Don Paul: What led to the surprise tornado, and what comes next?
"Many weaker, short-lived smaller tornadoes go undetected by the nation’s network of NWS Doppler radars or, if detected in the multiple scans, are already dissipated by the time the data is generated," writes Don Paul.
Monday dawned as a day with a marginal/5% risk for severe thunderstorms for much of Western New York, with a 15% risk to the southeast, shown in yellow.
Severe thunderstorms can and do occasionally produce tornadoes, but in the broader scale weather pattern, the day didn’t begin as one in which meteorologists were thinking along tornadic lines. The lower atmosphere was very moist, and heating was adding to the buoyancy and instability of the lower atmosphere. Showers and thunderstorms were already in the forecast for Monday since Saturday morning. The Monday 11 a.m. surface map showed a weak frontal boundary with a small ripple of low pressure on the front just to our north.
The lamp post holding the street sign for Carolina Street and Prospect Avenue was ripped out of the ground during Monday’s tornado. Derek Gee/Buffalo News
One after-the-fact hint was the mean west-northwest flow over nearby Ontario and the west wind over Niagara Falls converging with the southwest flow in the Buffalo metro area. With hindsight, that kind of directional convergence, combined with somewhat stronger dynamics, had helped to develop some spin in thunderstorms of greater intensity in the past. The most notable metro area example was the July 30, 1987 Cheektowaga tornado.
Monday’s tornado, in some social media quarters, is thought to have begun as a waterspout. Actually, the same parent cell had caused a brief tornado touchdown in Fort Erie before the vortex moved out over the water. This image is from the Fort Erie Community Watch Facebook page.
When the tornado moved out to cross the water, it became a tornadic waterspout (many fair weather waterspouts are not tornadic), and when it moved onshore in Buffalo, it was a tornado. It turned out to be a short-lived tornado, which did not produce what is called a TVS/Tornadic Vortex Signature on the sophisticated National Weather Service Doppler radar. It should be known that radar takes multiple scans of the atmosphere at different altitudes to gain a more detailed slice of storms and wind flow. This tornado simply was too small and short-lived to be detected within those multiple scans. Had it been stronger and had it tossed up more debris, the radar might have detected the debris. But its short, six-minute track and lack of detectable debris are two of the factors that made the issuance of a timely tornado warning all but impossible.
In fact, many weaker, short-lived smaller tornadoes go undetected by the nation’s network of NWS Doppler radars or, if detected in the multiple scans, are already dissipated by the time the data is generated. It is the larger and stronger tornadoes that are usually detected and warned, many of those attached to supercell thunderstorms. A 1999 EF-5 tornado near Oklahoma City resulted in a rare one hour-in-advance warning due to the massive area of detected low level rotation on the NWS Norman, Okla., radar.
No doubt Monday’s pre-storm convergent flow in a moist, unstable atmosphere will make local meteorologists take notice of what seemed to be a not especially volatile environment. Here is the NWS preliminary report on what was, unquestionably, the most impactful tornado ever to strike the City of Buffalo, which has been nearly tornado-free during most of its history. Even a “weaker” EF-1 tornado can do serious damage in a densely congested city.
On Tuesday, the Storm Prediction Center outlined a narrow strip of 5% severe risk along the distant Southern Tier and Pennsylvania border.
Apart from that limited risk to the south, it was evident in guidance and on radar that plenty of soaking rain was on the way for the afternoon, approaching from the west on Detroit NWS radar.
All this moisture will be gone for the opening day of the Erie County Fair on Wednesday, and that includes excess humidity. Abundant sunshine with a pleasant northeast breeze and temperatures in the mid-to-upper 70s will be a pleasure after the long stretch of muggy days and Tuesday afternoon’s steadier rain.
Thursday will still be a fine day, with upper 70s highs and comfortable humidity. Some clouds will begin to mix in from the southeast, influenced by Tropical Storm Debby’s outermost cloud shield.
Due to weak steering currents, there is still uncertainty about the movement of Debby as we come to Friday, and how much interaction there may be between her wet circulation and a nontropical low approaching from the west.
On Friday, both the American GFS and European ECMWF models are bringing some of Debby’s rainfall into our region. Threading the needle, the ECMWF keeps more of the heavy rain just to the east of the eight WNY counties, but I can assure you there will need to be adjustments in this uncertain storm track during the week.
The GFS is similar, with heavier rain placement, at this point. For now, I would count on at least occasional showers on Friday, which, if realized, could put a figurative damper on the Fair. Should Debby's path be a little farther west, rainfall would be more significant. It will be humid, with a high approaching 80, unless more widespread rain moves into our region, which would hold temperatures in the 70s.
By Saturday, while there may be a stray shower under a partly sunny sky, most of the day will be dry and seasonably cool. The high will be in the mid 70s.
Sunday, a trough over the northern Great Lakes may bring a few sparse coverage showers for a minority of the day. Otherwise, it will be partly sunny and cool. A brisk northwest flow will keep highs in the low 70s.
The breeze will lighten on a partly sunny Monday, with fewer – if any – spotty showers, and a high near 75. Similar conditions will prevail on a mostly dry, partly sunny Tuesday. Readings will edge back into the upper 70s.
In the extended range, probabilities favor cooler than average temperatures in the 6-10 day outlook.
A little warming should be returning during the 8-14 day period.
There is no excessive heat in sight, and those upper 80s we experienced last week will not be returning any time soon.
Debby brings historical rain and catastrophic flooding
As of Tuesday, Tropical Storm Debby has moved inland, and winds have weakened to 40 mph. With slow-moving or stalled systems such as Debby, wind ceases to be the main threat. It is, simply put, the slow motion deluges that are being churned out. The weak steering currents will cause Debby to just meander around eastern South Carolina for at least 2 days before finally curving off to the northeast as a depression by the weekend.Weather Prediction Center additional rainfall estimates, with many flash flood warnings already issued, will produce catastrophic flooding in some locations. 12-20 inches will be falling in the outlined regions, turning quiet streams and creeks into raging torrents.
A rare high risk for flash floods covers a large stretch of territory, and even an eventual moderate risk (also fairly uncommon) reaches Philadelphia to New York City.
There will also be a risk of quick spin-up tornadoes in the eastern Carolinas.
So, while Debby no longer is a hurricane (so long as its circulation remains inland away from the heated Atlantic waters), the National Hurricane Center key messages for Debby’s impacts remain ominous. (It should be noted that if Debby takes a bit more of a turn more out to the very warm Atlantic, reintensification would occur.)
The current NHC track forecast keeps Debby just offshore by Wednesday and Thursday, but west of the extremely warm Gulf Stream waters. Even so, Debby is likely to regain top winds of at least 60 mph, producing a more significant storm surge for the Carolina coasts, on top of the grave flood threats in place.
