Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 270047
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
847 PM EDT WED JUL 26 2017

...VALID 01Z THU JUL 27 2017 - 12Z THU JUL 27 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NNE GBD 20 ESE ODX 25 NNE BVN 35 SSE YKN 25 NE SLB CCY
15 NW PDC 15 NW OVS 15 W FLD CAD 25 S OSC 25 SE BAX 25 SE CFS
10 ESE RNP GRR 15 NNW EKM 10 W FWA 10 WSW AID 20 S HUF BLV
40 SSW SZL 10 NW P28 10 NNE GBD.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 W SKX 20 NNW TEX 35 NNE MTJ 10 WNW EGE 40 ENE HDN 30 WSW LAR
15 S FNL 25 SSE GAG 60 W CVS CQC 20 W SKX.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 NW CMS 30 N EVW 20 W OGD 40 W SLC 30 S DPG CDC 20 WNW SGU
45 S P68 50 NNE WMC 40 NNW REO 25 SSW MEH 15 SSW DLN 10 NNW COD
25 SSW LND 30 NW CMS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 WSW LAA 20 ENE SPD 20 W GUY 30 NNE DUX 20 NE DHT 40 WNW CAO
15 WSW TAD 20 NNW VTP 40 E MYP 30 SW BJC 40 NE PUB 10 WSW LAA.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
BIE 15 WNW RDK 25 SSW DSM 10 NW AWG 10 NNE DVN 10 W RFD MDW
10 ENE IKK 10 SSW DNV 10 E MTO 20 NW 1H2 25 WNW SET COU
25 WSW IXD 25 SE SLN BIE.



...CENTRAL PLAINS ACROSS THE MID/UPPER MS VALLEY AND THE UPPER
GREAT LAKES..

TO THIS POINT...DEBRIS CLOUDINESS HAS STUNTED CONVECTIVE
DEVELOPMENT ACROSS PORTIONS OF NE/KS INTO SOUTHERN IA/NORTHERN
MO...WHERE INSTABILITY HAS YET TO RECOVER (NOTED THE SBCAPE UNDER
1000 J/KG ON THE 27/00Z KOAX SOUNDING). MOISTURE IS IN PLACE AHEAD
OF A FRONTAL BOUNDARY EXTENDING FROM WESTERN KS ACROSS EASTERN IA
(WITH A 2.40 INCH PRECIPITABLE WATER PEAK OVER SOUTHEAST NE INTO
NORTHERN MO...THOUGH THE 27/00Z KOAX SOUNDING WAS CLOSER TO 2.00
INCHES)...BUT THE LACK OF DEEPER INSTABILITY COULD PRECLUDE A
STRONGER FLASH FLOOD THREAT. MOST OF THE AVAILABLE HIGH RESOLUTION
GUIDANCE (EXCLUDING THE 26/18Z REGIONAL GEM AND 27/18Z NAM CONUS
NEST) ARE NOT NEARLY AS BULLISH WITH THE CONVECTIVE POTENTIAL HERE.

THE ABOVEMENTIONED MODELS SUGGEST A HEAVY RAIN THREAT REMAINS...AS
UPGLIDE OVER THE FRONT FOCUSES THE TROPICAL LIKE MOISTURE AND
MARGINAL INSTABILITY OVER NORTHERN MO...WHERE BOTH THE REGIONAL
GEM AND NAM CONUS NEST HAVE BULLSEYES OVER 5.00 INCHES. AS THE LOW
LEVEL JET INCREASES TO 25 TO 35 KNOTS ALONG AND NORTH OF THE
FRONT...THE ELEVATED CONVECTION COULD TAP THE DEEP MOISTURE AND
PRESENT A FLASH FLOOD THREAT. HOWEVER...OTHER THAN LOCAL 3.00+
INCH RAINFALL AMOUNTS...THIS APPEARS TO BE UNLIKELY GIVEN THE
CURRENT SETUP...AND THE CONSENSUS WAS TO DROP THE MODERATE RISK
BACK TO A SLIGHT RISK ACROSS EASTERN NE/NORTHEAST KS SOUTHERN IA
AND NORTHERN MO (THIS WAS COLLABORATED WITH WFOS OAX/EAX/DMX).
THERE IS STILL SOME POTENTIAL...ESPECIALLY IF THE ELEVATED
CONVECTION TRAINS NORTH OF THE BOUNDARY...BUT IT APPEARS AS THOUGH
THE THREAT THAT SUPPORTS A LARGER MODERATE RISK HAS ESSENTIALLY
PAST.

