This weekend forecast has been a struggle! For the last few days we’ve been trying to pin down the location and strength of a backdoor cold front which is nearly impossible to do. This morning when I first checked the models I knew our forecast probably was going to have to change again. The reason? A tropical wave off the Bahamas moving toward the Carolinas.
Whether or not this tropical wave becomes Tropical Storm Bonnie it doesn’t really matter. The low is going to open a conduit for a plume of tropical moisture to stream north into southern New England on Monday. You can see that here looking at precipitable water or PWAT forecast for Monday morning on the GFS (the Euro is actually even more impressive).
So what happens with that plume of moisture? Well, as the tropical juice streams north there’s also a jet streak in southern Quebec as a shortwave trough approaches from the lift. In the right entrance region of that jet streak air tends to rise and that will be right over southern New England.
The European model shows over 1″ of rain on Memorial Day here in Connecticut. A washout. The GFS shows rain but not to that extent. The European ensembles have an approximately 50% chance of >0.25″ of rain on Monday. Decent odds.
The actual “numbers” being printed out by the models aren’t particularly important at this point. The setup being forecast is one that looks to me like a wet one. Saturday and Sunday should be much better days. 2 out of 3 for a holiday weekend ain’t bad for the time of year!