000
FXUS04 KWBC 230952
QPFPFD

QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
551 AM EDT THU MAY 23 2013
FINAL DAY 1...DAY 2 AND DAY 3 QPF DISCUSSION
VALID MAY 23/1200 UTC THRU MAY 26/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR


THE 06Z MODEL RUNS WERE IN VERY GOOD AGREEMENT WITH THE 00Z
RUNS..AT LEAST MASS FIELD-WISE..SO MADE ONLY VERY
MINOR CHANGES TO THE PRELIM DAY 1 QPF.

DAY 1...

...GREAT LAKES/OH VALLEY AND MID ATLANTIC STATES INTO NEW
ENGLAND...

IT SHOULD BE A WET PERIOD FOR THESE REGIONS AND ESPECIALLY FROM
THE MID ATLANTIC STATES INTO NEW ENGLAND..AHEAD OF AN
H5 TROF DIGGING INTO THE EASTERN STATES WITH THE MID LEVEL FLOW
BACKING RATHER SIGNIFICANTLY INTO THE NORTHEASTERN STATES BY
FRIDAY MORNING.  THIS BACKING MID LEVEL FLOW AND A CONTINUED
SOUTH-SOUTHWESTERLY LOW LEVEL FLOW UP THRU THE MID ATLANTIC AND
NORTHEASTERN STATES WILL BRING IN AN AXIS OF MUCH ABOVE AVERAGE PW
VALUES..AT OR ABOVE 1.50 INCHES..ALONG AND AHEAD OF THE
ACCOMPANYING COLD FRONT.  THIS HIGH MOISTURE ALONG WITH RATHER
DECENT BOUNDARY LAYER CONVERGENCE AND FAVORABLE RIGHT ENTRANCE
REGION UPPER JET DYNAMICS SHOULD SUPPORT THE WIDESPREAD MODERATE
TO HEAVY RAINFALL EVENT.  THERE CONTINUES TO BE SOME MODEL QPF
DETAIL DIFFERENCES THRUOUT THE AREA..BUT IN GENERAL THEY ALL FAVOR
FAIRLY WIDESPREAD 0.50-1.00+ INCH RAINFALL TOTALS..WITH THE
HEAVIER AMOUNTS LIKELY CONFINED TO THE NORTHERN MID ATLANTIC AND
NEW ENGLAND STATES WHERE THE EVENT WILL PERSIST EVEN BEYOND THIS
PERIOD.


...SOUTHERN PLAINS...

NOT A LOT OF CONFIDENCE CONCERNING THE QPF ACROSS THIS PART OF THE
COUNTRY..GIVEN CONTINUED BIG SPREAD IN THE OPERATIONAL..HIRES AND
SREF GUIDANCE.  THE NAM AND GFS QPFS HIT THE HI PLAINS OF TX QUITE
HARD..WHILE THE NON-NCEP MODELS ARE SIGNIFICANTLY LIGHTER AND THE
HIRES GUIDANCE IS SOMEWHERE IN BETWEEN.  INITIAL THOUGHTS ARE TO
SHY AWAY FROM THE NCEP MODELS..GIVEN THE LIKELIHOOD OF FEEDBACK
PROBLEMS CONTAMINATING THEIR FORECASTS.  HOWEVER..THERE WILL BE A
WEAK FRONTAL BOUNDARY IN PLACE..THERE WILL BE A BROAD LOW LEVEL
WARM AIR ADVECTION PATTERN DEVELOPING DURING THE PERIOD UP THRU
THE SOUTHERN PLAINS..AND THERE APPEARS TO BE A WEAK H5 S/WV
VICINITY OF NORTHWESTERN OLD MEXICO/CENTRAL GULF OF CA WHICH COULD
BE IN A POSITION TO PROVIDE SOME ADDITIONAL LARGE SCALE LIFT LATER
THURSDAY AFTERNOON/EVENING.  SO..ALTHOUGH THE NCEP MODELS MAY BE
TOO HEAVY QPF-WISE..THE FRONT..WARM AIR ADVECTION AND H5 S/WV
SHOULD SUPPORT SOME CONVECTIVE DEVELOPMENT IN THE SOUTHERN PLAINS
AND ESPECIALLY OVER WESTERN TX LATER THURSDAY
AFTERNOON/EVENING..WITH SOME ACTIVITY TRYING TO FORM FARTHER NORTH
IN THE REGION LATER THURSDAY NIGHT.  MANUAL QPF WENT HEAVIER THAN
THE NON-NCEP SOLUTIONS (EXCEPT FOR THE GEM REGIONAL..WHICH SEEMED
TO BE A GOOD COMPROMISE) BUT NOT NEARLY AS HEAVY AS THE NCEP
MODELS..WITH POTENTIALLY SOME 1+ INCH RAINFALL AMOUNTS IN THE HIGH
PLAINS OF TX.


...PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES...

THE LATEST MODEL GUIDANCE CONTINUES TO SHOW FAIRLY GOOD AGREEMENT
WITH THE EVOLUTION OF THE STRONG PACIFIC NORTHWEST CLOSED H5
LOW..WITH THE CENTER BEING ONLY SLOWLY PROGRESSIVE BUT WITH A VERY
SIGNIFICANT S/WV ROTATING FARTHER INLAND THRU THE NORTHERN ROCKIES
DURING THE PERIOD.  MODEL QPF DISTRIBUTIONS ARE ALSO IN GOOD
AGREEMENT..SHOWING ONE MAX ALONG COASTAL SECTIONS OF WA/OR FROM
THE OLYMPICS SOUTHWARD ALONG THE COASTAL RANGE WHERE SOME WESTERLY
LOW LEVEL FLOW WILL PERSIST..AND ANOTHER MAX IN THE NORTHERN
ROCKIES ASSOCIATED WITH THE STRONG S/WV LIFTING THRU.  IN BOTH
AREAS..EXPECT SOME 0.50-1.00+ INCH RAINFALL AMOUNTS..WITH MAYBE
THE HIER RES NAM A LITTLE TOO HEAVY IN THE WA/OR AREA.


DAYS 2-3...


...PACIFIC NORTHWEST/INTERMOUNTAIN WEST...

THE CLOSED MID LEVEL LOW OVER THE PACIFIC NORTHWEST WILL RESULT IN
ONE MORE DAY OF RAIN BEFORE IT MOVES AWAY FROM THE AREA INTO BC
AND AB. THERE WAS GOOD MODEL CLUSTERING WITH THIS FEATURE...AND
THE QPF WAS BASED LARGELY ON A 00Z ECMWF/GFS/UKMET BLEND.

SHORT WAVES ROTATING AROUND THE CLOSED LOW WILL PROVIDE THE BEST
SYNOPTIC SCALE LIFT AND BEST CLUSTERING OF CONVECTIVELY DRIVEN
SHOWERS AND THUNDERSTORMS. COLD MID LEVEL TEMPERATURES WILL
PRODUCE STEEPENING LAPSE RATES AND MARGINAL
INSTABILITY...PARTICULARLY ACROSS INTERIOR WA AND OR...AS WELL AS
WESTERN MT. THERE IS LESS INFLOW ACROSS CENTRAL AND EASTERN
MT...AND THEREFORE LESS IN THE WAY OF ORGANIZED PRECIPITATION
THERE.

THE FIRST SHORT WAVE FOCUSES RAINFALL ACROSS EASTERN WA AND
WESTERN MT...AND QPF AMOUNTS IN THIS AREA WILL AVERAGE BETWEEN
0.15 AND 0.25 INCHES...MAINLY IN THE HIGHER TERRAIN. THE SECOND
SHORT WAVE CROSSING THE OR COAST LATE DURING DAY 2 WILL FOCUS THE
0.75 INCH PRECIPITABLE WATER AIR ON THE OR COASTAL RANGE...
PRODUCING 0.15 TO 0.25 INCHES OF QPF.


...CENTRAL/NORTHERN PLAINS/MIDWEST...

