Daily Archives: July 23, 2016

More Storms Possible Monday

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Hello everyone!

Strong to severe storms are impacting the region currently, as forecast. The strongest storms are across SW areas which is as forecast as well. Storms will continue across the region through this evening before dying out with the loss of heating from the sun. Tomorrow will be warm and dry as high pressure builds in but the quiet weather only lasts a day and by Monday, another cold front will be at our doorstep with the chance for showers and storms, some of which could be severe.

12Z GFS Showing The Setup Aloft Monday. Image Credit: Accuweather
12Z GFS Showing The Setup Aloft Monday. Image Credit: Accuweather

Another shortwave will be digging south across Eastern Canada Monday and out ahead of it, divergence aloft and convergence at the surface thanks to an approaching cold front will provide the large scale rising motion necessary for strong storms. As of now, model guidance is in agreement we will have a trigger for storms Monday. Also of note is that the large scale pattern of NW flow around the NE side of the Central US heat dome supports this shortwave crossing the area Monday. We have our trigger. Now will there be enough fuel for strong storms? Instability is the biggest question at the moment.

NAM Showing Onshore Winds Limiting Instability Monday. Image Credit: Weatherbell
NAM Showing Onshore Winds Limiting Instability Monday. Image Credit: Weatherbell

Most model guidance suggests that winds will be out of the SE for most of the day Monday. A SE wind is one off the cold Gulf of Maine which would keep temps in the 70’s for most. That SE wind and those low temps would sufficiently stabilize the atmosphere so that we would stay more or less storm free. This could change, however. A peek at the Euro ensemble guidance suggests that timing remains uncertain and the potential exists for winds more out of the S or SW following the passage of a warm front. Euro ensemble mean CAPE shows this potential with values between 1,000 and 1,500 j/kg Monday afternoon. The timing of both the warm and cold fronts will be watched closely in the coming days to determine if strong storms indeed can form.

GFS Showing A Juiced Atmosphere Monday. Image Credit: Weatherbell
GFS Showing A Juiced Atmosphere Monday. Image Credit: Weatherbell

One thing to keep in mind is that even without typical severe storm impacts (hail, wind, etc.), there could very well be heavy rain on Monday. Guidance is pointing to Precipitable Water values (PWATs) of near 2″ which is tropical. Be aware that even without a severe thunderstorm threat, there very well may be a heavy rain threat. We do need the rain, however as southern areas are in moderate to severe drought.

Warm and dry conditions return for the middle of next week and a more substantial rain event hopefully will arrive by the end of next week into next weekend. More on that as we get closer.

I’ll have more updates on this event on Twitter tonight and tomorrow.

-Jack

More Strong To Severe Storms Possible Today

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Hello everyone!

Today will feature slightly cooler temps, less humidity, and another chance for strong/severe thunderstorms. The thunderstorm threat will develop later this morning and continue through the early evening hours. Storms are more likely in SW areas where more energy will be available aloft. While most of the storms are not likely to become severe, some of the stronger cells do have the potential to mix down some strong wind gusts and perhaps some small hail. Frequent lightning and heavy rain are the main threats. Highs will range through the 80’s with dew points in the 60’s which is still warm and certainly not dry but far better than yesterday.

WV Imagery Showing A Disturbance Dropping SE This Morning. Image Credit: SSEC
WV Imagery Showing A Disturbance Dropping SE This Morning. Image Credit: SSEC

A vigorous disturbance is currently located north of the Great Lakes and is forecast to drop SE and intensify, arriving in our area bu sunset. Storms will form out ahead of it late this morning/early this afternoon. When I talk about forecasting thunderstorms, I talk about the trigger, the organizer, and the fuel. This disturbance will be the trigger for today’s storms.

40-50 Knots Of Deep Layer Shear Will Organize Storms Into Small Clusters Capable Of Some Damaging Wind Gusts. Image Credit: SPC
40-50 Knots Of Deep Layer Shear Will Organize Storms Into Small Clusters Capable Of Some Damaging Wind Gusts. Image Credit: SPC

A band of strong winds and powerful shear will rotate around the disturbance today. The strongest winds will be pointing at Southern New England while Northern Maine sits in the calm aloft associated with the disturbance being to their south. In southern Maine/New Hampshire, we’re a bit on the edge. We likely see enough shear to get some small clusters but large squall lines are unlikely. If that disturbance can intensify enough fast enough, it could pull some of those winds north and we could see a bit more action. If it remains a little weaker, those winds will continue screaming towards SNE. These winds will be our organizer.

Hi-Res NAM Showing Modest Instability With More Unstable Air Moving In From The West. Image Credit: Weatherbell
Hi-Res NAM Showing Modest Instability With More Unstable Air Moving In From The West. Image Credit: Weatherbell

The biggest question today is how unstable the air will be. A cold front moved through last night (remember those storms?). That front has moved offshore and has taken the extremely soupy/unstable air with it. We are left with marginal moisture and several areas of clouds to limit surface heating. Model guidance suggests that more unstable air will try to filter in from the west later today but I have to wonder if that will make it in time. Also of note with regard to instability is wind direction. Westerly winds don’t exactly bring in the warm moist air you need for big storms. Regardless, we do still have leftover moisture and dew points remain in the 60’s which is sufficient for at least some storms. Also, wide swaths of clear skies this morning support some solid surface heating which will bring temps up into the 80’s, also plenty sufficient for storms.

All that to say, ingredients are at least sufficient for some storms, a few of which could be severe with strong winds and small hail. However, I do have doubts as to how unstable the atmosphere is. Also, we don’t have optimal winds aloft for organizing storms into lines capable of widespread wind damage. While organized severe storms are not forecast, still do keep an eye to the sky today and be prepared to duck inside for a few minutes if you plan on heading outside.

More storms are possible Monday and Thursday with two more cold fronts.

-Jack