651  
FXUS04 KWBC 050902  
QPFPFD  
 
QUANTITATIVE PRECIPITATION FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
500 AM EDT TUE JUN 05 2018  
 
PRELIM DAY 1, DAY 2 AND DAY 3 QPF DISCUSSION  
VALID JUN 05/1200 UTC THRU JUN 08/1200 UTC  
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR  
 
DAY 1  
   
..NORTHERN PLAINS - UPPER MS VALLEY
 
 
UPPER RIDGE AXIS PUSHES EAST OF THE NORTHERN PLAINS AND UPPER MS  
VALLEY REGION TUE NIGHT. IN ITS WAKE, AN UPTICK IN BROAD SCALE  
UPPER FORCING (DIVERGENCE ALOFT) WILL ENSUE, AND GET A  
CONSIDERABLE BOOST WITHIN THE RIGHT ENTRANCE REGION OF AN UPPER  
LEVEL JET STREAK TRAVERSING SOUTHERN ONTARIO. MEANWHILE, THE  
INCREASING (AND VEERING) NOCTURNAL LLJ WILL LEAD TO RAPID  
LOW-LEVEL MOISTURE/THETA E TRANSPORT AHEAD OF A SHARPENING FRONTAL  
ZONE. BOTH SYNOPTIC AND THERMODYNAMIC INDICATORS GIVE CREDENCE TO  
THE THE MULTI-MODEL SIGNAL OF A DEVELOPING MCS OVERNIGHT ALONG THE  
"RING OF FIRE", THOUGH AS IS TYPICAL, THE MODEL SOLUTIONS ARE NOT  
WELL CLUSTERED WITH RESPECT TO THE DETAILS IN TERMS OF MCS TRACK  
AND THUS AXIS OF HEAVIEST RAINFALL. WPC DID NUDGE THE QPF AXIS A  
LITTLE FATHER SOUTH FROM THE PREVIOUS FORECAST -- ESSENTIALLY IN  
LINE WITH THE BLEND OF THE WRF-ARW, ARW2, AND NSSL-WRF (ALL OF  
WHICH ALIGNED REASONABLY WELL, WHILE THE NAM CONUS NEST, WRF-NMMB,  
NBM, AND GLOBAL GUIDANCE WERE FARTHER NORTH. DESPITE THE FAIRLY  
VIGOROUS MID-LEVEL CAP, BASED ON CLIMO LIKE THE AFOREMENTIONED  
HIGH-RES DEPICTION OF THE HEAVY RAINFALL FOOTPRINT FARTHER SOUTH,  
ALONG AND NORTH OF THE SURFACE BOUNDARY WHERE THE COUPLING OF  
ROBUST DEEP-LAYER ELEVATED INSTABILITY AND MOISTURE TRANSPORT WILL  
BE MAXIMIZED NORTH-NORTHEAST OF THE 700 MB +12C ISOTHERM. ALSO  
SUPPORTING A MORE SOUTHERN SOLUTION OF THE MCS TRACK/HEAVIEST QPF  
WOULD BE THE DEGREE OF SOUTHWARD PROPAGATION OVERNIGHT, AS THE  
S=SW LLJ BEGINS TO EXCEED THE SPEED OF THE MEAN 850-300 MB FLOW.  
AT THIS POINT, THE PROGGED SHEAR PROFILES WOULD SUPPORT A  
PROGRESSIVE MCS; HOWEVER, MULTIPLE ROUNDS OF CONVECTION AS NOTED  
FROM THE ARW/ARW2 (FIRST ONE ALONG THE INITIAL WNW-ESE WARM  
FRONTAL BOUNDARY) COULD POSE A MORE ENHANCED FLASH FLOOD RISK  
ACROSS FAR NORTHEAST SD AND SOUTHEAST ND.  
 
   
..CENTRAL GULF COAST REGION
 
 
MID-UPPER SHORTWAVE TROUGH -- BOLSTERED EARLY IN THE PERIOD THE  
MCV OVER THE ARKLATEX -- WILL BE THE CATALYST FOR ADDITIONAL  
DIURNALLY-ENHANCED CONVECTION ALONG THE SURFACE STATIONARY FRONT  
SOUTH TOWARD THE GULF COAST. 0-6KM BULK SHEAR VALUES AOA 25 KTS  
ALONG WITH ROBUST DEEP-LAYER INSTABILITY (MUCAPES AT 2000-3000+  
J/KG) WILL SUPPORT MORE ORGANIZED, WIDESPREAD COVERAGE DURING THE  
AFTERNOON THROUGH MID EVENING AHEAD OF THE UPPER TROUGH, WITH THE  
SURFACE MOISTURE CONVERGENCE GETTING AN ADDED BOOST FROM THE  
DEVELOPING GULF BREEZES. DESPITE THE RELATIVELY HIGH 1-3 HOURLY  
FFG (GENERALLY 2.5-3.0" IN 1 HOUR AND 3-4" IN 3 HOURS), LOCALIZED  
TOTALS OF 3-5" WITHIN A FEW HOURS PER THE HIGH-RES CAMS WOULD  
SUPPORT A MARGINAL RISK OF EXCESSIVE RAINFALL, PARTICULARLY OVER  
PORTIONS OF SE LA GIVEN THE RELATIVELY WETTER ANTECEDENT SOILS  
(LOWER FFG VALUES).  
 
