Area Forecast Discussion
Issued by NWS Boston, MA

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962 FXUS61 KBOX 241128 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 728 AM EDT SUN JUL 24 2016 .SYNOPSIS... Excessive heat and humidity is expected at times through the middle of next week, at least away from the immediate coast. Another risk for scattered showers and thunderstorms is possible late next week with a cold front dropping south. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... No major changes to the forecast this morning. Brought the near term forecast back in line with observed trends. Previous discussion... Convective CI has moved offshore this morning allowing for plenty of SKC. Cooler/drier air having moved in behind exiting shortwave has actually allowed for more widespread temps in the low 60s across the region overnight. In spite of the sunshine, this cooler start will combine with H85 temps that dropped back to an average of +17C, so highs today should only top out in around 90 in the CT valley where downsloping will help. Expect mainly 80s elsewhere except where sea breezes form. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Tonight... Outside of increasing high clouds late from convective debris upstream, mainly quiet night with temps dropping into the 60s. The initially SKC/weak pres gradient would help here, but expect slight increase in dwpts thanks to return flow. Mon... Potential to be one of the hottest days of the summer thus far as H85 temps will warm to +20C by afternoon. While this could easily support temps in the mid to even upper 90s at several spots, there is some question of the aforementioned cloud debris limiting initial mixing/warming. It looks like enough breaks across the W could support the heat across the CT valley, so will be issuing a heat advisory there as dwpts surge back into the mid-upper 60s. Not as confident elsewhere, but there is still some time to monitor trends. More heat advisories could well be needed in the next 24 hours. The other issue, given the very hot/humid airmass return, will be the risk for convective activity with an acute shortwave passage late in the day on Mon. ML CAPE values are progged to be near 1500j/kg by the late afternoon, and this is on the normally conservative ECMWF. This will come along with a decent cold pool aloft with mid lvl lapse rates nearing 6.5C/km. Shear is minimal to start but does increase through the day as the shortwave approaches. Therefore, will need to monitor for afternoon/evening strong-severe thunderstorm activity. Winds once again the primary issue thanks to good D-CAPE values and increasing LLJ. This correlates to current SPC Day 2 SWO. Given the lapse rates peak late, this could be another instance of very late day convection that lingers well into the overnight hours. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Excessive heat at times through mid week, at least away from the immediate coast * Monday night is the highest risk for scattered showers and thunderstorms with the threat for some severe weather, and even very localized urban type flooding * Cold front may bring another risk for scattered showers and thunderstorms sometime late this week but timing uncertain Details... Nearly zonal mid level flow persists through mid week, then transitions to a broad trough. Latest guidance remain consistent on this trend, with only minor variations in amplitude and timing. At the surface, a subtropical high pressure will keep the above normal temperatures and humid weather mainly in place. Will favor a consensus solution to smooth over the minor differences. Monday Night... A weak cold front associated with a low pressure in Quebec is expected to move across southern New England Monday night. While this has been a consistent signal in the guidance the past several days, we will need to watch if this boundary either washes out, or stalls. If this boundary stalls, there may be a very localized urban type flood threat, with precipitable water values around 2.0 inches. Still some uncertainty at this point. Severe weather threat should be diminishing with time, which is typical for our region. Tuesday and Wednesday... Assuming the weak cold front clears our region early Tuesday morning, dry weather should prevail into Wednesday. High temperatures should still be mainly in the 90s during this time away from the immediate coast. Should be less humid during this time, at least compared to Monday. Thursday through Saturday... Above normal temperatures will continue over this time, but probably not quite as hot as early this week. A frontal boundary may approach late this week, and bring the risk for another round or two of showers and thunderstorms. The timing of any showers and thunderstorms appears to be diurnal in nature, at this time. Not looking like a washout. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/... Today and tonight...high confidence. VFR, only ACK may see some localized late night fog. Otherwise, NW winds slacken through the day, allowing sea breezes to develop. Monday...moderate confidence. VFR starts the day, although very hot and hazy weather expected. Late day, localized thunderstorms and showers may bring some temporary IFR/MVFR conditions. KBOS TAF...High confidence. VFR. Sea breeze expected today, although start time may be an hour or so later than typical. KBDL TAF...High confidence. Outlook /Monday Night through Thursday/... Monday night...Moderate confidence. Mainly VFR outside of lower conditions in scattered showers and thunderstorms. Tuesday and Wednesday...High confidence. Mainly VFR. Lower confidence in a few hours of early morning patchy fog in the typically prone locations. Thursday...Moderate confidence. Mainly VFR. Briefly MVFR in scattered showers and thunderstorms. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...High confidence. Weak high pres builds over the waters today and lingers through most of Monday. Quiet boating weather is expected for most of this time. There is a risk for late day thunderstorms Monday which will need to be watched. Outlook /Monday Night through Thursday/...Moderate to high confidence. Winds and seas should generally remain below small craft advisory thresholds over this time. The main concern is the risk for scattered thunderstorms Monday night, and perhaps again on Thursday. && .EQUIPMENT... The KBOX radar continues operating in a degraded state. Radar returns are running about 10 dBZ too high. Please keep this in mind when evaluating its data. Technicians will be onsite later today to replace a defective part. The radar will be out of service while this is done. We apologize for the inconvenience. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory from 11 AM to 6 PM EDT Monday for CTZ002. MA...Heat Advisory from 11 AM to 6 PM EDT Monday for MAZ010-011. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/Doody NEAR TERM...Belk/Doody SHORT TERM...Doody LONG TERM...Belk AVIATION...Belk/Doody MARINE...Belk/Doody EQUIPMENT...Belk/Doody

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