Quantitative Precipitation Forecast
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445
FOUS30 KWBC 260053
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
852 PM EDT THU AUG 25 2016

...VALID 01Z FRI AUG 26 2016 - 12Z FRI AUG 26 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 ENE MLF 45 W 4HV 60 W 4BL 30 SE PGA 60 E GCN 20 NNE INW
25 SE INW 20 WSW SOW 50 SW SOW 20 NNE FFZ 20 N DVT PRC 45 E IGM
65 NNE IGM 30 WNW SGU 70 WNW CDC 55 W MLF 25 ENE MLF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 E KGVX 15 E LBX 10 NNE SGR 20 SW UTS PSN 10 ESE SLR
35 SSE RKR RUE 10 N SGT 10 NNW GLH 25 S TVR 25 NW LFT
25 ESE KCRH.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
80 SW MRF 25 W MRF 60 S GDP 20 SSW GDP 20 NNW GDP 15 NE ALM
15 ESE 4MY 20 ESE 4SL 20 W E33 25 NE DRO 20 ESE CEZ 35 SSE CNY
15 W GJT 20 WSW EEO 15 NNE 20V 20 WSW PUM 10 SSE PUM BJC
10 SE MNH 40 E COS 30 W LHX 35 E TAD 25 ENE SPD 20 E GCK
30 ESE CNK 15 ESE FNB 10 N IRK 15 N PIA 20 SE BMI 20 ESE TAZ
25 SSE SUS 20 SE VIH 15 NW HRO MKO 10 ENE FSI 45 S CDS BPG
50 NNE 6R6 55 S 6R6 105 SSW 6R6 125 S E38.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 W IPT 25 N AOO 15 WNW JST AGC 10 SSE BVI YNG 15 NNE GKJ
10 E JHW 25 E BUF 20 ESE ROC ITH 10 W IPT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
EWK 10 WSW IXD 15 E LXT DMO 25 WSW AIZ 20 W SGF 20 S JLN
15 SE SWO CSM 30 WNW CDS 20 E PVW 25 W LBB 60 NNE HOB 30 SSE CVS
40 ESE TCC 20 NE DUX 40 W P28 EWK.


01Z UPDATE...

THE SLIGHT RISK AREA WAS ADJUSTED A BIT FURTHER SOUTH ACROSS THE
CENTRAL AND INTO THE SOUTHERN HIGH PLAINS WHERE AN AXIS OF
NUMEROUS SHOWERS AND THUNDERSTORMS HAVE SET UP IN VICINITY OF A
FRONT. THE LAST FEW RUNS OF THE HRRR HAS BEEN SUGGESTING A BIT OF
A SOUTHWARD SHIFT IN THE SW/NE ORIENTED AXIS OVERNIGHT...AND SO
HAVE FOLLOWED THESE TRENDS. ELSEWHERE...MINOR ADJUSTMENTS WERE
MADE TO THE MARGINAL RISK AREA TO ACCOUNT FOR THE LATEST SATELLITE
AND RADAR TRENDS.

18Z UPDATE...

ADJUSTED SLIGHT RISK AREA A BIT SOUTHWARD ACRS THE TX PANHANDLE
INTO OK/ERN KS/WRN MO GIVEN TREND OF LATEST HI RES GUIDANCE WHICH
HAVE COME SOUTH AS WELL DURING THE THUR OVERNIGHT PD.  THIS TREND
LOOKS REASONABLE GIVEN  LOCATION OF FRONTAL BNDRY AS OF 18Z AND
POOL OF GREATER THAN 1000 J/KG MLCAPES ALIGNING ALONG AND JUST
SOUTH OF THE FRONT.  STGR SFC HEATING SOUTH OF THE BNDRY HAS
ALLOWED CU FIELD TO EXPAND ALONG AND SOUTH OF THE FRONT FIRST
CELLS BEGINNING TO SHOW UP ACRS THE TX PANHANDLE AND WRN OK
SUPPORTING RECENT HRRR TRENDS.  SLIGHT STRENGTHENING OF UPR WINDS
AHEAD OF WELL DEFINED UPR CIRC OVER SRN NM SHOULD ENCOURAGE
FURTHER EXPANSION OF STORMS ALONG AND JUST NORTH OF THE SFC FRONT
DURING THE REMAINDER OF THE AFTN AND ESPECIALLY TONIGHT.  INFLOW
INTO THE FRONT MAY BE BALANCED BY DEEPER LAYERED FLOW FOR A PERIOD
OVERNIGHT SUPPORTING A SLOW MOVING OR NEARLY STATIONARY BAND OF
STGR CONVECTION FROM THE TX PANHANDLE NEWD THRU WRN OK/SE KS AND
NRN MO..ALSO SUPPORTED BY DECENT RT ENTRANCE REGION JET. SULLIVAN
PREVIOUS DISCUSSION FOLLOWS

