Thursday’s Bust – What Went Wrong?

All the ingredients seemed to be lining up for a significant severe weather event, particularly in western Connecticut and adjacent parts of New York. What did we see? Sporadic damage reports and a dying squall line that moved out of the Poconos.

There was certainly a  lot of potential on Thursday. Models had been showing moderate amounts of instability and very strong shear. Forecast and observed hodographs indicated the potential for tornadoes in any discrete cells that developed or along squall lines.

18z NAM 6 hour HVN 0-3km hodograph forecast

While deep layer (and low level) shear was sufficient for supercells a strong cap near 850mb prevented convection from developing ahead of the main line. Here’s a 23z RAP sounding (initialization) for HVN and you can see right off the bat the problem.

Yikes!!! That’s a lot of CIN. The LFC is nearly 775mb with a large negative area on that sounding. While the squall line looked exceptionally impressive over Pennsylvania it began to fizzle as it worked east. The large amount of convective inhibition became problematic as the squall line’s cold pool was unable to force surface based parcels to the LFC.

Our models had shown that the CIN present during the day would weaken but apparently that was not the case. While low level moistening helped eliminate some of the negative area it was not enough. The cap was also quite low. Typically we see caps around 700 mb… not 850mb! The exceptional warm 850mb temperatures (over +22c) effectively served to cap convection.

With a convective temperature of 95F we just weren’t going to get rid of that CIN. The warm layer at 850mb (NAM did do well with this) was just too much. With stronger surface heating and more low level moistening things may have been different.

The storms were most certainly a bust. The Storm Prediction Center issued the first ever (that I can remember) day 2 moderate risk for Connecticut. The probabilities for severe wind and significant severe were some of the highest you’ll ever see in Connecticut.  In fact while the event was ongoing the SPC sent out a discussion saying they contemplated an upgrade to “high risk” which would have been the first time since May 31, 1998 parts of the state have been in a high risk! As the squall line was leaving the Poconos the SPC expected the storm to strengthen and called it a derecho.

In the end a lack of synoptic forecasting (500mb heights were neutral from 18z-00z) and strong CIN thanks to a stout low level cap did our severe chances in. Given the potential it was important to mention the possibilities. Severe weather is a challenge to forecast – certainly much more challenging than a winter snowstorm!

Surprise Storm for CL&P?

At a press conference this morning CL&P President and COO Jeff Butler commented that this storm was “far more significant than what had been forecasted.”

Interesting. Obviously CL&P either has a private forecasting firm that is just plain bad or they were not listening to some of us degreed meteorologists on TV in the state that were forecasting a crippling snowstorm. Friday morning Bob Maxon and I were forecasting up to a foot of snow that was “record-shattering and historic”. 36 hours out it’s not everyday we use words like “record-shattering” and “historic”.

In addition we were playing up the “impact” more than the actual amounts. With leaves on the trees and the heavy, wet type of snow expected we knew power outages could be a huge deal. It happened in greater Albany in 1987 and was most certainly on our minds.

Here’s my blog post from Friday morning 10/28:
“One of the reasons I’m unusually concerned about this storm is that the amount of leaves on the trees make them particularly vulnerable to damage. If the snow is of the heavy and wet variety we could have major and widespread power outages. We’re in uncharted territory here in terms of this type of storm this early in the season.”

This is from Thursday 10/27 (a full 48 hours before first flakes):
“A major snowstorm is on the way and will likely be a historic and unprecedented early season snowstorm. All the parameters and models are showing significant snow totals across the state.

Obviously the time of year gives me pause. The biggest October storm in the greater Hartford area was only 1.7″ back in 1979. The biggest storm in the entire state was 9.5″ in the town of Norfolk on October 4, 1987. Still, records are made to be broken and I am quite confident that in many areas this will be the biggest October snowstorm in recorded history.

It’s possible, but at this point not likely, that the storm will trend west and bring more rain as opposed to snow. It’s something to watch. The big concern for this storm may be damage to trees and powerlines given the amount of trees that are still fully foliated!”

The NWS was banging the drum too on Friday. Here are two discussions from Friday morning and Friday afternoon from the NWS in Albany. Notice the use of the word catastrophic!

“WE ARE NOT GOING TO TAKE ANY CHANCES WITH THIS STORM. THERE COULD
BE A MAJOR SOCIETAL IMPACT ACROSS A LARGE PORTION OF THE FCST
AREA. LEAVES ARE ON THE TREES IN THE VALLEYS /ESPECIALLY FROM THE
CAPITAL DISTRICT SOUTH/…AND ACROSS SOME OF THE HILLS. 3 TO 6
INCHES OF HEAVY WET SNOW COULD BE VERY PERILOUS BRINGING DOWN
NUMEROUS LIMBS AND POWER LINES. WE HAVE TRIED TO EMPHASIZE THIS IN THE
WATCH STATEMENT ! POTENTIALLY…THERE COULD BE NUMEROUS POWER
OUTAGES. DESPITE NOT HITTING THE 7 INCH OR GREATER CRITERIA…WE
FEEL THIS WATCH IS NECESSARY DUE TO THE POTENTIAL SOCIETAL IMPACT.”

“POWERFUL WINTER LIKE STORM WILL DEVELOP ALONG THE MID ATLANTIC COAST
ON SATURDAY AND AFFECT THE REGION THROUGH SATURDAY NIGHT AS IT MOVES
QUICKLY NORTHEAST. MODELS ARE GENERALLY IN AGREEMENT THAT THIS WILL
BE A HISTORIC OCTOBER SNOWSTORM FOR MUCH OF THE REGION. THE HEAVY
WET SNOW WILL LIKELY PRODUCE MAJOR TO CATASTROPHIC DAMAGE TO TREES
AND POWER LINES IN THE AREAS WHERE WARNINGS HAVE BEEN ISSUED AND
EXTENSIVE FOLLIAGE REMAINS ON THE TREES.”

I understand the need to make excuses but this should not have been a surprise. For one of the most anomalous storms of our lifetimes this was exceptionally well predicted 36-48 hours out.