MESOSCALE PRECIPITATION DISCUSSION 0212
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1224 AM EDT SUN AUG 11 2013
 
AREAS AFFECTED...CENTRAL WA...NORTHERN OR 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 110424Z - 110924Z
 
SUMMARY...TRAINING THUNDERSTORMS CAUSING FLASH FLOODING...WILL BE
ESPECIALLY FOCUSED ALONG THE EASTERN SLOPES OF THE CASCADES OF
OR/WA THROUGH AT LEAST 07Z BEFORE INSTABILITY DIMINISHES.

DISCUSSION...UNUSUALLY ORGANIZED AND LONGER LIVED CONVECTIVE EVENT
FOR THIS AREA...APPREARED TO BE NEAR THE MIDDLE OF ITS LIFE CYCLE
BY 04Z. THUNDERSTORMS HAD ALREAD TRAINED ACROSS CHELAN COUNTY
WA...AND OTHER DEEP...SLOW MOVING RADAR ECHOES HAD BEEN NOTED
CLOSER TO THE INTERNATIONAL BORDER WHERE RADAR COVERAGE IS MORE
SPOTTY ALONG THE EASTERN SLOPES OF THE CASCADES. PROGRESSIVE
ACTIVITY IN OREGON HAD PRODUCED NORTHWARD MOVING OUTFLOW.
THIS...ALONG WITH THE APPROACH OF THE TROUGH...SHOULD SUSTIAN
LIFTING FOR ANOTHER SEVERAL HOURS...ESPECIALLY SOUTHERN AND
CENTRAL WA. THIS IS WHERE THE 00Z NAM...SPC WRF...AND 12Z NSSL WRF
SHOW A CONSENSUS ON THE PLACEMENT OF A REGIONAL QPF MAXIMUM.
MEANWHILE...SPC MESOANALYSIS SHOWED 1000 J/KG MIXED LAYER CAPE
ALONG THE CASCADES...WITH ONLY MINIMAL CIN HAVING DEVELOPED. RAP
AND HRRR FORECASTS SUGGEST MIXED OR MOST UNSTABLE CAPE WILL STILL
SUPPORT VIGOROUS UPDRAFTS THROUGH 07-09Z. RADAR AT 04Z SHOWED
ENOUGH NEW ECHO REGENERATION AHEAD OF THE OUTFLOW BOUNDARY TO
CAUSE CONCERN FOR THOSE AREAS IN THE NATIONAL FORESTS AND
RECREATION AREAS NORTH OF WENATCHEE THAT HAD ALREADY RECEIVED
HEAVY RAIN.

PER SPC OUTLOOKS AND DISCUSSION...THERE WAS ENOUGH SHEAR IN THIS
REGION TO SUPPORT SOME SMALL HAIL...AND RADAR RAIN ESTIMATES
APPEARED OVERDONE BY AS MUCH AS 3 TIMES...JUDING BY THE TRINITY
SNOTEL GAUGE WEST OF LAKE CHELAN. EVEN CUTTING RADAR ESTIMATES BY
A THIRD WOULD MEAN SOME LOCATIONS HAD RECEIVED MORE THAN 2
INCHES...AND MORE HEAVY RAIN IS LIKELY AS THE EASTERLY 700 MB
UPSLOPE IS MAINTAINED AHEAD OF THE APPROACHING TROUGH.
HENCE...SOME ADDITIONAL FLASH FLOODING IS THOUGHT TO BE
LIKELY...WITH ANY ONGOING FLOODING PERHAPS WORSENING AS EVENT
TOTALS MAY EXCEED 3 INCHES LOCALLY. EXPECT DECREASING INTENSITY
AFTER 07Z.

BURKE

ATTN...WFO...OTX...PDT...SEW...PQR...

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

LAT...LON   49431993 48931960 48171940 47631881 46791744 46021829
            45781988 45092116 44512213 44882270 46012251 46962209
            48392169 48932171 49422108 49431993