099
FXUS04 KWBC 010909
QPFPFD
QUANTITATIVE PRECIPITATION FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
508 AM EDT FRI JUN 01 2018
FINAL DAY 1, DAY 2 AND DAY 3 QPF DISCUSSION
VALID JUN 01/1200 UTC THRU JUN 04/1200 UTC
REFERENCE AWIPS GRAPHICS UNDER...PRECIP ACCUM - 24HR
..CENTRAL-NORTHERN PLAINS
A WELL-DEFINED SHORTWAVE TROUGH WILL CONTINUE TO TRANSLATE EAST,
ASSUMING A NEGATIVE TILT AS IT PIVOTS ACROSS THE NORTHERN ROCKIES
AND INTO THE CENTRAL-NORTHERN PLAINS. FAVORABLE UPPER LEVEL
FORCING (ROBUST UPPER DIFLUENCE AND RESULTANT DEEP-LAYER QS VECTOR
FORCING) WILL RESULT IN HIGHLY-ANOMALOUS 850-700 MB MOISTURE FLUX
INTO THE CENTRAL AND ESPECIALLY NORTHERN PLAINS ON FRIDAY. PW
VALUES (1.5+ INCHES) WILL BE EQUALLY AS IMPRESSIVE, AVERAGING
ABOUT 2-2.5 STANDARD DEVIATIONS ABOVE NORMAL. BY AFTERNOON,
700-500 MB LAPSE RATES BETWEEN 8-8.5 C/KM WILL FOSTER VIGOROUS
DEEP-LAYER INSTABILITY (MUCAPES 2000-3000+ J/KG). THE 00Z
GUIDANCE, ESPECIALLY THE HIGH-RES CAMS, CONTINUE TO SHOW A SIGNAL
FOR HEAVY (POTENTIALLY EXCESSIVE) RAINFALL ACROSS ND (ESPECIALLY
CENTRAL ND) LATE THIS AFTERNOON INTO THE EVENING AS THE SOUTHERLY
LOW-LEVEL INFLOW INCREASES TO 50+ KTS. THE HIGH-RES SIMULATED
REFLECTIVITY IN FACT SHOWS THE CONVECTION GROWING UPSCALE (QLCS)
WHILE THE EASTWARD PROGRESSION BEGINS TO SLOW DOWN A BIT DURING
THE EVENING (CORRESPONDING TO THE STRENGTHENING LLJ), WHICH OWING
TO THE STRENGTH OF THE UPWIND PROPAGATION, WOULD LEAD TO A GREATER
POTENTIAL FOR CELL TRAINING. AS A RESULT, WPC WILL MAINTAIN A
SLIGHT RISK IN THE DAY 1 ERO, WHICH IS SUPPORTED BY THE 00Z HREF
PROBABILITIES OF 3 HOURLY QPF EXCEEDING FFG (50-70+ PERCENT ACROSS
WESTERN-CENTRAL ND BETWEEN 21-03Z).
FARTHER SOUTH -- THE GUIDANCE ALSO DEPICTS A HEAVY RAINFALL
FOOTPRINT ACROSS PORTIONS OF THE CENTRAL PLAINS INTO THE LOWER MO
VALLEY -- ESPECIALLY FROM EASTERN NE-NORTHEAST KS INTO NORTHWEST
MO. THIS AREA OF CONVECTION IS EXPECTED TO BE TRIGGERED BY THE
COMPACT UPPER JET STREAK/ASSOCIATED VORT LOBE THAT WILL TRAVERSE
THE 4 CORNERS AREA THIS MORNING AND LIFT INTO THE CENTRAL HIGH
PLAINS THIS EVENING. IN THIS REGION, ALSO EXPECT RATHER ROBUST
DEEP-LAYER INSTABILITY (AGAIN LARGELY DUE TO THE STEEP MID-LEVEL
LAPSE RATES) AS OVER THIS AREA MUCAPES WOULD BE MORE LIKELY TO
EXCEED 3000 J/KG PER THE MODELS. THE MODELS SHOW THE SOUTHERLY LLJ
IN THIS REGION NOT AS STRONG COMPARED TO THE NORTHERN PLAINS,
WHILE ALSO DENOTING CONSIDERABLY MORE DEEP LAYER SHEAR (BOTH
DIRECTIONAL AND SPEED SHEAR). AS A RESULT EXPECT MORE
FORWARD/DOWNWIND PROPAGATION THAN OTHERWISE AS THE CONVECTION
GROWS UPSCALE DURING THE PEAK LATE-DAY HEATING -- HOWEVER GIVEN
THE STRENGTH OF THE THERMODYNAMIC PARAMETERS (INSTABILITY AND
ANOMALOUS DEEP-LAYER MOISTURE), THE RISK FOR 1-3 HOUR QPF>FFG
EXCEEDANCE WILL CONTINUE TO WARRANT A SLIGHT RISK IN THE DAY 1 ERO.
