Quantitative Precipitation Forecast
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FOUS30 KWBC 151905
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 PM EDT MON MAY 15 2017

...VALID 1904Z MON MAY 15 2017 - 12Z TUE MAY 16 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
AMW 15 E SUX 30 SE ANW 25 SE BFF 50 NE DGW 35 E JDN 25 NW ISN
15 N KBAC 15 SE BFW 30 WSW CMX 15 NW P75 GOV 10 N EKM 15 SE LOT
10 SW IOW AMW.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WSW LDM 10 SE RAC 10 SE OVS MCW 15 NW SPW 10 WSW MWM
15 NW JYG STP 25 S RCX GRB 20 WSW LDM.


18Z UPDATE:

AS OF 18Z CURRENTLY HAVE ELEVATED CONVECTION OVER PORTIONS OF
IA/MN/WI. EXPECT THIS ACTIVITY TO CONTINUE TO MOVE EAST THIS
AFTERNOON...WITH THE NORTHERN EXTENT OF THE CONVECTION GENERALLY
LOSING INTENSITY BY THIS EVENING AS IT LEAVES THE INSTABILITY AND
BEGINS MOVING FROM EASTERN WI INTO MI. SHOULD SEE SOME SURFACE
BASED DEVELOPMENT ON THE SOUTHERN EDGE...WITH A POTENTIAL LINE
MOVING EAST SOUTHEAST ACROSS IA/IL. LOCALLY HEAVY RAINFALL RATES
ARE POSSIBLE WITH THIS ACTIVITY...ALTHOUGH IN GENERAL THE
PROGRESSIVE NATURE OF CONVECTION SHOULD LIMIT THE OVERALL FLASH
FLOOD THREAT.

THE BIGGER FLASH FLOOD CONCERN MAY END UP DEVELOPING THIS EVENING
INTO TONIGHT BEHIND THIS INITIAL BATCH OF CONVECTION ALONG A WEST
TO EAST WARM FRONT. A GROWING CONCERN THAT WE COULD SEE A WEST TO
EAST BAND OF TRAINING ELEVATED CONVECTION DEVELOP NEAR THE 850MB
FRONT AS LOW LEVEL FLOW INCREASES THIS EVENING. THE STRONG LOW
LEVEL FLOW RESULTS IN CORFIDI VECTORS FROM NORTH TO SOUTH INTO THE
FRONT..SUGGESTIVE OF BACKBUILDING/TRAINING. EVENTUALLY THE FRONT
WILL GET PUSHED NORTH AS BETTER HEIGHT FALLS BEGIN TO MOVE INTO
THE PLAINS. HOWEVER THERE COULD BE ENOUGH OF A PERIOD OF POTENTIAL
TRAINING TO CAUSE SOME FLOODING CONCERNS. THE LAST SEVERAL RUNS OF
THE HRRR EXPERIMENTAL SEEMS TO DEPICT THIS SOLUTION PRETTY WELL.
THE 12Z HRW ARW AND NSSL ARW ALSO BOTH SHOW THIS SIGNATURE...WITH
JUST SOME DIFFERENCES WITH REGARDS TO THE LATITUDE OF THE
TRAINING. THINK THE THREAT EXIST FOR ISOLATED TO SCATTERED 2-5"
AMOUNTS ACROSS PORTIONS OF FAR NORTHERN IA INTO SOUTHEAST MN AND
SOUTHERN/CENTRAL WI WITH THIS EVENING/OVERNIGHT CONVECTION. GIVEN
THE COMBINATION OF FAVORABLE ENVIRONMENTAL PARAMETERS...ANOMALOUS
PWAT VALUES...AND A GROWING MODEL SIGNAL...WILL UPGRADE THIS AREA
TO A SLIGHT RISK OF EXCESSIVE RAINFALL. STILL NOT A SURE BET...AND
AS MENTIONED ABOVE SOME UNCERTAINTY WITH THE LATITUDE...SO WILL
HAVE TO CONTINUE TO MONITOR. HOWEVER CONFIDENCE HAS INCREASED
ENOUGH FOR THE SLIGHT RISK ISSUANCE.

CHENARD

PREVIOUS DISCUSSION...


DAKOTAS INTO THE UPPER MS VALLEY...

A FAIRLY BROAD MARGINAL RISK OF EXCESSIVE RAINS HAS BEEN ISSUED
FOR PARTS OF THE DAKOTAS EWD INTO THE UPPER MS VALLEY PRIMARILY
DUE TO LARGE MODEL SPREAD AND UNCERTAINTY WITH REGARDS TO STGR
CONVECTIVE TIMING/PLACEMENT WITHIN BROAD WAA REGIME ACRS THIS
REGION MON/MON NIGHT.  BOTH GLOBAL AND CAM GUIDANCE SHOW POOR RUN
TO RUN CONTINUITY WITH LITTLE CONSENSUS AS TO WHERE THE MORE
ORGANIZED HEAVIER RAIN MIGHT DEVELOP ALONG AND NORTH OF RETURNING
WARM FRONT AHEAD OF DVLPG LOW FCST TO MOVED INTO THE VCNTY OF CNTL
SD BY TUES MRNG.  HOWEVER WITHIN THE CLUSTER OF STORMS EXPECTED TO
MOVE ACRS PORTIONS OF THE UPPER MS VALLEY FROM SD/NEB MON
MRNG/AFTN AND LIKELY EXPANDING SLIGHTLY IN COVERAGE MON NIGHT WITH
STRENGTHENING AND VEERING 85H FLOW INTO WI/LOWER MI..HI RES
GUIDANCE SHOWS THE POTENTIAL FOR SOME TRAINING LINE ELEMENTS THAT
COULD LEAD TO SHORT TERM RAINFALL AMOUNTS OF 1 TO 3 INCHES IN A
COUPLE HOURS.  LIKEWISE ADDITIONAL STORMS ARE LIKELY TO INITIATE
IN THE ELY UPSLOPE FLOW ACRS SE MT/NE WY MON EVENING AND LIKELY
INTENSIFY DOWNSTREAM ACRS WRN SD/SRN ND MON NIGHT INTO FAVORABLE
INSTABILITY AND UPPER JET COUPLING.   THESE TOO HAVE THE POTNL TO
PRODUCE SHORT TERM HEAVY RAINFALL THAT COULD PSBLY LEAD TO ISOLD
RUNOFF ISSUES.  AGAIN GIVEN THE LARGE MODEL SPREAD AND
UNCERTAINTY...FEEL A BROAD MARGINAL RISK AREA IS ALL THAT IS
WARRANTED AT THIS TIME..BUT WILL CONTINUE TO MONITOR TO SEE IF
SUBSEQUENT MODEL RUNS COME TO A STRONGER CONSENSUS.

SULLIVAN
$$





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