Lexington, Massachusetts, USA
000 FXUS61 KBOX 090553 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 153 AM EDT Fri Jun 9 2023 .SYNOPSIS... Scattered mainly diurnally driven showers are expected again Friday and Saturday. The activity will be most numerous on Friday with a few thunderstorms with small hail possible too. Temperatures will continue to run cooler than normal. A brief pattern change occurs Sunday and possibly lingering into Monday, bringing drier and warmer conditions to the region. Then the next frontal system may bring widespread rain to the region around Tuesday. && .NEAR TERM /UNTIL 5 AM THIS MORNING/... 155 AM Update... Mostly clear conditions and light winds have led to patchy fog across the region. Otherwise, dry weather prevails along with chilly temps mainly from the upper 40s to lower 50s, mid to upper 50s for Boston. && .SHORT TERM /5 AM THIS MORNING THROUGH 6 PM SATURDAY/... Highlights... * Numerous showers & scattered t-storms develop Fri * Small hail possible with the strongest storms * High Fri mainly in the 60s Details... Friday... Another piece of shortwave energy will drop down into southern New England from the main closed upper level low to our north on Friday. This piece of energy will be stronger than the one impacting the region this afternoon/evening. Therefore...when combined with the diurnal heating showers should be more numerous than today. In addition...mid level lapse rates will also be steeper on the order of 6.5-7.5 C/KM. While instability will be limited given an abundance of clouds and highs only in the 60s...we should be able to muster 300-600 J/KG of Cape. This should be enough to result in scattered thunderstorms. Given the steep mid level lapse rates and 700T are around -4C...small hail is possible with the strongest storms especially with surface temps only in the 60s. We can not rule out a rogue marginally severe t-storm or two given such cold temps aloft...but mainly just sub-severe storms with small hail. Activity may develop initially along the terrain and also on a pseudo backdoor cold front/narrow low level convergent zone. Lastly...lingering smoke from the Canadian Wildfires will be focused mainly near and south of a Hartford to Providence line according to the HRRR/RAP simulations. Air Quality alerts continue into Friday to cover this scenario. Friday night... The showers and scattered t-storms should dissipate during the evening with the loss of diurnal heating. Still enough shortwave energy wrapping around to support a few spot showers during the overnight hours but most of this time will probably be dry. We will need to watch for some low clouds and fog patches developing especially across the eastern half of the region overnight. Overnight low temps will bottom out mainly in the upper 40s to the lower 50s. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights * Warmer this weekend with more showers on Saturday, and drier weather on Sunday * Unsettled weather returns early next week as a new area of low pressure moves over The Northeast Significant changes finally expected to take hold during this portion of the forecast. Large-scale omega block should finally break down towards Sunday, which would permit the persistent mid level cutoff of this week to finally get picked up in the mid level flow and pushed out over the North Atlantic. This is expected to give us a little bit more than one day of dry weather, before we will have to contend with another low pressure arriving from the Great Lakes. At least this one should be moving, albeit not likely very quickly. Have average confidence in the details into Tuesday, then below average confidence thereafter. At this point, looking for a drying trend late Saturday through Sunday, and perhaps into Monday morning. Increasing risk for showers and thunderstorms late Monday into Tuesday. While a cold front should pass across southern New England by Wednesday, will still need to deal with a mid level cold pool, leading to more of what we saw this week: lingering showers with a low risk for thunderstorms. Trending drier towards late next week. Near to below normal temperatures expected Saturday, followed by near to slightly above normal conditions the rest of this period. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 06z update... Thru 12z...high confidence. VFR/MVFR vsbys in patchy fog with isolated IFR. Otherwise, mainly VFR cloud bases along with dry weather. Light WNW trending NNW toward sunrise. After 12z...moderate confidence. VFR/MVFR in patchy fog with isolated IFR at sunrise slowly improves to VFR. Dry weather then scattered to numerous showers and thunderstorms develop this afternoon. A few storms may contain small hail and gusty winds. Mainly VFR but brief MVFR possible in the stronger storms. Light WNW winds become locally onshore. Any vsby restriction due to smoke should be confined to the south coast of MA/RI. Friday night...moderate Confidence. The scattered showers and a few t-storms should wind down Friday evening. It does appear that MVFR-IFR ceilings/vsbys may develop across the region Friday night as a result of the cooling boundary layer and lingering low level moisture. Areal extent/coverage of these potential low clouds and fog patches is somewhat uncertain...but greatest risk will be across central and eastern sections of our region. Winds will be light/calm. Saturday...moderate confidence. Light NW winds but becoming locally onshore. VFR/MVFR in the morning will trend toward VFR cloud bases. Chance of scattered showers and thunderstorms after 15z especially across eastern MA. Lower risk across CT into western MA and a drying trend late in the day. KBOS Terminal...Moderate Confidence in TAF. Mainly VFR but a period of MVFR possible this morning and then again in the afternoon in scattered showers/thunderstorms. Small hail and gusty winds possible in the strongest storms. Light WNW predawn wind becomes north after sunrise then NE and finally east this afternoon. KBDL Terminal...High confidence in TAF. Main concern will be the potential for a few t-storms within the vicinity of the terminal Friday afternoon/early evening. A few of the stronger storms may contain small hail and gusty winds. Outlook /Saturday Night through Tuesday/... Saturday Night through Sunday: VFR. Sunday Night: VFR. Slight chance SHRA. Monday: VFR. Chance SHRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight through Friday night...High Confidence. Closed upper level near the Quebec/northern New England will continue to remain nearly stationary into Friday night. However...weak pressure gradient at the surface will keep winds/seas well below small craft advisory thresholds. Main issue for mariners will be reduced vsbys at times across our waters. A bit of that may be from overnight fog...but greater risk will be from Canadian forest fire smoke in the southern waters. Outlook /Saturday Night through Tuesday/... Saturday: Winds less than 25 kt. Chance of rain showers. Saturday Night through Sunday: Winds less than 25 kt. Sunday Night: Winds less than 25 kt. Slight chance of rain showers. Monday: Winds less than 25 kt. Chance of rain showers. && .FIRE WEATHER... Latest HRRR/RAP model simulations keep most of the near ground level smoke from the Quebec fires near and south of a Hartford to Providence line on Friday. This a result of the near ground level smoke wrapping all the way around from the southwest. Air Quality alerts have been extended for Friday into CT & RI to cover this scenario. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert until 1 PM EDT this afternoon for CTZ002>004. MA...Air Quality Alert until midnight EDT tonight for MAZ020>024. RI...Air Quality Alert until midnight EDT tonight for RIZ001>008. MARINE...None. && $$ SYNOPSIS...Belk/Frank NEAR TERM...Frank/Nocera/KP SHORT TERM...Frank LONG TERM...Belk AVIATION...Belk/Frank/Nocera/KP MARINE...Belk/Frank FIRE WEATHER...