Schoharie County Floods
of 14 June 2013 (Click on images to enlarge)
(Click on images to enlarge)
A broad longwave trough and cyclonic flow aloft amidst preexisting low-level moisture provided the focus for renewed shower/thunderstorm development during the early afternoon hours (initiation around 2pm) on June 14 2013. These showers and thunderstorms moved over areas that had received significant rainfall over the past several weeks from convection and an anomalously strong synoptic low pressure system that moved along the Mid-Atlantic States just a day before. An enhanced area of low-level convergence across Fulton/Montgomery/Schoharie aided by a piece of shortwave energy moving through the longwave trough provided the focus for a concentrated area of training thunderstorms that dumped 1-3 inches (reported and radar indicated) of rainfall across portions of Montgomery and Schoharie counties.
As the initial cells formed and continued to intensify, one of them near the Schenectady/Montgomery/Schoharie border became particularly strong with the 50dBZ core reaching the -20C level, along with indications of small hail with depressed CC values (~0.9-0.97) amidst higher ZDR values (>1 dB) and KDP (2-3 degrees/km). A SPS was then issued for this cell as dual pol data continued to indicate the potential for severe hail, along with the Hail Algorithm indicating 1 inch hail. As both the Dual Pol and Legacy data continued to suggest further indication of severe hail in the next volume scan, a Severe Thunderstorm Warning was issued for extreme southwestern Schenectady county, north central Schoharie county, and south central Montgomery county for a thunderstorm capable of producing "penny size hail" (see Equipment Problems below).
This cell went on to produce pea and half dollar size hail, but more importantly, became the initial storm that entered northwestern Schoharie County. Additional storms continued to redevelop immediately north of preexisting cells that tracked north to south across Schoharie County. Orographic lift appears to have been a major contributor to the continual regeneration of cells. An FLS was first issued for portions of Schoharie County before being upgraded to a FFW after the Legacy FFMP indicated that FFG had been exceeded along with receiving a report of flash flooding in the town of Middleburgh. Additional FFWs were issued for portions of Schoharie and Montgomery counties as well. These storms continued until around 6-7pm before finally dissipating with the loss of daytime heating. Several sources of information (Schoharie County EMA, Facebook, Twitter, local news stations, local law enforcement, local fire departments) were used to get reports of flash flooding.
HRRR and 15-min HRRR (http://rapidrefresh.noaa.gov/HRRRsubh/Welcome.cgi) did suggest training echoes west of I-87 but rainfall amounts were rather meager.
The town of Middleburgh in Schoharie County was the hardest hit by the flash flooding as small creeks and tributaries (surprisingly not the Schoharie Creek itself) (combined with elevation influences) resulted in much of the town experiencing flash flooding. Flash flooding was also reported in Sharon Springs, Schoharie, Richmondville, and Cobleskill. The biggest "news" story from this event was a group of elementary students at a school in Middleburgh remaining in a shelter in place during the flooding, since there was no way to get into Middleburgh during the height of the flooding. Although this story was widely reported by YNN and other local media, thankfully everyone was safe with no injuries or deaths reported.
Following parameters of note from the 00z June 15 KALY sounding - compared to values from the 12z morning sounding:
00z vs. 12z
SBCAPE: 1212 J/kg vs. 29 J/kg (forecasted SBCAPE)
PW: 1.00 inches vs. 0.82 inches
0-3km lapse rate: 8.4 C/km vs. 5.8 C/km
850-500mb lapse rate: 7.0 C/km vs. 5.1 C/km
Corfidi Downshear: 350/41kt vs. 21/9kt
Corfidi Upshear: 358/14kt vs. 161/3kt
Cloud bearing mean wind vector: 347/25kt vs. n/a
Mean mixing ratio: 8.5 g/kg vs. 7.4 g/kg
WBZ height: 8657ft vs. 7236ft
Freezing Level: 8691ft vs. 7601ft
An increase in WBZ and Freezing Level heights may have helped promote more efficient, warm rain processes in the updrafts that moved over Montgomery/Schoharie counties. Stronger midlevel lapse rates also helped in generating stronger updrafts that were higher in precipitation efficiency given the increase in PW and mean mixing ratio during the day as well. The storms also had modest CAPE to work with in a relatively tall and skinny CAPE profile. The theta-e profile slightly decreased with height suggesting a modestly convectively unstable profile. In addition to orographic influences, the Corfidi vectors also provide a look into storm mode/evolution as the downshear vector supports the anvil-bearing winds to allow for good storm ventilation downstream (to the south), while the upshear vector also helped support regeneration of cells due north of the preexisting cells. 12z runs of the Nam and GFS with forecasts hours at 18z also suggest a thermodynamic environment similar to the 00z sounding.
Both the Dual Pol QPE and Legacy versions of FFMP should be
open at the same time - in case there is significant differences between the
two. For this case, the QPE severely underestimated the potential basin threat,
with the Legacy doing a much better job. Both the QPE and Legacy did fairly well
in terms of actual rainfall via the STP/STA vs. reported rainfall. For some
reason, the Dual Pol QPE is not working well with FFMP and it has been suggested
that the Legacy FFMP should be used right now until the QPE issue can be fixed.
Although Corfidi vectors are usually primarily used for forward and backward propagating MCSs, they can still be useful when trying to assess individual cell movement in a unidirectional flow environment. The VWP can also be useful in determining storm movement, as the VWP indicated due northerly winds throughout almost the entire column.
Above: Soundings from KALB on 14 June 2013 at 1200 UTC (left) and 0000 UTC (left center) and forecast soundings for KALB at 1800 UTC from the GFS (right center) and NAM (right).
Above: SPC mesoscale analysis loops of precipitable water (left), surface-based CAPE (left center), low-level lapse rates (center), moisture convergence (right center), and midlevel lapse rates (right).
Above: Loops of predicted radar reflectivity from the HRRR (left), WRF (center) and NAM (right).
Above: Loops of KENX radar Base Reflectivity (left) and legacy Storm Total Precipitation (right).
Above: Flash Flood Monitoring Program (FFMP) for 1.5 hours based on KENX legacy Storm Total Precipitation (left) and the Dual Pol Storm Total Accumulation (right).
Above: Flash Flood Monitoring Program (FFMP) for 6 hours based on KENX legacy Storm Total Precipitation (left) and the Dual Pol Storm Total Accumulation (right).
Above: KENX legacy Storm Total Precipitation (left) and Dual Pol Storm Total Accumulation (right).
Above: Pictures from around Middleburgh in Schoharie County.