BASED ON RADAR TRENDS AND HIGH RESOLUTION GUIDANCE...THE SLIGHT
RISK AREA WAS PARED BACK ACROSS NORTHERN AND CENTRAL IA...AS THE
AIRMASS THERE HAS CHANGED...AND THE UPGLIDE MAXIMIZES SOUTH OF
THAT AREA (THIS CHANGE WAS COLLABORATED WITH WFO DVN). THE SLIGHT
RISK WAS LEFT IN PLACE ACROSS PORTIONS OF NORTHERN IL...SINCE ONE
AND THREE HOUR FLASH FLOOD GUIDANCE VALUES ARE AS LOW AS 1.50
INCHES.


...GREAT BASIN/ROCKIES...

DEEPER MOISTURE FROM THE CENTRAL PLAINS HAS REACHED EASTERN CO
THIS EVENING...AS THE 27/00Z KDNR SOUNDING SHOWED A PRECIPITABLE
WATER VALUE OF 1.35 INCHES. THE UPSLOPE COMPONENT OF THE FLOW IS
EXPECTED TO INCREASE THIS EVENING BEHIND THE FRONT...AND 00Z
SOUNDINGS INDICATE THERE SHOULD BE ENOUGH INSTABILITY TO SUPPORT
AN EXPANSION OF CONVECTION FROM CENTRAL AND SOUTHEAST CO INTO A
PORTION OF FAR WESTERN OK AND THE FAR NORTHERN PORTION OF NORTH TX
THROUGH 27/08Z. THE 850-300 MB FLOW BECOMES WEAKER WITH TIME
ACROSS THIS AREA...AND THIS COULD ALLOW THE CONVECTION THAT
DEVELOPS TO TRAIN...MAINLY ACROSS SOUTHEAST CO. SOME OF THE MOST
RECENT HIGH RESOLUTION GUIDANCE (SUCH AS THE LATEST RAP AND THE
18Z REGIONAL GEM/18Z NAM CONUS NEST) INDICATED THE POTENTIAL FOR
LOCAL 2.00+ INCH RAINFALL AMOUNTS HERE...AND SHORT TERM TRAINING
COULD PRODUCE THOSE RAINFALL AMOUNTS. ONE AND THREE HOUR FLASH
GUIDANCE VALUES ARE AS LOW AS 1.50 INCHES...SO THE SLIGHT RISK WAS
LEFT IN PLACE HERE THROUGH 27/12Z.

THERE IS SUFFICIENT MOISTURE AND INSTABILITY TO SUPPORT SCATTERED
CONVECTION ACROSS PORTIONS OF EASTERN OR/EASTERN NV INTO SOUTHERN
ID AND WESTERN WY TO JUSTIFY A MARGINAL RISK FOR THESE AREAS
THROUGH THE EVENING HOURS. MLCAPE VALUES BETWEEN 500-1000 J/KG
(SUPPORTED BY 27/00Z SOUNDINGS FROM KSLC AND KBOI) AND
PRECIPITABLE WATER VALUES NEAR AN INCH HAVE FED SCATTERED
CONVECTION...WITH THE GREATEST CONCENTRATION ACROSS SOUTHERN ID
AND PORTIONS OF EASTERN NV. THE STORMS ARE MOVING NORTHEAST WITH
THE MID LEVEL FLOW ON THE BACK SIDE OF THE MID LEVEL RIDGE...AND
PROPAGATION VECTORS BECOMING BETTER ALIGNED WITH THE 850-300 MB
WIND SUGGEST THAT TRAINING COULD BE AN ISSUE THROUGH ABOUT 02Z.
LACK OF INSTABILITY AND BETTER SYNOPTIC SCALE FORCING ARE EXPECTED
TO MITIGATE ANY LARGER SCALE FLASH FLOOD THREAT.

HAYES

$$





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