918
FXUS04 KWBC 312230
QPFPFD
QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
629 PM EDT THU MAY 31 2018
FINAL DAY 1, DAY 2 AND DAY 3 QPF DISCUSSION
VALID JUN 01/0000 UTC THRU JUN 04/0000 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR
FOR THE 00Z QPF ISSUANCE, THERE WAS LITTLE CHANGE FROM THE 30/18Z
ISSUANCE. MINOR TWEAKS WERE MADE IN THE FIRST FORECAST PERIOD,
BASED PRIMARILY ON RADAR TRENDS AND TRENDS IN THE HRRR.
...LOWER-MID MISSISSIPPI VALLEY INTO THE LOWER OHIO AND TENNESSEE
VALLEYS...
ONGOING CONVECTION ACROSS THE LOWER OHIO VALLEY WILL CONTINUE TO
MOVE EAST TOWARD THE CENTRAL APPALACHIANS AS A SHORTWAVE
ASSOCIATED WITH OVERNIGHT CONVECTION OVER THE CENTRAL PLAINS
CONTINUES TO TRANSLATE EAST ACROSS THE REGION. THERE REMAINS A
GOOD MODEL SIGNAL FOR ADDITIONAL DEVELOPMENT FURTHER WEST BACK
ACROSS THE MID MISSISSIPPI VALLEY THIS AFTERNOON AS TRAILING
ENERGY MOVES OUT OF THE CENTRAL PLAINS. AS ENERGY ALOFT INTERACTS
WITH ANOMALOUS MOISTURE, THESE STORMS WILL HAVE THE POTENTIAL TO
PRODUCE HEAVY AMOUNTS. THE GFS SHOW PWS REMAINING AT OR ABOVE 1.5
INCHES (1-2 STANDARD DEVIATIONS ABOVE NORMAL) AHEAD OF FRONTAL
BOUNDARY EXTENDING SOUTHWEST FROM THE GREAT LAKES BACK INTO THE
CENTRAL PLAINS. THESE STORMS ARE EXPECTED TO PUSH EAST FROM THE
MID MISSISSIPPI INTO THE LOWER OHIO VALLEY. HOWEVER THE HI-RES
GUIDANCE SHOWS A GOOD SIGNAL FOR STORMS TO DEVELOP AND DROP SOUTH
ALONG A TRAILING OUTFLOW BOUNDARY WHICH IS FORECAST TO MOVE INTO
NORTHERN AND CENTRAL ARKANSAS OVERNIGHT. LOW LEVEL SOUTHWESTERLY
INFLOW INTO THE WESTERN FLANK OF THIS BOUNDARY MAY SUPPORT A
PERIOD OF BACK-BUILDING TRAINING CONVECTION, RESULTING IN LOCALLY
HEAVY TOTALS ACROSS THIS REGION. WPC QPF REFLECTS A BLEND OF THE
HREF MEAN WITH RECENT RUNS OF THE HRRR FOR THE AFTERNOON AND EVEN
PERIODS, WITH SIGNIFICANT WEIGHTING GIVEN TO THE HREF MEAN THROUGH
THE REMAINDER OF THE PERIOD.
...LOWER GREAT LAKES / UPPER OHIO VALLEY / CENTRAL APPALACHIANS /
MID ATLANTIC...
A WARM FRONT EXTENDING FROM THE GREAT LAKES THROUGH THE
MID-ATLANTIC STATES WILL PUSH NORTH THIS PERIOD WITH BACKING FLOW
SUPPORTING A SURGE OF DEEPER MOISTURE ALONG THE MID ATLANTIC
SEABOARD THIS AFTERNOON/EVENING. THIS WILL SUPPORT SHOWER AND
THUNDERSTORMS MOVING NORTH WITH A CONTINUED THREAT FOR ADDITIONAL
MODERATE TO HEAVY AMOUNTS EXTENDING TO THE SOUTH ACROSS THE
REGION. GIVEN THE ANOMALOUS MOISTURE, THERE REMAINS THE THREAT
FOR LOCALLY HEAVY AMOUNTS WITH THESE STORMS.
