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:
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:
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.
If we match up the CAPE values with Convective Inhibition. If you are W of New York you need to monitor this closely. pic.twitter.com/dNoj9ho2kM
— Wx_Expert (@Wx_Expert) July 15, 2015
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.
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.
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:
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.
Energy Helicity at 3km is pretty frigging high: pic.twitter.com/GcTWPGcT0n
— NE Weather Authority (Your Petty Meteorologist) (@_NEweather) July 16, 2015
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.