Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 121125
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
425 AM PDT Sat Jul 12 2014

.Synopsis...
Warmer daytime temperatures into Monday then slight cooling back
down to near normal by the end of next week. A chance of Sierra
crest thunderstorms returning Monday spreading northward on
Tuesday. A slight chance of thunderstorms over the Shasta county
mountains and Sierra cascade range Wednesday. A diminishing shower
threat towards the end of the week as the upper level flow becomes
more westerly.

&&

.Discussion...
Northern California under stable southwest flow between a high
pressure ridge over the Great Basin and a low pressure system over
the eastern Pacific. A weak disturbance moving through this
southwest flow is bringing some high cloudiness to northeast
California this morning. Skies are mainly fair elsewhere except
the delta where some coastal stratus has moved inland. Upper ridge
is forecast to retrograde westward today bringing a warm up in the
general airmass. Should see daytime highs today on the order of 5
degrees warmer than on Friday. Subsidence under the ridge will
keep the CWA under fair skies today while RH values lower under
drying airmass. Airmass continues to warm and dry on Sunday as the
upper ridge amplifies and shifts over the west coast. This will
bring still warmer temperatures and drying. Airmass warms just a
bit more on Monday as the upper ridge axis develops along the
coast bringing what will likely be the warmest temperatures of the
week under minimal onshore flow. Humidity values drop as well with
minimum RH likely in the teens most areas. Subtropical moisture
does start to make its way northward however and may see effects of
this moisture beginning in the afternoon in the form of a Sierra
thunderstorm along the Sierra crest south of Tahoe. Subtropical
monsoon moisture continues to work its way northward on Tuesday.
The combination of cloud cover and a cooler airmass will bring the
beginning of a cooling trend starting Tuesday and lasting through
the end of the week. RH values should begin to creep up while
instability progs indicate the thunderstorm threat will likely
start to shift northward up the Sierra crest.


.Extended Discussion (Wednesday through Saturday)

Precipitable water forecasts from GFS model show TPW on Wednesday
ranging from a little over an inch to nearly 1.5 inches over NORCAL.
More moderate RH values should result with instability forecasts
showing the best chance of thunderstorms over the Sierra Cascade
range and the Shasta county mountains. Models showing plenty of
moisture and sufficient instability but lack of lift should
confine and thunderstorms to where mountains can provide the lift.
Extended models in fairly good agreement in moving an upper low
into the Pacific Northwest around next Thursday. This will bring a
more westerly flow aloft which will keep any thunderstorm
development limited to the Sierra cascade range. The passage of
the upper low to the north will bring a continue slight cool down
as well. Temperatures continue to cool Friday and Saturday as a
trough develops along the coast. Models vary on strength of this
trough but for the most part forecast area looks to remain under
fair skies with daytime highs dropping to near normal and more
moderate humidity.

&&

.Aviation...

VFR conditions expected to continue for the next 24 hours except
for local areas west of KSUU this morning. Marine stratus nudging
into the western side of the delta will have MVFR ceilings with
BKN010-015 during morning hours. Near the delta...SW winds at 15-25 kt will
continue with gusts up to 30 kt. Onshore flow through the delta
will bring south to west winds at 5-15 kt today for the Sacramento
Valley TAF sites. Northern San Joaquin valley will have west to
northwest winds also at 5-15 kt today.  JBB


&&

.STO Watches/Warnings/Advisories...
None.
&&

$$






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