(Click on thumbnails for larger images and movies)
There was no outlook for our region from
SPC. There was an SWOMCD for the storms in the BUF and BGM area, stating that
the storms would diminish around sunset. Then, when the storms blew up east and
Thunderstorms formed in PA during the early afternoon, and tracked through
There was a strong upper level jet segment that was tracking into our region. During the afternoon, our region was in the left exit region of the upper jet. It is quite likely that the enhanced upper divergence helped support/sustain the convection.
The showers and thunderstorms tracked east and southeast, with the northern half of the area weakening as it headed into the
We continued with NOWs, including gusty winds. The strongest part of the area of showers and thunderstorms continued to weaken, and by the time the shallow convection reached
We received a report from a spotter in Colonie of a 30 MPH wind gust, and George called from
We warned down the line in locations east and south of
What we learned:
The day before this event, operational
models did provide some hints that strong convection was possible over our
region. There was a concensus that a strong surface dew point gradient would be
over our region, although there was disagreement in exactly where the dewpoint
boundary would set up. There was also a consensus that the upper jet segment
would be tracking into the region, but the exact position and timing was not
completely clear, and small changes in timing and position could have big
implications on whether we would be in a favorable region of the upper jet. All
MOS guidance showed chance POPs for POU and HFD, with slight chances for ALB,
PSF and AQW.
On the day of the event, the morning data suggested cooling aloft was advecting into the region, and there was instability out toward BUF and PIT. There was a strong gradient of dew points over the region with 40s to the north and 60s to the south, suggesting there may be enough instability and forcing for strong convection. Once the convection formed over the
The convection was much like cold season convection, shallow and low reflectivities. This was very uncharacteristic of August. The low reflectivities were deceiving, and in the future, reports of trees and wires down associated with any system that even has the hint of exhibiting convection, or looked more convective in the past (I.E. higher reflectivities), should be closely analyzed. The radar Base Velocity did not show severe winds until the stronger convection began to develop over the ALB area, but 40 Kt winds should alert a forecaster. A considerable portion of BGMs severe weather reports were associated with a well-defined 50+ Kt wind maximum on their radar in the 4-bit Base Velocity, but not all. We kept an eye on our radar for winds closer to 50 Kt.
Mesoscale analyses were consulted, but the questionably convective nature to the rain, along with the low dew points advecting south suggested any strong wind potential would be with the strongest convection, in southern areas, where there was a strong dew point gradien, and the Taconics and southern Berkshires had dew points in the 60s. There was some convergence seen in the wind barbs, but 3-hour pressure rises and LAPS soundings were not consulted due to the lack of expectation of severe weather, with no SPC outlook and such low surface dew point suggesting lack of instability, plus the seemingly weakening nature of the northern portion of the area of showers and storms.
This event may be interpreted as a gradient wind that evolved into a convective wind gust once the convection re-established itself. In other words, the
Figure 1. Upper air sounding from
Figure 2. Upper air soundings from Albany, NY (KALB) for a) 1200 UTC Friday 17 August, and b) 0000 UTC 18 August. Note the relatively stable soundings and weak wind shear.
Figure 3. Upper air soundings from Buffalo, NY (KBUF) for a) 1200 UTC Friday 17 August, and b) 0000 UTC 18 August. Note the relatively stable soundings and weak wind shear.
Figure 4. Water vapor satellite imagery at 2210 UTC 17 August. Note the enhanced moisture over western and northern NY. Click on the image for a movie of the water vapor imagery.
Figure 5. Visible satellite imagery with lightning overlay at 2155 UTC 17 August. Note the convection over western NY, and a separate cluster in northern NJ. Click on the image for a movie of the visible imagery. Note in the movie, that the lightning diminished to just a few strikes by 0035 UTC 18 August.
Figure 6. MSAS surface dew point analysis at 2200 UTC 17 August. Click on image for a movie. Note in the movie, the impressive dew point gradient across the Berkshires, Taconics and Catskills. There were also some relatively higher dew points in western NY representing a small area of warm advection ahead of the strong upper impulse.
Figure 7. MSAS rise/fall couplets at 2200 UTC 17 August. Click on image for movie.
Figure 9. Severe Weather Outlook for day 1 from the
Figure 10. Initialized/observed 500 hPa heights and vorticity from the 0000 UTC 18 August NAM80. Click on image for movie. Note in the movie, the difference in timing, intensity and track of the upper vorticity center.
Figure 11. Initialized/observed wind barbs and isotachs at 250 hPa at 0600 UTC 18 August (click on image for larger image). Click on image at right for movie of forecasts from the 1200 UTC run of the NAM80. Note the location of the observed jet maximum further east at 0600 UTC as opposed to the forecasted evolution of the upper jet segment in the movie of the NAM80 forecast.
Figure 12. Wind barbs and isotachs at 850 hPa initialized/observed from the 0000 UTC 18 August NAM80. Click on image for movie. Note in the movie, the differences in the initialized/observed winds (top), the NAM80 forecasted winds (lower left), and the SREF winds (lower right). Also note that the SREF winds forecast was closest to what actually happened.
Figure 13. LAPS soundings at 0000 UTC 18 August from a)
Figure 14. Radar reflectivity at 0.5˚ from KTYX early in the event. Click on the image for a movie.
Figure 15. Radar Base Velocity at 0.5˚ from KTYX at a) 2247 UTC 17 August, and b) 2259 UTC 17 August. Note the high base velocities just east of the radar site that weakened slightly as the storms moved east. The weakening winds might be attributed to the radar returns being slightly higher above ground level.
Figure 16. Radar reflectivity at 0.5˚ from KBGM early in the event. Click on the image for a movie.
Figure 17. Radar Base Velocity at 0.5˚ at KBGM from a) 2249 UTC 17 August, and b) 0033 UTC 18 August. Note the high winds northwest of KBGM that tracked through and southeast of KBGM.
Figure 19. Radar reflectivity at 0.5˚ from KENX at 00001 UTC 18 August. Click on images for movies of the convective line in different stages. Note the decrease in reflectivity, but the bowing leading edge of the showers and storms. Also note the speed of movement of the radar echoes, indicative of the strong steering wind flow. The convection strengthened east and south of the Capital District, with much higher reflectivities developing.
Figure 20. Radar Base Velocity at 0.5˚ from KENX at 0001 UTC 18 August. Note the development of 40Kt+ winds northwest of the Capital District, then 50Kt winds appearing just east of the radar as the leading edge of the showers and storms tracked through the Capital District. The strong wind signature continued as the convection strengthened east and south of the Capital District.
Figure 21. Radar echo tops from KENX at 0105 UTC 18 August. Note the echo tops of 20,000-25,000ft, illustrating the low-topped nature of the convection.