As New England continues to experience all that the weather spectrum has to offer this month, tomorrow’s forecast brings with it the threat of severe weather! The Storm Prediction Center in Norman, Oklahoma has issued an Enhanced Risk for severe thunderstorms tomorrow across the region.
SPC Day 2 Outlook
As shown in the legend bottom right in the graphic above, an Enhanced Risk is the 3rd of 5 outlook categories.
So, what might the day on Friday look like?
12 am -> 8 am
A few sprinkles or showers leftover from Thursday’s convection move through the region very early Friday morning.
Midnight to 8 am Simulated Radar – WeatherBell, LLC
8 am -> 2 pm
Once the leftover showers push off the coast all eyes turn to the southwest. The atmosphere over southern New England Friday morning is not conducive for thunderstorms. But during the day on Friday a warm front will progress northward through the region and warm, dew point rich air will flood the area.
Shown below are 2m dew point temperatures from 8 am to 2 pm. It’s easy to see how moisture rich air moves in from the southwest.
2m Dew Points: 8 am to 2 pm – WeatherBell, LLC
The combination of a moisture rich atmosphere and temperatures in the mid 70s primes the atmosphere for convection. Now all that is missing is a trigger.
2 pm -> 8 pm
That’s where atmospheric fronts come in. Front’s represent the boundary between two air masses with different characteristics. Shown in the loop above was a warm front lifting northward through the area pushing dry air northward and allowing moisture rich air into the region.
Friday afternoon that same warm front will still be hanging around while a cold front moves in from the west.
Friday Evening Frontal Set-up – Pivotal Weather, LLC
These front combined with a favorable upper atmospheric wind profile will trigger thunderstorms during the afternoon. There is some discrepancies in terms of storm timing among the computer guidance, but in general, the threat of thunder lasts from 3 pm to 10 pm.
The simulated radar for Friday afternoon from one of the computer guidance models looks like so:
Friday 3 pm to 10 pm Simulated Radar – WeatherBell, LLC
In general, areas outside of 495 are favored for the combination of storm timing and distance from cool ocean water. The wild card in tomorrow’s forecast is a potential backdoor cold front. A backdoor cold front is when cool marine air moves from east to west across the region. These often occur during warm spring days when ocean temperatures are cool. Right now most guidance keeps it confined to the immediate coast and inland areas of north shore, but it’s something to keep an eye on.
Assuming the forecast holds overnight, a morning blog will provide the latest.
-Chris
Chris Hampton Weather 