502  
FXUS04 KWBC 012049  
QPFPFD  
 
QUANTITATIVE PRECIPITATION FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
448 PM EDT FRI JUN 01 2018  
 
FINAL DAY 1, DAY 2 AND DAY 3 QPF DISCUSSION  
VALID JUN 02/0000 UTC THRU JUN 05/0000 UTC  
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR  
 
FOR THE 02/00Z QPF ISSUANCE: NOT MUCH IN THE WAY OF CHANGE TO THE  
01/18Z ISSUANCE. A FEW TWEAKS WERE MADE ACROSS NE AND ND, BASED  
MAINLY ON RADAR TRENDS (ND) AND TRENDS IN THE HRRR (NE).  
   
..CENTRAL-NORTHERN PLAINS AND UPPER MIDWEST
 
 
THERE REMAINS A GOOD MODEL SIGNAL FOR TWO DISTINCT AREAS OF  
MODERATE TO HEAVY RAINFALL DEVELOPING THIS AFTERNOON AND EVENING  
ACROSS THE NORTHERN AND CENTRAL PLAINS INTO THE MISSISSIPPI VALLEY  
AS STRONG UPPER DYNAMICS, DEEP MOISTURE AND INSTABILITY CONVERGE  
ACROSS THE REGION. THE LOW LEVEL JET IS EXPECTED TO AMPLIFY OVER  
THE CENTRAL AND NORTHERN PLAINS THIS AFTERNOON-EVENING AS A  
NEGATIVELY-TILTED UPPER TROUGH TRANSLATES EAST ACROSS THE NORTHERN  
AND CENTRAL ROCKIES. GUIDANCE SHOWS PWS INCREASING IN EXCESS OF  
1.5 INCHES ALONG A 40-50+ KT LOW LEVEL JET CENTERED ACROSS  
NEBRASKA AND THE DAKOTAS. THIS MOISTURE INTERACTING WITH AMPLE  
INSTABILITY AND THE AFOREMENTIONED TROUGH IS FORECAST TO SUPPORT  
DEVELOPING STORMS, PRODUCING HEAVY RAINS ACROSS THE DAKOTAS LATER  
THIS AFTERNOON. AS NOTED IN THE OVERNIGHT DISCUSSION, WITH THE  
STRENGTHENING LOW LEVEL JET, THE HI-RES MODELS CONTINUE TO SHOW A  
PERIOD OF SLOWER EASTWARD PROGRESSION/CELL TRAINING - RAISING THE  
POTENTIAL FOR HEAVY AMOUNTS FLASH-FLOODING ACROSS THIS REGION.  
DURING THE OVERNIGHT HOURS, THE GENERAL MODEL CONSENSUS SHOWED  
CONVECTION MOVING MORE PROGRESSIVELY EASTWARD ACROSS EASTERN NORTH  
DAKOTA INTO MINNESOTA WITH A GENERAL DOWNWARD TREND IN RAINFALL  
RATES AS A DEVELOPING CONVECTIVE COMPLEX TO THE SOUTH BEGINS THE  
INTERRUPT THE INFLOW OF DEEPER MOISTURE. WPC QPF LARGELY UTILIZED  
THE HREF MEAN AS STARTING POINT ACROSS THIS REGION.  
 
FURTHER TO THE SOUTH, THERE REMAINS A STRONG SIGNAL FOR A  
CONVECTIVE COMPLEX DEVELOPING AND TRACKING SOUTHEAST FROM CENTRAL  
NEBRASKA TOWARD THE MID MISSISSIPPI AND LOWER MISSOURI VALLEYS  
OVERNIGHT. RECENT RUNS OF THE RAP SHOW PWS INCREASING TO AROUND 2  
INCHES ON THE NOSE OF 50 KT SOUTHERLY INFLOW. UPON ORGANIZING,  
THIS SYSTEM SHOULD BECOME FAIRLY PROGRESSIVE, HOWEVER STRONG  
SOUTHWESTERLY INFLOW MAY PROMOTE A PERIOD OF BACKBUILDING/TRAINING  
CONVECTION, FURTHER RAISING THE THREAT FOR HEAVY AMOUNTS ACROSS  
PORTIONS OF CENTRAL NEBRASKA TO NORTHEAST KANSAS AND NORTHERN  
MISSOURI. CONVECTION IS EXPECTED TO WANE AS THE COMPLEX CONTINUES  
FURTHER SOUTHEAST TOWARD THE LOWER OHIO AND TENNESSEE VALLEYS  
DURING THE MORNING HOURS ON SATURDAY. HOWEVER MODELS SHOW  
CONVECTION REDEVELOPING LATER IN THE DAY ALONG AND AHEAD OF COLD  
FRONT PUSHING FROM THE PLAINS INTO THE MISSISSIPPI VALLEY. DURING  
THE FRI EVENING INTO THE OVERNIGHT HOURS, WPC QPF REFLECTS A  
NORTHWARD SHIFT IN HEAVIER AMOUNTS, SIMILAR TO THE HREF MEAN.  
HOWEVER, DID NOT GO AS FAR NORTH AS THE HRW-ARW AND NSSL-WRF RUNS,  
BUT INSTEAD GAVE MORE WEIGHT TO THE MORE SOUTHERLY HRW-NMMB AND  
NAM CONEST SOLUTIONS ACROSS NEBRASKA INTO KANSAS AND MISSOURI  
OVERNIGHT.  
   
