709
FXUS61 KBOX 191137
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
737 AM EDT TUE MAY 19 2026
WHAT HAS CHANGED
SMALL CRAFT ADVISORY EXTENDED INTO WEDNESDAY NIGHT FOR THE SOUTHERN
OUTER WATERS.
KEY MESSAGES
- RECORD HEAT POSSIBLE TUESDAY WITH MARGINAL HUMIDITY, KICKING OFF A
MULTI-DAY STRETCH OF ANOMALOUSLY HOT TEMPERATURES (IN THE MID TO
UPPER 90S AWAY FROM THE SOUTH COAST).
- ISOLATED THUNDERSTORMS POSSIBLE TODAY, MAINLY NORTH AND WEST OF I-
95. BETTER CHANCES FOR STRONG TO SEVERE THUNDERSTORMS ON WEDNESDAY
WITH STRONG DAMAGING WINDS THE MAIN RISK.
- COOLER AND UNSETTLED WEATHER IS POSSIBLE MEMORIAL DAY WEEKEND,
BUT CONFIDENCE REMAINS LOW.
DISCUSSION
KEY MESSAGE 1...RECORD HEAT POSSIBLE TUESDAY WITH MARGINAL HUMIDITY,
KICKING OFF A MULTI-DAY STRETCH OF ANOMALOUSLY HOT TEMPERATURES (IN
THE MID TO UPPER 90S AWAY FROM THE SOUTH COAST).
A HEAT ADVISORY REMAINS IN EFFECT FOR MUCH OF SOUTHERN NEW ENGLAND
ON TUESDAY AND WEDNESDAY, NOT NECESSARILY BECAUSE OF THE EXPECTATION
FOR AN EXCEPTIONALLY OPPRESSIVE HEAT/HUMIDITY COMBO BUT DUE TO A
VERY EARLY ARRIVAL OF WELL ABOVE NORMAL HEAT FOR MID MAY IN SOUTHERN
NEW ENGLAND. THIS ANOMALOUSLY WARM AIRMASS COMES COURTESY OF A
BUILDING MID LEVEL RIDGE TODAY PUSHING 850 MB TEMPS INTO THE 18-20C
RANGE WHICH WOLD BE 2-3 SD ABOVE CLIMATOLOGY. GIVEN AN EXPECTED WELL
MIXED BOUNDARY LAYER SURFACE TEMPERATURES SHOULD BE ABLE TO REACH
WELL INTO THE 90S. WARMEST LOCATIONS WILL BE THE CT AND MERRIMACK
VALLEYS WHERE DOWNSLOPE FLOW WILL HELP PUSH TEMPS INTO THE MID 90S
WITH LOW TO MID 90S ELSEWHERE. THE EXCEPTION WILL BE ALONG THE SOUTH
COAST WHERE THAT SW WIND TRAJECTORY OFF OF THE OCEAN KEEPS TEMPS
COMFORTABLY IN THE MID 70S. THE RIDGE BEGINS TO BREAK DOWN ON
WEDNESDAY WITH FALLING HEIGHTS, BUT EVEN SO TEMPS WILL REMAIN
ELEVATED AHEAD OF THE COLD FRONT; INCREASING CLOUD COVER AHEAD OF
THE SURFACE TROUGH WILL HELP KEEP TEMPS A FEW DEGREES COOLER, BUT
MANY LOCATIONS INLAND STILL SEE LOW TO MID 90S AWAY FROM THE WATER.
DEWPOINTS IN THE LOW TO MID 60S (DISCOUNTING THE OUTLIER NAM) WILL
MAKE IT FEEL HUMID BUT NOT TROPICAL BY ANY MEANS.
KEY MESSAGE 2...ISOLATED THUNDERSTORMS POSSIBLE TODAY, MAINLY NORTH
AND WEST OF I-95. BETTER CHANCES FOR STRONG TO SEVERE THUNDERSTORMS
ON WEDNESDAY WITH STRONG DAMAGING WINDS THE MAIN RISK.
WHEN IT COMES TO THUNDERSTORM THREAT EACH DAY, WEDNESDAY LOOKS TO BE
THE MORE FAVORABLE DAY FOR STRONG TO SEVERE STORM COVERAGE BECAUSE
WHILE BOTH DAYS FEATURE THE NECESSARY MOISTURE AND INSTABILITY, THE
LIFT MECHANISM IS MUCH MORE ROBUST ON WEDNESDAY (THE COLD FRONT).
