Quantitative Precipitation Forecast
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FOUS30 KWBC 250102
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
901 PM EDT SAT SEP 24 2016

...VALID 01Z SUN SEP 25 2016 - 12Z SUN SEP 25 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NW CYBR 35 NNW MIB 30 W KHZE 15 NW HEI 60 N IKA 25 E MLS
35 NNW SDY 25 NNW CYEN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NNW MMCU 25 NW MRF FST 20 NNW BPG 20 E CSM 25 SW SLN
25 SSW BIE 20 NE SLB 15 NE AXN 15 NE SAZ SGS 20 ESE IIB
30 NNW IRK 20 NW SZL 20 E PPF 15 SW AQR 35 NNW 6R9 10 WSW UVA
50 NNW MMAN.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NNE MMCU 20 WSW MRF 40 SW 6R6 45 SSE MAF 25 NNE SNK
20 ESE LTS 15 NE JWG 25 NNE HUT 30 ESE BIE 20 E CIN 15 SW KACQ
20 NW CCY 15 SSE MIW 10 SE CNC 15 W CDJ 25 NNE CNU 15 ESE ADM
40 N JCT 50 SSW MMPG.


...01Z UPDATE...

ADJUSTMENTS TO THE PREVIOUS OUTLOOK BASED UPON RECENT
SATELLITE/RADAR TRENDS AS WELL AS THE RECENT RUNS OF THE
OPERATIONAL AND EXPERIMENTAL HRRR INCLUDE THE REMOVAL OF THE
MARGINAL RISK ACROSS SOUTHEAST TX.  ALSO CONSOLIDATED THE SLIGHT
RISK CENTERED OVER IA WITH THE AREA FURTHER TO THE SOUTH THAT
EXTENDED FROM THE CENTRAL TO THE SOUTHERN PLAINS INTO ONE AREA
THAT NOW INCLUDES PORTIONS OF EASTERN KS AND NEB AS WELL.  LATEST
RUNS OF THE HRRR SUGGEST THAT ONGOING TRAINING CONVECTION WILL
CONTINUE ACROSS PORTIONS OF THIS REGION...PROLONGING THE THREAT
FOR FLASH FLOODING INTO THE OVERNIGHT HOURS.

REFER TO MPD #697 FOR FURTHER INFO REGARDING THE ONGOING FLASH
FLOODING THREAT ACROSS PORTIONS OF THE CENTRAL OK AND KS.  REFER
TO MPD #696 AND FORTHCOMING MPD #697 FOR DETAILS CONCERNING THE
FLASH FLOODING THREAT ACROSS PORTIONS OF WEST TX.


...15Z UPDATE...

...IOWA AND SOUTHERN MINNESOTA...

COORDINATED WITH WFO MPX...ARX...DMX...DVN TO INTRODUCE SLIGHT
RISK OVER CENTRAL IOWA AND SOUTHERN MINNESOTA. PARTS OF THIS
REGION ARE DEALING WITH ONGOING RIVER FLOODING AND SATURATED
SOILS. SOME OF THE HEAVIER QPF IN THE MODELS IS A LITTLE CLOSE FOR
COMFORT...FALLING OVER WESTERN IOWA. THERE ARE SOME
REASONS...THOUGH...TO EXPECT CONVECTION FARTHER EAST MAY EXCEED
EXPECTATIONS...AS A WEDGE OF MODERATE CAPE WILL LIKELY FORM TODAY
IN BETWEEN THE SLOWLY RETREATING WARM FRONT OVER NORTHEAST IOWA
AND THE APPROACHING BROKEN LINES OF CONVECTION FROM THE WEST.
ALTHOUGH STRONGEST FOCUS FOR DEEP LAYER ASCENT LIFTS NORTHWARD
INTO MINNESOTA...THERE WILL BE AN INCREASINGLY HEALTHY FETCH OF
LOW LEVEL SOUTHERLY FLOW ADVECTING MOISTURE AND INSTABILITY INTO
NORTH-CENTRAL AND NORTHEAST IOWA AND SOUTHERN MINNESOTA...AND WE
MAY SEE HEAVIER MODEL QPFS TREND INTO THOSE AREAS.

FLASH FLOOD GUIDANCE IS AROUND ONE INCH IN AN HOUR...AND MAY NOT
BE FULLY REPRESENTATIVE AS PARTS OF THIS REGION RECENTLY RECEIVED
7 TO 14 INCHES OF RAIN...AND SWOLLEN RIVERS AND SATURATED SOILS
WILL CONTRIBUTE TO RAPID RUNOFF. AS NOTED BY THE
WFOS...THERMODYNAMICS FAVOR A DEEP WARM CLOUD LAYER...AND
PRECIPITABLE WATER VALUES RISE TO 3 STANDARD DEVIATIONS ABOVE
CLIMATOLOGY...ALL SUGGESTING AN EFFICIENT RAINFALL PROCESS EVEN IF
IT IS NOT ANCHORED...OR IS RELATIVELY SHORT LIVED AS THE UPPER
FORCING COMES THROUGH THIS EVENING / TONIGHT.