..EASTERN U.S.
 
 
SLOW-MOVING, POSITIVELY-TILTED UPPER TROUGH WILL NUDGE EASTWARD  
TOWARD THE ATLANTIC COAST BY SATURDAY. UNTIL THEN, A BROAD AREA OF  
MODEST DYNAMICAL FORCING EAST OF THE TROUGH AXIS AND SURFACE FRONT  
WILL FAVOR SCATTERED-WIDESPREAD CONVECTION ONCE AGAIN TODAY,  
ESPECIALLY DURING THE PEAK HEATING HOURS FROM LATE-AFTERNOON INTO  
EARLY EVENING. THIS MAY RAISE ADDITIONAL FLASH FLOODING CONCERNS,  
PARTICULARLY ACROSS PORTIONS OF THE CENTRAL APPALACHIAN INTO THE  
MID-ATLANTIC REGION WHERE FLASH FLOOD GUIDANCE VALUES ARE QUITE  
LOW GIVEN THE RECENT HEAVY RAINS IMPACTING THE REGION.  
 
THEN ON SATURDAY MODELS SHOW ENERGY OVER THE GREAT LAKES DROPPING  
SOUTHEAST INTO THE MID-ATLANTIC, SUPPORTING SURFACE LOW  
DEVELOPMENT ALONG THE DELARMVA COAST. DEEP MOISTURE POOLING NEAR  
THE CENTER WILL FUEL AN INCREASING THREAT FOR DEVELOPING MODERATE  
TO HEAVY RAINS ACROSS THE MID-ATLANTIC REGION DURING THE AFTERNOON  
INTO THE EVENING HOURS.  
 
DAYS 2  
 
   
..UPPER MS VALLEY INTO THE GREAT LAKES
 
 
FOR DAY 2---MODELS ARE FAIRLY SIMILAR IN TAKING AN INCREASINGLY  
NEGATIVELY TILTED TROF EASTWARD FROM THE UPPER MS VALLEY THROUGH  
THE GREAT LAKES. THERE ARE SOME TIMING DIFFERENCES THAT BEGIN TO  
DEVELOP WITH THIS TROF TOWARD THE END OF DAY 2 THAT HAVE  
CONSEQUENCES WITH QPF TIMING AMONG THE MODELS. THE TYPICALLY MORE  
PROGRESSIVE GFS IS AMPLIFYING THE SOUTHERN PORTION OF THIS  
NEGATIVELY TILTED TROF MORE THAN THE REMAINDER OF THE GUIDANCE AND  
IS SUBSEQUENTLY SLOWER. GIVEN ITS OUTLIER STATUS DAY 2---WE  
TRENDED MORE PROGRESSIVE WITH THE QPF DETAILS. WITH PW VALUES  
EXPECTED TO BE ABOVE AVERAGE ALONG AND AHEAD OF THIS TROF AND THE  
ASSOCIATED FRONTAL BOUNDARY---MODERATE TO ISOLATED HEAVY PRECIP  
TOTALS POSSIBLE. THE GFS BESIDES BEING SLOW IS ALSO SHOWING A  
MORE WIDESPREAD AREA OF HEAVY PRECIP OVER PORTIONS OF THE UPPER MS  
VALLEY INTO THE UPPER LAKES. DAY 2 QPF LEANED TOWARD A MORE TONED  
DOWN VERSION AND MORE PROGRESSIVE---SHOWING AREAL AVERAGE  
.25-.50"+ AMOUNTS ACROSS THESE AREAS. L  
   
..MID TO LOWER MS VALLEY INTO THE SOUTHERN PLAINS
 
 
SCATTERED CONVECTION LIKELY SOUTH AND SOUTHWESTWARD ALONG THE  
FRONTAL BOUNDARY EXTENDING INTO THE SOUTHERN PLAINS. DYNAMICS ARE  
NOT AS STRONG ALONG THIS PORTION OF THE FRONT BUT INSTABILITY IS  
MUCH GREATER---ESPECIALLY AT THE BEGINNING OF DAY 2. MODERATE  
AREAL AVERAGE TOTALS DEPICTED WITH ISOLATED HEAVY AMOUNTS POSSIBLE  
WHERE CONVECTION DOES BECOME ORGANIZED.  
 