..NORTHERN INTERMOUNTAIN WEST / NORTHERN ROCKIES AND PLAINS
A WELL-DEFINED SHORTWAVE TROUGH WILL CONTINUE TO TRANSLATE EAST,
ASSUMING A NEGATIVE TILT AS IT PIVOTS ACROSS THE INTERMOUNTAIN
WEST INTO THE ROCKIES LATE THU INTO EARLY FRI. FAVORABLE UPPER
JET FORCING ALONG WITH LOW LEVEL CONVERGENCE/FRONTOGENESIS IS
EXPECTED TO SUPPORT WIDESPREAD LIGHT TO MODERATE AMOUNTS FROM THE
NORTHERN INTERMOUNTAIN WEST INTO THE NORTHERN ROCKIES AND HIGH
PLAINS THIS EVENING AND OVERNIGHT. THEN AS THE SYSTEM PIVOTS
FURTHER EAST, GUIDANCE SHOWS AN AMPLIFYING SOUTHERLY LOW LEVEL JET
SUPPORTING INCREASING PWS OF 1.5 INCH OR MORE ACROSS THE CENTRAL
DAKOTAS TOMORROW AFTERNOON-EVENING. THIS ALONG WITH APPROACHING
UPPER TROUGH IS EXPECTED TO SPUR THE THREAT FOR DEVELOPING SHOWERS
AND THUNDERSTORMS WITH HEAVY RAINS ACROSS PORTIONS OF THE DAKOTAS
AND NEBRASKA. WPC QPF GAVE SIGNIFICANT WEIGHT TO THE HREF MEAN
THROUGH THE PERIOD.
DAYS 2/3
..NORTHERN TO CENTRAL PLAINS TOWARD THE UPPER TO MID MS VALLEY
CONVECTION SHOULD BE ACTIVE AT THE BEGINNING OF THE DAY 2 PERIOD
AHEAD OF THE WELL DEFINED TROF PUSHING EAST ACROSS THE NORTHERN
AND CENTRAL PLAINS TOWARD THE MID TO UPPER MS VALLEY. GIVEN THE
OVERALL STRONG UPPER DYNAMICS AHEAD OF THIS TROF IN AN AXIS OF PW
VALUES 1.5 TO 2+ STANDARD DEVIATIONS ABOVE THE MEAN---CONFIDENCE
IS FAIRLY HIGH ON THE OVERALL POTENTIAL FOR WIDESPREAD MODERATE TO
HEAVY PRECIPITATION TOTALS STRETCHING ACROSS LARGE PORTIONS OF THE
NORTHERN TO CENTRAL PLAINS TOWARD THE UPPER TO MID MS VALLEY.
THERE ARE SOME SIGNIFICANT DIFFERENCES---HOWEVER--ON SOME OF THE
PLACEMENT DETAILS---ESPECIALLY AT THE BEGINNING OF THE DAY 2
PERIOD WITH HOW FAR TO THE SOUTH THE SOUTHERN PORTION OF THIS
ORGANIZED CONVECTION MAY BE. THE NAM CONEST AND NMMB WERE ON THE
FARTHER SOUTH END COMPARED TO MOST OF THE REMAINING GUIDANCE. CAN
NOT RULE OUT THE SOUTHERN SOLUTIONS GIVEN THE GENERAL MODEL BIAS
OF BEING TOO FAR NORTH WITH CONVECTION. DAY 2 QPF LEANED TOWARD
AN IN BETWEEN SOLUTION OFFERED BY IN HOUSE HI RES MEAN---SHOWING
THE SOUTHERN MAX IN THE VICINITY OF SOUTHEAST NE INTO NORTHEAST
KS---WHILE A SECOND NORTHERN MAX WAS SITUATED OVER THE EASTERN
DAKOTAS. THESE TWO AREAS SHOULD PROGRESS STEADILY EASTWARD
THROUGH THE REMAINDER OF THE DAY 2 PERIOD--POSSIBLE WEAKENING
SOMEWHAT POST 1200 UTC SATURDAY.
MODERATE TO HEAVY PRECIP THREAT WILL CONTINUE DAY 3 FOR POINTS
EASTWARD FROM THE MID TO UPPER MS VALLEY INTO THE GREAT LAKES.
LEANED CLOSER TO THE GFS AND ECMWF WHICH WERE SLIGHTLY FASTER THAN
SOME OF THE ENSEMBLE MEANS BUT SEEMED TO FIT BETTER THE EASTWARD
PUSH OF THE STRONG HEIGHT FALLS.
ACROSS THE SOUTHERN PLAINS---OUR FIRST IMPRESSION IS THAT MODELS
MAY BE UNDER DONE WITH CONVECTIVE POTENTIAL TOWARD THE END OF THE
DAY 2 PERIOD CONTINUING INTO THE DAY 3 PERIOD ALONG AND AHEAD OF
COLD FRONT PUSHING SOUTH THROUGH THE SOUTHERN PLAINS AND TOWARD
THE LOWER MS VALLEY. THE NAM AND GFS BOTH SHOW AN EXPANDING AREA
OF INSTABILITY AHEAD OF THE BOUNDARY FROM NORTHEAST TX INTO
SOUTHEAST OK...NORTHWEST AR TO SOUTHERN MO LATE DAY 2 CONTINUING
INTO EARLY DAY 3---WITH FORECAST MUCAPE VALUES PEAKING SHORTLY
AFTER 0000 UTC SUN IN THE 3000-4000 J/KG ACROSS THESE AREAS.
