06:51 Tue Oct 15, 2019
First Big Storm Of The Season And It's Looking To Be A Doozy
Wednesday night into Thursday there will be two areas of low pressure that will merge and potentially undergo explosive development or bombogenesis, meaning that it will likely fall 24 mbars in pressure within 24 hours. The forecasting challenge with these types of setups is that one of the areas of low pressure will likely rapidly develop off the coast of New Jersey and race up along the coast within 24 hours of developing. As of 00z on Tuesday, this developing Low won’t form into a closed Low for another 48 hours (overnight Wednesday). Once it develops, forecasters will have a much better idea of what will happen, as far as local effects are concerned. As for the summit of Mount Washington, it will depend on where the two systems merge and how close the center of the merged Low is relative to the White Mountains. If it forms to the southwest over CT and Mass then the summits will likely see sustained wind speeds of 100+ mph with gusts of 130+ and potentially even higher! This scenario would prove to be most exciting for us, and you, if you tune in. If the newly merged center forms at all to the east of the Whites then we will still see some initial high winds but not as impressive. The highest winds for the latter scenario would occur on the backside of the system as it heads out into the Gulf of Maine. Either way, it will be an impressive storm producing a significant icing event with several types of precipitation, high winds, and exciting moments for sure. In the meantime, let’s look at a handful model runs to see what is causing this powerful storm to develop and intensify.
The area of low pressure that will develop and rapidly intensify off the coast of New Jersey is caused by a whole mess of factors, but a few really stick out to me which I have researched and found to be large contributing factors. I’m going to let the diagrams and pretty colors do most of the describing here so I don’t turn this into a case study and get carried away. Below, is the Thursday 00z 850 mbar Geopotential Height and Cyclonic Vorticity (localized rotation of the air). Where there is strong cyclonic vorticity advection, meaning the localized area of rotation is stretching to the surface, there is a deepening in the surface low. This is seen in the deep red color just off the coast of New Jersey. This is where the surface low will develop and ultimately intensify into quite the storm.
GFS 850 mbar Geopotential Height (dam) and Cyclonic Vorticity (10-5 s1) 00z Thursday
What is causing this area of vorticity? Well, there is air entering the base of the trough and that air is relatively warmer and more humid than its surrounding environment. You can see the wind direction by looking at the wind barbs in either the Geopotential Height plot above or the 10-meter wind plot below. I'll show you in the next two plots of 2-meter temperatures and 10-meter winds for the same time of Thursday 00Z that these two differing air masses are colliding with each other and producing a fascinating phenomena.
GFS 2-m temperature (F) at 00z Thursday
GFS 10-m Wind Speeds (knots) at 00z Thursday
For the 10- meter wind speed plot you can not only see a southern air mass entering the trough from the south, but where the green elevated wind speeds are, westerly flow is converging with southerly flow. If we refer back to the 2-meter temperature plot, the westerly flow is much cooler than the southerly flow and is undercutting the warm southerly flow. This is a good example of a Cold Conveyor Belt in which cold temperatures help to lift the humid warm air aloft. The southerly warm flow is called the Warm Conveyor Belt.
Okay, now lets pull it all together. One of my favorite plots to use in Northeastern Extra-Tropical Cyclones is a Theta-E plot or Equivalent Potential Temperature. Think of it as an indicator of latent heat release which will be described in detail in the next Windswept, if you are a member! Sorry for the promotion, but it was a good time to plug it in. I digress, latent heat release is essentially the stored heat as water changes phases between vapor to liquid to snow or ice. That heat is released into the atmosphere, which then furthers the uplift, advects the cyclonic vorticity towards the surface, and in turn deepens the surface low, while providing plenty of moisture for it snow!!!
GFS Theta-E (K) at 00z Thursday
Isn't it great how all of this lines up perfectly?! Stay tuned for the most recent forecast at the Observatory's Higher Summits Forecast Page!
Jay Broccolo, Weather Observer/Meteorologist