MESO: Mesoscale Discussion 2070

ACUS11 KWNS 070528
SWOMCD
SPC MCD 070528
CAZ000-NVZ000-071130-

MESOSCALE DISCUSSION 2070
NWS STORM PREDICTION CENTER NORMAN OK
1128 PM CST FRI DEC 06 2013

AREAS AFFECTED...PORTIONS OF NRN/CNTRL CA

CONCERNING...HEAVY SNOW

VALID 070528Z - 071130Z

SUMMARY...SNOWFALL WILL INCREASE INTO EARLY SAT MORNING ACROSS THE
NRN/CNTRL SIERRA...WITH RATES OF 2-3 INCHES PER HR BECOMING COMMON.
A CHANGEOVER FROM RAIN TO SNOW MAY ALSO OCCUR AT LOWER ELEVATION
FOOTHILLS INTO THE CENTRAL VALLEY...ALTHOUGH RATES WILL BE MUCH
LIGHTER.

DISCUSSION...RADAR TRENDS SHOW AN AREAL INCREASE IN PRECIPITATION IS
OCCURRING OVER NRN CA OVER THE PAST SEVERAL HRS...AHEAD OF A STRONG
UPPER TROUGH AND ACCOMPANYING SPEED MAX PROGRESSING S-SEWD TOWARDS
THE NRN CA COAST. OBSERVATIONS SUGGEST MOSTLY RAIN ON THE VALLEY
FLOOR...WHILE MODERATE TO HEAVY SNOW IS FALLING IN HIGHER ELEVATION
LOCATIONS IN THE MOUNTAINS/FOOTHILLS OF THE SIERRA. MOISTURE IS
INCREASING FROM THE W AHEAD OF THIS SYSTEM...WITH GPS-IPW
MEASUREMENTS INDICATING AN INCREASE TO 0.5-0.6 INCH INTO THE NRN
CENTRAL VALLEY...AND HIGHER VALUES UPSTREAM.

THE SWATH OF PRECIPITATION WILL CONTINUE SHIFTING SWD THROUGHOUT THE
EVENING AND INTO EARLY SAT MORNING TOWARDS CNTRL CA IN CONJUNCTION
WITH THE DIGGING UPPER TROUGH. SNOWFALL RATES ARE SIMULTANEOUSLY
FORECAST TO INCREASE IN RESPONSE TO DCVA AND LIFT ON THE CYCLONIC
SIDE OF THE IMPINGING UPPER JET...AS WELL AS OROGRAPHIC UPLIFT WITH
MEAN SWLY 0-2 AGL LAYER FLOW. HOURLY RATES OF 2 INCHES OR HIGHER
WILL BECOME COMMON OVER THE NRN/CNTRL SIERRA.

IN LOWER ELEVATION LOCATIONS...INCLUDING THE VALLEY FLOOR AND WRN
FOOTHILLS OF THE SIERRA...SFC OBS FROM 05Z SHOW TEMPERATURES ABOVE
FREEZING...BUT INCREASING T-TD SPREADS WITH SWD EXTENT. WET-BULB
COOLING AND SATURATION OF THE LOWER-TROPOSPHERE IS EVENTUALLY
EXPECTED TO SUPPORT THERMAL PROFILES FAVORABLE FOR SNOW...PERHAPS AS
EARLY AS 09-11Z IN CNTRL CA. DESPITE MUCH DRIER MIDLEVEL AIR ABOVE
600 MB...SATURATION THROUGH THE DENDRITIC GROWTH ZONE WILL FAVOR AT
LEAST LIGHT TO MODERATE SNOW...WITH RATES INCREASING WITH
ELEVATION/EWD EXTENT.

..ROGERS.. 12/07/2013

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...VEF...REV...HNX...STO...

LAT...LON 39402024 38381937 37311850 36811841 36681875 36721920
37232001 38062089 38862121 39452146 39772103 39402024

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