Thursday Discussion : High Severe Thunderstorm Threat

Hurricane Laura is approaching landfall in western Louisiana as of this post… and by the time most of you are reading this, Louisiana will have suffered its strongest hurricane landfall on record.  Hurricane Laura is currently a strong Cat 4 hurricane with sustained winds of 150mph.  Our thoughts and prayers will be with the residents of Louisiana and eastern Texas in the coming days, as the images of devastation will surely be horrifying.

Unfortunately, we’ve got our own problems to worry about on Thursday.  A warm front will push through in the morning on Thursday with scattered showers, maybe even a rumble of thunder.  That will give way to sunshine and clouds… and temps in the mid 80s for the afternoon.  We’ll have strong SW winds at the surface, and strong NW winds aloft.  So as a cold front begins dropping south during the afternoon, the stage will be set for strong to severe thunderstorms.

Chance of damaging wind gusts: 30% to 45%
Chance of large hail: 15% to 30%
Chance of Tornado: 5% to 10%

An enhanced risk of severe thunderstorms in the Hudson Valley signifies a rather widespread event, with a few intense storms possible.  The percent chance may seem low compared to the tone of this conversation, but the way we calculate that threat is like this…
Let’s say you’re in Poughkeepsie.  If you draw a circle around you that extends 30 miles outward from your location…

The chance that a report of damaging wind gusts occur somewhere within that circle, is between 30% and 45%… 15% to 30% that large hail occurs… and 5% to 10% that a tornado occurs within that circle.  Those are high odds of those events occurring on any given day.  So this is an event that should be taken very seriously.

Timing the Event
The timing on this event can be seen in the futurecast radar shown below

Shower & Thunderstorm threat:  12pm to 10pm
Severe Thunderstorm threat:  2pm to 8pm
Highest Risk Period: 3pm to 7pm

You can see that the line of thunderstorms develops along the frontal boundary near Albany around mid day… and then begins to dip southward into the Hudson Valley between 2pm and 6pm, redeveloping a bit, and slowly tracking southward.  The threat of the severe thunderstorms could be with us for several hours, as the front does not push through very quickly at all.  That may allow for long duration thunderstorms, or some areas to be hit by multiple storms.

The further north you live… the earlier the threat reaches you.  So areas like Hudson, Kingston, Saugerties… the threat is on your doorstep by 2pm, and could last several hours.  Areas like Poughkeepsie and Newburgh, you might not see the storms approach until after 4pm… and closer to 6pm for places like Warwick or Monroe.  We’ll have to adjust the timing as we get closer.

Again the major threat is potentially damaging wind gusts.  But hail and an isolated tornado or two cannot be ruled out.  The atmospheric shear will be quite high, and this could lend to areas of strong rotation, which could result in a tornado.  Everyone should be alert during the afternoon hours, as this has the ability to be a very busy afternoon.

We’ll try to have more updates as we go through the day on Thursday.