SOUTHERN PLAINS INTO THE MIDWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE MAIN RAINFALL FOCUS ACROSS THE LOWER 48 STATES THIS PD WILL BE
ALONG SLOWLY PROGRESSIVE FRONTAL BNDRY WHERE A POOL OF DEEPER
MOISTURE LURED AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL
RIDGE WILL BE LURED WITH LOW LEVEL INFLOW IN THE 20-30 KTS RANGE
THURSDAY NIGHT.  THERE IS A MODERATELY STRONG CONSENSUS BETWEEN
THE GLOBAL AND MESOSCALE GUIDANCE ON A MORE FOCUSED HEAVY QPF AREA
DEVELOPING THURSDAY NIGHT IN SOUTHEAST KS INTO WESTERN MO AS A
SHORTWAVE PIVOTS THROUGH CO.  THIS SHOULD HELP INCREASE LOW LEVEL
JET WITH THE USUAL NOCTURNAL TIMING.  A FAVORABLY SLIGHTLY CURVED
UPPER JET MAXIMUM LIES TO THE NORTH. FAIRLY UNIDIRECTIONAL FLOW
COULD SUPPORT CELL TRAINING.  THE MESOSCALE (AND 00Z NAM) GUIDANCE
INDICATE THE POTENTIAL FOR LOCAL AMOUNTS IN THE 3-6" RANGE, WHICH
WOULD EXCEED FLASH FLOOD GUIDANCE VALUES ACROSS SOUTHEAST KS AND
WESTERN MO.  CONSIDERED A MODERATE RISK, BUT ENOUGH SPREAD EXISTED
IN THE GUIDANCE TO LEAD TO ENOUGH UNCERTAINTY TO MAINTAIN THE
PREVIOUS DAY 2 IDEA OF A SLIGHT RISK.


SOUTHERN GREAT LAKES/NY/PA
~~~~~~~~~~~~~~~~~~~~~~~~~~
A CONTINUATION OF THE ONGOING CONVECTIVE COMPLEX IS EXPECTED TO
MOVE EASTWARD ALONG AND JUST SOUTH OF THE SOUTHERN FRINGES OF THE
GREAT LAKES BEFORE BRIEFLY WEAKENING DURING THE MORNING HOURS.
PRECIPITABLE WATER VALUES OF 1.75"+ ALONG WITH SUFFICIENT
LOW-LEVEL INFLOW AND BUILDING INSTABILITY DUE TO DAYTIME HEATING
DURING THE LATE MORNING/AFTERNOON AND OUTFLOW BOUNDARIES WITH
OVERNIGHT/MORNING ACTIVITY SHOULD REFIRE CONVECTION FROM SOUTHEAST
MI/NORTHERN OH INTO NORTHERN PA AND SOUTHERN NY.  THE EXACT AXIS
OF THE HIGHEST AMOUNTS IN THIS REGION REMAINS IN QUESTION.  LOCAL
AMOUNTS IN THE 2-4" RANGE ARE INDICATED BY THE MESOSCALE GUIDANCE
IN THIS AREA, WHICH COULD EXCEED THE LOCAL FLASH FLOOD GUIDANCE
VALUES OVER A SEVERAL COUNTY AREA AROUND NORTHERN OH, SUGGESTING A
SLIGHT RISK.  UNCERTAINTY IN PLACEMENT OF THE QPF AXIS KEPT THIS
AREA IN THE MARGINAL RISK CATEGORY.


ROCKIES/GREAT BASIN/SOUTHWEST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
AN UPPER TROUGH AMPLIFYING ACROSS THE NORTHERN AND CENTRAL ROCKIES
WILL PROVIDE COOLING ALOFT, WHILE EMBEDDED WEAKER IMPULSES
INTERACTING WITH AVERAGE AMOUNTS OF MOISTURE FOR LATE AUGUST WILL
SUPPORT WIDESPREAD SCATTERED CONVECTION ACROSS MUCH OF THE
ROCKIES, GREAT BASIN, AND SOUTHWEST.  SOME LOCALLY ENHANCED
AMOUNTS WILL BE POSSIBLE ACROSS EASTERN CO DUE TO A MODEST UPSLOPE
COMPONENT.  THE MESOSCALE GUIDANCE INDICATES LOCAL AMOUNTS IN THE
2-3" RANGE ARE POSSIBLE, WHICH COULD EXCEED THE RELATIVELY LOW
FLASH FLOOD GUIDANCE VALUES IN CO AND CAUSE ROCK/MUD SLIDES IN
DESERT LOCATIONS.  SINCE ONLY A FEW SPOTS ARE EXPECTED TO SEE THIS
SORT OF RAIN, CONTINUED THE MARGINAL RISKS PREVIOUSLY SEEN IN THE
DAY 2 EXCESSIVE RAINFALL FORECAST.


LOUISIANA/ARKANSAS
~~~~~~~~~~~~~~~~~~
AN AXIS OF ABOVE AVERAGE PW VALUES MOVING WEST ALONG SOUTHERN
PERIPHERY OF SUBTROPICAL RIDGE -- ASSOCIATED WITH A DYING RELIC OF
A FRONTAL ZONE -- WILL MOVE INTO THE CENTRAL AND WESTERN GULF
COAST LEADING TO AN EXPANSION OF MAINLY DIURNAL THUNDERSTORMS.
THE MESOSCALE GUIDANCE SHOWS LOCAL AMOUNTS IN THE 2-4" RANGE,
WHICH WOULD CAUSE PROBLEMS IN ANY RIVER BASINS STILL EXPERIENCING
FLOODING FROM THE RAINS OF A COUPLE WEEKS AGO ACROSS SOUTHERN LA.
THIS INDICATES A SLIGHT RISK COULD BE WARRANTED.  HOWEVER, FLASH
FLOOD GUIDANCE VALUES HAVE NEARLY RECOVERED IN THE INTERIM AND THE
GUIDANCE INDICATE A RANDOM SMATTERING OF HIGHER AMOUNTS, DUE TO
THE PULSE THUNDERSTORM ENVIRONMENT EXPECTED.  MAINTAINED THE
MARGINAL RISK DUE TO THE LACK OF ORGANIZATION EXPECTED IN THIS
CONVECTIVE REGIME.

ORRISON/SULLIVAN/ROTH
$$





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