Quantitative Precipitation Forecast
Issued by NWS

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000 FOUS30 KWBC 300035 QPFERD EXCESSIVE RAINFALL DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 834 PM EDT MON MAY 29 2017 ...VALID 01Z TUE MAY 30 2017 - 12Z TUE MAY 30 2017... ...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL... MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM CHA 15 E CHA 20 E CHA 25 NNW AVL 15 SSE TNB 20 ESE UKF 10 NE INT TDF 10 WNW LHZ 15 SE RDU 30 NW UDG 30 NE DNL 20 SW HQU 20 ENE CSG 55 NW GZH 25 NNW MCB HEZ 10 NNW HEZ 25 NW HEZ 30 E MLU 35 ENE BQP 25 E GLH 20 WNW GWO 40 WSW TUP 20 NNW TUP 25 WNW MSL 25 NE MSL 15 NW MDQ 10 N MDQ 20 W CHA CHA. ...01 UTC UPDATE... ...NO CHANGES FROM THE PREVIOUS UPDATE... SCHICHTEL 1900 UTC UPDATE CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK ARE TO REMOVE THE MARGINAL RISK OVER PORTIONS OF SOUTH TX AS CONVECTION HAS DIMINISHED ACROSS THIS REGION. NO CHANGES MADE TO THE OTHER MARGINAL RISK AREA FROM THE LOWER MS VALLEY INTO THE SOUTHEAST AND SOUTHERN MID ATLANTIC. 1500 UTC UPDATE CHANGES TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK WERE TO CONCENTRATE THE LARGEST MARGINAL RISK AREA TO THE EAST AND NORTHEAST OF THE VORT MOVING EASTWARD ALONG THE CENTRAL GULF COAST. THIS AREA WILL HAVE THE BEST LARGE SCALE LIFT IN A REGION OF FAVORABLE RIGHT ENTRANCE REGION JET DYNAMICS. THE MARGINAL RISK AREA WAS EXTENDED SLIGHTLY TO THE NORTH AND NORTHEAST TO COVER THE MODEL SPREAD ACROSS THESE REGIONS. A SMALL MARGINAL RISK AREA WAS MAINTAINED OVER SOUTH TX FOR CURRENT SLOW MOVING CONVECTION FIRING IN THE WAKE OF THE ORGANIZED ACTIVITY THAT MOVED OFFSHORE EARLIER THIS MORNING. THIS ACTIVITY MAY MOVE ACROSS AREAS THAT RECEIVED HEAVY RAINS EARLIER. ORAVEC INITIAL DISCUSSION ...WESTERN GULF COAST NORTHEAST THROUGH THE LOWER MISSISSIPPI VALLEY AND INTO THE SOUTHEAST... THE SLOW-MOVING MID/UPPER LEVEL LOW ACROSS THE UPPER MIDWEST WILL MAINTAIN THE CONFLUENT UPPER FLOW AND RESULTANT JET AXIS ACROSS THE MID MS VALLEY INTO THE NORTHERN MID ATLANTIC-NORTHEAST REGION DURING THE DAY 1 PERIOD. THIS SETUP WILL CONTINUE TO REINFORCE THE QUASI-STATIONARY SURFACE BOUNDARY DRAPED FROM SOUTH TX ENE THROUGH THE LOWER MS VALLEY...TN VALLEY...AND LOWER MID ATLANTIC REGION. RAINFALL COVERAGE/INTENSITY ALONG AND SOUTH OF THIS BOUNDARY WILL REMAIN THE PRIMARY FORECAST CHALLENGE...ESPECIALLY GIVEN THE CONVECTIVE COMPONENT AS MID/UPPER LEVEL PERTURBATIONS (MCV/S) CONTINUE TO CAUSE WAVES ALONG THE FRONT ALONG WITH A RE-DISTRIBUTION OF DEEP LAYER FORCING. THE NON-NAM MODELS ARE IN FAIRLY GOOD AGREEMENT WITH THE MORE PRONOUNCED MCV ACROSS SOUTH TX EARLY MON LIFTING ENE ALONG THE WESTERN-CENTRAL GULF COAST LATER MON-MON NIGHT. THE NAM MEANWHILE IS AN OUTLIER SOLUTION IN THAT IT DEPICTS A MORE ELONGATED VORT LOBE STRETCHING NORTHWARD IN THE LOWER MS/LOWER TN VALLEY. THE TRACK OF THIS MCV... ALONG WITH ENHANCED DEEP-LAYER ASCENT/LOW-LEVEL FGEN WITHIN THE RIGHT ENTRANCE REGION OF PERIODIC UPPER JET STREAKS TRAVERSING THE MID MS VALLEY-OH VALLEY...WILL MAINTAIN A NON-UNIFORMITY OF FAVORABLE FORCING AND THUS A SOMEWHAT DISJOINTED PCPN PATTERN ALONG AND SOUTH OF THE SURFACE FRONT. WPC CONTINUED TO LEAN MORE HEAVILY ON THE HIGH-RES CAMS...WRF-ARW AND PARALLEL ARW IN PARTICULAR...WITH THE TIMING AND PLACEMENT OF AMOUNTS. DESPITE THE FAVORABLE THERMODYNAMIC PATTERN AHEAD OF THE FRONT (PWS 1.75-2.0+ INCHES...MIXED-LAYER CAPES AOA 1500-2000 J/KG)...ALONG WITH THE DYNAMICAL FORCING AHEAD OF THE MCV AND/OR WITHIN THE REGION OF FAVORABLE UPPER JET FORCING...THE RELATIVELY WEAK LOW-LEVEL INFLOW AND NEGLIGIBLE MOISTURE FLUX ANOMALIES WILL LIMIT THE PERSISTENCE OF HEAVY RAIN AREAS. MOREOVER...THE AIRMASS BEHIND THE DEPARTING MCV WILL LIKELY REQUIRE SEVERAL HOURS TO RE-DESTABILIZE. AS A RESULT...WPC WILL MAINTAIN ONLY A MARGINAL RISK FOR EXCESSIVE RAINFALL...WITH THE ANTICIPATION THAT ANY SHORT-TERM RUNOFF ISSUES WOULD BE ISOLATED AT MOST CONSIDERING THE CURRENT SOIL MOISTURE/FFG VALUES. HURLEY $$

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