Warm & Humid Mid-Week, Thunderstorm Threat Follows

Finally!  I think it is safe to say that summer has arrived in New England!  I hope everyone was able to enjoy the weather on our Tuesday.  This day was my pick of the week.  The weather is about to change even more on Wednesday and Thursday.  After a very comfortable Tuesday, one in which blue skies prevailed with very little evidence of the haze one sees on a typical summer day, the weather is about to change.  The biggest headlines can be traced to increasing humidity on Wednesday, and an increase in the thunderstorm threat Wednesday through Thursday afternoon.     

Humidity levels will begin to noticeably increase overnight tonight.  In fact, some areas may see patchy fog tomorrow morning, with Downeast Maine being the most likely location.  The combination of high humidity and lack of cloud cover will set the stage for a very hot and humid Wednesday.  The "Knowledge Corridor" portion of the Connecticut River Valley appears most likely to see various locations reach and pass the 90 degree mark during the day.  Temperatures farther north will be more comfortable generally in the 80's.

The weather should remain dry during the daytime hours in Southern New England on Wednesday.  The same cannot be said for Northern New England.  A cold front looks to move through this region during the afternoon.  A threat for showers and thunderstorms will rapidly increase.  In fact, the atmosphere may become moderately unstable, possibly supporting strong to severe thunderstorms capable of producing large hail and gusty winds.  Given abundant moisture, heavy rain will be a threat with any storm that can develop.  This threat is dependent on cold frontal timing, and whether or not enough surface heating can take place before peak heating hours of the day.  The greatest threat looks to exist across Maine, New Hampshire and Vermont during the afternoon.  The severe threat may then continue into Massachusetts during the early evening hours, then into Connecticut and possibly Rhode Island after dark.  Because we will have lost daytime heating and hence instability, thunderstorms will likely lose their punch before reaching southernmost areas.

To see Wednesday's severe weather threat, check out this outlook issued by the Storm Prediction Center:

http://www.spc.noaa.gov/products/outlook/archive/2011/day2otlk_20110705_1730.html


Thursday continues warm and humid, with the front expected to move through Southern New England during the afternoon.  Again, the atmosphere could become unstable enough to support the threat for strong to severe thunderstorms capable of gusty winds, large hail and heavy downpours.  This will all depend on the timing of the cold front.

The models have varied on the timing of the passage of this impending cold front and its impact on Southern New England.

1.) One model wants to slowly drag the cold front across Southern New England on Thursday, stalling it out across this same area.

• This would keep the threat of showers and thunderstorms in the forecast for Southern New England, some of which could become severe, with gusty winds, large hail, and heavy rain.  Thursday would remain fairly humid out ahead of the front. 

2.) Another model wants to scoot the front through overnight Wednesday, clearing the area by Thursday morning, keeping the day mostly settled.

• Aside from a possible thunderstorm early in the day, most of Thursday would actually turn out to be dry and pleasant, with a slight decrease in humidity.  Temperatures could still threaten the 90 degree mark, especially in the Connecticut River Valley.

Pending that Scenario #1 ensues, a thunderstorm threat may exist once again on Friday.  While heavy downpours would be possible in this tropical airmass, regardless of how Friday shapes up, it should not be a washout.  Pending that Scenario # 2 ensues, Friday should shape up to be another great weather day!  The first half of the weekend in the very least is shaping up to be fantastic as well!

Keeping an eye on the Tropics, one model shows an area of developing low pressure off the coast of Florida, scooting up the eastern seaboard Thursday and Friday.  The cold front which will pass through Thursday, coupled with a Bermuda High to our east will create a conveyor belt-like setup and carry this area of enhanced tropical moisture out to sea, not carrying any effect into New England this weekend.

-Alex Avalos