Chatham, MA 02650 Weather

What has changed

Issued a Small Craft Advisory for the waters valid from this afternoon through Saturday morning.

Key messages

- A much drier air mass arrives today as a cold front pushes offshore. Expect windy conditions this afternoon behind the front.

- Yet more high pressure arrives this weekend into much of next week with a moderating temperature trend. The next bonafide chance for widespread precipitation arrives later next week.

Discussion

KEY MESSAGE 1: A much drier air mass arrives today as a cold front pushes offshore. Expect windy conditions this afternoon behind the front.

Cold front quickly pushes offshore early this morning. It will be moisture starved with a very dry antecedent air mass. Will see increasing winds and falling dewpoints this afternoon as the boundary layer becomes well-mixed. The combination of falling relative humidity values (>40%) and gusty winds between 25 and 35 mph will pair to increase the fire risk. While we typically look for RH values at 35 percent and below, the prolonged dry stretch and leaf drop prior to today's elevated wind along with input from state forestry and fire weather partners has prompted fire weather SPS's for the entire region. In terms of temperatures, expect a warmer day along the I-95 corridor with highs near 70 degrees. Further inland, locations will see cooler temps as diabatic warming competes with moderate to strong cold air advection. A sustained pretty tight pressure gradient continues into Friday evening, which casts some uncertainty on low temperatures. We opted to keep temps from the mid 30s to the low/mid 40s, highest towards the RI/eastern MA coasts where winds will take longer to slacken off, and coolest readings inland.

KEY MESSAGE 2: Yet more high pressure arrives this weekend into much of next week with a moderating temperature trend. The next bonafide chance for widespread precipitation arrives later next week.

A series of high pressures will dominate the weather pattern over southern New England this weekend clear through much of next week. The post frontal airmass kicks off the weekend much cooler as 925 mb temps drop from 12-15C Friday to 0-3C Saturday. Under dry NW flow beneath a high building in from New York we'll see high temperatures climb just into the mid to upper 50s on Halloween with evening temps in the 40s. Fortunately, by then the pressure gradient should have lessened enough that winds will be light. The light winds and clear post-frontal skies allow for radiational cooling Halloween night with lows in the 20s inland and 30s across the coastal plain. Similar weather picture on Sunday albeit a bit warmer as a weak southwesterly return flow develops as the center of high pressure moves offshore.

A mid-level trough looks to pass well to our northeast around Tuesday but lack of moisture and the transient nature of the feature will likely keep rain away before another high pressure takes hold Wednesday into Thursday keeping dry and warmer than average weather in place until the pattern may break down moving into next weekend. Guidance is still largely split on the eventual evolution of the upper level pattern with a wide range of solutions possible. The most aggressive guidance wrt to a pattern change is the GFS which depicts a deep shortwave trough over the eastern CONUS by Thursday.

Aviation

Forecaster Confidence Levels:

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

06z TAF Update:

Today and Tonight: High confidence in TAF.

VFR. Gusty windshift to NW 14-18 kt with gusts 25-30 kt during at least the daytime hours. Guidance has trended towards maintaining breezy conditions through much of the overnight at most TAF sites.

KBOS Terminal: High confidence in TAF.

KBDL Terminal: High confidence in TAF.

Outlook /Saturday through Tuesday/:

Saturday: VFR. Breezy.

Saturday Night through Sunday Night: VFR.

Monday: VFR. Breezy.

Monday Night through Tuesday: VFR.

Marine

Forecaster Confidence Levels:

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Through Friday Night: High confidence.

SCA issued for the eastern near coastal and outer waters. SCA in effect from 18z Friday to 12z Saturday for the near coastal waters. SCA conditions linger a bit longer for the outer waters where the advisory is in effect through 18z Saturday. SCA conditions will be driven by a cold front which brings a period of gusty NW winds between 25-30 kt this afternoon into Saturday morning. Seas gradually build to 3-5 ft this afternoon and maintain through much of the day on Saturday. Conditions gradually improve Saturday evening and overnight.

Outlook /Saturday Night through Tuesday/:

Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft.

Sunday through Tuesday: Winds less than 25 kt.

Watches, warnings and advisories

CT: None. MA: None. RI: None. MARINE: Small Craft Advisory from 2 PM this afternoon to 8 AM EDT Saturday for ANZ231-232-255-256. Small Craft Advisory from 2 PM this afternoon to 2 PM EDT Saturday for ANZ250-254.