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May Day Severe


Drz1111

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Figured this was worth its own thread if anything fired off before the main line.  Looks like once the warm front clears out this mP air we're going to have some backed flow, plenty of moisture, and PERHAPS just enough CAPE, especially inland.  Low-level shear is about as good as we get, though on some of the CAMs it looks like there might be a subtle pre-frontal trough that tends to veer the winds closer to the main line on the front.  If that earlier trough initiates storms, though, it could be interesting.  Mid level lapse rates are probably the biggest problem, which makes sense given that this air has been thoroughly convectively overturned over the last couple of days in the plains and Midwest.  

i think the area on the eastern edge of the enhanced risk doesn't look terrible - IF (big if) storms initiate ahead of the main line, they'll have marginal cape but some nice backed low-level winds. 

 

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KOKX doesn't seem too impressed:

Note: Most of the area is under a slight risk for severe
storms today/tonight, with an enhanced risk across far western
Orange County and a marginal risk over New London County and
most of the Twin Forks. The main threat would be from any severe
storms (possible squall line) that develop late today over
Upstate NY/PA then tracks into the area this evening. The
question is, how fast would any such storms weaken as the move
into an area dominated by a marine airmass in the low levels
(even at KSWF per BUFKIT soundings). The main threat will be
from gusty winds, but large hail cannot be completely ruled out.

 

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I think OKX is being a bit too negative.  For example, below is a forecast sounding for western NJ, near Morristown, off the most recent run of the HRR, for 5 pm tonight.  CAPE very marginal but it wouldnt take much of an underestimation of heating to make this a very interesting setup.  FWIW some of the CAM runs are firing off isolated cells just west of this in NE Pa - those are the storms to watch because of they can establish good mid level rotation in the better environment out in PA, they should be able to persist in marginal CAPE in western NJ.

http://www.pivotalweather.com/model.php?m=hrrr&p=refcmp_ptype&rh=2017050111&fh=10&r=conus&lat=40.7948&lon=-74.9221&metar=

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5 minutes ago, NJwx85 said:

Meh,

The timing is terrible. You're going to watch a wicked looking squall line over Central PA disintegrate as it crosses the mountains. 

This isn't about the squall line; the risk is for discrete storms that form along a pre-frontal trough earlier in the day with more low-level shear.  It's conditional and nothing may happen, but it's worth watching.  Agree that the squall line itself should be nothing but gusty rain for us.

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4 minutes ago, NJwx85 said:

SPC pulls way back on new update.

day1otlk_1300.gif?1493644159611

No, they didn't.  The enhanced risk and tornado risk are almost the exact same spots,.  They reduced the risk for downstream wind/squall line at the coast, which is like, duh, look outside your window. 

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6 minutes ago, Drz1111 said:

No, they didn't.  The enhanced risk and tornado risk are almost the exact same spots,.  They reduced the risk for downstream wind/squall line at the coast, which is like, duh, look outside your window. 

Storm motion is also a problem, looks like things are moving more SW to NE.

The 12z HRRR pushes all the action into upstate NY.

hrrr_ref_frzn_neus_9.png

hrrr_ref_frzn_neus_12.png

hrrr_ref_frzn_neus_14.png

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Special Weather Statement
National Weather Service Binghamton NY
946 AM EDT Mon May 1 2017

NYZ009-015>018-022>025-036-037-044>046-055>057-062-PAZ038>040-043-
044-047-048-072-011800-
Northern Oneida-Yates-Seneca-Southern Cayuga-Onondaga-Steuben-
Schuyler-Chemung-Tompkins-Madison-Southern Oneida-Cortland-
Chenango-Otsego-Tioga-Broome-Delaware-Sullivan-Bradford-
Susquehanna-Northern Wayne-Wyoming-Lackawanna-Luzerne-Pike-
Southern Wayne-
946 AM EDT Mon May 1 2017

...SEVERE WEATHER OUTBREAK POSSIBLE THIS AFTERNOON AND EVENING...

Thunderstorms, potentially severe, are expected to develop ahead
of a strong cold front this afternoon through evening. Damaging
winds will be the primary threat from these storms, but isolated
tornadoes will be possible. Also, the storms may contain heavy
rainfall with the potential for localized urban and small stream
flooding.

Make sure you are very aware of the weather this afternoon through
evening, and have multiple ways to receive warnings. Generally
speaking, the main period of concern will be 4 PM to 10 PM west of
Interstate 81, and 6 PM to midnight east of Interstate 81.
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The high res models continue to show a window with marginal CAPE and favorable low level shear at around 20-21Z.  The question is whether we get any convection at that time.  The later squall line isn't going to do squat around here.

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It looks like the main action today is going to be with the main squall line, which certainly reduces the risk in our area.   Convection ahead of the line seems to be lacking lift.  I like the State College area for some semi-discrete action near the bottom of the main line.

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2 minutes ago, Drz1111 said:

It looks like the main action today is going to be with the main squall line, which certainly reduces the risk in our area.   Convection ahead of the line seems to be lacking lift.  I like the State College area for some semi-discrete action near the bottom of the main line.

We're close to getting into the warm sector, even up here in far NE NJ I am now full sunshine with only some cirrus overhead. Temperature is up to 77.8F and DP is up to 60.

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Just now, Drz1111 said:

That tornado-warned embedded supercell looks NASTY, even though it has no TDS.  Lots of hail, strong midlevel circulation.  That could drop a tornado at any time.  

And that same cell has been tor warned now 4 or 5 times. Seems to keep cycling. 

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6 minutes ago, NJwx85 said:

And that same cell has been tor warned now 4 or 5 times. Seems to keep cycling. 

The HRRR has hinted at a dominant embedded supercell along the NY/PA border for the last few runs.  This cell might be it.  Certainly its in the best environment, but hard for something in the line to produce given that's its being undercut by the gust front.

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