510
FXUS61 KBOX 180819
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
419 AM EDT THU OCT 18 2018
SYNOPSIS
UNSEASONABLY CHILLY AND WINDY WEATHER TODAY WILL BE FOLLOWED BY
DIMINISHING WINDS BUT SUB-FREEZING LOW TEMPERATURES IN MANY
LOCATIONS TONIGHT. MILDER TEMPERATURES RETURN FRIDAY AFTERNOON
ALONG WITH PLENTY OF SUNSHINE. SERIES OF SWEEPING COLD FRONTS
LATE WEEK INTO THE WEEKEND. LIGHT SHOWERY WEATHER SURROUNDING,
NOTHING OF A WASHOUT, ALONG WITH BREEZY WINDS. IN WAKE, CANADIAN
HIGH PRESSURE, FROST / FREEZE CONDITIONS FOR AN OVERNIGHT
PERIOD BEFORE TEMPERATURES REBOUND.
NEAR TERM /UNTIL 6 PM THIS EVENING/
* WINDY AND UNSEASONABLY CHILLY TODAY
STRONG COLD ADVECTION BEHIND LAST EVENING/S COLD FRONT WILL
ALLOW 850T TO DROP TO BETWEEN -8C AND -10C THROUGH MID
AFTERNOON. MODEL CROSS SECTIONS INDICATE A LOT OF DRY AIR
THROUGH THE COLUMN...SO EXPECT PLENTY OF SUNSHINE.
NONETHELESS...THE ANOMALOUS COLD AIR ALOFT WILL RESULT IN HIGH
TEMPERATURES ONLY IN THE LOWER 40S ACROSS THE HIGHER TERRAIN
WITH MAINLY UPPER 40S ELSEWHERE.
THE ATMOSPHERE WILL BE SUPER ADIABATIC AND ALLOW STRONGER WINDS
ALOFT TO MIX DOWN. ALTHOUGH MUCH OF THE REGION SHOULD REMAIN
BELOW WIND ADVISORY CRITERIA...EXPECT A BRIEF PERIOD OF 30 TO 35
KNOT WIND GUSTS ROUGHLY BETWEEN 10Z AND 15Z. WE CAN NOT RULE OUT
A FEW GUSTS NEAR 40 KNOTS FOR A VERY SHORT TIME. WITH ALL THAT
SAID DROPPED THE WIND ADVISORY FOR MUCH OF THE REGION...BUT
OPTED TO KEEP IT FOR THE WORCESTER HILLS AND NORTHEAST MA WHERE
THE GREATEST POTENTIAL EXISTS FOR CRITERIA BEING APPROACHED.
WE ALSO CONTINUED THE ADVISORY FOR ACK/CAPE COD. EVEN IF GUSTS
ONLY APPROACH 35 KNOTS...MINOR TREE DAMAGE/ISOLATED POWER
OUTAGES ARE POSSIBLE GIVEN THE FULLY LEAFED TREES.
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/
* WIDESPREAD FROST/FREEZE CONDITIONS OVERNIGHT
TONIGHT...
A RIDGE OF HIGH PRESSURE WILL BUILD SOUTH OF OUR REGION FROM THE
WEST. THIS WILL ALLOW WINDS TO DECOUPLE IN MANY LOCATIONS AND
WITH MAINLY CLEAR SKIES AN IDEAL NIGHT OF RADIATIONAL COOLING
CONDITIONS ARE EXPECTED. LOW TEMPS SHOULD RANGE FROM THE MIDDLE
20S IN THE NORMALLY COLDEST OUTLYING LOCATIONS...TO THE UPPER
20S AND LOWER 30S IN MOST OTHER LOCATIONS. FREEZE/FROST
HEADLINES ARE POSTED OVERNIGHT FOR MANY LOCATIONS WHERE THE
GROWING SEASON HAS NOT OFFICIALLY ENDED. EVEN ALONG THE
IMMEDIATE COAST...LOW TEMPERATURES SHOULD DROP WELL DOWN INTO
THE 30S AND FROST HEADLINES ARE POSTED FOR MANY OTHER LOCATIONS.
THE EXCEPTION IS DOWNTOWN BOSTON/NANTUCKET, WHERE LOW TEMPS
SHOULD GENERALLY REMAIN IN THE UPPER 30S.
FRIDAY...
THE RIDGE OF HIGH PRESSURE WILL MOVE EAST OF THE MID ATLANTIC
COAST FRIDAY. THE RESULT WILL BE A QUICK RETURN TO A MUCH MILDER
SOUTHWEST FLOW OF AIR. IN FACT...850T WILL RISE TO +8C TO +10C
BY FRIDAY AFTERNOON. GIVEN THE COLD START AND THE LOWERING
OCTOBER SUN ANGLE...THIS MID LEVEL WARMTH WILL NOT BE COMPLETELY
REALIZED AT THE SURFACE. NONETHELESS...STILL EXPECT A
SIGNIFICANTLY MILDER DAY WITH MANY LOCATIONS REACHING THE LOWER
60S. GUSTY SOUTHWEST WINDS SHOULD DEVELOP ALONG THE COASTAL
PLAIN DURING THE AFTERNOON.
LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/
*/ HIGHLIGHTS...
- TEMPERATURE UNDULATIONS AROUND SWEEPING COLD FRONTS
- WITH ANY FRONTAL PASSAGES, EXPECT SHOWERY WEATHER, BREEZY WINDS
- IN WAKE, FROST / FREEZE CONDITIONS POSSIBLE
*/ OVERVIEW...
UNDULATING AIRMASSES OF AUTUMN. NE ATLANTIC ANTI-CYCLONIC WAVE BREAK
EVOLVES INTO AN OMEGA BLOCK SLOWING THE UPSTREAM H5 LONGWAVE PATTERN
ALLOWING STORM MATURATION OVER E CANADA NE TOWARDS THE NORWEGIAN SEA.
OBTAINING GREATER CURVATURE / ANGULAR MOMENTUM, STORM DEEPENING NETS
CROSS-POLAR FLOW INTO EASTERN N AMERICA THROUGH A PREFERRED H5 TROF
AIDED BY A +PNA / +AO TREND. UP AGAINST AN UPSTREAM -EPO AND SPLIT-
FLOW REGIME, PREFERRED H5 TROF WAVERS AT TIMES, RELOADING WHEN +PNA
W CONUS H5 RIDGE SURGES. STRENGTH CRUCIAL WHEN IT COMES TO H5 TROF
DIPS OVER BAROCLINIC REGIONS, WHERE MORE FAVORABLE STORM DEVELOPMENT
WILL OCCUR, WHETHER ACTING ON THE S-STREAM.
ASIDE, WITH H5 TROF DIPS, ISALLOBARIC / PRESSURE-GRADIENT RESPONSE
TO PATTERN AMPLIFICATION, DOWNWARD REFLECTION WITH SURFACE - H85
COLD AIR ADVECTION ROUGHLY -1 TO -2 STANDARD DEVIATION AIDING IN
STEEP LOW-LEVEL LAPSE RATES, SUBSEQUENT MIX-DOWN OF FASTER MOMENTUM
AND DRIER AIR. WET-WEATHER CHANCES ALONG ASSOCIATED SWEEPING COLD
FRONTS.
ROSSBY WAVE TRANSITION INTO THE END OF OCTOBER, A +EPO EVOLVES. W
CONUS ONSHORE PACIFIC AIR, THE UPSTREAM PREFERRED H5 TROF PATTERN
LOOKS TO BREAK, ALBEIT BRIEFLY, LESS ACTIVE PATTERN.
*/ DISCUSSION...
FRIDAY NIGHT INTO SATURDAY NIGHT ... CHANCE POPS UPON A CONTINENTAL
AIRMASS UNDERGOING ASCENT ABOVE A LIFTING COLD FRONT. SHOWERY, NOT A
WASHOUT. WIND WATCH. BREEZY SW WINDS WITH ADVISORY-LEVEL CONCERNS
GIVEN POTENTIAL MIXING TO H8 WHERE 45 MPH WINDS ARE MODELED. A LULL
LATE SATURDAY INTO SATURDAY EVENING WITH COLD FRONTAL PASSAGE, THEN
FOCUS ON COLD AIR ADVECTION, STEEPENING LAPSE RATES, ALLOWANCE OF
FAST NW WINDS TO MIX DOWN.
SUNDAY INTO SUNDAY NIGHT ... BREEZY NW WINDS DIMINISHING. CLEARING
UNDER HIGH PRESSURE INFLUENCE SHIFTING SE. LIGHT WINDS, COLD ALOFT.
FROST / FREEZE CONCERNS INTO MONDAY MORNING.
MONDAY THRU WEDNESDAY ... TEMPERATURE SWINGS ROUND ANOTHER SWEEPING
COLD FRONT TUESDAY EVENING. CHANCE POPS WITH SHOWERY WEATHER, FAIRLY
VOID OF MOISTURE, ANOTHER CONTINENTAL AIRMASS. BREEZY WINDS POSSIBLE
AGAIN WITH FROST / FREEZE CONCERNS IN COLD FRONTAL WAKE.
LATE WEEK ONWARD ... WAY TOO MUCH DETERMINISTIC / ENSEMBLE MODEL
SPREAD TO MAKE ANY DETERMINATION. -EPO HAVING WEAKENED, LOW PRESSURE
DEVELOPING OVER THE GULF OF AK, N PACIFIC OPENS AND MILD PACIFIC AIR
STREAMS ASHORE SEEMS CERTAIN, HOWEVER DOWNSTREAM OUTCOMES ARE WIDELY
UNKNOWN.
AVIATION /08Z THURSDAY THROUGH MONDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
SHORT TERM /THROUGH FRIDAY/...