PRECIP WAS INCREASED TO AREAL AVERAGE MODERATE TOTALS DAY 3...
.25-.50"+ FROM NORTHEAST TX---FAR SOUTHEAST OK---CENTRAL TO
SOUTHERN AR---SOUTHEASTWARD TOWARD THE LOWER MS VALLEY. DAY 3 QPF
WAS DRAWN TO SHOW POTENTIAL FOR A FAIRLY ORGANIZED LINE OF
CONVECTION PUSHING SOUTHEASTWARD.
...SOUTHERN TO CENTRAL APPALACHIANS---MID-ATLANTIC INTO SOUTHERN
NEW ENGLAND...
HEIGHT FALLS IN A NORTHERN AND SOUTHERN STREAM MOVING IN TANDEM
LATE DAY 1 FROM THE GREAT LAKES INTO THE OH VALLEY WILL BEGIN TO
SEPARATE MORE DAY 2 WITH THE NORTHERN STREAM HEIGHT FALLS MORE
PROGRESSIVE ACROSS NEW ENGLAND---WHILE SOUTHERN STREAM HEIGHT
FALLS EXPECTED TO BE SLOWER FROM THE CENTRAL APPALACHIANS INTO THE
MID-ATLANTIC. THE MORE PROGRESSIVE NORTHERN STREAM HEIGHT FALLS
WILL FAVOR LIGHT TO LOCALLY MODERATE TOTALS--WHILE MODERATE TO
HEAVY TOTALS POSSIBLE DAY 2 FROM THE CENTRAL APPALACHIANS INTO THE
MID-ATLANTIC WHERE PW VALUES ARE EXPECTED TO RISE TO 2"+. THIS
SLOW MOTION OF THE MID LEVEL HEIGHT FALLS AND MUCH ABOVE AVERAGE
PW VALUES WILL PERSIST INTO DAY 3 FROM THE CENTRAL APPALACHIANS
INTO THE MID-ATLANTIC---WITH ADDITIONAL MODERATE TO HEAVY PRECIP
LIKELY ACROSS THESE AREAS. AN EXCESSIVE RAINFALL THREAT WILL
PERSIST DAY 2-3 ACROSS THE CENTRAL APPALACHIANS INTO THE
MID-ATLANTIC---ESPECIALLY DURING THE BEGINNING OF THE DAY 2 TIME
PERIOD WHEN INSTABILITY WILL BE GREATEST ALONG AND AHEAD OF THE
SOUTHWARD MOVING WEST TO EAST ORIENTED FRONT MOVING ACROSS THESE
REGIONS. INCREASING STABLE SURFACE CONDITIONS LIKELY DAY 3 ACROSS
THESE AREAS WITH MORE OF AN OVERRUNNING REGIME LIKELY.
..CENTRAL TO SOUTHERN ROCKIES
HEIGHT FALLS MOVING SLOWLY NORTHEASTWARD FROM THE SOUTHWEST TOWARD
THE FOUR CORNERS REGION DAY 3 WILL DRAW HIGHER PW VALUES NORTHWARD
INTO THE SOUTHERN TO CENTRAL ROCKIES. THIS SHOULD SUPPORT
INCREASING SCATTERED CONVECTION ACROSS THESE AREAS WITH LIGHT TO
MODERATE AREAL AVERAGE TOTALS DEPICTED.
..PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES
NORTHEAST PACIFIC HEIGHT FALLS ROTATING AROUND THE BASE OF THE
CLOSED LOW OFF THE ALASKAN PANHANDLE/B.C. COAST WILL PUSH AN
ASSOCIATED FRONTAL BOUNDARY TOWARD THE PACIFIC NORTHWEST DAY 3.
DAY 3 WPC QPF DID NOT DEVIATE FROM THE MODEL CONSENSUS OF LIGHT TO
MODERATE TOTALS FROM THE PACIFIC NORTHWEST INTO THE NORTHERN
ROCKIES.
PEREIRA/ORAVEC
GRAPHICS AVAILABLE AT WWW.WPC.NCEP.NOAA.GOV/QPF/QPF2.SHTML
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