...SOUTHERN TO CENTRAL ROCKIES..  
 
THE UPPER TROF THAT MOVES NORTHEASTWARD INTO THE SOUTHWEST DAY 1  
WILL CONTINUE TO MOVE NORTHEAST DAY 2 INTO THE FOUR  
CORNERS/SOUTHERN TO CENTRAL ROCKIES REGION. THIS SYSTEM WILL HELP  
DRAW INCREASING PW VALUES NORTHWARD THROUGH THE SOUTHERN TO  
CENTRAL ROCKIES AND SOUTHERN HIGH PLAINS. THIS WILL SUPPORT  
INCREASING CONVECTION ACROSS THESE AREA SUNDAY AFTERNOON IN A  
REGION OF FAIRLY WELL DEFINED UPPER DIFLUENCE AHEAD OF THESE  
HEIGHT FALLS. THE GENERAL MODEL CONSENSUS IS FOR AREAL AVERAGE  
MODERATE TOTALS WITH ISOLATED HEAVY AMOUNTS POSSIBLE.  
   
.CENTRAL APPALACHIANS INTO THE MID-ATLANTIC
 
 
THE SLOW MOVING MID TO UPPER LEVEL TROF MOVING OUT OF THE CENTRAL  
APPALACHIANS INTO THE MID-ATLANTIC DAY 1 WILL CONTINUE TO PRESS  
SLOWLY EASTWARD ACROSS THE MID-ATLANTIC DAY 2. WHILE THERE IS A  
TYPICAL AMOUNT OF SPREAD FOR DAY 2 WITH THE EXACT AXIS OF THIS  
PRECIP AREA---THERE IS CONSENSUS FOR ADDITIONAL MODERATE TO HEAVY  
TOTALS ACROSS THESE AREAS AND THE CONTINUATION OF POTENTIAL FOR  
LOCAL RUNOFF ISSUES GIVEN LOW FFG VALUES ACROSS THIS AREA.  
 
DAY 3  
 
...EASTERN GREAT LAKES---NORTHERN MID-ATLANTIC INTO SOUTHERN NEW  
ENGLAND...  
 
THE DAY 2 ISSUES WITH THE STRENGTH OF THE SOUTHERN PORTION OF THE  
ELONGATED TROF OVER THE GREAT LAKES CONTINUES AS THIS TROF PUSHES  
EASTWARD ACROSS THE EASTERN GREAT LAKES---NORTHERN MID-ATLANTIC  
AND INTO NEW ENGLAND. THE GFS CONTINUES MORE AMPLIFIED AND SLOWER  
WITH THE TROF AND HEAVIER WITH THE PRECIP AHEAD OF IT---ESPECIALLY  
FROM THE COASTAL NORTHERN MID-ATLANTIC---EASTERN NY STATE INTO  
SOUTHERN NEW ENGLAND. THERE ARE A VARIETY OF QPF SOLUTIONS ACROSS  
THESE AREAS FROM THE HEAVY GFS TO THE DRY NAM AND SOLUTIONS IN  
BETWEEN. NOT WANTING TO FAVOR EITHER OF THE OUTLIER SOLUTIONS  
HERE---DAY 3 QPF LEANED FOR LIGHTER PRECIP THAN THE GFS BUT  
HEAVIER THAN THE NAM ACROSS THESE AREAS---MORE IN LINE WITH THE  
LATEST ECMWF (1200 UTC)---DEPICTING .25-.50"+ AMOUNTS. TIMING  
WISE...ALSO TRENDING FASTER THAN THE GFS TOWARD THE LATEST ECMWF.  
   
..SOUTHERN TO CENTRAL HIGH PLAINS
 
 
HEIGHT FALLS MOVING INTO THE SOUTHERN TO CENTRAL ROCKIES DAY 2  
WILL PRESS EASTWARD INTO THE CENTRAL TO SOUTHERN HIGH PLAINS DAY  
3. STRENGTHENING SOUTHERLY LOW LEVEL FLOW AHEAD OF THESE HEIGHT  
FALLS WILL SUPPORT INCREASING PW VALUES AND INCREASING CHANCES OF  
ORGANIZED CONVECTION MOVING EASTWARD INTO THE SOUTHERN TO CENTRAL  
HIGH PLAINS. MODEL ARE SHOWING POTENTIAL FOR BOTH A NORTHERN AND  
SOUTHERN AREA OF ORGANIZED PRECIP DAY 3. NOT A LOT OF CONFIDENCE  
IN EXACT PLACEMENT---BUT MODERATE TO LOCALLY HEAVY TOTALS POSSIBLE  
AS THE HEIGHT FALLS PUSH EAST DAY 3.  
 
PEREIRA/ORAVEC  
 
GRAPHICS AVAILABLE AT WWW.WPC.NCEP.NOAA.GOV/QPF/QPF2.SHTML  
 

 
 
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