...CENTRAL-SOUTHERN PLAINS...

RISK AREAS INHERITED FROM THE 12Z ISSUANCE APPEAR TO BE NEARLY
IDEALLY PLACED. WE DID INTRODUCE A SMALL MARGINAL RISK OVER
SOUTHEAST TEXAS -SEE TEXT BELOW. WE ALSO EXPANDED THE RISK AREAS
IN NORTHWEST OKLAHOMA AND SOUTHWEST KANSAS A BIT TO CAPTURE
ONGOING ACTIVITY EARLY TODAY. CERTAINLY ANYWHERE ALONG THE LENGTHY
ZONE OF FORCED ASCENT AHEAD OF THE APPROACHING TROUGH THE WIND
PROFILES FAVOR SOME TRAINING AS CELLS LIFT NNE AND MERGE WITH LINE
SEGMENTS MOVING MORE NORTHEASTWARD. THE HRRR...HOWEVER...DOES
SUGGEST SOME OUTFLOW DOMINANCE OVER OKLAHOMA...ESPECIALLY AS THE
MORE PRONOUNCED SHORTWAVE LIFTS NORTHWARD...CAUSING SOME SUBTLE
VEERING IN THE MID LEVELS. THIS WOULD FAVOR SOME COMBINATION OF
THE 00Z NSSL WRF AND WRF-ARW...AND WHEN OVERLAYING A 50/50 BLEND
OF QPF FROM THOSE MODELS...THE EXISTING RISK AREAS LOOKED TO BE ON
TARGET.

...PREVIOUS...

A LINE OF MOD-HEAVY RAINFALL IS STILL ON TRACK ALONG AND AHEAD OF
THE COLD FRONT. THE MORE SIGNIFICANT/PROGRESSIVE HEIGHT FALLS WILL
PUSH ACROSS THE NORTHERN PLAINS INTO THE NORTHERN PLAINS DURING
THE PERIOD. GIVEN THE FASTER W-E FRONTAL PROGRESSION ALONG WITH
WEAKER AVAILABLE DEEP-LAYER INSTABILITY...RAINFALL AMOUNTS ACROSS
THE NORTHERN PLAINS INTO THE UPPER MS VALLEY WILL AVERAGE LESS IN
COMPARISON TO THE CENTRAL AND SOUTHERN PLAINS.

DESPITE THE SLOWER UPPER TROUGH/SURFACE FRONTAL PROGRESSION...WPC
DID LEAN TOWARD THE HIGH-RES GUIDANCE (WRF-ARW...NMMB...AND RGEM)
WITH RESPECT TO THE EASTWARD PROGRESSION OF THE HEAVY RAINFALL
AXIS OVER THE CENTRAL AND SOUTHERN PLAINS THIS AFTERNOON INTO
EARLY EVENING...GIVEN THE MORE ROBUST DEGREE OF PRE-FRONTAL
INSTABILITY (DEVELOPING COLD POOLS/OUTFLOW
BOUNDARIES)...INCREASING VERTICAL WIND SHEAR...AND TIGHTENING PW
GRADIENT. HOWEVER... EXPECT AN UPTICK IN PRE-FRONTAL LOW-LEVEL
INFLOW OVERNIGHT...WHILE BECOMING MORE ALIGNED WITH THE MEAN
850-300 MB FLOW. THIS WILL ALLOW FOR AN INCREASED POTENTIAL A
SLOWER QLCS PROGRESSION AND THUS CELL TRAINING...AS NOTED PER THE
WEAKENING CORFIDI VECTORS WHICH THE MODELS SHOW BECOMING MORE
EASTERLY WITH TIME OVERNIGHT (INDICATIVE OF THE INCREASING UPWIND
PROPAGATION). DESPITE THE WEAKENING DEEP-LAYER INSTABILITY DURING
THE OVERNIGHT HOURS...MUCAPES OF 1000-1500 J/KG ALONG WITH THE
FAVORABLE MOIST PROFILE (PWS OF 1.75-2.00") AND HIGHER LIKELIHOOD
OF CELL TRAINING WILL BE MORE THAN SUFFICIENT TO SUPPORT A SLIGHT
RISK IN THE EXCESSIVE RAINFALL OUTLOOK. IN TERMS OF THE QPF...WPC
UTILIZED A MULTI-MODEL ENSEMBLE WITH THE AREAL-AVERAGE AMOUNTS
(MAX STRIPE OF 1-1.5")...HOWEVER THE HIGH-RES CAMS SHOW POCKETS OF
MUCH HIGHER TOTALS (3-6") GIVEN THE AFOREMENTIONED FAVORABLE
THERMODYNAMIC AND KINEMATIC PROFILE...ESPECIALLY LATE SAT INTO
EARLY SUN.


