Heat, Humidity Returns for Weekend; Dangerous Storms Saturday?

The heat and the humidity will return on this weekend, but there is a thunderstorm threat for both Saturday and Sunday afternoon. Right now, we’ll focus on Saturday, because things could get interesting with good possibilities for severe storms. First off, the CAPE values are very high:

The NAM has VERY high CAPE values:

18z NAM run on Wednesday shows CAPE values at 21:00 GMT Saturday up to 5000

18z NAM run on Wednesday shows CAPE values at 21:00 GMT Saturday up to 5000

The NAM shows CAPE values as little as 2500 in Long Island to as much as 5000 in parts of NJ and PA. This is very good for severe weather!

The GFS, however, is a little less:

18z GFS run Wednesday shows CAPE values at 21:00 GMT Saturday

18z GFS run Wednesday shows CAPE values at 21:00 GMT Saturday

The GFS shows CAPE values only as high as 2000-2500in New Jersey. Still high, but not as high as the NAM. However, the GFS has been going back and forth a bit, so this has to be watched.

Convective inhibition is also low, mostly west of NYC, as @Wx_Expert pointed out on Wednesday.

There is also a third thing that supports severe thunderstorms on Saturday afternoon. The Supercell Composite. The NAM shows pretty high Supercell Composite for late Saturday.

NAM Supercell Composite at 21z Saturday

NAM Supercell Composite at 21z Saturday

NAM Supercell Composite at 00z Sunday

NAM Supercell Composite at 00z Sunday

 

I’m not going to really focus on the timing right now. Timing I will get to on Friday. But I am going to show you the 18z GFS run as of Wednesday evening just to give you the GFS’s idea on timing.

GFS at 06z Saturday

GFS at 06z Saturday

GFS at 12z Saturday

GFS at 12z Saturday

HEAT & HUMIDITY

Another thing that supports the storms is the heat and humidity that will be coming back. Here is the GFS temps for Saturday & Sunday:

GFS high temps for Saturday

GFS high temps for Saturday

GFS high temps on Sunday

GFS high temps on Sunday

Heat indices up to 90° or better are likely, especially on Sunday.

 

 

So let’s recap. There is a chance for storms on both Saturday and Sunday. Let me stress that this weekend is not a full washout! These storms will start to develop sometime in the afternoon, typical time for the summer season. Saturday looks like the more interesting day. We have high CAPE, little Convective Inhibition, heat, humidity, and high Supercell Composite. Joey at @_NEweather also pointed out that Energy Helicity is on the high side as well.

So we’ll continue to watch the weather models and bring you the latest information on this severe weather threat. Follow all the weather enthusiasts and meteorologists and future meteorologists out there to get some very good information, especially: @NY_WX, @nynjpaweather, @NEWeatherWx, @Northeast_blog, @_NEweather, @Wx_Expert, @CollinGrossWx, and @albo1912. Tomorrow, Saturday’s SPC thunderstorm outlook comes into view (Day 3). We’ll see how the NWS SPC starts things and where we end up on Saturday. I feel like sometimes we forecast severe weather like we forecast snowstorms! But that’s because weather changes all the time, and that’s why everyone works so hard to keep you informed and safe. The end of the week looks great, so enjoy it while you can! I’ll probably have updated posts (with more information) on Thursday, Friday, and then one on Saturday morning if nothing changes from Friday night. Enjoy the current quiet weather and stay safe!

 

— Jonathon Rocco

You can follow me on twitter as well for the latest updates! (@jonathonrocco) As well as following all the people mentioned above!

 

**NOTICE: I’ll be tweeting my preliminary severe threat map sometime Wednesday night with updated maps on Thursday, Friday, and Saturday. I will also have heat indices maps for Saturday and Sunday out on Friday.

 

 

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