394
FXUS04 KWBC 310714
QPFPFD
QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 AM EDT THU MAY 31 2018
PRELIM DAY 1, DAY 2 AND DAY 3 QPF DISCUSSION
VALID MAY 31/1200 UTC THRU JUN 03/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR
...LOWER-MID MISSISSIPPI VALLEY INTO THE LOWER OHIO AND TENNESSEE
VALLEYS...
ONGOING MCS OVER THE SOUTHERN PLAINS EARLY THIS MORNING (AND
ENSUING MCV) WILL CERTAINLY HAVE IMPLICATIONS ON THE NEW DAY 1 QPF
DOWNSTREAM INTO THE LOWER-MID MS VALLEY-LOWER OH VALLEY, AND TN
VALLEY. WHILE STILL SHOWING A A GOOD HEAVY RAINFALL FOOTPRINT, THE
SPREAD AMONG THE 00Z HIGH-RES CAM GUIDANCE (NOTABLY N-S) WAS LESS
THAN DESIRABLE FOR A DAY 1 PERIOD. THE WPC QPF INITIALIZED WITH
CONTINUITY AND A BLEND WITH THE NBM AND HREF MEAN, HOWEVER EVOLVED
TOWARD A NSSL-WRF/WRF-ARW2 COMBINATION LATE THU AND THU NIGHT.
LIKE THE IDEA FROM THESE MODELS OF 2 MAIN AXES OF HIGHER TOTALS,
THE FIRST ONE FARTHER SOUTH (ACROSS MUCH OF ARKANSAS) WHERE THE
INSTABILITY POOL IN THE WARM SECTOR SHOULD BE MORE THAN SUFFICIENT
(WHILE MID LEVEL CAPPING NOT AN INHIBITION) IN SUPPORTING A
DEVELOPING QLCS SOUTH OF THE MCV. THE OTHER QPF MAX WAS NOTED
ACROSS THE MID MS VALLEY, INCLUDING SOUTHEAST MO, SOUTHERN IL-IN,
AND WESTERN KY GIVEN THE BOLSTERED 850-700 MB MOISTURE
FLUX/THETA-E TRANSPORT OUT AHEAD OF THE MCV TRACK.
...LOWER GREAT LAKES / UPPER OHIO VALLEY / CENTRAL APPALACHIANS /
MID ATLANTIC...
AS THE TROUGH OVER THE UPPER MIDWEST TRANSLATES EASTWARD THIS
PERIOD, AND THE UPPER RIDGE AXIS PUSHES OFF THE ATLANTIC COAST, A
NORTHWEST-SOUTHEAST ORIENTED BOUNDARY AND THE LEADING EDGE OF A
VERY MOIST AIRMASS EXTENDING FROM THE MID-ATLANTIC FROM THE GREAT
LAKES IS EXPECTED TO MOVE NORTH THIS PERIOD. GUIDANCE SHOWS DEEP
MOISTURE SURGING NORTH ALONG THE CENTRAL APPALACHIANS AND
MID-ATLANTIC AS THE LOW LEVEL FLOW BACKS AHEAD OF THE APPROACHING
TROUGH. THIS MOISTURE ALONG WITH AFTERNOON HEATING AND THE LARGER
SCALE FORCING AFFORDED BY THE APPROACHING TROUGH (BROAD-SCALE
UPPER DIFLUENCE) IS EXPECTED TO SUPPORT AND INCREASING THREAT FOR
MODERATE TO LOCALLY HEAVY AMOUNTS FOCUSED ALONG THE HIGHER TERRAIN
AND AHEAD OF A COLD FRONT PUSHING ACROSS THE LOWER GREAT LAKES.
WPC QPF GAVE SIGNIFICANT WEIGHTING TO THE HREF MEAN THROUGH MOST
OF THE PERIOD.
...NORTHERN INTERMOUNTAIN WEST / NORTHERN ROCKIES AND HIGH
PLAINS...
AS AN UPPER LEVEL TROUGH CONTINUES TO AMPLIFY ACROSS THE
NORTHWEST, A DEVELOPING UPPER JET STREAK ACROSS SOUTHERN
ALBERTA-MANITOBA ALONG WITH AMPLE (ANOMALOUS) MOISTURE ALONG AND
EAST OF THE LOW-LEVEL FRONT WILL SUPPORT MID-HEAVY RAINFALL ALONG
THE EASTERN SLOPES OF THE NORTHERN ROCKIES AND SPREADING INTO THE
NORTHERN PLAINS. WPC QPF REFLECTS A CONSENSUS OF THE HI-RES MODELS
HERE AS WELL. THE SHEAR PROFILES SUPPORT MORE FORWARD (DOWNWIND)
PROPAGATION OF CONVECTION THAN OTHERWISE; HOWEVER, GIVEN THE
ANTECEDENT WET SOILS (RELATIVELY LOW FFG ACROSS MUCH OF THE
REGION), AREAS THAT RECEIVE THE HEAVIEST RAINFALL MAY EXPERIENCE
ISOLATED RUNOFF ISSUES IN THE SHORT TERM.
DAYS 2/3...
