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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KBUF 201805
AFDBUF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BUFFALO NY
205 PM EDT MON MAY 20 2013

.SYNOPSIS...
A SOUTHWESTERLY FLOW OF WARM AND MORE HUMID AIR WILL CONTINUE ACROSS
THE REGION FOR MUCH OF THIS WEEK...WHILE A FRONTAL BOUNDARY ALSO
STALLS OUT ACROSS NEW YORK STATE AND SETS THE STAGE FOR INCREASING
CHANCES OF SHOWERS AND THUNDERSTORMS. THE MORE UNSETTLED CONDITIONS
WILL LAST THROUGH THURSDAY...BEFORE A COLD FRONT CROSSES THE AREA
AND USHERS IN COOLER AND DRIER WEATHER FOR THE END OF THE WEEK AND
THE MEMORIAL DAY WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
THE INLAND REGIONS HAVE FILLED IN WITH SHALLOW CUMULUS OR STRATOCU
THIS AFTERNOON. THE MID LEVEL AND UPPER RIDGE SHOULD BE STRONG
ENOUGH TO SUPPRESS FURTHER VERTICAL DEVELOPMENT THUS ONLY A SLIGHT
CHANCE OF ANY SHOWERS OR THUNDERSTORMS. THE ONLY EXCEPTION SHOULD
BE THE NORTH COUNTRY WHERE THERE IS A WEAK SURFACE BOUNDARY WHICH
MAY PROVIDE ENOUGH FOCUS AND LOW LEVEL LIFT TO FIRE OFF A COUPLE OF
SHOWERS OR THUNDERSTORMS. WILL CARRY LOW CHANCE POPS FOR JEFFERSON
AND LEWIS COUNTIES AND MUCH OF THE SAINT LAWRENCE VALLEY.

THIS EVENING...EXPECT FAIRLY QUIET CONDITIONS FOR THE FIRST HALF OF
THE NIGHT...THEN CONVECTIVE CHANCES WILL BEGIN TO INCREASE AGAIN
FROM NORTHWEST TO SOUTHEAST AS LOW PRESSURE DEVELOPS ACROSS THE
WESTERN AND CENTRAL LAKES AND SENDS INCREASING MOISTURE AND LIFT
EASTWARD ALONG THE SAGGING FRONTAL BOUNDARY. WITH THE SHORT TERM
MODEL GUIDANCE HAVING DIFFICULTY IN RESOLVING/AGREEING ON THE TIMING
AND PLACEMENT OF THE RESULTANT AREAS OF CONVECTION...FOR NOW HAVE
JUST INDICATED A GENERAL INCREASE IN POPS BACK TO THE LOW CHANCE
RANGE OVERNIGHT.

WITH RESPECT TO TEMPERATURES...850 MB TEMPS WILL CONTINUE TO CLIMB
TO THE +13 TO +15C RANGE TODAY...AND THIS SHOULD BE ENOUGH TO
SUPPORT WIDESPREAD HIGHS IN THE LOWER-MID 80S AWAY FROM LAKE
INFLUENCES...WITH COOLER READINGS FOUND NEAR THE LAKESHORES...AND IN
THE VICINITY OF THE FRONTAL BOUNDARY SAGGING INTO THE NORTH COUNTRY.
A RATHER WARM NIGHT WILL THEN FOLLOW FOR TONIGHT...WITH READINGS
ONLY DROPPING INTO THE LOWER TO MID 60S. WITH SFC DEWPOINTS ALSO
RISING INTO THE LOWER 60S...IT WILL ALSO BEGIN TO FEEL SOMEWHAT
HUMID.
-- End Changed Discussion --

&&

.SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
A CLOSED H5 LOW PARKED OVER THE NORTHERN PLAINS AT THE START OF THIS
PERIOD WILL KEEP A WARM RIDGE IN PLACE ACROSS OUR REGION THROUGH AT
LEAST WEDNESDAY. THIS WILL NOT ONLY SUPPLY US WITH SOME SUMMER LIKE
WARMTH BUT WILL GIVE US A TASTE OF SUMMER HUMIDITY AS WELL. WHILE WE
CAN SAY THIS WITH A HIGH DEGREE OF CERTAINTY...IT WILL CONTINUE TO
BE CHALLENGING TO PINPOINT THE TIMING AND EXTENT OF THE SHOWERS AND
THUNDERSTORMS THAT ARE EXPECTED DURING THIS TIME FRAME.

