level, a de-amplifying shortwave trough
will be moving through and lifting northeastward out of the Great
Lakes by Thursday morning. At the surface, an accompanying surface
low sits in the left exit region of a respectably strong (for the
season) upper jet streak of around 90 kts. It will track out of
southern Ontario and into Quebec on Thursday. A cold front trails to
its south and will slowly approach through the day. The mid-Atlantic
will be left in a warm sector air mass. Cloudiness and increased
moisture will keep our temperatures a bit cooler than previous days,
but with higher humidity, as will be discussed below.
By early Thursday morning, a light but steady southerly surface flow
will have developed in the modest gradient between the departing
high pressure and the approaching frontal system. Strengthening
southwesterly flow will also develop through the remainder of the
low and into the mid-levels. This will lead to a truly impressive
surge in PWAT values early tomorrow, from the mundane values of
around 1.25" today to a tropical 2-2.25" or even slightly higher by
late tomorrow. What appears to be aiding in this large and rapid
moisture surge is a direct connection to very rich moisture in the
Gulf of Mexico associated with a developing tropical cyclone there.
So the air mass ahead of this frontal system will have a definite
tropical fingerprint to it.
Given these ingredients, we are primed for locally heavy rainfall
tomorrow. The front itself is fairly progressive, and expect there
will be either a solid or more likely broken line of showers and
storms associated with the actual front which will move along fairly
steadily. What`s more concerning is the rapidly moistening and
uncapped environment ahead of the front, which would seem to favor
additional showers and thunderstorms developing well ahead of the
front tomorrow afternoon even as forcing is modest. Unlike recent
heavy rain events, the vertical wind profile tomorrow is not nearly
as stagnant; storms that develop will move, at least gradually.
However, more of a concern tomorrow will be training and
backbuilding convection within an air mass with deep moisture
funneling into it. Moderate deep layer shear profiles are supportive
of dominant multi-cellular activity with potential for back-
building, training, and regeneration especially given the high air
mass moisture values. Thus, localized flash flooding appears
possible especially given continued high soil moisture anomalies
from this wet spring and early summer. Strongly considered issuing a
Flash Flood Watch but after discussion with neighboring offices and
WPC will defer that decision for now and continue to carry the
mention in the HWO. Still a little hard to say what specific areas
will see the greatest threat, with a wide spread in guidance.
However, the fact that many of the hi-res models are showing QPF
bullseyes of 2-3" or greater is concerning, so this will bear close
watching.
The other concern tomorrow, while probably less of a threat than
excessive rain, is severe weather. Cloud cover may be fairly
extensive during the day, which would act to limit instability, but
guidance is generally supportive of at least 1000J/kg of MLCAPE
building by afternoon, perhaps up to 2000J/kg. Deep layer bulk shear
will be slowly increasing but still only moderate, not much better
than 30 kts from 0-6km during the day. Moisture obviously is not in
question. Main concern will be damaging wind gusts within multi-
cellular convection, especially if instability is greater than
expected. However, attention is also drawn to the southerly, or
perhaps even locally south-southeasterly, surface flow. This will
act to enhance low level veering given southwesterlies aloft, so
some rotation is possible in storms that develop and cannot rule out
a brief tornado especially if we see any fleeting supercellular
structures. Low LCLs associated with tropical moisture also lend
some support here. Latest SPC Day 2 outlook/discussion covers this
well also. Greatest severe weather threat will be across central and
western portions of the region.
Overnight, attention will turn more to the frontal line itself.
Given the overnight timing and what may be an increasingly worked
over atmosphere, that line will probably be fading out as it
approaches, and expect that if we have problems with flooding or
severe weather tomorrow it will happen more in the late afternoon
and evening as opposed to overnight when the front approaches.
Still, showers or storms are possible throughout the overnight as
the front will not move through until very late at night or more
likely on Friday. Locally heavy rain will remain possible in any
convection until the front passes. Warm and very humid overnight
since we remain in the tropical air ahead of the front.
&&
Upton:
.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...
Heights begin to fall Thu as a trough moving through the Great
Lakes and Ohio Valley approaches. A warm front will also be
approaching from the southwest. Cloud cover will increase and
there could be a few isold showers mainly W of NYC into the
early aftn. Shower/tstm chances increase thereafter into Thu
night as the front approaches, and PW will be increasing with
weak shear, thus any tstms that develop could be slow-moving
heavy rainers, in particular from late evening into the
overnight after midnight as a 25-30 kt H9 LLJ moves across.
Could see some isold flash flooding, especially with any storms
that move across the NY/NJ metro area and into southern
portions of the Lower Hudson Valley. This threat not expected to
be widespread, and WPC forecast in general agreement with only
a Day 2 marginal risk of excessive rainfall for the metro area
north/west.
High temps on Thu will be limited by cloud cover, with most
areas seeing 80-85, and upper 70s for the south shore of Long
Island and coastal SE CT. Thu night will be muggy, with lows in
the upper 60s/lower 70s and dewpoints in the same ballpark.
Upper troughing lags behind on Fri, so have sided with slower
progression of the cold front per NAM, with continued likely
showers/tstms out east into the morning. Activity should be
more scattered into the afternoon and late day with the
approaching cold front as mid levels dry out but blyr remains
moist.
High temps on Fri should reach the upper 80s/lower 90s in NE NJ
and NYC, and with high dewpoints the heat index could touch 95
in in parts of urban NE NJ. Highs just to the north/east will be
mid 80s, and lower 80s across the forks of Long Island and SE
CT.
There will be a moderate rip current risk at the ocean beaches
on Thursday.
.HYDROLOGY...
Moderate to locally heavy rainfall is likely late Thursday through
Thursday night, with additional rainfall possible Friday.
Rainfall totals of 3/4 to 1 inch are possible with locally
higher amounts, with a low risk for localized flash flooding,
mainly across the lower Hudson Valley into NE NJ. Localized
urban flooding is also possible.
&&
