863 FXUS61 KBOX 250548 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 148 AM EDT Thu Mar 25 2021 .SYNOPSIS... Weak low pressure will pass south of the area overnight, bringing a period of showers to the region. Morning clouds and fog will give way to sunny and warm conditions Thursday afternoon. Another storm system will bring more showers late Thursday and early Friday, followed by dry but windy conditions into early Saturday. Another round of wet weather is expected Sunday, with cooler and breezy conditions to start next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 140 AM UPDATE... Forecast remains largely on track. Main change was to increase the air and dew point temperatures by a few degrees to match observations. Precipitation has diminished over Western MA and Northern CT but we are tracking an area of heavier rainfall south of Long Island that could clip the Cape and Islands in the next 2-3 hours. There have also been reports of locally dense fog have also developed across Southeast MA and RI although some of that may be low stratus. PREVIOUS DISCUSSION... Forecast remains mostly on track. Made some slight adjustments to PoP grids as confidence has increased in the timing and overall coverage of light-moderate showers overnight. Have not begun to see any dense fog materialize near the coastal zones as of yet, but a few surface observations have had some intermittent reports of visibilities < 1 mile. Thus confidence is increasing that we'll see some areas of fog across the coastal plain overnight and into tomorrow morning. More likely to see patchy fog across the interior along with low-stratus. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... Followed a blend of the hi-res models which show the bulk of the showers pushing offshore first thing Thursday morning. After that, the rest of the day will be dry. However, the forecast challenge for tomorrow morning will be how widespread and how dense any fog is and how long will it take to dissipate. All the guidance I reviewed suggests it will take until late morning for the sun to finally break through, especially across the interior. Those of you out on the Cape and Islands --- sorry you won't have much, if any, sun tomorrow if the forecast works out. With dewpoints forecast to be into the 50s, and ocean temperatures around 40, that suggests fairly widespread sea fog and low clouds lingering all day along the coast and offshore. The other, probably more watched, aspect of tomorrow's weather will be the warmth. 925 mb temperatures are expected to be in the 12-14C range by afternoon. That would support the potential for highs well into the 70s, especially away from the coast where light onshore winds are expected. Although there is some question as to when we will see the sun break out, given the day will start fairly mild, we should be able to realize much of that warmth aloft. So blended in NBM 75th percentile temperatures across the interior and as a result still have widespread low to mid 70s. However coastal areas will only top out in the low to mid 60s, with 50s across the outer Cape and Islands thanks to the still very cold ocean. Although temperatures will be well above normal, they are likely to fall a few degrees shy of the records (see Climate section further below). Thursday evening starts off quiet, though low clouds and fog that will have stayed over the ocean during the day should start to ooze inland during the evening. A fairly potent storm system will be moving into the eastern Great Lakes after midnight. Out ahead of that low, moisture will be streaming into our region. Models suggest some elevated instability with negative showalter index values moving into the region after 2am or so. Given the signal, have gone ahead and added in a slight chance of thunder, primarily across western areas, for the pre-dawn hours on Friday. Stuck with the model blend for overnight lows -- which suggests a very mild night with lows mainly in the 50s (but 40s across the Cape thanks to the colder waters). && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... * Beneficial showers Fri morning, and again Sunday * Strong gusty winds possible Fri afternoon * Warmer than normal Friday, then trending cooler each day Saturday through Monday, then warming into mid week Latest guidance suite is rather good overall agreement through this portion of the forecast, with typically variations in timing and magnitude of features towards the middle of next week. Nothing out of the ordinary. Only a couple of opportunities for precipitation during this stretch. The first risk will be along a cold front Friday morning as the parent low pressure moves through the Great Lakes and northern New England. Decent mid level lapse rates, so cannot completely dismiss the idea of some elevated thunderstorms. Low level winds at 925 mb are quite strong. Some question as to how much of this wind can be mixed to the surface. Throw a few thunderstorms into the mix, and seeing at least some stronger gusts becomes more of a possibility. Will need to watch this closely over the coming days, especially for Friday afternoon into Friday evening with the decent cold air advection. The next risk for precipitation should be Saturday night into Sunday evening as another low pressure moves through the Great Lakes and northern New England. This is looking like the most likely period for some much needed rainfall. Still some time to work out the details such as the timing and amounts. High pressure should arrive early next week into the middle of next week. Temperatures stay warmer than normal Friday, at least until the cold front comes through. Temperatures then trend lower Saturday through Monday, but still near to slightly above normal for late March. Out region should warm up again toward the middle of next week. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 0540z Update... Moderate confidence in the 06Z TAF this morning. A coastal low- pressure system moving south of New England has brought widespread IFR to LIFR conditions over the past few hours. IFR ceilings with embedded LIFR are forecast through tomorrow morning with -SHRA. IFR visibilities are expected as well, especially at The Cape/Island terminals where there will be the greatest likelihood of fog. Conditions will improve back to VFR by mid morning for the Western MA/Northern CT terminals and late morning/early afternoon for the Eastern MA/RI terminals as visibilities and improve and ceilings lift. KBOS TAF...Moderate confidence. KBDL TAF...Moderate confidence. Outlook /Friday Night through Monday/... Friday: MVFR/IFR conditions possible. Windy with gusts up to 35 kt. Chance SHRA. Patchy BR. Friday Night: Mainly VFR, with local MVFR possible. Windy with gusts up to 35 kt. Saturday: VFR. Breezy. Saturday Night: Mainly VFR, with local MVFR possible. Chance RA or SN. Sunday: MVFR/IFR conditions possible. Breezy. RA, slight chance FZRA. Sunday Night: Mainly VFR, with local MVFR possible. Windy with gusts up to 30 kt. Chance RA. Monday: VFR. Windy with gusts up to 30 kt. && .MARINE... Marginally rough sea conditions will linger overnight into early Thursday morning primarily further off the eastern and southern coasts with wave heights, so will maintain the Small Craft Advisory until tomorrow morning. Generally light winds and subsiding seas for Thursday afternoon and evening. However we expect winds to start to increase later Thursday night, likely exceeding small craft advisory thresholds. Stronger gale force winds are expected Friday. Outlook /Friday Night through Monday/... Friday: Moderate risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Chance of rain showers. Patchy fog. Local visibility 1 nm or less. Friday Night: Strong winds with gusts up to 35 kt. Rough seas up to 11 ft. Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Rain. Local visibility 1 to 3 nm. Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 8 ft. Chance of rain. Monday: Strong winds with local gusts up to 30 kt. Rough seas up to 11 ft. && .CLIMATE... Record High Temperatures Thu 3/25... BOS...78...1963 PVD...73...1964 BDL...78...1910 ORH...75...1910 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ250- 254>256. && $$ SYNOPSIS...Belk/Nash NEAR TERM...Chai/RM SHORT TERM...Nash LONG TERM...Belk AVIATION...RM MARINE...Belk/Nash CLIMATE...