344 FXUS61 KBOX 241723 AFDBOXArea Forecast Discussion National Weather Service Boston/Norton MA 123 PM EDT Wed Sep 24 2025
.SYNOPSIS... A weak front moves south of the coast with NE flow bringing cooler weather today along with the risk of showers. A period of widespread showers and a few thunderstorms Thursday into Thursday night as another front moves into the region. Locally heavy rainfall is possible. Unsettled weather pattern may linger into Friday, then gradual improvement this weekend. Above normal temperatures expected into early next week.
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.NEAR TERM /UNTIL 6 PM THIS EVENING/... Key Messages:
* A few showers or embedded thunder possible this morning near the south coast
Widespread showers and a few embedded t-storms assocd with mid level shortwave will move to the east before daybreak, but may see more scattered convection develop near the south coast and Cape Cod this morning. Scattered showers are increasing in coverage across Long Island and HREF hitting the south coast with low probs of brief heavy rain with convective showers and possible thunder.
Otherwise, weak cold front will stall just south of the coast today as high pres builds south from the Maritimes. This will set up a cooler NE flow with abundant low level moisture leading to a cloudy and cooler day. 1.5-1.75" PWAT plume remains across SNE with marginal elevated instability and a weak shortwave to move through so expect scattered showers to continue, and can`t rule out an isolated t-storm this afternoon especially across CT closest to best instability. Not much temp recovery today with NE flow and cloud cover with temps holding in the mid-upper 60s, with lower 70s possible in the lower CT valley and near the south coast.
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.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/... Key Messages:
* More widespread showers developing from late tonight into Thu night. A few t-storms possible
* Localized heavy rainfall may result in minor urban and poor drainage street flooding
There may be a lull in the shower activity this evening as shortwave exits to the east, but more widespread showers should develop and move in from the west late tonight into Thu evening as more shortwave energy approaches from the west along with a modest low level jet. PWATs forecast to increase to near 2 inches with elevated instability and marginal surface instability so potential for heavier convective showers and a few t-storms. It appears the window for most active weather will be Thu into Thu evening, then cold front moves into the region overnight with somewhat drier air moving in from the west.
SPC has highlighted the region in a marginal risk of severe storms for Thu and CSU machine learning probs are also indicating a low risk for severe. Low level and deep layer shear is favorable with low level jet moving into the region, but surface instability is lacking. It appears best chance will be to the west where instability is greater, but if better instability can be realized the severe risk would increase with even a low prob of a tornado as warm front will be in the vicinity. Something to watch.
Hi-res guidance is more robust than global guidance with heavy rain potential and this seems reasonable given anomalous PWAT plume 2-3SD above normal, modest low level jet and elevated instability. Looking at 1-2 inches of rain, with heaviest likely in the interior. HREF PMM which represents a reasonable worst case scenario offers localized amounts up to 3 inches. If these higher amounts are realized there could be some minor street flooding in urban and poor drainage areas.
Warm front will be lifting north across SNE during Thu with temps warming into the lower 70s while dewpoints climb well into the 60s to near 70 near the south coast so there will be a rather humid feel to the airmass. Temps Thu night will remain in the 60s.
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.LONG TERM /FRIDAY THROUGH TUESDAY/... Key Messages:
* Above normal temps will prevail Fri into early next week with potential for some 80 degree readings
* Mainly dry this weekend but watching southern stream moisture to the south which may bring a few showers
Despite drier air moving in from the west, pattern is still somewhat unsettled on Fri as mid level trough and shortwave move through. Can`t rule out a few showers Fri but a washout is not expected. Then during the weekend a cut off low develops over the TN valley with upper level confluence nearby to the north with SNE on the NW periphery of Atlantic subtropical ridge. The uncertainty this weekend is with the northern extent of deeper moisture from southern stream system. Based on ensemble guidance there are low probs for some showers, mainly Sat night into Sun, but it could remain to the south if upper confluence holds strong. Then early next week will have to monitor the tropics as GFS and ECMWF show a potential tropical system approaching from the south, although GEFS and EPS ensembles keep it well to the south through Tue.
Above normal temps are expected through the period with temps well into the 70s into early next week. Ensembles are indicating low probs for 80F so some 80 degree readings are possible for a few days.
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.AVIATION /18Z WEDNESDAY THROUGH MONDAY/... Forecaster Confidence Levels...
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
18z TAF Update...Moderate confidence.
MVFR/IFR CIGS will continue to deteriorate this afternoon with pop up showers and drizzle. Winds remain out of the east at 5-10 knots
Tonight...Moderate Confidence
IFR/LIFR esspically near coastal terminals. It will likely take rain to clear out LIFR fog, and guidance is in disagreement on its arrival, from as early as 08z to as late as 14z.
Tomorrow...Low Confidence
IFR with perhaps some pockets of MVFR where rain can help clear low visibility out. Rain will continue off and on through much of the day with embedded thunder possibly esspically in the afternoon.
Tomorrow night...Low Confidence
Even behind the cold front, CIGS may struggle to improve as ground fog forms due to the antecedent wet conditions.
KBOS Terminal...Moderate confidence in TAF.
MVFR CIGS will eventually drop to IFR this afternoon with off and on showers through much of the day. Overnight, CIGS should drop to IFR/LIFR with NE winds, but may see improvements towards day break as winds turn more SE and moderate to heavy rain moves in.
KBDL Terminal...Moderate confidence in TAF.
Off and on showers this afternoon with perhaps a rumble or two of thunder. CIGS remain IFR tonight with moderate to heavy rain moving in sometime between 06z-10z tonight and continuing into much of tomorrow. Low chance for severe weather tomorrow afternoon, but thunder probs remain low due to low topped nature of convection.
Outlook /Friday through Sunday/...
Friday: VFR. Slight chance SHRA.
Friday Night: VFR.
Saturday through Sunday: VFR. Slight chance SHRA.
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.MARINE... Forecaster Confidence Levels...
Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent.
Through Thursday...High Confidence.
Winds below SCA thresholds with NE flow today shifting to S during Thu. As low level jet moves into the region, some risk for gusts approaching 25 kt Thu afternoon. 5 ft seas over the outer waters slowly subside today into tonight.
Outlook /Friday through Sunday/...
Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.
Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.
Saturday: Winds less than 25 kt. Slight chance of rain showers.
Saturday Night: Winds less than 25 kt. Chance of rain showers.
Sunday: Winds less than 25 kt. Slight chance of rain showers.
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.BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Thursday for ANZ250. Small Craft Advisory until 2 PM EDT this afternoon for ANZ254.
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SYNOPSIS...KJC NEAR TERM...KJC SHORT TERM...KJC LONG TERM...KJC AVIATION...KP MARINE...KJC
NWS BOX Office Area Forecast Discussion