000
FXUS66 KSTO 212255
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
355 PM PDT TUE MAY 21 2013

.SHORT TERM DISCUSSION...

UPPER LOW IS JUST OFF THE OREGON/WASHINGTON COAST THIS AFTERNOON.
THE SYSTEM IS RELATIVELY DRY WITH ONLY ISOLATED SHOWERS POSSIBLE
OVER THE MOUNTAINS OF SHASTA COUNTY THIS EVENING. HAVE SEEN A FEW
RETURNS NORTH OF MOUNT SHASTA. WINDS ARE GUSTING TO 30 MPH AT
TRAVIS AFB AND EXPECT GUSTS TO 35 MPH THROUGH THE DELTA DURING THE
EVENING. COLD AIR ADVECTION CONTINUES OVER THE NRN SAC VALLEY WITH
COLD FRONT CURRENT NEAR YUBA CITY WHICH IS MARKED BY A SHIFT TO
NORTHERLY WINDS. THE FRONT WILL MOVE SOUTH OVER THE VALLEY DURING
THE EVENING AND PASS THROUGH THE SACRAMENTO AREA AFTER 7 PM. TEMPS
WILL COOL INTO THE UPPER 40`S AND LOW 50`S FOR OVERNIGHT LOWS
BEHIND THE FRONT.

UPPER LOW WILL SHIFT SLIGHTLY EAST OVER WASHINGTON AND OREGON
TOMORROW. THE ATMOSPHERE WILL REMAIN DRY AND PRECIP CHANCES WILL
BE LOW. STRONG NORTHERLY FLOW AND COLD AIR ADVECTION WILL COOL
TEMPS TO BELOW NORMAL READINGS WITH VALLEY HIGHS GENERALLY IN THE
LOW TO MID 70`S. NORTH WINDS WILL GUSTS TO 30 MPH AT TIMES OVER
THE SAC VALLEY...AS GRADIENT TIGHTENS.

UPPER LOW WILL REMAIN OVER WASHINGTON/OREGON THURSDAY AND FRIDAY
WITH A STRONGER PIECE OF ENERGY ROTATING BELOW THE LOW OVER NRN
CALIFORNIA. THIS WILL BRING SLIGHT SHOWER CHANCES OVER THE NRN
MOUNTAINS AND NRN SIERRA. QPFS WILL BE ON THE LOW SIDE WITH THE
LIMITED MOISTURE. TEMPS WILL REMAIN BELOW NORMAL IN THE 70`S.

&&

.EXTENDED DISCUSSION (SATURDAY THROUGH TUESDAY)

A MEAN TROUGH WILL LINGER OVER THE WEST COAST THROUGH THE WEEKEND
AND INTO THE FIRST PART OF NEXT WEEK. SEVERAL WEAK DISTURBANCES
WILL MOVE THROUGH THE LONGWAVE TROUGH AND BRUSH FAR NORTHERN
CALIFORNIA. MODELS ARE NOT IN AGREEMENT HOWEVER WITH THE
AMPLITUDE AND TIMING OF THESE FEATURES. THE ECMWF SOLUTION HAS
THE LEAST IMPACT FOR US AS IT IS LESS AMPLIFIED WITH THE LONGWAVE
TROUGH AND CONSEQUENTLY KEEPS OUR AREA DRY THROUGH THE PERIOD.
THE GFS AND GEM MEANWHILE HAVE COMPACT SHORTWAVES MOVING THROUGH
SATURDAY NIGHT AND MONDAY NIGHT...WITH LINGERING MOUNTAIN SHOWERS
IN-BETWEEN. THE GFS IS EVEN SHOWING SOME CHANCE OF CONVECTION
SATURDAY NIGHT FOR THE COASTAL MOUNTAINS AND LASSEN VICINITY. WITH
LIMITED CERTAINTY...HAVE OPTED FOR A SLIGHT CHANCE OF SHOWERS
THROUGH THE PERIOD OVER THE MOUNTAINS FROM AROUND RED BLUFF
NORTHWARD. HAVE ADDED A MENTION OF THUNDER SAT AFTERNOON/EVENING
TO ACCOUNT FOR SFC-BASED INSTABILITY PROGGED BY THE GFS...WHICH
ALSO HAPPENS TO MATCH UP WELL WITH NEIGHBORING FORECAST OFFICES.

REGARDLESS OF WHICH SOLUTION VERIFIES...THE ONLY IMPACT FOR THE
CENTRAL VALLEY WOULD BE CONTINUED SEASONAL TEMPERATURES WITH
ONSHORE FLOW AND A FEW CLOUDS. -DVC

&&

.AVIATION...

VFR CONDITIONS CONTINUE NEXT 24 HOURS FOR INTERIOR NORCAL TAF
SITES. A LOW PRESSURE SYSTEM BRUSHING NORCAL TO THE NORTH WILL
SHIFT CENTRAL VALLEY WINDS TO THE NORTH OVERNIGHT AROUND 10KTS
AND BRING SOME MID-LEVEL CLOUDS BY WEDNESDAY AFTERNOON. -DVC


&&

.STO WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$