Forecast: Brandt on Boston
Visible Satellite Image as of 1832Z
The Boston area has started off Monday with dry, mostly sunny weather. The dominant flow to this point has been out of the south to southwest in advance of an approaching cold front, though areas closer to the coast have seen easterly winds develop over the course of the first half of the day.
Surface Observations at 1843Z; note easterly winds at BOS
Temperatures generally rose quickly throughout the day, though there is a significant temperature difference from areas along the coast to areas farther inland. Central and Western parts of the forecast area saw temperatures rise into the mid-to-upper 80s by noontime, and highs may even exceed 90 degrees in isolated locations; however, cool sea surface temperatures (just below 50 deg. F) have led to the formation of a sea breeze moving in along the coast, affecting the eastern part of the Boston area. While record high temperatures are possible or even likely today across most of the forecast area, regions closer to the coast will have a more difficult time reaching record numbers.
The short term forecast will be dominated by an approaching low system located over the upper peninsula of Michigan as of 18Z on Monday. This surface low is forecast to pass well north of the area-- through southern Quebec-- overnight tonight.
Precipitation is not expected across the area, but the cold front associated with the surface low will pass through the area on Tuesday, bringing significantly cooler temperatures following the frontal passage early Tuesday afternoon. Forecast lows look to be fifteen degrees cooler Tuesday night than on Monday night, and highs on Wednesday will return to normal values, as they are expected to top out in the upper 50s.
In the second half of the work week, a gradual warming trend is expected across the forecast area, with high temperatures rising to near 70 degrees on Thursday and Friday. Fair weather is expected over that period, though it will be relatively short-lived. A weakening area of low pressure will pass through the area late on Friday, but recent GFS runs have the precipitation from that system passing to the north of the area. The best chance of precipitation will come during the period of Sunday afternoon through Monday evening, in advance of a low pressure system moving northeast out of the Southeastern US.
12Z GFS 500 mb heights, abs. vorticity, winds @ 09Z Tue
500mb height patterns show a deeply digging trough, but models are not yet in agreement as to whether or not the system will cut off over the Southeast. Forcing looks good for this system in recent GFS runs; low-level WAA and good advection of a strong 500mb vortmax in combination with ample moisture suggest the possibility for high precipitation totals from this system, though more model consensus will be necessary to make a more decisive forecast.
On April 16th, Boston set a new record by reaching 87 degrees for a high, beating the old record by 3°F. Between 18:43 and 19:43 UTC, Boston recorded a major wind shift, and, correspondingly, witnessed a 5° jump in temperatures over the course of an hour. The sea breeze cooled the area down, but it did not stay in place long enough to prevent the city from reaching a record high temperature value.
The high temperature for Boston on April 17th was officially recorded to be 84 °F, which, while not a record, was still significantly above average. Despite the winds shifting to out of the northwest by the morning hours, Boston remained comparatively warm-- areas in the western part of the state (near the NY border) failed to rise above the mid-60s on Tuesday, for instance. Northerly winds, originally rising to 15 knots, weakened across Eastern MA over the course of Tuesday afternoon, allowing the Boston area to remain warm for one more afternoon.
Over the course of the morning hours, however, the cooler air finally did reach Boston, which reached Wednesday's high of 62 degrees just after midnight local time, and witnessed falling temperatures after about 16Z. Boston spent the remainder of the afternoon with temperatures hovering just above 50 °F.
A disturbance which brought showers over Virginia, West Virginia, and Maryland brought clouds across the forecast area around 21Z, but none of the precipitation-- even that which showed up on the radar-- fell as measurable precipitation.