992  
FXUS04 KWBC 310928  
QPFPFD  
 
QUANTITATIVE PRECIPITATION FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
528 AM EDT THU MAY 31 2018  
 
FINAL 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 SE 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 SHORT-TERM RUNOFF ISSUES, ESPECIALLY ACROSS MUCH OF  
CENTRAL AND WESTERN MT.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page