THOSE ELEVATED TEMPS AND DEWPOINTS WILL CONTRIBUTE TO INSTABILITY
VALUES ON THE ORDER OF 1000-1500 J/KG OF SURFACE BASED CAPE EACH DAY
WHILE DEWPOINTS ARE IN THE LOW TO MID 60S AS PREVIOUSLY MENTIONED. 0-
6KM BULK SHEAR VALUES, WHILE FINE (25-30 KTS), ARE LESS FAVORABLE
FOR ORGANIZED SEVERE WEATHER THAN THEY ARE FURTHER NORTH WHERE THE
STRONGER MID LEVEL FLOW RESIDES. SO, THE INGREDIENTS ARE THERE FOR
SOME STRONG TO SEVERE STORMS. THE LIFTING MECHANISM IS MUCH LESS
ROBUST ON TUESDAY, BUT GUIDANCE INDICATES A WEAK SURFACE TROUGH AND
MID LEVEL SHORTWAVE WHICH WILL LIKELY BE ENOUGH TO KICK OFF SOME
STORMS. DESPITE VERY STRONG LOW LEVEL LAPSE RATES, THE LONGEVITY AND
STRENGTH/HEIGHT OF THESE STORMS WILL BE LIMITED BY POOR MID LEVEL
LAPSE RATES. WEDNESDAY THE COLD FRONT WILL SERVE AS A BETTER LIFTING
MECHANISM, TIMED COINCIDENT WITH PEAK DIURNAL HEATING SO WOULD
EXPECT MORE COVERAGE OF STORMS AND ANY STORMS THAT DO FORM HAVE THE
CHANCE TO PRODUCE STRONG TO DAMAGING WINDS PRIMARILY GIVEN INVERTED-
V SOUNDINGS.
KEY MESSAGE 3...COOLER AND UNSETTLED WEATHER IS POSSIBLE MEMORIAL
DAY WEEKEND, BUT CONFIDENCE REMAINS LOW.
AFTER HIGH PRESSURE DELIVERS DRY AND SEASONABLE WEATHER TO END THE
WEEK, ATTENTION TURNS TO THE HOLIDAY WEEKEND. UNFORTUNATELY IT'S NOT
A CUT-AND-DRY FORECAST AT THIS POINT (5-7 DAYS OUT) AS GUIDANCE
REMAINS IN TWO DISTINCT CAMPS. ONE WOULD RESULT IN A COOL (OR
DOWNRIGHT COLD FOR LATE MAY) AND WET WEEKEND WHILE ANOTHER KEEPS
THINGS DRY AND SEASONABLE. UP TO THIS POINT DETERMINISTIC GUIDANCE
HAS INDICATED A RAINY SAT/SUN AHEAD OF A LOW COMING OUT OF THE OH
VALLEY WHILE THE AI GUIDANCE LIKE THE AIGFS AND ECMWF AIFS KEEP IT
SUPPRESSED TO THE SOUTH BY HIGH PRESSURE, AT LEAST THROUGH SUNDAY.
OBVIOUSLY THIS WOULD HAVE A BIG IMPACT ON THE WEEKEND, WITH RESPECT
TO BOTH RAIN AND TEMPERATURES. FOR WHAT IT'S WORTH, THE LATEST GFS
GUIDANCE HAS SHOWN THAT SUPPRESSION TO THE SOUTH AS WELL, BUT CAN'T
PUT ANY CONFIDENCE IN AN INDIVIDUAL RUN. ENSEMBLE GUIDANCE CONTINUES
TO SHOW A DECENT CHANCE OF RAIN FOR THE WEEKEND.
AVIATION /12Z TUESDAY THROUGH SATURDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
12Z TAF UPDATE:
TODAY AND TONIGHT...HIGH CONFIDENCE.
VFR. ISO'D TSRA POSSIBLE BY THE AFTERNOON, THOUGH CONFIDENCE IS
INCREASING IN IMPACTS TO BOS, BED, BDL, AND ORH. S-SW WIND 8 TO
12 KT, GUSTS TO 25 KT DEVELOPING THIS MORNING INTO THE AFTERNOON.
VFR OVERNIGHT, WITH MVFR CEILINGS ACROSS THE CAPE AND ISLANDS.
