Quantitative Precipitation Forecast
Issued by NWS

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000 FOUS30 KWBC 060059 QPFERD EXCESSIVE RAINFALL DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 858 PM EDT SUN JUL 05 2015 ...VALID 01Z MON JUL 06 2015 - 12Z MON JUL 06 2015... ...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL... SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM 10 ENE JKL 45 WNW HTS UNI 30 ENE PKB 25 SSW 2G4 25 WSW OKV 10 NNW CJR 10 ENE OFP 20 NE ORF NTU CPK RZZ 15 SE MTV 10 WSW GEV 20 S TRI 15 WNW TRI 10 ENE JKL. SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM 40 W CDR 25 ESE CUT 30 SSW PIR VVV 15 S ADC 15 NW XVG 15 N HIB 15 NW BFW 30 WNW ASX SGS 20 SSW AEL 10 W BNW 10 WSW HNR 25 ESE ONL 25 ENE ANW 50 ESE IEN 15 NNW AIA 30 N BFF 40 W CDR. ...PORTIONS OF THE NORTHERN PLAINS INTO THE UPPER MS VALLEY... 01Z TRENDS...CONVECTION HAD BEGUN TO BREAK OUT ALONG AND IMMEDIATELY NORTH OF THE SURFACE COLD FRONT ACROSS SD AND MN BY MID EVENING. THE PRE-FRONTAL ENVIRONMENT WAS RELATIVELY UNINTERRUPTED BY THUNDERSTORMS EXCEPT OVER WESTERN NEBRASKA. EARLY EVENING RUNS OF THE HRRR WERE CONSISTENT WITH EARLIER THINKING OF AN EXTENSIVE SWATH OF MODERATE TO HEAVY RAINFALL TO OCCUR OVERNIGHT WHERE A STRONG LOW LEVEL JET INTERSECTS THE FRONTAL ZONE NEAR THE NE/SD BORDER AND RUNS PARALLEL TO IT THROUGH SOUTHERN AND EASTERN MN. EXPECTATIONS MAY HAVE SHIFTED SLIGHTLY SOUTH...HOWEVER...BASED ON OBSERVATIONAL TRENDS OF A STRONGER PUSH ON THE FRONT...OWING TO THE LEAD WAVE THAT WAS GRAZING NORTHERN MN. THE HRRR PLACES HEAVIER RAINFALL DOWN INTO EASTERN NE AND WESTERN IA OVERNIGHT...CONSISTENT NOT ONLY WITH A FASTER COLD FRONT...BUT ALSO WITH THE INFLUENCE OF A DEEPLY MIXED WARM SECTOR ALLOWING FOR FORWARD PROPAGATION OF THUNDERSTORM CLUSTERS. THE OUTFLOW SHOULD HANG UP OR MOVE RELATIVELY MORE SLOW DURING THE PEAK OF THE LOW LEVEL JET CYCLE...PLACING A SOMEWHAT MORE FOCUSED RISK OF EXCESSIVE RAINFALL IN THE AREA SURROUNDING SOUTHEAST SD...INCLUDING ADJACENT PORTIONS OF NE/IA/MN. THE SLIGHT RISK AREA WAS EXPANDED SOUTHWARD...AND ITS NORTHERN EXTENT WAS REDUCED SOMEWHAT. PREVIOUS DISCUSSION...THE DIGGING OF THE SOUTHWESTERN CANADA H5 TROF INTO THE NORTHERN PLAINS/UPPER MS VALLEY WILL BE ACCOMPANIED BY A WELL DEFINED COLD FRONT. FRONTAL CONVERGENCE AIDED BY A WEAK AREA OF LOW PRESSURE MOVING ALONG THE FRONT SUNDAY NIGHT...WILL SUPPORT INCREASINGLY ORGANIZED CONVECTION WITH HEAVY RAINS. MOISTURE TRANSPORT BECOMES PARTICULARLY FOCUSED BY LATE EVENING OVER THE EASTERN HALF OF SOUTH DAKOTA AND SOUTHWEST MINNESOTA...AS LOW LEVEL JET WINDS STRENGTHEN TO 35-40 KNOTS AND MOISTURE POOLING / CONVECTIVE OVERTURNING PUSHES PRECIPITABLE WATER VALUES FROM NEAR 1.5 INCHES IN THE PRE-CONVECTIVE ENVIRONMENT UP CLOSER TO 2.0 INCHES DURING THE PRECIPITATION EVENT. MODEL MASS FIELDS WERE IN VERY GOOD AGREEMENT ON THIS DEVELOPING SYSTEM...LEADING TO RATHER HIGH CONFIDENCE IN THE RESULTING CONVECTIVE EVENT. INCH RAINFALL TOTALS LIKELY FROM EASTERN SD INTO MUCH OF MN...WITH SOME ISOLATED GREATER THAN 3 INCH AMOUNTS POSSIBLE. ...CENTRAL APPALACHIANS TOWARD SOUTHEAST VIRGINIA... A WELL DEFINED AND SMALL CLOSED OFF MID LEVEL SYSTEM OVER THE EASTERN TN VALLEY IS FORECAST SIMILARLY BY ALL OF THE LATEST MODEL GUIDANCE TO LIFT SLOWLY EAST-NORTHEASTWARD INTO THE CENTRAL APPALACHIANS/PARTS OF THE SOUTHERN MID ATLANTIC STATES BY MONDAY MORNING. A STATIONARY FRONT IN SOUTHERN VIRGINIA WILL BECOME A WARM FRONT...AND HAD ALREADY SERVED AS A FOCUS FOR DEEP CONVECTION LATE SUNDAY AFTERNOON. EXPECT SLOW MOVING CELLS ALONG THE WARM FRONT...TO EXHIBIT SOME SHEAR / PROPAGATION TO THE RIGHT...WHICH COULD LEAD TO TRAINING NEAR THE FRONT IN A MOISTURE RICH ENVIRONMENT. BACK WEST...INDIVIDUAL CELLS AND SMALL LINE SEGMENTS WILL CONTINUALLY ROTATE AROUND THE MID LEVEL LOW...WITH RAIN RATES DIURNALLY ENHANCED BY INSTABILITY EARLY SUNDAY EVENING. EACH OF THESE MECHANISMS FOR HEAVY RAIN FALL WILL OCCUR WHERE FLASH FLOOD GUIDANCE VALUES ARE LOW. ...SOUTHWEST U.S... IT WAS AN ACTIVE SUNDAY AFTERNOON AND EARLY EVENING OF MONSOONAL RAINFALL IN THE SOUTHWEST. CLOUD BASE INFLOW WAS NOT PARTICULARLY STRONG THROUGHOUT THE REGION...BUT MODERATE SURFACE DEWPOINTS AND MIXED LAYER CAPE VALUES...ESPECIALLY FROM SOUTHERN CO INTO WESTERN NM AND ALL OF AZ...HAD CONTRIBUTED TO ROBUST UPDRAFTS. WITH MEAN LAYER 0-6 KM WINDS OF 0-10 KNOTS...CELLS WERE VERY SLOW MOVING. SMALL SCALE OCCURRENCES OF MORE THAN AN INCH OF RAIN CAN BE EXPECTED...WITH AN ASSOCIATED RISK OF FLASH FLOODING. CONVECTIVE COVERAGE AND INTENSITY SHOULD DECREASE BEYOND 03Z AND BE MUCH REDUCED BY 06Z. BURKE/PEREIRA $$

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