ON TUESDAY...THE CONTROLLING RIDGE THAT UP TO THIS POINT HAD BEEN
PROTECTING MOST OF THE REGION WITH ITS ASSOCIATED SUBSIDENT FLOW
WILL START TO WEAKEN. MEANWHILE AT THE SFC...A SLOW MOVING FRONTAL
BOUNDARY WILL SAG SOUTH FROM SOUTHERN ONTARIO...LIKELY STALLING OVER
OUR WESTERN COUNTIES. CONVECTION IS LIKELY TO DEVELOP ALONG AND
SOUTH OF THIS BOUNDARY WHERE DEW POINTS IN THE LOW-MID 60S SHOULD
HELP TO ESTABLISH AFTERNOON CAPE VALUES >1000 J/KG AWAY FROM THE
LAKES ALONG WITH LI`S IN THE VCNTY OF -4/-5. THE DIURNALLY DRIVEN
CONVECTION WILL BE AIDED BY INCREASING AMOUNTS OF LOW LEVEL MOISTURE
OUT OF THE OHIO VALLEY...WITH PWAT VALUES POSSIBLY CLIMBING OVER 1.5
INCHES. GIVEN THE LACK OF CONFIDENCE ON THE FRONTAL POSITION...WILL
HAVE TO BROAD BRUSH WITH LIKELY POPS FOR THE AFTERNOON. OTHERWISE AS
ALREADY MENTIONED...IT WILL BE WARM AND HUMID TUESDAY WITH HIGHS OF
80 TO 85 OVER THE WRN COUNTIES AND 70S EAST OF LK ONTARIO.

THE SHOWERS AND THUNDERSTORMS OVER THE WESTERN COUNTIES WILL TAPER
OFF EARLY TUESDAY NIGHT AS THE BOUNDARY LAYER WILL PARTIALLY
STABILIZE WITH THE REMOVAL OF DIURNAL HEATING. MID LEVEL RIDGING
WILL BECOME RE-ESTABLISHED OVER OUR FORECAST AREA DURING THE NIGHT
AS WELL...SO THIS SHOULD ALSO HELP IN TEMPORARILY ENDING ANY PCPN.
SHOWERS AND POSSIBLE THUNDERSTORMS SHOULD BE A LITTLE MORE COMMON IN
THE VCNTY OF THE FRONTAL BOUNDARY EAST OF LK ONTARIO DURING THE
OVERNIGHT THOUGH. OTHERWISE...THIS WILL LEAVE A RELATIVELY WARM AND
HUMID NIGHT ACROSS THE REGION...ESPECIALLY OVER THE WESTERN COUNTIES
(SOUTH OF LK ONTARIO AND THE FRONTAL BOUNDARY).

THE EARLY SUMMER AIRMASS WILL REMAIN IN PLACE ACROSS THE FORECAST
AREA ON WEDNESDAY AS THE CLOSED LOW OVER THE NORTHERN PLAINS WILL
GRADUALLY OPEN UP WHILE KEEPING A MOISTURE RICH LOW LEVEL INTACT
FROM THE OHIO VALLEY. THIS LOW LEVEL FEED WILL BE ENHANCED BY BROAD
LOW PRESSURE THAT WILL APPROACH OUR FORECAST AREA FROM LOWER
MICHIGAN. THIS SHOULD LEAD TO MORE EXTENSIVE CLOUD COVER...WHICH IN
TURN WILL MINIMIZE DIURNAL INSTABILITY OVER OUR REGION.
NEVERTHELESS...SBCAPES OF 500 J/KG SHOULD BE MORE THAN ENOUGH TO
GENERATE SOME SHOWERS AND THUNDERSTORMS WITH PWAT VALUES OF >1.5
SUPPORTING SOME LOCALIZED HIGH QPF. WILL ONCE AGAIN BROAD BRUSH WITH
LIKELY POPS.

