textproduct: Boston / Norton

WHAT HAS CHANGED

Public and marine forecasts remain on track. Updated aviation forecasts and added wind shear for tomorrow.

KEY MESSAGES

- Chilly and damp at times rest of today into Friday morning, then turning much milder & drier Friday PM, with highs in the 60s!

- Backdoor cold front Sat brings falling temps into the 40s across eastern MA...while the CT Valley might reach 65-70+.

- Southwest flow returns Sun with highs into the 60s for many locales...but a period of widespread showers expected with a cold front.

- Chilly temps for the first half of next week with mainly dry weather, but a brief period of rain/showers possible around Tue.

DISCUSSION

KEY MESSAGE 1...Chilly and damp rest of today into Friday morning, then turning much milder & drier Friday PM, with highs in the low to mid 60s away from the south coast.

1040 mb high over southeast Quebec provides cool air damming across SNE today, tonight and into Friday morning. Thus, chilly temps with most locations remaining in the 30s, with a stiff NE wind making it feel colder. As for precip, spotty light rain/drizzle in the cool sector, may become more widespread late tonight/early Fri AM, as WAA aloft increases with front lifting north. Most locations remain above freezing, however the highest terrain may dip to around 32. Therefore, there could be some light spotty freezing rain/drizzle at elevations above 500 ft. However, given such marginal temps and not covering much real estate, not expecting much if any impacts. Hence, no headlines necessary. As the warm front lifts north toward morning, there could be some areas of dense fog late tonight and then impacting the early morning commute Friday.

Boundary south of New England today/Thursday, lifts north as warm front Friday afternoon. Good model agreement, including hi res guidance, that warm sector overspreads the region during the afternoon, with increasing sunshine and highs warming into the low and mid 60s across northern portion of CT/RI/MA and into the greater Boston area. Could be late day (after 4-5 pm) high temps, as low clouds may take some time to burn off. However, southwest flow and strong April sunshine will win out eventually away from the south coast. Much cooler across southern RI into southeast MA, as low clouds may only lift to higher cloud bases and not completely burn off. This combined with SSW wind trajectory off the cold ocean, highs here may only climb into the 50s, upper 40s Cape and Islands. Still much milder than today. Also, it will turn breezy Fri afternoon, especially away from the south coast in the afternoon, as temps warming into the low and mid 60s, will mix down SW winds 15-25 mph.

Precipitation...there could be some spotty light rain/drizzle in the morning as the warm front lifts north. Otherwise a dry afternoon. A cold front approaches from the west late in the day. There could be a few decaying showers exiting NYS that reach western MA/CT during the evening. Otherwise, dry weather prevails Friday evening and night.

KEY MESSAGE 2...Backdoor cold front Sat brings falling temps into the 40s across eastern MA...while the CT Valley might reach 65-70+.

Low pressure will lift northeastward across the Great Lakes as large Canadian high pressure drops into the Maritimes on Sat. This will result in a backdoor cold front pushing westward across the region during the day Sat. Timing is tricky at this point...but temps should fall into the 40s across eastern MA by or during Sat afternoon. In fact...not out of the question temps drop into the upper 30s near the immediate eastern MA coast. Meanwhile...parts of western MA/CT may reach 65-70+ with the later arrival of the front. Keep in mind...these temps will be significantly impacted by a 2-4 earlier/later passage of this front so changes may certainly be needed.

Much of Sat may end up dry...but will have to watch for a few passing showers and perhaps some drizzle/fog behind the backdoor cold front.

KEY MESSAGE 3...Southwest flow returns Sun with highs into the 60s for many locales...but a period of widespread showers expected with a cold front.

Low pressure lifts northeast across Quebec on Sun with a cold front extending southward from it. The shallow cool inversion should mix out on Sun ahead of the approaching cold front. This should allow highs to reach back into the 60s across many locations despite an abundance of clouds. We also expect a period of widespread showers on Sun as this cold front crosses the region. While these showers should be progressive...modest southerly LLJ/Pwat plume may result in brief downpours and even a rumble of thunder with the activity.

