Although the nws (and therefore most commercial weather forecasts including the weather channel) have kept a weekend forecast with temps around 70 and a slight chance of showers, they have been hedging their bets because the computer models are flip-flopping and in disagreement with each other. So, it may end up being anywhere between 70F and 90F+, especially on Sunday, with strong thunderstorms likelier as it gets hotter. They have already pulled the highs up toward 80F last night.
Or in other words, you may want to bring extra beverages.
Here is the current discussion, the site is in the interior (not coast):
AREA FORECAST DISCUSSION..FINAL MID SHIFT
National Weather Service Taunton MA
625 AM EDT Wed May 19 2004
Very large forecast temp error potential developing this weekend/early next week for sne (especially Boston area)
Pattern: Confidence very low on [forecast] high temperatures this weekend with 30 degree errors possible on a day 2 fcst [Sunday].
Overall the day to day runs of the normalized Canadian 10 day [ensemble continue] steadfast for a continuation of the significantly warmer than normal pattern. Successive 12z/00z gfs ensembles and gfs [operational] runs are osscilating hot and cool for this [weekend] into early next week though the 850mb trend is warming for a day or 2 in the 3 day prd Sat-Mon. 00Z/19 gfs/ukmet/ggem runs all suggest early summer warmth and humidity for Saturday (at least the interior) and possibly again Monday whereas ecmwf keeps us chilly and possibly wet.
This May relate to subtle differences in the path and intensity of the 500 mb cold pool crossing the labrador highlands and upstream short wave interactions with the [northern] stream.
While the answers wont be in til next Monday 5/24 we Hope to have trended correctly this morning with 00z multi model consensus and warmed temperatures significantly Saturday and also at night from Fri night thru Sunday night with winds shifted from E to S-SW On Saturday. Even warmer adjustments May be needed in future issuances, esp the 00z/19 gfs ensembles which are becoming more and more coherent for a strong thrust of 90+ heat toward sne (at least bdl-Cef and possibly fit) this wknd. Yet the 06z eta is definitely warmer now than its 00z predecessor which was already hinting warm.
This pattern also hints strongly at thunderstorm clusters at times. the 00z/19 gfs ens pops are mostly north of our area and the timing uncertain. Rain could be heavy if storms track through sne.
Friday, could be the pick of the week! quite a nice day for comfortable warmth!
Saturday, could be 91 at Boston or 58 depending on wind direction and any shower timing. CT Rvr Valley Seems more certain to warm to at least 78F if not near 90F. Quite unstable on the gfs in the aftn/night!
Sunday, frontal boundary May sag south, at least into coastal Mass where 2PM temps May range from 58 at bos to 80+ at bdl.