21 August – severe weather
Synoptic Setup: A large upper level trough approached
the region as a strong mid-level jet rotated through its base. A rather potent
surface cold front approached from the
There were two distinct rounds of severe weather. The afternoon round was well expected ahead of the cold front. However, the late morning into early afternoon was not. The first round ended up being the more significant of the two. The first round was associated with mid-level short wave, low and mid-–level thermal advection along with mixed layer instability. The models including the HISRESWFR and HRRR-3km did not pick up on the evolution of organized lines with the late morning convection.
OUR HIRES WRF BASE REF PRODUCT SEEMS TO HAVE A GOOD HANDLE ON
THINGS AT THIS POINT...AND IT SHOWS A RATHER INTENSE LINE OF
CONVECTION FORMING TOWARDS 20Z...AND CROSSING THE FORECAST AREA BY
THE 12Z KALB SOUNDING SHOWS ONLY 0-6 KM SHEAR VALUES OF 24 KTS
NOW...BUT WE EXPECT THE DEEP SHEAR TO INCREASE TO 40-50 KTS BY THE
LATE PM WITH A MULTICELL LINE...AND PERHAPS SOME SUPERCELL
STRUCTURES WITH MLCAPE/SBCAPES GENERALLY 1000-2000 J/G OVER THE
FCST AREA. THE 12Z SOUNDING ALL SHOWS H850-500 LAPSE RATES OF 6.8
C/KM WITH A WET BULB ZERO HEIGHT OF 10.3 KFT. THERE IS LOW-LEVEL
VEERING IN THE BOUNDARY LAYER...BUT WITH THE STRONG CYCLONICALLY
CURVED MID/UPPER LEVEL JET STREAK APPROACHING LATER TODAY WE
BELIEVE THE PRIMARY SEVERE THREAT WILL BE WIND...WITH SOME HAIL.
THE LATEST MAGLENTA SEVERE WEATHER INDEX CAME OUT WITH A MAJOR
SEVERE WEATHER EVENT POSSIBLE. THIS IS A CONDITIONAL POINT INDEX
FROM PAST COMET RESEARCH.
HERE ARE THE PARAMETERS INPUTTED:
MAX SOUNDING WINDS = 65
EHI = 1.0
SRH (0-3 KM) = 150 (M/S)2
STORM SPEED = 30 KTS
Convection initiated before over the southern
The first SVR warning was issued at about . That cell developed an inflow and
became a supercell with not one, but two gate to gate couplet signatures over
30kts. The SVR was upgraded to a TOR
Other severe thunderstorm warnings were issued for
the Capital District and southern
The other significant cell indicated gate to gate
Coordination with SPC for Severe Thunderstorm Watch #795 came while we were in the thick of issuing warnings. Some storms produced torrential downpours including here at the office where we picked 0.96 inches of rain in about 15-20 minutes along with dime size hail. Three flash flood warnings were issued.
Above: Loop of surface maps showing the passage of the cold front.
Above: Storm reports from 21 August.
Pictures of damage in