..PLAINS/MIDWEST
THE GUIDANCE SUGGESTS THAT A WET PATTERN IS IN STORE FROM THE
DAKOTAS/NEBRASKA EASTWARD INTO THE UPPER AND MIDDLE MISSISSIPPI
VALLEY IN A VERY DIFFLUENT PATTERN. THE HIGHEST AMOUNTS ARE
LIKELY TO BE WITHIN THE SOUTHERN PORTION OF SPLAYED
HEIGHT/THICKNESS PATTERN NEAR THE NE/KS BORDER EASTWARD IN THE
MID-MISSISSIPPI VALLEY DUE TO CONVECTIVE COMPLEXES HEMMED IN TO
THE SOUTH BY VERY WARM 700 HPA TEMPERATURES/A MID-LEVEL CAPPING
INVERSION. TO THE NORTH ACROSS THE UPPER MISSISSIPPI VALLEY AND
MIDWEST, SOME FRONTOGENESIS IN THE LOW- TO MID-LEVELS INTERACTS
WITH PROGRESSIVE ANOMALOUS MOISTURE ACROSS MN/IA TO YIELD HEAVY
PRECIPITATION. ON FRIDAY/FRIDAY NIGHT, THE PATTERN BEST RESEMBLES
A COMPROMISE OF THE 00Z GFS/12Z & 00Z ECMWF SOLUTIONS. FOR
SATURDAY/SATURDAY NIGHT, THE PATTERN IS A COMPROMISE OF THE 00Z
GFS AND A SOUTHWARD-ADJUSTED IN-HOUSE BIAS CORRECTED ENSEMBLE QPF.
FOR MN/WI, HEAVY AMOUNTS APPEARED UNCERTAIN AS, DESPITE A HIGHLY
FAVORABLE DIVERGENT FLOW PATTERN ALOFT AHEAD OF A NEGATIVELY
TILTED SHORTWAVE, LOW-LEVEL INFLOW APPEARS TO BE FADING -- AND IN
SOUTHERN WI DIVERGING -- AS THE SYSTEM BUTTS UP AGAINST A SMALL
PSEUDO REX BLOCK WITH THE SOUTHERN MEMBER NEAR THE MID-ATLANTIC
STATES CAUSING ISSUES IN THE LOW-LEVELS. KEPT AMOUNTS MODEST
THERE, FOR NOW. EXCESSIVE RAINFALL AREAS HAVE BEEN DEPICTED IN
THIS AREA BOTH DAYS, WITH A BROAD MARGINAL RISK TO ACCOUNT FOR
FORECAST UNCERTAINTY.
...TN VALLEY/CENTRAL APPALACHIANS/MID-ATLANTIC STATES
CONFLUENT FLOW AT 850 HPA ASSOCIATED WITH HIGH PRECIPITABLE WATER
VALUES AND A SLOWLY PROGRESSIVE FRONTAL BOUNDARY ARE EXPECTED TO
YIELD HEAVY RAINS FROM THE OH/WV/PA BORDER JUNCTION ON FRIDAY
AFTERNOON AND EVENING TO MD/NORTHERN VA/THE EASTERN SHORE SATURDAY
AFTERNOON/EVENING. A DEEP LAYER LOW IN THE MID-ATLANTIC STATES
SHOULD GENERATE HIGHLY EFFICIENT RAINFALL. USED A ROUGH
COMPROMISE OF THE 12Z & 00Z ECMWF/00Z GFS HERE BUT AMPED UP THE
VOLUME OF THE HEAVY RAINS TO FIT 00Z GFS MASS FIELDS TOWARDS THE
IN-HOUSE BIAS-CORRECTED ENSEMBLE QPF. EXCESSIVE RAINFALL AREAS
HAVE BEEN DEPICTED IN THIS AREA BOTH DAYS.
..FLORIDA
A SHORTWAVE MOVING ACROSS THE EASTERN GULF INTO FL IS EXPECTED TO
LEAD TO HEAVY RAINS ACROSS PORTIONS OF THE SOUTHERN AND CENTRAL FL
PENINSULA FRIDAY AFTERNOON/EVENING AS IT INTERACTS WITH SEA BREEZE
FRONTS MERGING IN THE WESTERN PENINSULA AND 2"+ PRECIPITABLE WATER
VALUES. AMOUNTS SHOULD LOWER SATURDAY AFTERNOON/EVENING WITHIN A
SLIGHTLY LESS MOIST AIRMASS ACROSS CENTRAL AND SOUTHERN SECTIONS
OF THE PENINSULA NEAR AND SOUTHEAST OF THE UPPER TROUGH. WENT FOR
BROADER COVERAGE SATURDAY MOST SIMILAR TO THE 00Z UKMET AS COOLER
AIR ALOFT SHOULD ALLOW FOR CONVECTION UP INTO THE CENTRAL
PENINSULA, UNLIKE THE MORE SUPPRESSED SOLUTIONS OF THE 00Z GFS/12Z
ECMWF.
HURLEY/ROTH
GRAPHICS AVAILABLE AT WWW.WPC.NCEP.NOAA.GOV/QPF/QPF2.SHTML
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