...SOUTHEAST TEXAS...

THIS REGION REMAINS BENEATH THE CENTER OF A SMALL UPPER LEVEL
ANTICYCLONE...BUT AT LOW LEVELS INFLOW OFF THE GULF WILL CONTINUE
TO GRADUALLY INCREASE IN RESPONSE TO UPSTREAM HEIGHT FALLS...AND
RICH TROPICAL MOISTURE WAS IN PLACE THROUGHOUT THE COLUMN. DIURNAL
THUNDERSTORMS NEAR AND JUST INLAND FROM THE COAST WILL HAVE LITTLE
ORGANIZATION OWING TO WEAK SHEAR...BUT SUFFICIENT INFLOW AND SLOW
MOVEMENT...TO PERHAPS YIELD ISOLATED 2 TO 3 INCH RAIN AMOUNTS OVER
A SHORT PERIOD OF TIME. THOUGH THE REGION HAS BEEN GENERALLY
DRY...FLASH FLOOD GUIDANCE VALUES HAVE COME DOWN TO AROUND 2.5
INCHES PER HOUR WITH SIMILAR DIURNAL CONVECTION HAVING OCCURRED A
FEW DAYS IN A ROW. THE ODDS OF FLASH FLOODING ARE LOW...BUT WORTH
MENTIONING...AS A COUPLE OF THE HEAVIER DOWNPOURS COULD CAUSE
RAPID RUNOFF DEPENDING WHERE THEY FALL.


...NORTHERN ROCKIES...

CLOSED MID-UPPER LEVEL LOW OVER THE CENTRAL ROCKIES EARLY WILL
SLOWLY LIFT NORTHEAST INTO THE NORTHERN PLAINS TODAY AND TONIGHT.
THE N-S ORIENTED JET STREAK ON THE BACK SIDE OF THE TROUGH WILL
ENHANCE THE MID LEVEL DEFORMATION ON THE BACKSIDE OF THE
TROUGH...EVIDENCED BY THE NARROW N-S VORT LOBE (NARROW AXIS) JUST
BEHIND THE MAIN MID LEVEL VORT CENTER. AS A RESULT...WILL CONTINUE
TO SEE A RATHER ABRUPT END TO THE WESTWARD EXTENT OF THE COMMA
HEAD...THOUGH WHILE RELATIVELY NARROW THE ENHANCED FGEN WILL MAKE
FOR A PRODUCTIVE TROWAL IN TERMS OF PCPN
EFFICIENCY/PRODUCTION...PARTICULARLY THROUGH 00Z SUN. WITH PW
ANOMALIES STILL A HEALTHY 3 TO 4 STANDARD DEVIATIONS ABOVE NORMAL
DURING THAT TIME...THE MODELS (BOTH GLOBAL AND HIGH-RES) CONTINUE
TO DEPICT SOME RATHER ROBUST TOTALS ACROSS NORTHEAST WY INTO
EASTERN MT AND WESTERN ND. USING A MULTI-MODEL CONSENSUS...WPC
NOTED AREAL-AVERAGE AMOUNTS BETWEEN 1-2" ACROSS THIS AREA...WHILE
THE HIGH-RES CAMS SHOW ISOLATED POCKETS OF 3-4" OVER NORTHEAST WY
AND SOUTHEAST MT GIVEN THE UPSLOPE ENHANCEMENT WITH THE 850-700 MB
NORTHERLY FLOW. AS WOULD BE EXPECTED...DEEP-LAYER INSTABILITY WILL
BE SORELY LACKING OVER THIS REGION (AS THUS WILL SHORT-TERM
RAINFALL RATES)...AS CURRENT AND MODEL FORECAST CAPES OF ANY
SIGNIFICANCE (ABOVE 200 J/KG) WERE NOTED FARTHER EAST OF THE
TROWAL/MAX PCPN SHIELD...I.E. FARTHER EAST INTO THE DAKOTAS. AS A
RESULT...THE RISK FOR SHORT-TERM RUNOFF ISSUES WILL BE
MARGINAL/ISOLATED AT BEST.


PEREIRA/BURKE/HURLEY
$$





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