GUSTS DROP OFF FOR TERMINALS NOT ON THE CAPE AND ISLANDS AFTER
00Z TONIGHT.
WEDNESDAY...HIGH CONFIDENCE.
VFR. SCATTERED TSRA ALONG AND AHEAD OF A COLD FRONT IN THE
AFTERNOON AND EVENING. S-SW WIND 8-10KT WITH GUSTS 20-25 KTS
TURNING NW BEHIND THE COLD FRONT BETWEEN 15-00Z. STRONG GUSTS
POSSIBLE IN ANY THUNDERSTORMS.
KBOS...HIGH CONFIDENCE IN TAF.
KBDL...HIGH CONFIDENCE IN TAF.
OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
WEDNESDAY NIGHT: VFR. BREEZY.
THURSDAY THROUGH FRIDAY: VFR.
FRIDAY NIGHT: VFR. CHANCE SHRA.
SATURDAY: MAINLY VFR, WITH LOCAL IFR POSSIBLE. SHRA LIKELY.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH WEDNESDAY: HIGH CONFIDENCE.
SMALL CRAFT ADVISORIES REMAIN IN EFFECT 12Z TUESDAY THROUGH
WEDNESDAY EVENING. SW WINDS WILL BE INCREASING TO AROUND 15-25
KT TUESDAY AND REMAIN SO THROUGH WEDNESDAY, HIGHER OVER THE
SOUTHERN WATERS. SEAS WILL ALSO BE BUILDING TO AROUND 4-6 FT,
WITH SOME 7 FOOTERS POSSIBLE TUESDAY NIGHT OVER THE SOUTHERN
WATERS.
MAINLY DRY WEATHER PREVAILS THROUGH TUESDAY NIGHT, ALTHOUGH FOG
MAY DEVELOP BOTH TONIGHT AND TUESDAY NIGHT.
OUTLOOK /WEDNESDAY THROUGH SATURDAY/...
WEDNESDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS
UP TO 25 KT. LOCAL ROUGH SEAS. CHANCE OF RAIN SHOWERS, ISOLATED
THUNDERSTORMS.
WEDNESDAY NIGHT: WINDS LESS THAN 25 KT. AREAS OF SEAS
APPROACHING 5 FT. CHANCE OF RAIN SHOWERS.
THURSDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.
THURSDAY NIGHT THROUGH FRIDAY: WINDS LESS THAN 25 KT.
FRIDAY NIGHT: WINDS LESS THAN 25 KT. CHANCE OF RAIN SHOWERS.
SATURDAY: WINDS LESS THAN 25 KT. RAIN SHOWERS LIKELY.
CLIMATE
RECORD HIGHS FOR TUE MAY 19...
BOS 90/2017
BDL 94/1962
PVD 91/2017
ORH 92/1962
RECORD HIGHS FOR WED MAY 20...
BOS 91/1996
BDL 99/1996
PVD 95/1996
ORH 91/1903
BOX WATCHES/WARNINGS/ADVISORIES
CT...HEAT ADVISORY FROM 11 AM THIS MORNING TO 8 PM EDT WEDNESDAY
FOR CTZ002>004.
AIR QUALITY ALERT FROM 11 AM THIS MORNING TO 11 PM EDT THIS
EVENING FOR CTZ003-004.
MA...HEAT ADVISORY FROM 11 AM THIS MORNING TO 8 PM EDT WEDNESDAY
FOR MAZ003>007-010>019-026.
AIR QUALITY ALERT FROM 11 AM THIS MORNING TO 11 PM EDT THIS
EVENING FOR MAZ006-007-013>019.
RI...HEAT ADVISORY FROM 11 AM THIS MORNING TO 8 PM EDT WEDNESDAY
FOR RIZ001>004.
AIR QUALITY ALERT FROM 11 AM THIS MORNING TO 11 PM EDT THIS
EVENING FOR RIZ001>008.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM THIS MORNING TO 2 AM EDT
THURSDAY FOR ANZ254>256.
DISCUSSION...BW
AVIATION...BW/HRENCECIN
MARINE...BW
CLIMATE...BW/HRENCECIN
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