Lexington, Massachusetts, USA
000 FXUS61 KBOX 190706 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 306 AM EDT Fri Apr 19 2024 .SYNOPSIS... Partial sunshine and seasonable temperatures return to the region today...but it will be cooler on the immediate coast. An approaching cold front will bring a period of showers and a few downpours very late tonight into Saturday morning. Gradual partial clearing and pleasant temperatures are in store for later Saturday. Elevated fire weather potential possible Sunday through Tuesday due dry and gusty winds. Our next opportunity for unsettled wet weather returns mid week with colder temperatures. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 305 AM Update... * Partly sunny today with highs near 60...but 50-55 on the coast Considerable mid-level cloudiness covered the region very early this morning with even a left over spot shower. Brief upper level ridging does build into the region today. This should probably result in enough subsidence for a period of partial sunshine later this morning and afternoon. Confidence on sky conditions today is a lower than normal for a near term forecast...so later shifts may need to make adjustments. Given the mild start...this should be enough to push high temps to near 60 in most locations. However...onshore surface winds will keep high temperatures generally in the 50 to 55 degree range along much of the immediate coast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Key Points... * Period of showers late tonight into Saturday am with some downpours * Partial sunshine returns later Sat with highs well into the 60s Details... Tonight and Saturday... A cold front/shortwave will be approaching the region late tonight into Saturday morning. The guidance has increased the low level moisture return & forcing associated with this front over its last few cycles. A modest southwest LLJ coupled with Pwats increasing to over 1 inch support a period of widespread showers late tonight into Sat morning. We also expect some downpours given this combination. There is even a low risk for a rumble of thunder...but did not feel it was worth inserting into the forecast at this point. Most of the showers will have exited the coast by Saturday afternoon. In fact...we expect some partial sunshine to develop from west to east as drier air works into the region. Despite cooling temps aloft...a mild start and the increasing April sun angle should push afternoon highs well into the 60s across most locations. While generally dry weather is expected Saturday afternoon...enough heating coupled with a cold pool aloft may trigger a few brief spot showers. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights * Dry and breezy Sun through Tue. Elevated fire weather concerns possible. * Shower chances return late Tue through Wed. Temps trending cooler. * Turning drier on Thu with much colder temps. Saturday Night through Tuesday... Cyclonic flow in place through this timeframe. Will have a shortwave skirt through New England on Sun. A southern stream trough will remain shunted well to our south of Mon. Another trough slides into/across the Great Lakes on Tue. A mid level ridge builds from the Northern Plains late Sat into the Great Lakes/Mississippi River Valley by early Mon and into/offshore of New England by late Tue. High pressure begins nudging into our region from the center of the country late Sat/Sun. The high builds into the Lower Mississippi River Valley to OH Valley by late Mon and offshore on Tue. Dry and quiet weather expected through this timeframe. Though there could be a few lingering showers tapering off late Sat. Main concern during this timeframe is elevated fire weather concerns. Despite the high nudging in we remain gusty Sun/Mon due to a tightened pressure gradient between the high and the lows well off to our north and east. The GFS and NAM both show we should be able to mix to roughly 800 hPa per Bufkit soundings. The GFS also shows us being this well mixed on Tue as well. This should allow drier air to mix down fairly easily aloft. With this in mind and given the pre-greenup have increased temps and lowered dew points/RH values during this timeframe from the default NBM. As we saw earlier in the week we tend to overachieve in these set ups, so am anticipating the same. At this point though am more confident for the Sun/Mon timeframe given upper flow will be out of the W/WNW, which will aid in downsloping. Could be a bit tougher on Tue as winds turn southerly ahead of our next incoming system. Increased temps to the 75th percentile of guidance for now and results in temps ranging from the upper 50s to mid 60s. Lowered RH/dew points to the 10th percentile of guidance for Sun/Mon and the 25th for Tue. Min RH values bottoming out in the mid 20s to the low 40s. Given the 20-30 mph gusts there could be elevated fire weather concerns. Tuesday Night through Thursday... Another period where we are caught in cyclonic flow. A trough will dig into the Great Lakes region Tue Night into early Wed. The trough/cutoff digs into New England on Wed. The trough/cutoff may still be overhead or kicked out of the region on Thu. Our next opportunity for unsettled/wet weather late Tue into Wed as a system slides in and perhaps through. The system may still be nearby on Thu. A cold frontal system swings through New England late Tue through Wed. At this point appears that the be opportunity for widespread rain showers comes during the Wed timeframe. The PWAT plume not appearing overly impressive with only low probs (10-20 percent) of PWATs AOA 1 inch per the EPS/GEFS and GEPS. Do have a deeper S/SWly low level jet at 850 hPa, which could really help squeeze out the moisture available. At this point deterministic guidance show roughly 30-50+ kt jet in place. Should remain mild as the system is swinging through, so precip will be all rain. However, as things are winding down much colder air filters in late Wed into early Thu. Would not be surprised if there are some snowflakes mixing in. At this point total precip appearing to be generally between 0.1 and 0.5 inches. We've got mod to high (30-80+ percent) probs of totals AOA 0.1 inches and low probs (10-30 percent) of 0.5 inches. For now have just stuck with WPC. Will be seeing temperatures trending downward through this timeframe. Much cooler on Thu with highs in the 50s. && .AVIATION /07Z FRIDAY THROUGH TUESDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. 06z TAF Update... Today...High Confidence. VFR. SSE winds 5 to 15 knots. Tonight and Saturday...High Confidence. An approaching cold front will bring a period of MVFR-IFR conditions very late tonight into Sat morning. This will also be accompanied by several hours of showers with a few downpours too. Most locations should see conditions improve to VFR by early Saturday afternoon...but this process may take a few hours longer towards the Cape and Islands. S winds 5 to 10 knots tonight becoming W at 10 to 15 knots by Sat afternoon. A few gusts in the 20 to 25 knot range may also develop across the interior by mid to late afternoon. KBOS TAF...High Confidence in TAF. KBDL TAF...High Confidence in TAF. Outlook /Saturday Night through Tuesday/... Saturday Night through Monday: VFR. Breezy. Monday Night: VFR. Tuesday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today through Saturday...High Confidence. Continued small craft headlines this morning for our far southwest waters from leftover lingering marginal 5 foot swell...but these should diminish by early afternoon. Otherwise...a relatively weak pressure gradient should keeps winds & seas below small craft advisory thresholds into Saturday. Outlook /Saturday Night through Tuesday/... Saturday Night: Winds less than 25 kt. Sunday through Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Monday through Monday Night: Winds less than 25 kt. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 1 PM EDT this afternoon for ANZ255- 256. && $$ SYNOPSIS...Frank/BL NEAR TERM...Frank SHORT TERM...Frank LONG TERM...BL AVIATION...Frank/BL MARINE...Frank/BL
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