Wednesday, April 21, 2021 Low Topped Squall Line

[weatherwiz]

A nice little "pre-game" before severe weather season kicks in but looks like we'll see a low topped squall line move across much of southern New England late Wednesday afternoon and early evening. While the greatest threat for damaging wind gusts likely exists to our west (across NY and northern PA) the potential will exist for much of the region for localized embedded damaging wind gusts and perhaps even some small hail. 

Instability is not the driver in this event as instability will be quite marginal with temperatures only into the 60's and dewpoints in the 40's to 50's, however, the presence of steep mid-level lapse rates aloft results in modest instability (500 - 750 J/KG of MLCAPE). The driver here is strong forcing from the approaching cold front and very strong jet dynamics characterized by 50-60+ knots at 500mb and 35-40+ knots at 850mb. Fairly steep low-level lapse rates, low-level dry air, and strong LLJ will also favor embedded damaging wind gusts, likely on the leading edge of the line. With steep mid-level lapse rates and cold air aloft, small hail is also possible. 

 

[crossbowftw3]

17 hours ago, weatherwiz said:

A nice little "pre-game" before severe weather season kicks in but looks like we'll see a low topped squall line move across much of southern New England late Wednesday afternoon and early evening. While the greatest threat for damaging wind gusts likely exists to our west (across NY and northern PA) the potential will exist for much of the region for localized embedded damaging wind gusts and perhaps even some small hail. 

Instability is not the driver in this event as instability will be quite marginal with temperatures only into the 60's and dewpoints in the 40's to 50's, however, the presence of steep mid-level lapse rates aloft results in modest instability (500 - 750 J/KG of MLCAPE). The driver here is strong forcing from the approaching cold front and very strong jet dynamics characterized by 50-60+ knots at 500mb and 35-40+ knots at 850mb. Fairly steep low-level lapse rates, low-level dry air, and strong LLJ will also favor embedded damaging wind gusts, likely on the leading edge of the line. With steep mid-level lapse rates and cold air aloft, small hail is also possible. 

 

Perfectly timed too as it looks like the grander pattern implies severe weather season across the eastern 2/3rds of America looks primed to really kick off starting this weekend.

[radiator]

Interestingly, the WX Underground forecast for NW CT shows chance of thunderstorms on Wed for each hour from 8 AM through 2 PM, which seems to be a bit earlier than the late Wednesday afternoon and early evening "pre-game" show timing mentioned above.

 

[weatherwiz]

19 minutes ago, radiator said:

Interestingly, the WX Underground forecast for NW CT shows chance of thunderstorms on Wed for each hour from 8 AM through 2 PM, which seems to be a bit earlier than the late Wednesday afternoon and early evening "pre-game" show timing mentioned above.

 

eh those hourly things are kinda crap

[Brian5671]

1 hour ago, radiator said:

Interestingly, the WX Underground forecast for NW CT shows chance of thunderstorms on Wed for each hour from 8 AM through 2 PM, which seems to be a bit earlier than the late Wednesday afternoon and early evening "pre-game" show timing mentioned above.

 

8AM? Bust.  No model has anything that early

[weatherwiz]

HRRR pretty bullish with a few decent UD swaths...not likely but certainly room for a brief tornado as well today

[HoarfrostHubb]

Mid to late afternoon could be fun

[Ginx snewx]

10 minutes ago, weatherwiz said:

HRRR pretty bullish with a few decent UD swaths...not likely but certainly room for a brief tornado as well today

2010 May 5th?

[ineedsnow]

Cumulus clouds this morning.. Unstable already?

[CoastalWx]

HRRR seems to overdo it at times. 3k NAM not as excited, but I do think a few strong storms into wrn CT/MA/srn VT possible. HRRR has shown a bow into the Berks.

[CoastalWx]

Good lapse rates aloft.

[Chrisrotary12]

Ok. Consider me slightly intrigued.

[weatherwiz]

1 hour ago, Ginx snewx said:

2010 May 5th?

let's do it!

[weatherwiz]

45 minutes ago, CoastalWx said:

HRRR seems to overdo it at times. 3k NAM not as excited, but I do think a few strong storms into wrn CT/MA/srn VT possible. HRRR has shown a bow into the Berks.

Yeah the HRRR has been pretty consistent with that bowing feature. 

