Area forecast discussion
National Weather Service Sacramento California
348 am PDT Thursday Jun 20 2013
Synopsis...
warm and dry conditions to end the week and kick off the official
first few days of Summer. This will all change Sunday into early
next week as an unseasonably wet and cool weather pattern moves
into northern California.
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Short term discussion...
despite the weather system across the Pacific northwest...dry air
over norcal will keep ample sunshine and warming temperatures for
today. A slight increase in the Delta breeze and north winds
over the western Sacramento and northwest San Joaquin valleys will
also be seen today.
Tonight through Friday a broad trough will remain over the region
with a weak shortwave rotating through the north early Friday.
Limited moisture with this wave will result in little to no shower
activity. This wave will help to keep northerly flow going over
the interior for Friday with temperatures warming into the upper
80s and lower 90s.
A weak ridge will build over the area Saturday in advance of
the next weather system. This will allow temperatures to warm a
few more degrees for readings in the lower to middle 90s. The
northerly flow will weaken and may shift direction in the
afternoon and evening to a more up valley flow.
Extended discussion (sunday through thursday)
An unseasonable moisture source...more similar to a Fall weather
pattern is anticipated to move into the West Coast Sunday and
impact the region through early Wednesday. The models continue to
struggle with exact placement but have a general consensus that
northern California will see widespread steady rainfall. With the
increased rainfall temperatures are also expected to cool below
seasonal through this time frame. Confidence is moderate with
this event occurring...but the exact amount and extent of the rain
is still uncertain.
The moisture plume has well above seasonal preciptable water
values (over 1.7 inches). This moisture combined with multiple
waves rotating through the broad trough off the coast...there is
the potential for moderate rain. While much of the Sacramento
Valley and northern San Joaquin Valley will see rain during this
time frame...the northern Sacramento Valley is expected to see the
heaviest amounts. Daily record rainfall amounts are possible in some
spots in that area. Most of the rain will be the steady...stratiform
type. Convection should be limited and mainly over the far
northern mountains.
There continues to be some discrepancies in the models with
regards to the strength of the first wave on Sunday. However...all
models do advertise rain moving into interior California by Sunday
evening. Showers are expected to linger behind this first wave
into early Monday.
A deep low moves off the Pacific northwest coast Monday night and
Tuesday. These looks like the wettest period for interior northern
California. The 12z European model (ecmwf) has actually moved a little further north
which would focus the weight of the impact of the storm over the
northern mountains and into the northern Sacramento Valley. Some
lighter precipitation is possible as far south as the Interstate
80 corridor.
Precipitation should diminish during the day Wednesday as
Continental ridging shifts westward into the region.
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Aviation...
A broad trough over the western United States will keep some high thin
clouds over interior California. North winds generally less than
15 knots with higher gusts will develop mainly across the western
valley.
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Sto watches/warnings/advisories...
none.
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$$