IN TERMS OF THE POTENTIAL FOR STRONG TO SEVERE STORMS...WILL
REITERATE THE THINKING FROM THE PREVIOUS DISCUSSIONS. MID LEVEL
LAPSE RATES FOR BOTH TUESDAY AND WEDNESDAY ARE ONLY IN THE VCNTY OF
6 DEG C/KM WITH EQUALLY UNIMPRESSIVE KINEMATIC FIELDS (EX. 0-3KM
SHEAR <25 M/S).

THE AFOREMENTIONED SFC LOW WILL CROSS TO OUR NORTH WEDNESDAY NIGHT
WHILE ITS TRAILING FRONTAL BOUNDARY WILL HANG BACK TO A FRONTAL WAVE
IN THE VCNTY OF WRN LK ERIE. THIS WILL KEEP SHOWERS AND POSSIBLE
THUNDERSTORMS OVER OUR REGION...BUT DO NOT EXPECT STRONG ENOUGH
FORCING TO SUPPORT SIGNIFICANT QPF.

ON THURSDAY AND THURSDAY EVENING...THE WAVY FRONTAL BOUNDARY WILL
SLOWLY DRIFT ACROSS OUR FORECAST AREA. FROM THE 00Z MODEL RUNS...
THE GFS WAS SOME 3-6 HOURS FASTER WITH THIS PASSAGE THAN ITS
EUROPEAN COUNTERPART. IN ANY CASE...THIS WILL LIKELY GENERATE
ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS WITH DAYTIME TEMPERATURES
AVERAGING SOME 10 DEG F LOWER THAN THE PREVIOUS FEW DAYS. THIS WILL
TRANSLATE INTO EARLY AFTERNOON HIGHS IN THE LOWER 70S FOR MOST
AREAS.

WHILE THURSDAY NIGHT SHOULD PROVE TO BE NOTICEABLY COOLER...THERE
WILL BE SOME LINGERING SHOWERS WITH SKIES STUBBORN TO CLEAR. IN
FACT...MOST AREAS MAY KEEP THEIR LOW CLOUD COVER RIGHT THROUGH
DAYBREAK ON FRIDAY. THIS WILL ESPECIALLY BE TRUE FOR SITES EAST OF
THE GENESEE VALLEY. TEMPERATURES ARE EXPECTED TO DROP INTO THE
40S...WHICH WILL BE AT LEAST 15 DEG LOWER THAN PREVIOUS OVERNIGHT
LOWS.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
THE VARIOUS MEDIUM RANGE GUIDANCE PACKAGES ARE IN STRONG AGREEMENT
THAT GENERALLY FAIR AND SEASONABLY COOL CONDITIONS WILL BE IN PLACE
DURING THIS PERIOD...INCLUDING THE BULK OF THE MEMORIAL DAY WEEKEND.
A BROAD BASED RIDGE WILL BE POSITIONED OVER THE NATIONS MID SECTION
AND THIS WILL LEAVE TWIN TROUGHS OFF THE COASTS OF VANCOUVER AND
EASTERN QUEBEC...WHERE COOLER THAN AVERAGE TEMPERATURES ARE
EXPECTED.

