textproduct: Boston / Norton

WHAT HAS CHANGED

The Small Craft Advisory has been expanded into the inner waters on Monday and an SPS has been issued for elevated fire weather potential on Monday for all of Southern New England except for Cape Cod and the islands. Wind gusts have been increased during the afternoon hours into mid- week.

KEY MESSAGES

- Drying trend Monday with warmer temperatures and breezy to gusty southwest winds.

- Mainly dry, windy & unseasonably warm away from the south coast Tue. Low risk for iso t-storms late across northwest MA.

- Periods of showers arrive from west to east Wed and may persist into Thu/Thu night...But that is more uncertain and dependent on a secondary wave of low pressure.

- Near/slightly below normal temps Fri into next weekend with perhaps a few showers at times...But not a washout. Mild days/cool nights with potentially some frost at times.

DISCUSSION

KEY MESSAGE 1...Drying trend Monday with warmer temperatures and breezy to gusty southwest winds.

As expected, despite a mostly dry atmospheric column, stubborn moisture in the 850mb layer together with the lingering trough/cyclonic flow aloft have led this morning's sun to be replaced by thick diurnal cloudcover. That, combined with some light rain over the eastern half of the region has led to a cool, raw day. Things are looking up, though as we head into the next 24-48 hours. This is thanks to expected rising mid level heights as a ridge of surface high pressure moves in to replace the offshore low. This will push temperatures up...flow turns SW and pushes 850mb temps from 0C to +6C by Monday afternoon. Given the expected well mixed boundary layer up to 800mb with full sun, expecting high temperatures to be 10 to 15 degrees warmer than Sunday. The warmest spots will be the CT valley where downsloping wind helps push temp into the low 70s while areas along the immediate south coast will be coolest in the low to mid 60s. This good mixing also leads to a gusty day; with a 25-35kt 850mb jet overhead, expecting to mix down gusts of 25 to 35 mph. This, combined with the drier air (RH values down to 25-30 percent) has led us to issue a Special Weather Statement for elevated fire weather potential covering all of southern New England with the exception of Cape Cod and the islands.

KEY MESSAGE 2...Mainly dry, windy & unseasonably warm away from the south coast Tue. Low risk for iso t-storms late across northwest MA.

A cold front slowly pushes into the eastern Great Lakes will combined with high pressure moving further east out in the Atlantic on Tue. The result will be a gusty SW winds and unseasonably warm temperatures away from the marine modified airmass towards the south coast. 925T on the order of +17C/+18C should allow highs to reach near 80 in the lower elevations northwest of I-95. The gusty southwest winds will hold highs in the 60s near the south coast, Cape and Islands. It is possible that Nantucket does not even break 60 degrees! Bufkit soundings support southwest wind gusts of 25 to 35 mph with a few gusts of 40-45 mph possible towards the upper Cape.

Mainly dry weather prevails Tue as most of the synoptic scale forcing will remain well to our west in the vicinity of the cold front. However...low risk enough instability develops for a few late Tue afternoon/evening showers/t-storms across northwest MA.

KEY MESSAGE 3...Periods of showers arrive from west to east Wed and may persist into Thu/Thu night...But that is more uncertain and dependent on a secondary wave of low pressure.

A slow moving cold front approaches the region from the west on Wed. Still some timing differences...But we do expect a band of showers to overspread the region from west to east as the day wears along. This may take until mid-late afternoon to reach the I-95 corridor...but again the timing still needs to be worked out. There might be an embedded t-storm or two as well...But instability does not look to be high enough for any severe weather.

This cold front slowly sags south of our region Wed night into Thu bringing cooler temps. We will then need to watch for a secondary wave of low pressure that may bring more rain to parts of the region sometime Thu into Thu night...But that remains uncertain. The GFS is quickest with this secondary wave and also furthest north...bringing a soaking rain to the region Thu. Meanwhile...the Canadian/ECMWF are further south showing the best chance for another period of steady rain will not be until later Thu into Thu night and that may be just a glancing blow across parts of RI/SE MA. This will need to be sorted out once the guidance comes into better agreement. This will also have a significant impact on temperatures during the day Thu depending on if we see rain or end up mainly dry.

KEY MESSAGE 4...Near/slightly below normal temps Fri into next weekend with perhaps a few showers at times...But not a washout. Mild days/cool nights with potentially some frost at times.

The long range ensembles are in good agreement in an upper trough with below normal height fields re-establishing itself Fri into the weekend. Modest westerly flow this time of year coupled with the strong May sun angle should keep high temps near or just slightly below normal though. Highs should still mainly be in the 60s. The night/s will be potentially cool though with lows in the 40s and potentially some 30s along with a frost risk if we have enough clearing.

As for precipitation chances...some shortwave energy with the associated upper trough/cold pool aloft may bring the potential for a few showers at times. However...not expecting a washout with plenty of dry weather expected as well over this time.

AVIATION /00Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

00z TAF Update...

VFR conditions continue tonight through Monday night. Gusty WNW quickly diminish after sunset and become light from a SW/WSW direction overnight. SW winds increase later Mon morning and especially in the afternoon with gusts on the order of 25 to 35 knots with perhaps a few gusts near 40 knots towards the typically prone locations near KFMH. The gusts gradually diminish Mon evening...but still expect sustained S-SW winds of 5 to 15 knots overnight with a few gusts up to 20 knots persisting.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy.

Tuesday Night: VFR. Breezy. Slight chance SHRA.

Wednesday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA.

Wednesday Night: Mainly VFR, with local IFR possible. Breezy. SHRA likely.

Thursday: Mainly MVFR, with local VFR possible. Breezy. SHRA likely.

Thursday Night: VFR. Breezy. Chance SHRA.

Friday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

High confidence.

Through Monday night...

NW winds gust to 25kts today, diminishing overnight and increasing again on Monday out of the SW gusting 25-30 kts. Will also see seas build to 4-6 feet across the outer waters thru Monday. Given these conditions, the Small Craft Advisory has been extended into Monday night for the outer waters and expanded into the inner waters on Monday.

Outlook /Monday Night through Friday/...

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas.

Tuesday Night: Strong winds with gusts up to 30 kt. Areas of rough seas.

Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain showers.

Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Rain showers likely.

Thursday: Winds less than 25 kt. Local rough seas. Rain showers likely.

Thursday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, slight chance of thunderstorms.

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM to 8 PM EDT Monday for ANZ230>237-251. Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-254>256.