The next two days will be dominated by continued dry and quiet weather as high pressure moves across the region. On Tuesday, there will be a strengthening storm system well to the east of New England. The pressure gradient between the building high and the strengthening low will bring continued breezy weather with gusts of 20-25mph. The high pressure will eventually move overhead, leading to a slackening of the breeze as the afternoon progresses.
The combination of breezy conditions, low humidity and (obviously) dry conditions has resulted in the 13th red flag warning in the last five weeks for New England. Today's warning is only in effect for Massachusetts. The alert was issued only for Massachusetts due to "active brush fire activity" across the state in the last 24 hours, including a 100+ acre one in Boxford and one approaching 50 acres in the Blue Hills Reservation.
After a dry Wednesday, New England's first serious rainmaker in several weeks will begin to arrive from the south and west. A deepening trough near the Great Lakes will spawn a surface low pressure system just to the south of New England along an occluded front (the purple one on the map below).
This will rotate around the upper low on Thursday, which will stay to the west of New England, allowing for a period of widespread rainfall. Exactly where both the upper-low and surface low tracks will determine who gets what with this storm as well as how much.
The initial band of rainfall associated with the occluded front will move into southwest New England Thursday morning before continuing to lift north and east through the rest of the morning. By the afternoon, wet weather will likely have spread across most of New England. The exception will be much of Maine, where an exiting high pressure system will delay the start time of rain until Thursday night.
Below: Euro showing potential weather Thursday mid-morning (1st image) and Thursday mid-afternoon (2nd image):
The formation of the secondary, surface low along the occluded front will help create a more widespread, soaking type rainfall. The exact track of both the upper-low and surface low remains a bit of a question mark. The farther north the surface low lifts, the better the chance southern New England could get into a "dry" slot Thursday afternoon. This would reduce widespread rain to scattered showers in the afternoon or evening.
By Friday morning, the slug of widespread rainfall will move across northern and eastern Maine, finally bringing the steadier rainfall to the area. On Friday, the surface low will continue to shift east across New England while the upper-low shifts eastward, toward western New England (again, the timing and track of both these lows remains a bit of an uncertainty, which is expected in a blocking-type pattern). With the upper-low continuing to hang out, continued scattered showers will be likely across all of New England.
The upper-low will be with us into Saturday, keeping the threat of unsettled weather around, though a general drying trend is likely to commence through the day on Saturday with the highest chances of additional rain/snow showers in the higher terrain. Additional spokes of energy may wrap around the system through Saturday, bringing periods of steadier precipitation Thursday night through Saturday from south to north, but whether this occurs (or if it remains lighter, more showery weather) is a high uncertainty.
When all is said and done, modest rainfall amounts are likely across New England with at least 0.5 to 1 inches of rainfall for everyone. There is a chance of some 1 to 1.5+ inch amounts across New England as well. These amounts would be most likely across western New England and Maine. Much of New England is running several inches below average in rainfall for the fall season, so this won't be a total drought-buster, however, it is a drought-denter and will significantly ease the relentless brush fire risk.
Over the past several weeks, we've watched what could have been decent rain events shrivel up into mere isolated shower chances. Is there a difference with this one that promotes a higher confidence? Yes. There is a clear indication of high moisture from the Gulf of Mexico streaming northward into the system this week, as seen in precipitable water (shown below). Moisture content in New England won't be overly high, which is helping to keep rainfall amounts in check to an extent.
As colder air filters around the back side of the system beginning Thursday night, a switch to a wintry mix or snow showers will be possible across the higher terrain. During the evening and overnight Thursday night and Friday night, snow levels may drop to around 1,500 feet, allowing for light accumulations in the mountain valleys. Snowfall will be highly elevation dependent and also dependent on the storm's overall track. The farther north the low tracks, the more cold air can be drawn into the system.
Any real snowfall accumulations are currently looking to remain at 2,000 feet and higher. With that said, a changeover to a wintry mix or snow will be possible as low as 1,000 feet across western New England. For levels to drop into the 1,000 to 1,500 feet range, steady to heavy precipitation would be needed to help draw the colder air lower in elevation. Overall, the snow potential remains rather low confidence, but areas lower than 1,000 feet can count on all rainfall.
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