A MORE DETAILED LOOK AT OUR REGION REVEALS THAT WE WILL HAVE SOME
LEFTOVER LOW CLOUDS AND LIGHT SHOWERS FRIDAY MORNING (MAINLY EAST OF
GENESEE VALLEY) IN THE WAKE OF THE DEPARTING FRONTAL SYSTEM...BUT AS
LOW LEVEL RIDGING BUILDS SOUTH ACROSS THE GREAT LAKES...OUR SKIES
WILL CLEAR OUT. H85 TEMPS WILL DROP TO AROUND 5C...SO FRIDAY WILL BE
MUCH COOLER WITH AFTERNOON TEMPS GENERALLY IN THE LOWER 60S (50S
ACROSS THE NORTH COUNTRY).

EXPANSIVE HIGH PRESSURE WILL BUILD SOUTH ACROSS THE REGION FROM
CANADA SATURDAY AND SUNDAY...WITH H85 TEMPS FORECAST TO BE IN THE
VCNTY OF 4C BOTH DAYS. THIS WILL KEEP THE AFTERNOONS COOL AND THE
NIGHTS CHILLY WITH SOME FROST POSSIBLE...MAINLY ACROSS THE SOUTHERN
TIER AND EASTERN LAKE ONTARIO REGIONS.

A PEEK AHEAD TO MEMORIAL DAY SUGGESTS THAT FAIR DRY WEATHER WILL BE
IN PLACE WITH A MODERATION IN TEMPERATURES TO NEAR SEASONAL LEVELS.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
AFTERNOON WARMTH DEVELOPING SCT/BKN SKY CONDITION ACROSS THE INLAND
REGION OF THE FORECAST AREA WITH MOST OF THE TAF SITES TO REMAIN
BEHIND LAKE BREEZE BOUNDARIES AND THUS IN MORE STABLE AIR...WITH VFR
CONDITIONS CONTINUING.

TONIGHT...EXPECT VFR CONDITIONS TO CONTINUE TO PREVAIL FOR MUCH OF
THE NIGHT...BEFORE SOME ADDITIONAL CONVECTION POSSIBLE ACROSS THE
NORTH COUNTRY LATE. WITH THE TIMING AND PLACEMENT OF THIS  VERY
UNCERTAIN AT THIS POINT...FOR NOW HAVE JUST ADDED VCSH TO THE TAFS
TO COVER THIS POTENTIAL.

THE UPPER AND MID LEVEL RIDGE AXES TO PASS ACROSS THE REGION AND TO
THE EAST ON TUESDAY. WILL HAVE A SLIGHTLY BETTER CHANCE OF AFTERNOON
AND EVENING CONVECTION...ALONG THE LAKE BREEZE BOUNDARIES AND OVER
THE INTERIOR OF THE FORECAST AREA.

OUTLOOK...
TUESDAY THROUGH THURSDAY...NUMEROUS SHOWERS AND THUNDERSTORMS WITH
ASSOCIATED BRIEF MVFR/IFR...OTHERWISE VFR.
FRIDAY...MAINLY VFR WITH A CHANCE OF SHOWERS.
SATURDAY...VFR.
-- End Changed Discussion --

&&

.MARINE...
THROUGH MUCH OF THIS WEEK...WINDS WILL REMAIN RELATIVELY LIGHT AND
VARIABLE IN DIRECTION DUE TO A NEARLY STATIONARY FRONTAL BOUNDARY
THAT WILL REMAIN DRAPED ACROSS THE REGION...AS WELL AS THE DAILY
DEVELOPMENT OF LAKE BREEZES. AS A RESULT...WAVE HEIGHTS SHOULD ALSO
REMAIN MINIMAL. OTHERWISE...AFTER A MAINLY DRY DAY TODAY...SHOWER
AND THUNDERSTORM CHANCES WILL INCREASE MARKEDLY FOR THE TUESDAY
THROUGH THURSDAY TIME FRAME.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...NONE.
MARINE...NONE.

&&

$$

SYNOPSIS...JJR
NEAR TERM...WCH
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...WCH
MARINE...JJR