Flash Flood Guidance
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000
AWUS01 KWNH 260157
FFGMPD
MTZ000-IDZ000-ORZ000-WAZ000-260705-

MESOSCALE PRECIPITATION DISCUSSION 0199...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
956 PM EDT FRI MAY 25 2018

CORRECTED FOR CONCERNING LINE: FLASH FLOODING RISK IS CONSIDERED
LIKELY

AREAS AFFECTED...NORTHEAST OR...CENTRAL ID...WESTERN MT...EXT
SOUTHEAST WA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 260135Z - 260705Z

SUMMARY...DEEP CONVECTION TRAINING THEN MERGING ALONG DEFORMATION
ZONE TO PROLONG MODERATE TO HVY RAINFALL CONTINUING TO POSE FLASH
FLOOD RISK THROUGH EARLY OVERNIGHT HOURS.

DISCUSSION...IDEAL SYNOPTIC SETUP FOR A STRONG WELL DEFINED
DEFORMATION ZONE BETWEEN STRONG CLOSED LOW OVER CENTRAL CA COAST
AND FAST MOVING SHORTWAVE/JET STREAK OVER VANCOUVER ISLAND
SHARPENING THE NW SIDE OF THE ZONE.  COMBINE THIS WITH SOLID
SHORTWAVE WITHIN LEFT EXIT REGION OF 80KT JET OVER NW NV/SE OR
SUPPORTING STRONG DPVA AND SURFACE AND LOW LEVEL CYCLOGENESIS
SUPPORTING DEEP LOW LAYER WARM CONVEYOR ACROSS EASTERN NV BENDING
BACK ACROSS INTO THE DEFORMATION ZONE.  CLEAR SKIES AHEAD OF THE
GROWING CLOUD SHIELD OVER THE DEFORMATION ZONE WILL CONTINUE TO
PROVIDE AMPLE BUOYANCY FOR ADDITIONAL CONVECTIVE DEVELOPMENT AS
THE ZONE LIFTS SLOWLY NORTH ACROSS NE OR INTO CENTRAL ID.
UNCAPPED SBCAPES UP TO 1500 AND MUCAPES TO 1750 J/KG ALONG WITH
TPWS IN THE 1.0-1.2" RANGE. GOES-16 VIS AND LIGHTNING DETECTION
NETWORK DENOTE STRONG UPDRAFTS BUT ALSO FAIRLY SOLID DENSITY OF
CONVECTIVE CORES ALONG THE THE DEFORMATION ZONE EVEN INTO CENTRAL
ID AND W MT CURRENTLY

A NNW-SSE BAND EXTENDS FROM THE GENERAL TRIPLE POINT NEAR S
GRANT/NE HARNEY COUNTY BACK TOWARD OWYHEE COUNTY...HAS SOME
REDUCED VALUES DUE TO LOWER MST ABOVE 7H PER CIRA LAYERED PW
ANALYSIS BUT STRONGER CONVERGENCE ALONG THIS EFFECTIVE FRONTAL
ZONE PROVIDE SOLID MOISTURE FLUX FOR EFFICIENT RAINFALL PRODUCTION
IN THE AREA LOCALLY UP TO 1"/HR.  CLOUD BEARING FLOW IS GENERALLY
PERPENDICULAR TO THE BOUNDARY SUPPORTING TRAINING PROFILE UNTIL
CELLS REACH THE DEFORMATION ZONE WITH MERGERS POSSIBLE SUPPORTING
SHORT TERM RATES TO 1.5"/HR.  MODERATE PERSISTENT SHOWERS ALONG
THE WESTERN BRANCH OF THE TROWAL BACK TO THE SW AHEAD OF THE
SHORTWAVE HAS THE POTENTIAL FOR .5"/HR RATES FOR A LONGER DURATION
POSING A FLOODING/FLASH FLOODING RISK AS FAR SW AS NE LAKE THROUGH
06Z.

HI-RES CAMS SUCH AS THE WRF-NMMB, NAM-CONEST AND GEM REGION DEPICT
A GOOD EVOLUTION OF CURRENT TRENDS WITH 1-3" TOTALS LIKELY ALONG
THIS LINE MAXIMIZING NEAR THE BLUE MTN RANGE AT THE EFFECTIVE
TRIPLE POINT AND POTENTIAL FOR LONGEST RAINFALL DURATION THROUGH
THE OVERNIGHT HOURS.  ADDITIONALLY, FFG VALUES IN THE VICINITY ARE
IN THE .5-.75"/HR RANGE AND 1-1.5" RANGE FOR 3-6HRS...GIVEN THIS
SETUP WOULD CONSIDER FLASH FLOODING LIKELY THOUGH IN LOCALIZED
POCKETS FROM CROOK,ORE TO IDAHO, ID COUNTIES.

FURTHER EAST INTO WESTERN MT...GREATER INSOLATION AND INSTABILITY
WILL GENERATE THUNDERSTORMS BUT SHOULD LIFT GENERALLY NORTH IN AN
W-E LINE SO TRAINING WILL BE LIMITED BUT SHORT-TERM RATES MAY POSE
SOME CONCERNS FOR HIGHLY LOCALIZED FLOODING RISK.

GALLINA

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...BOI...MFR...MSO...OTX...PDT...

ATTN...RFC...NWRFC...

LAT...LON   47621365 46481308 46311353 45821506 44951555
            43831573 43251570 42921622 43111697 43621784
            43701876 43332029 43862067 45051999 46351828
            47311621



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