KEY MESSAGE 4...Chilly temps for the first half of next week with mainly dry weather, but a brief period of rain/showers possible around Tue.

Ensemble model guidance in very good agreement in an upper trough building across the northeast for the first half of next week. This will result in chilly and mainly dry weather...but a period of rain/snow showers possible around Tue with a shortwave/mid level trough crossing the region. Highs Mon/Tue/Wed mainly in the middle 40s to the lower 50s...but turning milder on Thu with southwest flow developing ahead of our next cold front.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

00z TAF update

overall moderate confidence.

generally no big changes from the 18z TAFs, though did add wind shear for all locations starting 15z or so Friday.

Overnight, expect IFR ceilings to be predominate, with visibilities starting out VFR but should trend to MVFR and IFR as the night goes on. Have a batch of light precipitation that will have moved offshore by 00z, so start off with a dry forecast. However guidance continues to suggest the potential for spotty light showers after 06z. Added in PROB30s for that. Winds start NE, but slowly shift to the SE by 12z. As the winds shift SE, we should also see lowering visibilities as fog develops in most areas.

Friday expected to start with IFR conditions with perhaps some drizzle. Winds will continue to veer to the SW by 16z or so. Around this time, SW winds 2000-3000ft AGL should have increased to 40-50kt just above a strong inversion at that level. So have added in mention of wind shear from that time, through pretty much 00z. The inversion slowly weakens as the afternoon progresses. As this happens, we will see surface winds start to gust 20kt or so, ceilings slowly lifting to VFR across the interior and visibilities also becoming VFR inland. However across the south coast, Cape and Islands, the warmer SW winds blowing across the cold waters will keep IFR ceilings locked in, with MVFR visibilities as well. PVD will be on the fringe.

Friday night we could see those lower ceilings advance further north across all of southeast New England. The LLWS will slowly diminish as the low level jet moves offshore.

KBOS Terminal...moderate confidence. Trends should be good, but the specific timing of onset of IFR ceilings and MVFR visibilities have an error bar of a couple of hours. Similarly with the timing of improvement in conditions mid-day Friday.

KBDL Terminal...moderate confidence, primarily due to uncertainty in timing of the transitions to MVFR/IFR tonight and then back to VFR mid-day Friday.

Outlook /Saturday through Tuesday/...

Saturday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA.

Saturday Night: Mainly MVFR, with areas IFR possible. Breezy. Chance SHRA, patchy BR.

Sunday: Mainly MVFR, with areas IFR possible. Windy with gusts up to 35 kt. SHRA likely.

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

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday: Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

2 PM update...High confidence through Friday night.

1040 mb high over southeast Quebec provides chilly ENE winds across the MA/RI waters Thu afternoon. As the high noses southward, gusty ENE winds slacken Thu evening and become SE overnight. Despite winds slackening, seas will take sometime to subside. Thus, SCAs continue. Boundary south of New England Thursday, lifts north as a warm front Friday, accompanied by a wind shift to the SW at speeds 15-20 kt, gusting up to 25 kt at times. Before the frontal passage, areas of dense fog are possible along and ahead of the warm front late tonight into Friday morning. Improved vsby and drier weather Fri afternoon. Tranquil and dry weather Friday night, as a weak and decaying cold front approaches the waters from the NW.

Outlook /Friday Night through Tuesday/...

Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Patchy fog.

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Slight chance of rain showers, patchy fog.

Sunday: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 11 ft. Rain showers likely.

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

Monday: Winds less than 25 kt. Local rough seas.

Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231>234-251. Small Craft Advisory until 11 PM EDT this evening for ANZ235- 237. Small Craft Advisory until 6 AM EDT Friday for ANZ250. Small Craft Advisory until 2 AM EDT Friday for ANZ254>256.