Looking at the models this evening not much has changed. While there will likely be showers in the morning tomorrow, the heaviest rain will hold off until the afternoon. This is also when the wind will increase. Bottom line, the later in the day we progress, the worse the weather conditions. The loop below projects the rainfall through 9AM Monday.
Runners and supporters at the 119th Boston Marathon can expect rain along the entire course by noon.
While it won't be as warm today as yesterday, it's still going to be a very nice afternoon with plenty of sunshine and pleasantly mild air. The coastal areas around Boston reached near 60F Saturday morning before the famed east wind kicked in and readings fell back into the 40s for afternoon. If you lived a few miles west of the coastline it stayed in the upper 50s to lower 60s. Metro west and other areas further away from the influence of the sea breeze were up near 70F much day.
Cool and Becoming Wet
Tomorrow is Patriots Day and also the running of the Boston Marathon. The weather for the runners will be quite good early in the morning with cool cloudy conditions. The ideal scenario for many would be temperatures in the mid-40s and a tail wind with cloudy skies and perhaps a bit of mist in the air to keep the runners from dehydrating as easily.
This year temperatures will be in in the mid to upper 40s, the sweet spot for a runner. This means if you are watching the race along the route, it's going to feel chilly standing there, even if you are cheering loudly. Temperatures can be quite hot as we saw as recently as 2012.
The map below shows temperatures around 11 a.m. They will be within a few degrees of these numbers the entire day.
The wind tomorrow will be coming from the east. This is a head wind and is quite typical for Boston in spring. Some years runners begin with a tail wind and end up with a head wind, but this year it's all head wind start to finish.
As the buses get the runners to the course early Monday it should be rain free. There might be some mist or drizzle starting to develop around 8-10 a.m. After 10 a.m. the chance of rain continues to increase hour by hour and by noon at the latest it should be raining along the entire course route. During the afternoon the rain will become heavier with some embedded downpours.
The predictive radar below from one computer model shows rain falling steadily by late morning.
It will be important for the runners to get dry and stay warm after the race. I suspect we will see a lot of racers wrapped up in those silver blankets at the finish line. If you are meeting someone at the end of the race, bring them something warm and dry, they'll appreciate it.
How Much Rain
I am expecting an inch to as much as an inch and a half of rain between mid-morning Monday and Tuesday morning. The bulk of the rain will fall from about noon tomorrow until 10 p.m. tomorrow night. There will be scattered showers and even thunderstorms after this window of time.
Clearing takes place Tuesday night and Wednesday will be a very nice day with plenty of sunshine and pleasant temperatures. It turns cold and somewhat unsettled the rest of the week with some sunshine in the morning giving way to afternoon clouds and perhaps some showers for Thursday and Friday. It will feel quite chilly with highs only in the mid-50s.
You can follow my weather updates on the timing of this storm and others on Twitter @growingwisdom