TODAY...HIGH CONFIDENCE IN VFR. NW WIND GUSTS OF 25 TO 35 KNOTS.
TONIGHT...HIGH CONFIDENCE. VFR WITH DIMINISHING WINDS THIS
EVENING.
FRIDAY...HIGH CONFIDENCE. VFR CONDITIONS CONTINUE. SW WIND GUSTS
INCREASE TO BETWEEN 20 AND 25 KNOTS DURING THE AFTERNOON ALONG
THE COASTAL PLAIN. A FEW GUSTS AROUND 30 KNOTS EXPECTED ACROSS
THE FAR SOUTHEAST NEW ENGLAND COAST.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.
OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/...MODERATE-HIGH CONFIDENCE.
FRIDAY NIGHT: VFR. WINDY WITH GUSTS TO 30 KT. SLIGHT CHANCE
SHRA.
SATURDAY: VFR. WINDY WITH GUSTS TO 35 KT. CHANCE SHRA.
SATURDAY NIGHT: VFR. BREEZY. SLIGHT CHANCE SHRA.
SUNDAY THROUGH SUNDAY NIGHT: VFR. WINDY WITH AREAS GUSTS TO
30 KT.
MONDAY: VFR. BREEZY.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
SHORT TERM /THROUGH FRIDAY/...HIGH CONFIDENCE.
TODAY...GALE WARNINGS REMAIN POSTED THIS MORNING FOR ALL
WATERS WITH NORTHWEST WIND GUSTS OF 30 TO 40 KNOTS. THE
STRONGEST OF THE WINDS WILL GRADUALLY DIMINISH FROM WEST TO EAST
THIS AFTERNOON...BUT WILL NEED TO CONTINUE GALE HEADLINES
THROUGH LATE AFTERNOON ACROSS MOST OUTER-WATERS.
TONIGHT...WHILE WIND GUSTS SHOULD DROP BELOW 25 KNOTS THIS
EVENING...SMALL CRAFT HEADLINES WILL STILL BE NEEDED FOR MUCH
OF TONIGHT ACROSS THE OUTER-WATERS FOR LEFT OVER
SEAS...ALTHOUGH THEY WILL BE ON THE DOWNWARD TREND.
FRIDAY...SMALL CRAFT HEADLINES WILL BE REQUIRED FOR ALL WATERS
AS HIGH PRESSURE MOVES FURTHER EAST AND AWAY FROM THE MID
ATLANTIC COAST. THIS WILL GENERATE SOUTHWEST WIND GUSTS OF 20 TO
30 KNOTS AND ROUGH SEAS...PARTICULARLY ON THE SOUTHERN WATERS
WITH LONG FETCH.
OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/...MODERATE TO HIGH
FRIDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 30 KT. AREAS OF ROUGH SEAS. SLIGHT CHANCE OF RAIN
SHOWERS.
SATURDAY: LOW RISK FOR GALE FORCE WINDS WITH GUSTS UP TO 35 KT.
AREAS OF ROUGH SEAS. CHANCE OF RAIN SHOWERS.
SATURDAY NIGHT: WINDS LESS THAN 25 KT. LOCAL ROUGH SEAS. CHANCE
OF RAIN SHOWERS.
SUNDAY: STRONG WINDS WITH AREAS OF GUSTS UP TO 30 KT. AREAS OF
ROUGH SEAS. SLIGHT CHANCE OF RAIN SHOWERS.
SUNDAY NIGHT: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 30 KT. LOCAL ROUGH SEAS.
MONDAY: WINDS LESS THAN 25 KT. SEAS LOCALLY APPROACHING 5 FT.
CLIMATE
RECORD LOW MAXIMUM TEMPERATURES FOR TODAY
BOS 45 IN 1898
ORH 36 IN 1989
BDL 44 IN 2009
PVD 46 IN 1939
BOX WATCHES/WARNINGS/ADVISORIES
CT...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR
CTZ002>004.
MA...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR
MAZ007-014-019-022-023.
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR
MAZ005-006-009>013-017-018-020-021.
WIND ADVISORY UNTIL 11 AM EDT THIS MORNING FOR MAZ004>007-
012>016-022-024-026.
RI...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR
RIZ002-004>007.
FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT FRIDAY FOR
RIZ001-003.
MARINE...GALE WARNING UNTIL 2 PM EDT THIS AFTERNOON FOR ANZ231-232-251.
GALE WARNING UNTIL 11 AM EDT THIS MORNING FOR ANZ230-233>237.
GALE WARNING UNTIL 4 PM EDT THIS AFTERNOON FOR ANZ250-254>256.
SYNOPSIS...FRANK/SIPPRELL
NEAR TERM...FRANK
SHORT TERM...FRANK
LONG TERM...SIPPRELL
AVIATION...FRANK/SIPPRELL
MARINE...FRANK/SIPPRELL
CLIMATE...STAFF
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