MOISTURE RIDING UP AND OVER A FRONTAL BOUNDARY EXTENDING ACROSS
THE NORTHERN AND CENTRAL PLAINS INTO THE MIDWEST WILL BE THE FOCUS
FOR QPF FOR BOTH DAYS 2 AND 3. THERE WAS GOOD MODEL CONSENSUS
CONCERNING THE FRONTAL POSITION AND MASS FIELDS HERE...AND THE QPF
WAS BASED MAINLY ON A 00Z ECMWF/GFS BLEND.

A 35 KNOT SOUTHERLY LOW LEVEL JET WILL TRANSPORT 1.25 TO 1.50 INCH
PRECIPITABLE WATER AIR UP AND OVER THE WARM FRONT EXTENDING ACROSS
THE NORTHERN AND CENTRAL PLAINS DURING DAY 2. SOUTH OF THE
FRONT...MODEL SOUNDINGS SHOW MODERATE INSTABILITY WITH VEERING IN
THE LOW LEVELS...AND DIFLUENCE WILL BE SUPPLIED IN BY A 90 KNOT
JET STREAK...SUPPORTING SCATTERED CONVECTION IN KS AND NE DURING
THE AFTERNOON AND EVENING HOURS. THE CONVECTION SUPPORTS AN AREA
OF 0.15 TO 0.25 INCHES OF QPF DURING THE AFTERNOON AND EVENING
HOURS.

ANOTHER SURGE OF MOISTURE...RIDING ON THE NOSE OF A 40 TO 50 KNOT
LOW LEVEL JET...IS TRANSPORTED ACROSS THE CENTRAL PLAINS INTO THE
MIDWEST FOR THE SECOND HALF OF DAY 2. THE BEST LOW LEVEL MOISTURE
FLUX ACCOMPANIES THE JET...AND THERE IS SOME MODEL SUPPORT FOR THE
DEVELOPMENT OF AN MCS ACROSS NE...WHICH MOVES INTO THE MIDWEST BY
THE END OF DAY 2. FOR NOW...AN AREA OF 0.50 TO 0.75 INCHES OF QPF
WAS PLACED ALONG THE EXPECTED TRACK OF MCS IN NE AND WESTERN IA.

ON DAY 3...QPF WAS PLACED ON THE EXPECTED TRACK OF THE DECAYING
MCS EARLY. AFTER THIS...THE CONVECTION POTENTIAL WILL BE FOCUSED
ON THE FRONTAL BOUNDARY...WHICH SHOULD BE STRETCHED FROM THE
NORTHERN PLAINS INTO THE MIDWEST. A STRIPE OF 0.25 TO 0.50 INCHES
OF QPF WAS PLACED ALONG THE BOUNDARY.


...SOUTHERN PLAINS...

A MODERATELY MOISTURE RICH FLOW RIDING NORTH ON A LOW LEVEL
SOUTHERLY JET WILL PROVIDE FUEL FOR SCATTERED THUNDERSTORMS FOR
BOTH DAYS 2 AND 3 ACROSS THE SOUTHERN PLAINS. THE 00Z MODEL SUITE
CLUSTERED FAIRLY WELL CONCERNING THIS POTENTIAL... AND THE QPF WAS
BASED ON A 00Z ECMWF/GFS BLEND.

MOISTURE STREAMING NORTH FROM THE WESTERN GULF OF MEXICO ON THE
NOSE OF A 35 TO 40 KNOT LOW LEVEL SOUTHERLY JET WILL AID IN THE
DEVELOPMENT OF SCATTERED THUNDERSTORMS ACROSS TX INTO OK AND
KS...MAINLY ON AND AHEAD OF THE DRY LINE.  PRECIPITABLE WATER
VALUES NEAR 1.25 INCHES...AS WELL AS CAPPING AND CIN EARLY (AS
SHOWN BY MODEL SOUNDINGS) SHOULD LIMIT THE EXTENT OF THE
CONVECTION. HOWEVER...A WEAK SHORT WAVE MOVING OUT OF NORTHERN
MEXICO WILL PROVIDE SOME SYNOPTIC SCALE LIFT...PARTICULARLY OVER
TX. THIS WARRANTS AN AREA OF GENERALLY 0.25 TO 0.50 INCHES OF QPF
FOR MUCH OF CENTRAL TX INTO SOUTHWEST OK.

