Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service Sacramento California
325 PM PDT Thu Apr 17 2014

weak low pressure system will bring a slight chance to chance of showers
north of Interstate 80 tonight and then showers and isolated
thunderstorms are possible along the Sierra on Friday. Temperatures will
continue above normal through Sunday...then are forecast to cool
to near to below normal early next week. An unsettled weather
pattern moving over the region will bring a chance of showers over
interior northern California next week with the best chance Monday
night into Tuesday night along with a slight chance of
thunderstorms on Tuesday.


Short term discussion...
two systems bringing clouds to northern California this afternoon
and tonight. A disturbance off the Southern California coast is
bringing mid and high clouds to around the Interstate 80 corridor
this afternoon. An upper level trough digging along the West
Coast is bringing clouds to the northern portion of the area. The
upper level trough will dominate tonight into Friday as the
southern disturbance moves into Southern California. The upper
level trough will bring some clouds and a chance of precipitation
north of I-80...mainly over the mountains tonight and showers and
isolated thunderstorms possible along the Sierra on Friday.
Temperatures this afternoon are running similar to yesterday
with temperatures in the upper 70s to low 80s in the valley and
mid 50s to low 70s in the mountains except a little cooler near
the Delta with onshore flow (suu winds SW about 20 mph) and
temperatures in the low to mid 70s. These temperatures are about 6
to 12 degrees above normal for mid April. Precipitable water
around an inch with this system for some moisture but dynamics
fairly weak so precipitation amounts will generally be less than a
tenth of an inch. Snow levels are expected to be around 9000 ft.
Temperatures will be similar to a little cooler on Friday with
high temperatures in the mid 70s to around 80 in the valley and
50s and 60s in the mountains. The instability moves to the central
Sierra and east on Saturday but may still see some cumulus
development in alpine and Tuolumne counties. Another trough moves
through the Pacific northwest on Saturday but looks like it will stay
dry in interior northern California. Temperatures will be similar
on Saturday. Weak shortwave ridging on Sunday ahead of a stronger
and deeper low for a little warmer temperatures and dry weather.
The deeper low will bring cooler and wetter weather for early next

Extended discussion (monday through thursday)
pattern change starts Monday with cooler and wetter weather on
the way. The ECMWF, GFS, and Gem models are in very good agreement
for the main arrival of a large upper low from the Gulf of Alaska.
Although light mountain showers could start Monday morning, the
brunt of this system will start impacting norcal Monday evening.
Showers will spread southward across our County Warning Area Monday into Tuesday.
Have kept the mention of slight thunderstorm chances Tuesday as
forecast instability appears favorable for the valley. Cooler
temperatures will be noticeable as valley highs go from the low
80s on Sunday cooling to mid-upper 70s on Monday and mid 60s-low
70s by Tuesday. Those cooler temps on Tuesday will continue into
Wednesday with lingering showers. Upper ridge will build back into
the area Thursday with warmer temperatures...but north winds may
occur as the ridge approaches.



VFR conditions will continue next 24 hours for taf sites. Onshore
flow will develop later in the afternoon into early evening,
bringing some moderate winds to the Delta Region while also
bringing a few local gusts of 15-20 kts to the SAC/Stockton Metro
area between 22-03z today. Otherwise, light winds tonight. Gusty
north winds 15-20 kts possible for portions of the SAC valley
late Friday morning. -Dvc.


Sto watches/warnings/advisories...