..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
(WEAK UPPER AGEOSTROPHIC DIVERGENCE AND DEEP LAYER QS VECTOR
CONVERGENCE) WILL FAVOR SCATTERED-WIDESPREAD CONVECTION ONCE AGAIN
TODAY, ESPECIALLY DURING THE PEAK HEATING HOURS FROM
LATE-AFTERNOON INTO EARLY EVENING, THOUGH ALSO WITH AN EARLY ONSET
(BY EARLY AFTERNOON) GIVEN THE ABSENCE OF A CAPPING INVERSION AND
THUS RELATIVELY LOW CONVECTIVE TEMPS. THE RELATIVELY LOW 0-6 KM
BULK SHEAR VALUES AGAIN WOULD SUPPORT MOSTLY LIMITED
UPSCALE/ORGANIZATIONAL GROWTH OUTSIDE OF PULSE-TYPE CLUSTERS WITH
LIMITED PERSISTENCE. ONE EXCEPTION WOULD BE OVER PORTIONS OF THE
DEEP SOUTH (NORTHERN AL-INTO NORTHWEST GA), WHERE THE HIGH-RES
CAMS SIMULATE MORE W-E ORIENTED CONVECTION LATER THIS AFTERNOON
AND EVENING, ON THE SOUTHERN PERIPHERY OF THE MID-LEVEL VORT LOBE
WHERE STEEPER 700-500 MB LAPSE RATES ARE EXPECTED TO LIE (BETWEEN
7-8 C/KM). THE LATEST HIGH-RES PROJECTIONS SHOW AN UPTICK IN THE
WSW LOW-LEVEL WIND (20-25 KTS AT 850 MB) ACROSS THIS REGION,
WHICH GIVEN THE WIND PROFILES ALOFT SUPPORT SOME UPWIND
PROPAGATION/BACKBUILDING AND THUS A HEIGHTENED RISK OF CELL
TRAINING. WPC NOTED A SLIGHT RISK AREA ACROSS THIS PARTICULAR
AREA, WHICH INCLUDES BHM, HSV, AND RMG.
ELSEWHERE TO THE N-NE, WPC INCLUDED ANOTHER MORE FOCUSED SLIGHT
RISK AREA ACROSS EASTERN PORTIONS OF THE OH VALLEY INTO THE
CENTRAL APPALACHIANS, SHENANDOAH VALLEY, BLUE RIDGE MTNS, AND INTO
PARTS OF THE PIEDMONT WHERE 1/3/6 HOURLY FFG VALUES REMAIN QUITE
LOW. GIVEN THE CONTINUED FAVORABLE DEEP SUBTROPICAL MOISTURE ALONG
WITH MODEST INSTABILITY (TALL/SKINNY CAPE DISTRIBUTION WITH
EQUILIBRIUM LAYERS AOA 45 KFT), THE HIGHLY-EFFICIENT SHORT-TERM
RAINFALL RATES, EVEN LESS THAN 1 HOUR, COULD CERTAINLY ECLIPSE
THESE LOW 1 HOURLY FFG VALUES DESPITE THE PULSE NATURE OF THE
CONVECTION.
DAYS 2/3
..UPPER TO MIDDLE MS VALLEY
A MID-LEVEL TROUGH OVER THE DAKOTAS SATURDAY MORNING BECOMES
NEGATIVELY TILTED AS IT SHIFTS EAST TO THE GREAT LAKES THROUGH
SATURDAY NIGHT. STRONG UPPER DYNAMICS AHEAD OF THIS THROUGH IN AN
AXIS OF PW 2 STANDARD DEVIATIONS ABOVE THE MEAN, CONFIDENCE IS
FAIRLY HIGH FOR WIDESPREAD MODERATE TO HEAVY PRECIPITATION MOVING
INTO THE UPPER TO MIDDLE MS VALLEY SATURDAY. NOTABLE DIFFERENCES
IN THE PLACEMENT AND STRENGTH OF THE UPPER TROUGH PERSIST IN THE
00Z MODEL SUITE, INCLUDING THE NUMBER OF AND LOCATION FOR MCS
ACTIVITY. INSTABILITY DECREASES NORTH WHILE DYNAMICS INCREASE
NORTH. MAINTAINED TWO SLIGHT RISKS OF EXCESSIVE RAINFALL FOR DAY 2
(12Z SAT-12Z SUN) WITH A NORTHWEST SHIFT IN LOCATION PER THE 00Z
GFS/NAM/ECMWF.
