textproduct: Boston / Norton

WHAT HAS CHANGED

Wind gusts associated with the cold front will likely bring small craft advisory conditions across the northern waters as well. Confidence continuing to increase in the chance for scattered showers and increased cloud cover associated with a weak low pressure Monday.

KEY MESSAGES

- Strong cold front brings a round of widespread showers today. Leaves colder temperatures and drier conditions in its wake.

- Cooler than normal Monday. Generally dry weather expected in the morning, then increased cloud cover and the chance for spotty showers moves in during the afternoon.

- Seasonable temperatures Wednesday, then another cold front arrives.

DISCUSSION

KEY MESSAGE 1...Strong cold front brings a round of widespread showers today. Leaves colder temperatures and drier conditions in its wake.

A strong cold front today will bring a round of widespread showers. This front is part of a strong upper level trough that will continue shifting east from the Great Lakes today into Monday. Ahead of this front and trough, PWAT values this morning ahead of the front are elevated, reaching 1.4". This is part of a moisture plume that will help set the stage for the widespread rain today. Given these higher values, moderate to heavy rainfall rates are a possibility. The progressive nature of these incoming showers with the front should keep any flash flooding threat at bay, however, localized rainfall totals of around an inch cannot be ruled out in any convective showers that develop. MUCAPE around 500 J/kg this afternoon is indicative of some marginal instability that could lead to some embedded thunderstorms/convective showers.

Colder and drier air is left in the front's wake, reinforced by breezy W to NW winds starting this afternoon. Gusts to 30 MPH are a possibility post-front, particularly towards the Cape and Islands. Elsewhere, gusts to 25 MPH can be expected. Showers may be mixed with some snow in the higher elevations of western MA as this colder airmass takes hold, but any accumulations more than a coating at most are not expected at this time. Lows tonight will likely fall to the upper 20s, while more urban areas, the Cape and Islands, and the CT Valley can expect lows in the mid to upper 30s.

KEY MESSAGE 2...Cooler than normal Monday. Generally dry weather expected in the morning, then increased cloud cover and the chance for spotty showers moves in during the afternoon.

The upper level trough settles overhead Monday, and with it, an unseasonably cold airmass moves in. 925 mb temperatures fall below 0C during the day, then further to -5C heading into the overnight hours. Breezy W to NW winds continue, and highs may not climb out of the upper 40s and low 50s. Winds will start to diminish as high pressure approaches from the west, and lows Monday night may fall into the 20s for much of southern New England, aside from the coastal areas where 30s can be expected. Even with approaching high pressure, guidance has continued to indicate a weak low pressure moving into the region Monday that would bring increased clouds and scattered showers. Across different guidance suites, high res and global scale models have continued to trend towards scattered showers popping up in the afternoon hours. Some spatial and temporal discrepancies do still exist, but latest trends indicate the chance for these showers starting out in the interior by the late morning/early afternoon hours, then moving east through the day. Showers would then be expected out in eastern MA by the late afternoon/evening hours if this trend holds. Outside of system, incoming high pressure should keep the region dry for much of the start of the week.

KEY MESSAGE 3...Seasonable temperatures Wednesday, then another cold front arrives.

Some showers are a possibility once again heading into Wednesday as another shortwave approaches, but more seasonable temperatures make a return as the trough from early in the week exits. 925 mb temperatures recover to around 5C, supporting more seasonable highs in the upper 50s/low 60s. NW flow makes a return towards Thursday/Friday in the wake of another front passing through sometime late Wednesday, and high pressure builds back in as ridging approaches, which should keep the region dry. Discrepancies regarding the placement of the edge of the trough over northern New England and parts of eastern Canada may also affect how far east the warmer temperatures aloft make it for the second half of the week. These would likely, in turn, affect highs later in the week. High pressure returns going into Friday as a ridge approaches, but guidance is hinting at another approaching disturbance in the Great Lakes region towards the end of the week that could bring increased rain chances.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

Through 00z: Moderate Confidence.

Convective showers have developed ahead of the cold front and has produced isolated lightning, opt'd to include TSRA for terminals along this line of showers through 18-19z. Continue to anticipate poor flight categories, IFR-LIFR with pockets of MVFR through 21z. There after, MVFR conditions through 00z. Clearing to VFR shortly after 00z with the departure of RA and the cold front. As for wind, those are increasing as of 18z with gusts 20-30 kts from the W-WNW.

Tonight...High confidence.

VFR. Diminishing wind gusts. W wind 5-10 kts.

Monday...Moderate confidence.

Low-end VFR ceilings (040 to 060) along with sct'd showers. Cannot rule out wet snow flakes mixing in after sunset. WNW to NW wind at 10-15 kts.

Monday Night...High confidence.

VFR. Skies becoming clear, NW wind becomes NNW to N 5-10 kts.

KBOS Terminal... Moderate Confidence in TAF.

Sct'd convective showers could produce an isolated lightning strike near KBOS over the next 90 minutes, ending around 1830z. Gusty W-WNW winds increase as well, gusting 25-30 knots through 00-02z. There after becoming VFR with a W wind around 8-10 kts.

KBDL Terminal... High Confidence in TAF.

Outlook /Monday Night through Friday/...

Monday Night: VFR. Breezy.

Tuesday: VFR.

Tuesday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA.

Wednesday: Mainly VFR, with areas MVFR possible.

Wednesday Night through Thursday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Sunday Night: High Confidence.

Strong cold front today brings SCA conditions and rain, seas 3-5 feet, and W-NW gust up to 30 knots for most of the waters this evening into early Monday morning. Winds shift NW and ease following this frontal passage late tonight. Winds shift W over the southern waters and more S over the eastern/northern waters Monday and fall to 10-15 knots. Seas also fall to 2-3 ft.

Outlook /Monday Night through Friday/...

Monday Night: Winds less than 25 kt. Slight chance of rain showers.

Tuesday: Winds less than 25 kt.

Tuesday Night: Winds less than 25 kt. Slight chance of rain showers.

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

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

Thursday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230>234-236-250-251. Small Craft Advisory until 8 PM EDT this evening for ANZ235- 237. Small Craft Advisory until 11 PM EDT this evening for ANZ254>256.