Also want to add something for folks but this is a situation where the strongest winds are going to be on the leading edge of the line. It will still be gusty under the rain but the rain-cooled air will quickly reduce winds. This is for those who "meh" things when under the line  

 

[WxWatcher007]

Latest NAM looked decent for some storms in CT, especially in western CT. Sounding looked alright for the Hartford area. Would prefer more DCAPE but hopefully I can get some good pics today. 

[Cyclone-68]

I’ll be disappointed with anything less than a TORCON 7 this summer 

[WxWatcher007]

Just now, Cyclone-68 said:

I’ll be disappointed with anything less than a TORCON 7 this summer 

In Kansas?  

[Cyclone-68]

1 minute ago, WxWatcher007 said:

In Kansas?  

You are observant I didn’t actually say where lol 

[crossbowftw3]

7 minutes ago, WxWatcher007 said:

In Kansas?  

if the upcoming large scale pattern is to be believed you may see that happen in KS/OK....on the 10th anniversary of 4/27/11 no less 

[WxWatcher007]

Probably irrelevant, but I didn't expect it to be this breezy. My VP2 gusted to 24mph which is pretty decent given how it is sited. 

[HoarfrostHubb]

A few flakes possible tonight?

[weatherwiz]

1 minute ago, HoarfrostHubb said:

A few flakes possible tonight?

could see some squalls maybe tomorrow (perhaps moreso NYS, VT, and western MA)

[weatherwiz]

5 minutes ago, WxWatcher007 said:

Probably irrelevant, but I didn't expect it to be this breezy. My VP2 gusted to 24mph which is pretty decent given how it is sited. 

Pretty steep llvl lapse rates and strong llvl shear FTW

[Hoth]

Nice mammatus with this departing storm. Torrential rain and a few lightning strikes on Stein's grave.

[weatherwiz]

good sign to see some lightning with this initial activity. 

[WxWatcher007]

1 minute ago, weatherwiz said:

good sign to see some lightning with this initial activity. 

Yeah, that stuff moving into northern Hartford County looks pretty decent. 

[weatherwiz]

Just now, WxWatcher007 said:

Yeah, that stuff moving into northern Hartford County looks pretty decent. 

Just had a pretty decent gust of wind here (Windsor Locks). Looks like bulk of the line passes just north

[Cyclone-68]

Interesting just to see thunderstorms in the region before noon in late April 

[WxWatcher007]

I’m clearly bored

Mesoscale Discussion 0402
   NWS Storm Prediction Center Norman OK
   1049 AM CDT Wed Apr 21 2021

   Areas affected...Western MA...NY Hudson Valley...Western/Central
   Long Island...Western CT...NJ

   Concerning...Severe potential...Watch possible 

   Valid 211549Z - 211815Z

   Probability of Watch Issuance...60 percent

   SUMMARY...Thunderstorm development is anticipated over the next hour
   or two along a cold front progressing through the Northeast.
   Damaging wind gusts are possible with these storms and trends are
   being monitored for possible Severe Thunderstorm Watch issuance.

   DISCUSSION...Recent surface analysis places a low near the NY/NJ/PA
   border intersection. A warm front extends eastward/northeastward
   from this low across southern NY through western MA and off the far
   southern ME coast. This low is embedded within a broad area of low
   pressure preceding a strong frontal surge attendant to a shortwave
   moving into western PA/NY. This low is expected to deepen over the
   next few hours ahead of the front while the warm front lifts
   northward. As a result, temperatures in the low to mid 60s will
   likely be in place ahead of the front from western MA through
   central NJ. Low-level moisture will be modest (i.e. in upper 40s/low
   50s) but the steep low and mid-level lapse rates will foster modest
   buoyancy.

   Expectation is that deeper convection will begin developing along
   the front during the next hour or two before then moving quickly
   eastward across the region. Previously mentioned steep low-level
   lapse rates coupled with deep convection and strengthening low to
   mid-level flow will result in the potential for damaging wind gusts
   as the storms move through. Storm coverage may be high enough to
   merit watch issuance and convective trends are being monitored
   closely.

   ..Mosier/Guyer.. 04/21/2021

[crossbowftw3]

hearing some rumbles here in the Catskills, should be interesting for you guys once this thing really gets rolling.