June 3, 2014 - Severe Weather and Flash Flooding (click on image to enlarge)

An area of low pressure moving across the northern Great Lakes and attendant cold front spawned two rounds of showers and thunderstorms, in which the first round during the afternoon/evening hours resulted in heavy rainfall, areas of flash flooding, and wind damage across the Capital Region, Mid-Hudson valley, and Berkshire County. A second round of showers and thunderstorms developed during the evening hours and moved across the region overnight bringing additional rainfall to the region. When the event was over, most areas saw generally 1-2 inches of rainfall, with isolated locations of 2+ inches.

The first round of thunderstorms formed well ahead of the surface cold front, as the surface low was well north and west of the region (north of Lake Huron). Ahead of the cold front, however, was a prefrontal trough that helped trigger the convection. Additionally, the upper-level dynamics were favorable for lift, as the forecast area was sandwiched between an upper-level trough over the Great Lakes and area of low pressure in the Atlantic. This allowed for a diffluent height field aided in part by deformation as well.

The 12 UTC ALB sounding revealed some indications that it was going to be an active day. Although midlevel lapse rates were marginal at best (~6.0 deg C/km), there was the potential for instability to develop if enough surface heating could take place. This would depend on the amount of sun that we could get, as the convective temp was 85F (the high temp ended up reaching 89F). PWAT values were 1.32 inches, above normal for this time of year indicating that there was a lot of moisture to work with. Any storms that would form would move slowly to the NE, with just a mean wind profile of 241 degrees/10 knots. Warm rain processes were also favored, as the FZL was high at 13.4 ft and the -20C level at 24.2, hindering the threat for large hail. While heavy rain was the main threat of the day, an isolated wet microburst could not be ruled out given the high PWAT values, low mean wind, and disorganized hodograph profile that suggested pulse-type storms that could have the potential for precipitation loading in the updraft. K Index values during the afternoon hours on the SPC mesoanalysis page were in the mid 30s.

By the late morning/early afternoon hours, enough sunshine had occurred to allow for 1000-2000 J/kg of SBCAPE to develop across the region. Thunderstorms began to develop ahead of the prefrontal trough as early as 1700 UTC. The first batch of storms was concentrated in the Mohawk valley, with both the STP/STA indicating 1-2 inches of rain with rainfall rates between 1-1.5 inches per hour. Urban and small stream flood advisories were issued for Fulton and Montgomery Counties. Additional thunderstorms then began to develop southeast across Schenectady county and Schoharie, and these storms began to train. Flash flooding was expected in portions of Schoharie, Schenectady, Fulton, Montgomery, and Saratoga Counties. We did receive reports of flash flooding in Gloversville, Amsterdam, and Duanesburg. These storms struggled to have 50 dBZ cores reach the -20C level, acting more like Low Echo Centroid (LEC) storms. However, rather impressive ZDR/KDP columns accompanied the strongest updrafts, as these columns routinely reached the -10C level, lofting plenty of liquid water into the updrafts. Values within these columns also suggested giant raindrops, with ZDR values greater than 2 dB and KDP values as high as 4-6 deg/km without any hail! STP/STA indicated areas of 2-3 inches of rainfall, with rainfall rates as high as 3 inches per hour!

More thunderstorms began to develop just east of the flash flood area, across eastern Schenectady/western Albany/southern Saratoga Counties, and initially these storms also trained. With the expectation that these thunderstorms would continue to produce rainfall totals/rates like was already being seen, flash flooding was expected in the greater Capital Region, the heavy rain effecting the evening commute. Soon after the storms began affecting the Capital Region, the storms began to move at about 20 mph, and this may have been due to a slightly stronger wind field aloft moving into the region as the cold front continued to approach from the west. While most of the flooding across the Capital Region was poor drainage, there was a report of flash flooding in Delmar.

As these storms moved east, a wet microburst occurred in East Greenbush causing several reports of wind damage. The storms began to train again once they hit the Berkshires as flash flooding was expected in the Pittsfield/Adams area. We did receive reports of road closures/washouts in the Stockbridge area.

An impressive storm formed in Columbia County and was the strongest and deepest storm of the day with the 50 dBZ echo reaching as high as 34kft. A 70 dBZ core up to -20C accompanied this storm as well. We got reports of wind damage with this storm, and despite the high FZL, we received reports of nickel size hail.

Duanesburg received the heaviest rainfall with a report of 3.89 inches. Portions of Berkshire County were also hit with heavier rain totals ranging from 2-3 inches.

Both the STP and STA did well with this event, and were close to each other as well. This may have been due to the fact that there was little, if any, hail.  The STP can often overestimate in the presence of hail. Also, the STA is doing much better at ranges beyond the ML, which may be due to the dry snow coefficient change from 2.8 to 1.9 as a result from the ER QPE Field Study.

Descending KDP columns (especially in high moisture environments such as this event) are a great tool to use to assess the potential for wet microbursts in the presence of relatively low velocity values. The threat is enhanced if KDP values in the core of the column aloft are extremely high (3+ deg/km) without the presence of hail. Descending KDP columns accompanied both SVR warnings that had wind damage in Columbia County and the East Greenbush area.

CRH GIS graphics that plot up SVR/TOR/FFW warnings continue to be very useful for social media, as these posts on Facebook received a lot of likes and shares.  Social media was extremely useful for getting verification for this event. Multiple Facebook and Twitter posts allowed people to get quick information updates. As people commented on the Facebook posts, conversations allowed us to dig deeper to get reports of flash flooding/road closures/severe damage. While social media was useful, it also required some sifting as well, as there were a lot of posts (ex. "There's so much flooding going on!") that over-embellished what was actually going on. Also, a lot of pictures were shared on Facebook, which was extremely helpful for getting verification. Not only did we get verification from our Facebook page, but WRGB/WTEN/WNYT Facebook pages were also extremely helpful and the person using social media should keep these pages (and other pages) in mind when trying to get verification.

 

Outlook and morning data

 

Above:  The day 1 severe weather outlook from the Storm Prediction Center.  Note the northeastern U.S. is not outlooked.

Above:  Soundings at 1200 UTC 3 June from Albany, NY (ALB) (left), Buffalo, NY (BUF) (center) and Maniwaki, Quebec (WMW) (right).  Note that there was little instability and limited moisture at KALB but considerable instability and significant moisture upstream at KBUF and KWMW that could advect into the KALB region.

Above:  NWS Albany, NY Facebook post explaining the severe weather and flood threat for the day.

 

Above:  Upper air plots from the Storm Prediction Center at 1200 UTC 3 June at 850 hPa (left), 500 hPa (center) and 300 hPa (right).  Upper dynamics and upper jet energy were not very strong but strong westerly low level winds were building toward eastern NY.

Mesoscale analyses during the onset of the convection

Above:  Storm Prediction Center mesoscale analyses valid 1800 UTC 3 June for mean 850-300 hPa wind (left), midlevel 700-500 hPa lapse rates (left center), maximum unstable CAPE (right center) and Precipitable Water (right).  Deep shear was upstream as was greater instability and the axis of greatest moisture.

Above:  Loop of Infrared satellite imagery.  Deep convection developed and tracked through much of the NWS Albany forecast area.

Above:  Loop of Visible satellite imagery.  Deep convection developed and tracked through much of the NWS Albany forecast area.

Above:  Loop of KENX radar base reflectivity.  Deep convection developed and tracked through much of the NWS Albany forecast area.

Above:  Local storm report with severe weather and flood reports.