Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 162110

210 PM PDT Thu Apr 16 2015

High pressure over the west coast for mainly fair skies and
warmer than normal temperatures through the weekend. A weak low
forms over the Northern California coast for a slight threat of
mountain showers over the weekend and Monday. A cold upper level
trough moves into the area by mid week bringing cooler
temperatures and a chance of precipitation over all of interior
Northern California.


High pressure building over Northern California today bringing
warmer temperatures and lighter winds. North to northeast winds
are decreasing this afternoon as the surface pressure gradient
weakens this afternoon (MFR-SAC down to 5 mb at 1 pm (from 9 mb at
8 am) and SAC-RNO down to 4 mb (from 6 mb at 8 am). The lighter
winds will continue into Friday. Temperatures are running about 6
to 12 degrees warmer than yesterday afternoon due to a warmer
airmass and lighter winds. High temperatures will be in the low
to mid 80s in the Valley and 50s and 60s in the mountains. Airmass
warms a little more on Friday and Saturday bringing high
temperatures up to the mid 80s to around 90 in the Valley and upper
50s to mid 70s in the mountains. These temperatures are around 15
degrees above normal for this time of year. Temperatures remain
similar for Sunday. Although air temperatures are warm, water
temperatures in rivers and lakes remains cold in the low 40s to
low 60s. People going in the rivers and lakes this weekend should
use caution since cold water can lead to hypothermia.

A weak disturbance moves into Northern California on Saturday then
forms a weak upper level low off the Nor Cal coast late Saturday
into Sunday. This will bring some instability for a slight chance
of showers and thunderstorms over the mountains of interior
Northern California on Saturday afternoon and evening. The low moves
south down the California coast on Sunday for some instability
remaining over the Sierra for a slight chance of showers and thunderstorms.

.Extended Discussion (Monday through Thursday)

Warm, dry weather continues into Monday with above normal
temperatures across majority of the area. An upper level wave
rotating off the NorCal coast will bring the chance for showers
and thunderstorms across the Sierra on Monday into early Tuesday
with a bit of instability present. Moisture will be very limited
with this wave so not expecting anything widespread, more hit or
miss in nature. A larger, deeper system will drop SE toward
California later Tuesday into Thursday. Model details still differ
a bit at this long range. Regardless, cooler temperatures seem to
be a safe bet with temperatures dropping 5-10 degrees from Monday
to Tuesday and another few degrees from Tuesday thru Thursday.
This system will also bring a more widespread shot of
precipitation to most of the area. Have continued with generally a
broad-brushed approach to chance of precipitation until details are
better resolved. Snow levels will start out fairly high (7000-8500
feet) but may drop to around 6000 feet depending on track of the
low. Southerly winds will also be breezy at times from Tuesday
thru Thursday.




VFR conditions thru the period with clear skies. Northerly winds
will calm down this afternoon into evening with light and variable
winds generally under 5 kts thru Friday.


.STO Watches/Warnings/Advisories...

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