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WPC Met Watch

 
Mesoscale Precipitation Discussion: #0156
(Issued at 438 PM EDT WED MAY 16 2018 )

MPD Selection
 


Graphic for MPD #0156

MESOSCALE PRECIPITATION DISCUSSION 0156
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
438 PM EDT WED MAY 16 2018

AREAS AFFECTED...WRN MT...NRN ID...SERN WA...ERN OR

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 162036Z - 170230Z

SUMMARY...LOCALIZED FLASH FLOODING WILL BE POSSIBLE WITH SLOW
MOVING STORMS IN PORTIONS OF THE INTERIOR NORTHWEST AND NORTHERN
ROCKIES. RAIN RATES MAY REACH 1 IN/HR WHICH COULD CAUSE FLOODING.

DISCUSSION...GOES-15 IR AND VISIBLE SATELLITE LOOPS AND REGIONAL
RADAR MOSAICS SHOW SCATTERED CONVECTION BEGINNING TO BLOSSOM IN AN
ARC FROM OREGON TO THE NORTHEAST INTO MONTANA. THIS WAS GENERALLY
JUST THE THE NORTHWEST OF A +PV ANOMALY THAT WAS SLOWLY LIFTING
NNW...AS WELL AS RIGHT ALONG A 700 MB DEFORMATION AXIS. THE DEEP
LAYER FLOW WAS RELATIVELY WEAK IN THIS REGION...AND THERE WAS A
MINIMUM IN FORECAST STORM MOTION SPEEDS ROUGHLY COINCIDENT WITH
THE DEFORMATION ZONE. RADAR TRENDS INDICATE THIS AS WELL...WITH
SOME NEARLY STATIONARY CONVECTION.

THESE SLOW STORM MOTIONS ALSO COINCIDED WITH THE GREATEST
COMBINATION OF INSTABILITY AND PRECIPITABLE WATER ACROSS THE
REGION. SIMILAR INSTABILITY (MLCAPE 500-1000 J/KG) EXISTED FURTHER
SOUTH FROM NORTHERN NEVADA INTO THE SNAKE RIVER VALLEY AS
WELL...BUT PWATS WERE LOWER THAT FAR SOUTHEAST. WITH LIMITED WIND
SHEAR AND A LACK OF A STRONG CONVECTIVE FOCUS...ANY THUNDERSTORMS
THAT DO DEVELOP SHOULD BE RELATIVELY SCATTERED... CELLULAR... AND
DISORGANIZED. HOWEVER WITH THE ENVIRONMENT SUPPORTIVE OF
MARGINALLY STRONG UPDRAFTS AND PWATS (0.7 TO 1.0 INCHES) ABOVE THE
90TH PERCENTILE FOR MAY IN THIS REGION... SHOWERS AND
THUNDERSTORMS SHOULD BE CAPABLE OF PRODUCING HEAVY RAINFALL.

THE 12Z HREF FOCUSED THE HIGHEST PROBABILITIES OF 1 IN/HR RAIN
RATES AND FFG EXCEEDANCE ALONG THE 700MB DEFORMATION ZONE...AND
PARTICULARLY FROM NE OR INTO FAR NW MT (ROUGHLY FROM PENDLETON TO
LEWISTON TO MISSOULA). NEIGHBORHOOD PROBABILITIES OF EXCEEDING 1HR
FFG WERE AS HIGH AS 30-60 PERCENT IN SOME AREAS. THE SCATTERED
NATURE OF THE CONVECTION SHOULD KEEP THE THREAT OF FLASH FLOODING
LOCALIZED. GIVEN THE RELATIVELY HIGH FREEZING LEVELS...SOME AREAS
MAY SEE A COMBINATION OF RUNOFF FROM ONGOING RAINFALL AND SNOW
MELT...WITH SNOW STILL PRESENT AT SOME OF THE HIGHER ELEVATIONS.

LAMERS

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

ATTN...RFC...CNRFC...MBRFC...NWRFC...

LAT...LON   49241380 48971286 47851232 46791218 45691267
            45381475 45181574 44491665 43561724 42281798
            41981970 43042047 45241945 46961809 48241663
            48931554


Last Updated: 438 PM EDT WED MAY 16 2018
 

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Page last modified: Wednesday, 13-May-2015 19:29:02 GMT