Lexington, Massachusetts, USA
000 FXUS61 KBOX 221830 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 230 PM EDT Mon Apr 22 2024 .SYNOPSIS... A ridge of high pressure will result in dry weather through Tuesday with pleasant days and chilly frosty nights, along with elevated fire weather potential. Unsettled with showers and scattered thunderstorms on Wed. Winds will be gusty at times. Cool on Thu, but temperatures rebound late in the week and heading into the weekend with dry weather. && .NEAR TERM /THROUGH TONIGHT/... High pressure over the central Appalachians will move closer to our region overnight. A lingering front should move back north as a warm front late this afternoon and evening. Most of the near term guidance, such as the LAMP and HRRR, have been persistent and consistent with a brief seabreeze developing early this evening before being pushed out by the overall southerly synoptic flow. Mainly clear skies and diminishing wind will set the stage for very good radiational cooling. Expecting dew points to rise from the teens overnight, but it will take a while to do so. Thinking patchy frost will remain a concern, so the Frost Advisory continues. Can see a scenario where some of our usual effective radiators could get below freezing where the frost/freeze program has begun. However, also thinking these freezing temperatures will not be widespread enough to warrant an upgrade to a Freeze Warning. That possibility will need to be watched this evening. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... High pressure moves off the Eastern Seaboard for Tuesday and Tuesday night. Dry weather continues Tuesday with a persistent southerly wind. This should result in near normal temperatures for late April through Tuesday night. Our next chance for showers is anticipated to be late Tuesday night as a front approaches from the west. It is more likely these showers will impact the western half of southern New England by the Wednesday morning commute. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights * Showers spreading in late Tue night through Wed as a cold front slides through. Scattered thunderstorms along with gusty winds and could perhaps see some graupel as well. * Dry, breezy and cool on Thu. * Trending milder late in the week into the weekend. Generally dry, but we could see some showers pushing in late in the weekend. Wednesday... Caught under cyclonic flow through this timeframe. A trough will dig into the eastern Great Lakes/Mid Atlantic by early Wed. There is a northern stream trough digging toward northern New England on Wed, which may interact with that previous trough as it is lifting through our area on Wed. This will swing a cold front through out region. Main concern in the latest update is the thunderstorm risk along with gusty winds. Appears that there is some interaction going on between the two troughs on Wed, which given the cold pool aloft will steepen mid level lapse rates. At this point guidance showing values ranging from 6-8 degrees Celsius. We may even have low level lapse rates of a similar range, but there is some discrepancy amongst guidance. Do have some question on the instability at the NAM/GEM show a few hundred J/kg of MUCAPE along with the GEPS. The ECMWF/GFS along with their ensemble counterparts (EPS/GEFS respectively) are much more muted. Despite the discrepancy we've got a fairly dynamic system working its way in and a ribbon of 40-60 kts of deep layer shear moving in. Have added more thunder to the forecast as all guidance has good mid level lapse rates in place. Added a gusty wind mention given the setup and also think it is not out of the question there is a stronger storm or two. Though this may be limited by the moisture available (0.7-0.8 inches) along with the best instability and shear only briefly overlapping. Stay tuned for future updates. Regardless of the thunder potential do think we will have breezy conditions throughout the day Wed, especially during the afternoon as flow shifts from the SW to the NW. Still some uncertainty on the strength of the jet, but could range from 20-40 kts at 850 hPa. The default NBM appears fine at this juncture. High temps range from the mid 50s to the low 60s. Thursday through Sunday... Will initially be in cyclonic flow on Thu, but will have a ridge axis over the Plains. The ridge will build into the Mississippi River Valley by late Thu. The ridge builds into the TN Valley to central Great Lakes by late Fri and the East Coast by late Sat. Confidence high through this period. By Sun confidence lowers as the ridge may be reinforced over the region or a shortwave may ride/shunt the ridge offshore. High pressure nudges in from the Great Lakes Region on Thu and overhead on Fri/Sat. The high shifts offshore on Sun. Dry and quiet weather anticipated through the vast majority of this timeframe. Could be a bit breezy due to a tightened pressure gradient on Thu, but some uncertainty here as the high could build over the region a bit quicker than the latest NBM indicates. This would relax the gradient much fast and result in lighter winds. For now have stuck with the higher NBM. The other risk heading into Thu and Fri is there could be cold enough air in place where widespread frost develops. More confident in heading into Fri with the high overhead. For heading into Thu we may be a bit too windy for widespread frost development. Frost/freeze headlines may be needed in future updates. Coldest temps of the week on Thu with a -2 to -4 degree Celsius airmass overhead at 850 hPa. Will warm up Fri through the weekend as flow turns W on Fri and S/SW through the weekend. High temps ranging from the mid 50s to the mid 60s. Could be a bit warmer on Sun with us generally being in the 60s. There is uncertainty here given guidance is all over the place with our next shortwave lifting in. Some still have the high dominating, so for now have stuck with the NBM. This brings chances of showers. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Tuesday...High confidence. VFR. Gusty NW winds diminish this evening, permitting a brief seabreeze along the coasts before light S winds develop overnight into Tuesday. Tuesday Night...High confidence. Mainly VFR through the night. MVFR/IFR cigs should develop from west to east across the western half of southern New England after midnight. -SHRA increasing from west to east as well. KBOS TAF...High confidence in TAF. KBDL TAF...High Confidence in TAF. Outlook /Wednesday through Saturday/... Wednesday: Mainly MVFR, with local IFR possible. Breezy. SHRA likely. Wednesday Night through Thursday: VFR. Breezy. Thursday Night through Friday Night: VFR. Saturday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through Tuesday Night...High Confidence. High pressure moving off the Eastern Seaboard tonight into Tuesday will result in rather light winds and seas across the waters. Good visibility. Increasing risk for showers late Tuesday night. Increasing south winds may lead to rough seas across the outer coastal waters late Tuesday night. However, do not have enough confidence in the timing for a Small Craft Advisory at this time. Outlook /Wednesday through Saturday/... Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Thursday Night through Saturday: Winds less than 25 kt. && .FIRE WEATHER... Tuesday... There will be elevated fire weather concerns Tuesday. Given that we are in a pre-greenup and a very dry atmosphere is in control, expecting minimum afternoon relative humidities to drop to between 20 and 30 percent. Winds will be from the south with some gusts again of 15 to 20 mph. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for CTZ002>004. MA...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for MAZ013-016>023. RI...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for RIZ001>008. MARINE...None. && $$ SYNOPSIS...Belk/KJC NEAR TERM...Belk SHORT TERM...Belk LONG TERM...BL AVIATION...Belk/KJC MARINE...Belk/KJC FIRE WEATHER...Belk
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