Lexington, Massachusetts, USA
000 FXUS61 KBOX 140723 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 323 AM EDT Sun Apr 14 2024 .SYNOPSIS... Brief period of sunshine early this morning but will see increasing clouds as a frontal system moves in this afternoon and tonight. This frontal system to bring a risk for showers and embedded thunderstorms over western Massachusetts, western and southern Connecticut and southern Rhode Island later this afternoon into early tonight. Only light rains are expected elsewhere in Southern New England. Showers then diminish late tonight. Dry and seasonably mild Monday through Wednesday. Unsettled pattern develops late week with near normal temperatures a few chances for rain Thursday into the weekend. && .NEAR TERM /THROUGH TONIGHT/... 310 AM Update: The deep mid/upper level trough responsible for scattered to overcast cloud cover and blustery westerly winds yesterday is slowly but surely exiting into the eastern outer waters early this morning. Starting to see decreased cloud cover over western New England, with still considerable cloud cover east, and with west breezes around 10- 15 mph, current temps are still mainly in the 40s (lower/mid 40s interior MA/northern CT, and mid/upper 40s RI and eastern MA). Taking a wider view, well to the northwest over the Upper Midwest is a noticeable but weak-amplitude shortwave disturbance embedded in rather strong NW flow aloft, with weak sfc low near northern WI. This feature separates the exiting cooler airmass over the Northeast CONUS with warmer, conditionally unstable air over the Midwest and OH Valley. This latter frontal system will be affecting our area later today and tonight. Should see skies trend mostly clear for a brief period of time this morning, allowing for some sunshine for a short period of time. However mid to high clouds race in pretty quickly by mid to late this morning from W to E, which will gradually lower and thicken as we move into the afternoon with the approach of weak low pressure that's now over the western Great Lakes. Some models generate light showers later this morning/early afternoon, but RH profiles are still somewhat dry, so I'd expect it to be a generally dry day through the early afternoon. Better chances for at least showers develop around midafternoon today, but not expecting any washout. However a portion of the low pressure's warm sector still looks to spread into western MA, western/southwestern CT and perhaps into southern RI later this afternoon, and that could spark thunderstorms across a portion of that area later this afternoon. It is still a bit unclear how far north and east the thunder potential would extend. Flow fields are quite strong through a deep depth of atmosphere, which should favor enough convergence for t-storms to fire on. Advection of steeper mid- level lapse rates takes place too, around 6.5-7.5 C/km between 700- 500 mb. In addition, there is a rise in dewpoints into the upper 40s. There isn't much of any surface-based CAPE to speak of, but there is about 200-600 J/kg of most-unstable CAPE associated with the steeper lapse rates in western CT, parts of western MA and into central/southern RI. The various convective-permitting models and HREF key on areas well to our southwest in PA/far southern NY as having the greatest severe-storm potential, and I can't really disagree with that evolution. But I do think there is the potential for t-storms from a rough Springfield to Providence line SW later this afternoon into tonight; a couple of the strongest cells could be strong enough to produce small hail given the mid-level lapse rates and stronger flow in midlevels. Didn't go with any extra wording as yet though because I think the risk is more isolated, and SPC also has backed off its level 1 of 5 severe-thunderstorm risk from yesterday, restricting it to the Berkshires and Hartford County with its update this morning. PoP was raised into the Likely/low Categorical range, with a 10-30% chance for thunderstorms. Should be warmer than yesterday too, with highs in the 50s to lower 60s. Should be fairly breezy from the SW today, around 10-15 mph. For tonight...the frontal system from this afternoon producing showers and a few thunderstorms is expected to shift ESE into the waters early tonight. Rain chances end around midnight toward dry weather, and we should see a gradual decrease in cloud cover later tonight/overnight as high pressure ridges in. Lows in the 40s with light NW winds. && .SHORT TERM /MONDAY/... Showers and a few rumbles of thunder come to and end well before daybreak Monday. Mid level trough persists over southern New England as weak surface low moves northeast into the Canadian Maritimes. The forecast for Monday has trended a bit cloudier compared to previous updates. Morning clouds will mix out quickly as drying W/NW flow develops, but residual moisture at the top of the mixed layer will yield diurnal cumulus development at or around 5,000ft. While mainly dry, cannot rule out a stray shower or two, particularly during peak diurnal cu coverage in the late afternoon across eastern MA. All in all, the vast majority of localities will remain dry for the duration of Patriots Day with a mix of clouds and sun. With daytime mixing, winds atop the boundary layer of around 20kt will mix gusts of 10 to perhaps 20kt to the surface, highest across the terrain of central and western MA. Aforementioned drying northwest flow will result in a bit of downsloping that will influence temperatures with 925mb temperatures ranging between 6-8C and 850mb temperatures as high as 5C by afternoon. Given foliage is beginning to green up, especially in urban centers and south of the MA Turnpike, combined with dewpoints in the 40s, downsloping influence will not be as significant as we experienced during our last "warm spell" a week or so ago. Still, highs should climb into the low to mid 60s for much of the region. