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Weather Threats: 2020 Edition


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You are out of your mind. This winter has been over for 45 days already. It’s never too early for warmth if it isn’t going to snow. 

interesting times are pending  

The 1st one to post an 840 hour GFS snowstorm next winter gets a 72 hour vacation! 

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How hot it ultimately gets in early July will largely depend on how quickly the cut-off low next week does or doesn't clear out of the northeast...those pesky upper lows have already saved us from a few very warm to hot days this summer. 

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29 minutes ago, Thundersnow3765 said:

Let's not keep these coming as we head deeper into hurricane season...

Watch that'll be our drought buster in a month or so.  This pattern is getting long in the tooth for many, especially those wanting 90+ heat daily in the NYC area.

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...Eastern Ohio to Long Island...
   Convection is expected to be ongoing Saturday morning and casting
   uncertainty regarding the magnitude of destabilization, especially
   in NY.  Yet, models indicate a belt of strong 700mb flow will
   overspread much of PA into NJ during peak heating with steep 0-3 km
   lapse rates.  Several clusters/bands of thunderstorms are forecast
   to develop by midday/early afternoon and move east into a
   destabilizing airmass over the Delaware River Valley.  It is over
   eastern PA, NJ, and perhaps as far north as the lower Hudson Valley
   that a greater concentration of strong to severe gusts (50-70 mph)
   may occur.  Because of the uncertainty at this time, will defer to
   later outlooks for a possible upgrade to 30-percent wind
   probabilities.  Farther south over the MD/VA vicinity, lower storm
   coverage is expected amidst weaker westerly flow.  However, ample
   heating and stronger storms possibly developing over the terrain and
   spreading east, may pose a risk for wind damage during the mid-late
   afternoon and early evening.
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Mt.Holly (KDIX) radar has been down since last night. I guess that upgrade really did alot for it. Hopefully it comes back up tonight or by tomorrow morning.

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Excellent AFD from Mt. Holly on tomorrows severe weather potential. A rather concerning read.

 

***Severe Thunderstorms Possible Saturday Afternoon and Evening***

Summary: An active day of weather is expected Saturday. Severe
thunderstorms, mainly in the afternoon and evening, will be capable
of producing potentially widespread wind damage. There remains a
fair amount of uncertainty in the forecast regarding both the
location and severity of the greatest threat. However, interests in
the area should continue to monitor Saturday`s forecast and be
prepared to take action should severe thunderstorms threaten.

Synoptic Overview...

Steady west-northwest flow at the H5 level will characterize the
pattern through Saturday. Multiple convectively enhanced shortwaves
will propagate through the flow from the Great Lakes into the
Northeast and mid-Atlantic through Saturday evening. Upstream trends
through tonight will be critical for outcomes locally on Saturday.
MCS formation is expected over the southern Great Lakes states this
(Friday) afternoon and evening. That MCS will then propagate into
western New York and Pennsylvania overnight. By Saturday morning,
what remains of that feature will serve as our "Round 1" of
convection, bringing clouds, showers, and possibly thunderstorms to
the area, mainly north of Philadelphia. Not expecting severe weather
with that as the presence of little if any instability in the
morning should favor a weakening trend of that activity as it moves
east. Later in the day, an additional convectively enhanced
shortwave will approach from the west. That will serve as a forcing
mechanism for another and likely more significant round of
convection in the afternoon and evening. Some concern that the
second shortwave may be a little too weak or strung out to force
severe convection, but most indications are that it will provide
sufficient lift in an unstable atmosphere (conditional on clearing
behind the initial round) to support thunderstorms.

Details/Possible Outcomes...

