After my post 2 days ago about what constitutes a nor’easter and that I didn’t expect this storm to fit the bill – I’ve changed my mind!
As late as midday yesterday our computer models were showing a large storm (area-wise) but a somewhat unimpressive storm in the wind department. The rainfall forecast (amounts and timing) worked out great but the wind exceeded my expectations! The National Weather Service was in the same boat yesterday with no gale warnings or wind advisories prior to the onset of strongest winds to having to post the advisories in the middle of the storm.
It was the nor’easter that wasn’t but turned out to be! Here’s the midday GFS run for wind speeds about a mile above the ground (850mb) valid at 8 p.m. yesterday. It’s only a 12-hour forecast.
As it turned out, vigorous thunderstorm development and the presence of several “meso-lows” (basically, just a fancy term for smaller scale low pressure systems) were able to modulate the wind profile and result in a narrow band of much stronger winds than originally forecast.
Here’s a look at the analysis of winds at 850mb last night and you can see things turned out a bit more impressive than originally forecast.
Closer to the surface the difference was even more noticeable. Here’s a forecast sounding for KOKX (where the weather balloons are launched on Long Island) off the GFS model valid at 8 p.m. yesterday.
Here’s the analysis off the 00z NAM which is much closer to reality though based off the 00z balloon launch is still a bit underdone (balloon measured winds of 55 knots at 901 mb and 50 knots as low as 935mb).
The inversion starts quite a bit higher (around 880mb) than modeled. The combination of a stronger wind profile and a deeper mixed layer lead to a much windier storm than originally expected. Thankfully, the winds weren’t strong enough to cause any significant issues here in Connecticut besides sporadic power outages. If nothing else the storm was a fantastic one to fall asleep to last night with strong wind gusts, periods of heavy rain, and occasional thunder and lightning.
The final verdict on this one: nor’easter and overperformer. Lessons learned? For a storm with such vigorous convection nearby (and in some cases overhead) some of the higher resolution non-hydrostatic models deserve some extra love. It’s easy to dismiss them since they seem to always produce funky and extreme solutions – but in an overly dynamic storm they may be the way to go!