LESS SYNOPTIC SCALE FORCING ON DAY 3 PROBABLY MEANS LESS
THUNDERSTORM COVERAGE... AS THE AIRMASS REMAINS MORE OR LESS THE
SAME. THIS SHOULD YIELD QPF AMOUNTS OF 0.15 TO 0.25 INCHES ACROSS
NORTH TX INTO CENTRAL OK AND SOUTHEAST KS.


...MID ATLANTIC/NORTHEAST...

A SLOW MOVING LONG WAVE TROUGH WILL GO NEGATIVE AS IT CLOSES OFF
ACROSS THE MID ATLANTIC INTO THE NORTHEAST DURING DAYS 2 AND 3.
THERE HAS BEEN SOME MODEL SPREAD CONCERNING THE EVOLUTION OF THE
MID LEVEL PATTERN AND ATTENDANT SURFACE LOW...AND THIS WILL HAVE
BEARING ON QPF AMOUNTS AND THE PLACEMENT OF THE MAXIMUM. FOR THIS
FORECAST...A BLEND OF THE 00Z GFS/UKMET WAS USED FOR THE QPF...AND
THIS FORECAST NECESSITATES THE RETENTION OF THE SLIGHT RISK OF
EXCESSIVE RAINFALL AREA ACROSS PORTIONS OF NEW ENGLAND.

FOR DAY 2...THE LAST OF THE DEEPER MOISTURE AHEAD OF THE SURFACE
FRONT WILL EXIT EASTERN AND NORTHERN NEW ENGLAND. THE HIGHER
PRECIPITABLE WATER VALUES SHOULD SUPPORT 0.50 TO 0.75 INCHES OF
QPF ACROSS EASTERN MA AND EASTERN ME...WITH LIMITED CONVECTIVE
POTENTIAL AHEAD OF THE FRONT DUE TO CLOUDINESS. AFTER THIS...THE
QPF FOCUS BECOMES MORE SYNOPTICALLY DRIVEN...AS THE CLOSED LOW
MOVES NORTHEAST INTO NEW ENGLAND.

THE PROCESS BECOMES MORE FRONTOGENETICALLY DRIVEN ACROSS THE
HIGHER TERRAIN OF WESTERN NEW ENGLAND. THE FLOW AHEAD OF THE
CLOSED MID LEVEL SYSTEM SUPPORTS UPSLOPE FLOW FROM FROM WESTERN ME
AND NORTHERN NH INTO WESTERN MA AND CT. PRECIPITABLE WATER VALUES
REMAIN CLOSE TO AN INCH IN THIS AREA...AND THE QPF FORECAST
REFLECTS THIS. A STRIPE OF 0.50 TO 1.00 INCHES WAS PLACED IN THE
HIGHER TERRAIN MENTIONED ABOVE.

ON DAY 3...THE FRONTOGENETIC FORCING IS AGAIN FOCUSED ACROSS THE
HIGHER TERRAIN OF WESTERN AND CENTRAL NEW ENGLAND...AS THE CLOSED
LOW TRUNDLES NORTHEASTWARD. MODEL SOUNDINGS SHOW THE POTENTIAL FOR
ELEVATED INSTABILITY ACROSS WESTERN ME AND NORTHERN NH INTO
NORTHEAST VT...ENHANCING RAINFALL IN THE UPSLOPE FLOW. ONCE
AGAIN...PRECIPITABLE WATER VALUES NEAR 0.75 INCHES SUPPORT THE
POTENTIAL FOR HEAVY RAIN IN THESE AREAS. QPF AMOUNTS OF 0.75 TO
1.50 INCHES WERE PLACED IN WESTERN ME...NORTHERN H AND EASTERN VT.
THIS IS CLOSE TO THE THREE HOUR FLASH FLOOD VALUES IN THE
AREA...AND GIVEN THAT HEAVY RAIN WILL FALL HERE ON DAY 2...THE
SLIGHT RISK OF EXCESSIVE RAINFALL AREA WAS RETAINED.


TERRY/HAYES


GRAPHICS AVAILABLE ON THE WEB AT WWW.WPC.NCEP.NOAA.GOV