Warm and dry conditions today will give way to increasingly hot and humid weather as we head towards the latter part of the week. By Thursday and Friday, heat indexes could soar above 100. Dewpoints will climb into the low to mid 70’s which means that not only will it feel oppressively humid, there will also be tons of moisture in the air. A cold front will stall over us tomorrow and weak waves will begin to ride along it Friday. Each wave will push the front slightly farther south and by the middle of next week, we will again be dry and cool.
Today’s forecast worked out pretty well with temps largely in the 70’s with some 80’s in SW ME and NH. Temps warmed up a little more than forecast over S NH where a few 90’s were reported. The sea breeze developed as expected and brought slightly cooler temps to the coastline and adjacent inland areas. It did stay dry today, as forecast, but there were a few more cirrus clouds than expected. Overall, not a great forecast, but not a huge bust either.
Some showers and thunderstorms currently over Ohio will be moving NE into NY tonight. By tomorrow morning, they will be entering Western New England en route to ME and NH. There will be two chances for precip. The first will involve showers and embedded thunder in the morning. This round will be steadiest and heaviest over southern areas. The second round will be scattered showers and storms that develop with daytime heating and ahead of the approaching front. The second round will be more scattered in nature but also stronger with heavy rain and some gusty winds possible in the stronger cells. All activity will die off towards the evening as the front settles over the region and daytime heating is lost. Highs tomorrow will be similar to those today but the noticeable change will be in dew points which will rise into the upper 60’s making the low 80’s feel quite a bit more uncomfortable than today.
Thursday will be our hottest day with highs in the low to mid 90’s and stifling dew points in the low to mid 70’s. These two factors will combine to create heat index values right around the century mark in southern areas. There are some hints that SW NH could see heat indexes of 105 though that seems to be the upper edge of the guidance range. Do keep in mind that heat index values >95 are dangerous and can cause serious issues if proper precautions aren’t taken. Be sure to hydrate and stay in the A/C during the worst of the heat.
Friday will begin a period of wet weather and slowly cooling temps. A trough is digging into the Pacific NW today and will continue to move SE through the next several days. This will amp up the flow by turning winds SW as a ridge builds downstream (near Bermuda) in response to the trough. The S/SW winds ahead of the trough and behind the ridge will carry tropical moisture associated with the tropical disturbance in the Gulf of Mexico northward. Meanwhile to our north, a seasonably strong storm over Hudson Bay will drive a cold front south into the area tomorrow which will stall over us for the weekend. Several waves of low pressure will ride along the front bringing enhanced rain and shifting the front a little south each time they pass.
The 12Z GFS does a good job highlighting the main trends of the week although I disagree with some of its specifics. Heat and humidity peak Thursday and Friday (pink box) before clouds and showers slowly cool temps heading into next week. Waves of low pressure enhance rains periodically (green bars) but each wave pulls the front a little south leaving us less and less moisture (notice how each successive cluster of bars is smaller). Remember, on this graphic time moves from right to left with the far right side representing now and the far left, a week from now.
Confidence in the general pattern and setup is high but the details are still fairly uncertain. The biggest question is where exactly the front sets up. If it sets up even a little bit to our south, we could be robbed of beneficial rains. If it sets up to our north, we will have even more moisture available and bigger rains are possible. A stronger disturbance aloft and low at the surface will bring an end to the rains by the middle of next week though it could be drier sooner should the front end up sliding a little farther south. Temps will be gradually cooling as cool air from Canada gradually tries to filter in on the north side of the front. The large scale pattern would support more rain by next weekend but being so far out, the details on that are obviously a bit hazy.
More in the coming days. As a bit of a programming note, I won’t have updates from Friday evening through Sunday evening as I will be in the Catskill mountains on a brief hiatus before preseason starts on Monday. During that time, please revert to your primary source for weather information, whether that be the NWS or local media.