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights: * Broad trough settled over the region for much of the week with a brief period of mid level ridging in the Tuesday-Wednesday timeframe * Above normal temperatures give way to seasonable conditions as an unsettled pattern develops mid to late week Tuesday and Wednesday... Pesky broad trough finally relinquishes its grasp on southern New England Tuesday afternoon as mid level ridging builds in from the west; the ridge cresting over our region late Wednesday. Efficient mixing to ~775mb Tuesday with downsloping flow will set up another above average day with temperatures expected to tack a few degrees onto Monday's highs; generally in the mid 60s with a few 70s possible in the CT River Valley. Persistent NW flow will limit diurnal cumulus development, with Tuesday looking to be our sunniest day of the week. Surface winds shift to the north and eventually east on Wednesday. With still cool SSTs, in the 40s, and increasing cloud cover ahead of our next potential precip maker, expecting a cooler day Wednesday even with stronger ridging aloft. Highs will range from the low 50s on the outer Cape to low and mid 60s inland. Wednesday Night and Beyond... Cutoff low over the Great Lakes attempts to make a run for New England late Wednesday night and Thursday, but surface high centered just east of Nantucket looks to eat away, at least initially, at the precipitation shield of the advancing front. By Thursday, cutoff weakens significantly and moves north into Ontario as mid level ridging redevelops. Anticipating unsettled conditions Thursday with near normal temperatures, but trends towards a drier day have started to emerge compared to previous forecasts. Will note, that there is significant uncertainty regarding the timeframe with temperatures directly influenced by how far east the precipitation shield can advance, so populated both the PoPs and temps with NBM; placing a cap on PoPs at "40" to highlight the drier trend. More defined trough drops south into the Great Lakes on Friday as mid level ridging moves seaward. Another chance for rain is possible to round out the work week/start next weekend, but uncertainty again remains high at this time. && .AVIATION /07Z SUNDAY THROUGH THURSDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. 06z TAF Update: Through 12z Sunday: High confidence. SCT-OVC VFR cloudiness, bases 035-060, but decreasing by daybreak from west to east. W to WSW winds around 10-12 kt, with occasional 20-kt gusts eastern TAFs. Today and Tonight: High confidence in TAF/trends, moderate on t-storm coverage and timing. Categories should be primarily VFR. Increasing mid to high clouds thru the morning hrs from W to E. By afternoon, a frontal system arrives from the WNW spreading at least light showers after 18z. Potential exists for thunder late in the day (after 22z) but the best chance is at BAF and BDL where PROB30 -TSRA was indicated. It is possible that PVD could see -TSRA too, but think the best chance is southwest of there. Winds to back from W to SW/S and increase in speed to around 10-15 kt; gusts to 20-25 kt over southeast MA. Likely ongoing SHRA (possible TS for southern/southwestern airports) to then shift SE into the waters by 02-04z. SCT-BKN VFR ceilings to then predominate for the evening/overnight. SW winds shift to W/WNW and decrease to around 5-10 kt by daybreak. Monday: High confidence. VFR. NW winds increase to around 8-12 kt with gusts 18-22 kt, with strongest gusts over the terrain. KBOS TAF...High confidence in TAF. Mainly VFR through the period. That said, risk of -SHRA could start as soon as 18z but thinking best chance is after 22z. Showers end after 02z. W winds around 10-13 kt this morning shift to SW at similar speeds, with occasional gusts to 20 kt. Winds shift to W/WNW tonight. KBDL TAF...Moderate to high confidence in TAF. VFR most of today, although could see temporary/brief MVFR/IFR visby if TSRA can develop around 22-02z. W winds become S today around 10-12 kt, then shifting to SW-W-WNW tonight. Outlook /Monday Night through Thursday/... Monday Night through Tuesday: VFR. Breezy. Tuesday Night: VFR. Wednesday: VFR. Slight chance RA. Wednesday Night: Mainly VFR, with local MVFR possible. Breezy. Chance RA. Thursday: VFR. Breezy. Chance RA, chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Overall high confidence. SCAs are in effect for most waters through today, then continue into Monday over the southern waters. SW gusts today start around 15-25 kt, but then increase over the southern waters to around 25-30 kt this afternoon. Winds then shift to W/NW and decrease tonight to around 10-15 kt by daybreak Monday, continuing at these levels through Monday. Seas around 5-8 ft over the outer waters this afternoon continuing into tonight, then a slower decrease in seas to around 3-5 ft through Monday. There is a risk for thunderstorms later this afternoon into tonight over the southern waters, with light showers over the eastern waters. Otherwise, dry weather to prevail for Monday. Outlook /Monday Night through Thursday/... Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday through Tuesday Night: Winds less than 25 kt. Wednesday: Winds less than 25 kt. Slight chance of rain. Wednesday Night: Winds less than 25 kt. Chance of rain. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of rain, chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ230. Small Craft Advisory until 2 PM EDT this afternoon for ANZ231- 251. Small Craft Advisory until 2 PM EDT Monday for ANZ232>235-237- 250. Small Craft Advisory until 8 PM EDT Monday for ANZ254>256. && $$ SYNOPSIS...Loconto/KS NEAR TERM...Loconto SHORT TERM...KS LONG TERM...KS AVIATION...Loconto/KS MARINE...Loconto/KS
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