HURLEY  
 
DAY 2  
 
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE CENTRAL  
PLAINS...  
   
..NORTHERN ROCKIES TO CENTRAL PLAINS
 
 
WEAK SHORTWAVE ENERGY ROUNDING A BROAD MID-UPPER LEVEL RIDGE AXIS  
EXTENDING UP THE HIGH PLAINS WILL CROSS THE NORTH-CENTRAL GREAT  
PLAINS WEDNESDAY. A LOW LEVEL JET UNDER THE RIDGE WILL BRING GULF  
MOISTURE NORTH WITH 1.5 INCH PW OVER NE/IA WHICH IS TWO STANDARD  
DEVIATIONS ABOVE NORMAL. THE COMBINATION OF HIGH MOISTURE,  
INSTABILITY, AND MID LEVEL FORCING SHOULD BE ENOUGH TO BREAK THE  
CAP AND TRIGGER SCATTERED HEAVY THUNDERSTORMS THAT WILL SHIFT  
SOUTHEAST IN THE ANTICYCLONIC FLOW. MCS DEVELOPMENT IS LIKELY  
GIVEN THE STRONG INSTABILITY AND EXPECTED FORWARD PROPAGATION.  
 
QPF WAS BASED ON A BLEND OF THE 00Z GFS/NAM/ECMWF AND IN-HOUSE  
BIAS-CORRECTED BLEND. THE MARGINAL RISK IS FOR THE MAIN CONVECTIVE  
STORM BREEDING GROUND EAST OF THE SAND HILLS WHERE 6-HR FFG IS  
GENERALLY 2 TO 2.5 INCHES. PROGRESSION OF ORGANIZED/MCS ACTIVITY  
MAY NEED TO BE ACCOUNTED FOR IN SUBSEQUENT QPF AND ERO.  
 
   
..FLORIDA
 
 
A SWATH OF 1.75 INCH PW ALONG A STALLED FRONT WILL ALLOW HEAVY  
RAIN ACROSS CENTRAL FL. LIGHT EASTERLY MEAN FLOW COULD ALLOW  
REPEATING CELLS OFF THE GULF. FFG IS QUITE HIGH IN CENTRAL FL, SO  
FLASH FLOODING IS LIKELY LIMITED LOCALLY.  
 
DAY 3  
 
...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER THE CENTRAL  
PLAINS AND NORTHERN HIGH PLAINS...  
   
..NORTHERN ROCKIES TO CENTRAL PLAINS
 
 
WEAK SHORTWAVE ENERGY ROUNDING A BROAD MID-UPPER LEVEL RIDGE AXIS  
EXTENDING UP THE HIGH PLAINS WILL CROSS THE NORTHERN GREAT PLAINS  
THURSDAY. A WAKE FROM WEDNESDAY ACTIVITY SHOULD EXIST OVER THE  
NORTH-CENTRAL PLAINS THURSDAY WITH DEVELOPMENT LIKELY INITIATION  
ALONG REMNANT BOUNDARIES. 1.25 TO 1.5 INCH PW IS 1.5 TO 2 STANDARD  
DEVIATIONS ABOVE NORMAL. INSTABILITY IS PROGGED TO BE STRONGER  
OVER THE CENTRAL PLAINS THEN MT WHICH MAY ALLOW FOR GREATER MCS  
DEVELOPMENT. MORE DETAILS ON MESOSCALE PROCESSES ON SUBSEQUENT  
FORECASTS.  
 
QPF WAS BASED ON A BLEND OF THE 00Z GFS/NAM/ECMWF AND IN-HOUSE  
BIAS-CORRECTED BLEND. THE MARGINAL RISKS OVER MT AND NE/KS/IA IS  
BASED ON 00Z CONSENSUS FOR THE LOW POSITION ALONG WITH MORE  
SENSITIVE FFG.  
 
HURLEY/JACKSON  
 
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