..SOUTHERN PLAINS TO GULF COAST
LOW LEVEL FORCING/A COLD FRONT PUSHES SOUTH THROUGH THE SOUTHERN
PLAINS AND TOWARD THE LOWER MS VALLEY SATURDAY. STRONG INSTABILITY
(MUCAPE PEAKING AROUND 00Z SUNDAY IN THE 3000-4000 J/KG RANGE)
TAKES ADVANTAGE OF GULF MOISTURE. EXPECT ORGANIZED CONVECTIVE
ACTIVITY TO SHIFT FROM OK/AR SATURDAY TO THE GULF COAST SUNDAY.
BETTER UPPER LEVEL FORCING NORTH SHOULD KEEP THE GREATER EXCESSIVE
RAIN RISK NORTH OF THIS AREA BOTH DAYS.
..SOUTHERN TO CENTRAL APPALACHIANS---MID-ATLANTIC
SLOW MOVING NEGATIVELY TILTED TROUGH CROSSES THE EASTERN CONUS
SATURDAY NIGHT THROUGH SUNDAY NIGHT. SLOW MOTION OF THE MID LEVEL
HEIGHT FALLS AND MUCH ABOVE AVERAGE PW VALUES WILL PERSIST BOTH
DAYS FROM THE CENTRAL APPALACHIANS INTO THE MID-ATLANTIC---WITH
ADDITIONAL MODERATE TO HEAVY PRECIP LIKELY ACROSS THESE AREAS. A
SLIGHT EXCESSIVE RAINFALL RISK IS MAINTAINED FOR THE CENTRAL
MID-ATLANTIC, PARTICULARLY SATURDAY WHEN INSTABILITY WILL BE
GREATEST ALONG AND AHEAD OF THE SOUTHWARD MOVING WEST TO EAST
ORIENTED FRONT MOVING ACROSS THESE REGIONS.
INCREASINGLY STABLE SURFACE CONDITIONS DAY 3 ACROSS THESE AREAS AS
AN OVERRUNNING REGIME SETS UP AS LOW PRESSURE STALLS ON THE
SOUTHERN MID-ATLANTIC COAST. A MARGINAL RISK WAS RAISED FOR MUCH
OF THIS REGION FOR DAY 3 (12Z SUN-12Z MON).
..CENTRAL TO SOUTHERN ROCKIES
A CUTOFF UPPER LOW DRIFTS NORTHEAST FROM YUMA SATURDAY. DESERT
INFLOW DOMINATES WITH LITTLE TO NO QPF ON DAY 2. HOWEVER, BY
SUNDAY THE OPENING LOW CROSSES THE FOUR CORNERS AND BEGINS TO DRAW
GULF MOISTURE TOWARD CO. MODEST INSTABILITY WITH DIFLUENCE ALOFT
ALLOWS CONVECTIVE THUNDERSTORMS OVER THE TERRAIN. NORTHERN NM
LOOKS PREFERRED AT THIS TIME WITH A MARGINAL RISK OF EXCESSIVE
RAINFALL INTRODUCED FOR DAY 3 (12Z SUN-12Z MON).
..PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES
A SHORTWAVE TROUGH SWINGS AROUND THE BASE OF A CLOSED LOW OFF BC
AND COMES ASHORE WITH 0.75 INCH PW OVER WA LATE SUNDAY. LIGHT TO
MODERATE RAINFALL IS EXPECTED ON DAY 3 FOR THE NORTHERN CASCADES
INTO NORTHERN ID PER 00Z MODEL CONSENSUS.
HURLEY/JACKSON
GRAPHICS AVAILABLE AT WWW.WPC.NCEP.NOAA.GOV/QPF/QPF2.SHTML
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