Fine tuning Saturday’s hazardous weather threats

finger lakes weather forecast saturday july 17 2021 severe thunderstorms flash flooding
Important Saturday morning updates to the flash flooding and severe thunderstorm risk this afternoon. [Photo by Meteorologist Drew Montreuil]

Saturday Morning Update

Portions of the Finger Lakes continue to be under the gun for hazardous weather this afternoon.

Low pressure riding along a stalled out frontal boundary will provide a focal point for torrential downpours and severe thunderstorms this afternoon. A very sharp cut-off between an atmosphere supportive of thunderstorms and an atmosphere more hostile to thunderstorms is expected.

Pinpointing where this boundary sets up is not only a great challenge but the primary key to whether or not the Finger Lakes sees significant weather this afternoon.

Models continue to vary between keeping this boundary along or even south of the NY-PA State Line, or further north in the southern to central Finger Lakes. Thankfully, we are close enough to the event now that we can start to compare the model projections to the current conditions, giving at least some idea how well the models are doing so far.

Based on these trends, the greatest chances for severe thunderstorms this afternoon will probably be over Chemung, Tioga, and Broome counties, but Steuben, Schuyler, Tompkins, and Cortland Counties should also be on the lookout.

Next, is fine-tuning exactly what the hazards are.

From a severe thunderstorm standpoint, damaging winds will be the primary threat. A tornado threat does exist but is not looking quite as intense as the models had been showing.

Still, there may be a couple rotating supercells that require a tornado warning across the areas previously mentioned, extending south and southeast from there. In addition to a tornado threat, any of these supercells will be capable of damaging winds and torrential rain.

If storms stay more individual and cellular, there will be a higher chance for slow-moving and repeated downpours. This will make flash flooding a serious concern. Most of the aforementioned areas can take an inch or less of rain in an hour, yet rainfall rates will easily exceed that today.

On the flip side, if storms organize into more of a line, the threat for damaging winds would increase, but the flash flood threat would likely diminish somewhat with faster-moving storms.

The timing of the storms remains another point of uncertainty. A few storms may be possible during the first half of the afternoon, with more widespread action through the mid and late afternoon. Multiple storms are possible for any given location.

finger lakes weather forecast saturday july 17 2021 areas of concern
This map illustrates the areas that I am most concerned about for severe thunderstorms and flash flooding this afternoon.
finger lakes weather forecast saturday july 17 2021 areas of concern

Summary

So, the bottom line this morning is that threats remain for this afternoon, mostly over the southeastern Finger Lakes. The complexity of the setup, especially the razor-sharp cutoff between stable, less threatening air and highly unstable air, leads to a high degree of uncertainty in the location of the worst weather.

Calmly being prepared for threatening weather is the best course of action. This includes knowing where to get timely updates (hint: I will be live blogging this afternoon!) and having a plan in place should the weather threaten.

This may be as simple as going about your day but heading indoors when you hear thunder…to as complex as knowing how to react to a sudden flash flood if you are in a poor drainage area or near a small stream.

With a proper plan in place for getting information and acting on it, there should be no reason for panic.

The Rest of the FLX

Now, the rest of the Finger Lakes will have active weather too, but it should be less threatening. A combination of more soil tolerance for heavy rain and more stable air will keep the threats minimal.

Thundery downpours will still be possible, especially just north and west of the southeastern Finger Lakes. These include Allegany, Yates, Seneca, Cayuga, and Onondaga counties.

The further north and west, the lower the chances for excessive rain from downpours and the lower the chances for thunder. However, the further north and west, the greater the chance for steady rain throughout the day.

The severe threat should end before the sunsets, but a residual flooding threat will linger into the early evening. The heavy rain should taper to showers by midnight.

Models are unfortunately trending back towards a showery Sunday with low pressure to the east but slow to depart.

More Information:

» Finger Lakes Weather Radar

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Follow Meteorologist Drew Montreuil:
Meteorologist Drew Montreuil has been forecasting the weather in the Finger Lakes region since 2006 and has degrees in meteorology from SUNY Oswego (B.S. with Honors) and Cornell (M.S.). Drew and his wife have four young boys and also run a goat milk soap business, Ye Olde Goat Cart. When not working or playing with the boys, he is probably out for a run through the countryside.