Updated Wed 8:18 AM highlighted below (There are significant changes in the forecast based on last night’s GFS model.)

The ridge of high pressure that’s been providing the very dry weather will gradually break down over the next several days and will be replaced by an upper air trough over the weekend.

Tuesday into Wednesday

First, for tonight (Tuesday), a warm front will move through between 3 AM and 6 AM Wednesday morning. The models are showing several instability parameters consistent with showers and possibly an isolated thunderstorm tonight, although many models are downplaying this scenario. If you are awoken by a rumble of thunder tonight, it shouldn’t be a surprise.

Wed AM Update: latest models have the showers and thunderstorms moving through during Wednesday evening. Much of the heavier dynamics will move by to our west. Still only a small amount of rain (0.3 inches) at most

A cold front will move through on Wednesday. Most models have some showers and thunderstorms between 5-7 PM Wednesday and again between 11PM and 1 AM Thursday. While I’m providing likely timing, this may change. Some of these storms could be strong, but total rainfall in the region from this frontal passage won’t make that much of a dent in our recent rainfall deficit.

Friday

As the upper air flow transitions from a ridge to a trough, a surface low will track over us on Friday, with rain. (Hopefully!) Many models have between 0.7 and 1 inches of rain on Friday, starting early morning. If it plays out, this would be our first significant rainfall in awhile.

Memorial Day Weekend

An upper air trough develops over our area on Saturday and lifts out by Monday. The upper trough may pinch off into a “closed low”.

Depending upon the exact location of the closed upper low, the forecast below can change. Right now, most models have the closed low directly over us, which can be a good thing weather-wise. So this is the most optimistic forecast, based on current models.

Wed AM Update: The location of the closed upper low seems to have changed, now north of us. This may mean prolonged clouds and showers into Saturday.

Saturday

As a result of the upper closed low, Saturday may have a few showers lingering around daybreak, most of the day will be dry, and cloudy conditions will linger into at least the mid to late afternoon. A widely scattered sprinkle can’t be ruled out. It will be chilly with an easterly wind. High 63º sd 5.2º (very high spread – high uncertainty!)

(Average seasonal high is 77º-78º)

Sunday

Partly sunny skies some clouds at times. Still cool for the end of May. High 70º sd 2.4º Cloudy with a chance of sprinkles.

Monday

Mostly sunny and milder. High 75.5º sd 2.4º

Update Thurs 8 PM highlighted below
Update Fri 11:30 AM highlighted below

High pressure that brought in the chilly weather for Thursday will be well off the coast by Saturday.

Low pressure advancing towards us will develop as it moves in our direction. Depending upon the model, it will be right over us or just to our south Saturday night.

Saturday

A return flow of moisture ahead of this low pressure system will bring considerable cloudiness for Saturday, but no rain expected during the daytime.

Update: Saturday will be sunny in the morning, then thickening high clouds. Mostly cloudy by about 3-4 PM Saturday.

Rain should develop Saturday evening. Rain starts about 6-8 PM. Fairly heavy rain at night. Rain starts about 9-11 PM. Total amounts have decreased to about 0.6-0.9 inches of rain.

There are some differences between the Canadian and US models, but the US models have been consistent that we get about 0.75 + inches of rain Saturday night. (The Canadian GDPS has less development and much less rain.) High about 68º NBM Blue Bell with low spread (uncertainty) of 0.8º

Sunday

The big question is how much development, how quickly the storm leaves and how much of an increase in its size due to intensification on Sunday. The models have varied. The NAM has some clearing Sunday morning. The GFS, Canadian and Model Blend (NBM) have lingering showers and clouds into late morning or early afternoon.

Update: Most models are showing the rain ending in the early to mid morning Sunday with gradual clearing.

High about 65º NBM Blue Bell with moderate uncertainty of 2.8º Very Windy.

Wind Forecast

An upper air low pressure system will combine with a surface low pressure system off of Cape Cod. This somewhat static pattern with upper air low pressure systems nearby should continue to affect our weather over the weekend.

Saturday

A cyclonic flow around the low will bring instability and cloudiness as disturbances rotate around the low for Saturday. 

Saturday will be mostly cloudy. A quick, widely scattered sprinkle can’t be ruled out, but the day will essentially be dry. Chilly temperatures. High 53º as 2.1º (NBM Model, Blue Bell)

Sunday

The Sunday forecast is more uncertain. The same low pressure system should gradually move eastward, bringing less of a cyclonic flow. However some models are suggesting another upper air disturbance will move through from the west. Some sun in the morning. Considerable cloudiness, especially in the afternoon.

The GFS again cranks out a widely scattered sprinkle around 4 PM. The ICON model is also showing this upper air disturbance and a chance of sprinkles, especially far northern areas. High of 61.1º sd 3.0º (NBM Model, Blue Bell)

Seasonal average high right now is 64º.