The obvious recent analog to this event continues to remain June 3,
a similar northwest flow synoptic pattern which yielded widespread
damaging thunderstorms across the region. This setup is not quite as
dynamic, with mid-level flow a bit weaker and concerns about the
potency of the trailing shortwave. In addition, a notable
thermodynamic difference lies in the mid-level lapse rates. Whereas
June 3 had an impressive elevated mixed layer (EML) which helped
build instability, mid-level lapse rates tomorrow are closer to
6C/km. Not terrible, but will make it a little harder to support the
type of high end MCS we saw on June 3 by keeping the CAPE profile
skinnier. Otherwise, however, the environment on Saturday afternoon
is expected to be supportive of severe weather. Temperatures over
most of the area should reach well into the 80s to near 90, with dew
points climbing into the upper 60s to near 70. So while the CAPE
profiles will be a bit skinny, should still see 2000-2500J/kg of SB
CAPE build by afternoon. Good DCAPE values as well with inverted V
profiles in the lowest 1km or so, which will enhance the damaging
wind threat. A plume of higher PWAT values (1.6 to 1.8 inches) will
advect into the region from late tonight through the day on
Saturday, so air mass moisture is not in question. Wind fields are
solid, with bulk shear values around 40 kt and good flow through
much of the low and mid levels. Magnitude and orientation of the
shear vectors are supportive of a downwind propagating MCS.

Main question mark and potential failure mode on Saturday`s
convection revolves around the extent of destabilization following
morning clouds and showers. This is particularly true given marginal
mid level lapse rates, as we will really need the surface to heat up
to help build instability. Unfortunately, difficult to say before
upstream trends unfold how much of a concern this will be.
Evaluating 26.12z CAM guidance, would first note that the CAMs
should be used with caution over the next 24 hours, as they are
notoriously poor in handling MCS events. Having said that,
generally good agreement amongst the 12z runs (ARW, NMM, RGEM,
HRRR) that sufficient destabilization will occur to support
severe convection in the afternoon. Between this and the
synoptic pattern, feel the most likely outcome is for a line of
strong to severe thunderstorms to develop over northern and
central Pennsylvania during the early to mid afternoon, moving
east-southeastward through much of our area during the mid to
late afternoon and evening. A reasonable worst case scenario
would feature an MCS capable of producing potentially widespread
wind damage. The 12z hi-res NAM was a notable outlier versus
other CAMs in showing little or no convection over the region
Saturday. While this is a less likely outcome, it cannot be
ruled out if we fail to destabilize.

A few other thoughts come to mind in looking over Saturday`s
forecast. First, similar to June 3, would not be surprised to see
the higher severe risk shift a little south versus current
expectations. These MCS events tend to gravitate towards greater
heating and instability, and that should be found more the further
south you go, better removed from morning convective debris. The
Philly/Wilmington metro area as well as southern New Jersey are
certainly in play for severe storms, and latest SPC SWODY2 has
expanded the SLGT risk south a bit (with concerns over
destabilization precluding an upgrade to ENH for now). Next, storm
mode for Saturday is not a slam dunk. While linear modes should be
favored, there is decent veering in the low levels and some
clockwise turning in the hodographs. 0-1km SRH values of around 150
m2/s2 are possible in the afternoon. With moderate to strong bulk
shear in place, cannot rule out supercell development or supercell-
like structures within an MCS. A tornado or two is possible, but
definitely a more localized, conditional, and secondary threat
compared to straight line winds. Not expecting hail to be much of an
issue given warm low levels and relatively skinny CAPE profiles, and
while storms will produce torrential downpours, should be
progressive enough to limit hydro concerns. Overall, expecting an
active day, but the forecast will be a little bit touch-and-go over
the next 12-18 hours as we monitor upstream trends.

Shower and storm activity could linger into the early overnight, but
the trend overnight will be for drying out. A warm and muggy night
is expected with lows struggling to get below 70.


&&
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Thinking somewhere in the vicinity of NNJ/EPA is likely the place to be once again as its looking like those areas have the best overlap of parameters, not unlike the 3rd, but likely a good deal less potent than what that event posed...yet still fairly impressive all its own

 

Up here north of 84 I wouldn't be shocked if we fail to destabilize that much if at all if current trends hold.

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Looking like today's threat will indeed be more isolated in nature than initially believed, and still further south than anticipated as well. Better heating should be taking place south of NYC, but it does not spare most of us from perhaps seeing some redevelopment. 

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