Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 191051

351 AM PDT Sun Apr 19 2015

Very warm weather continues across the region into early next
week. Isolated late day showers and thunderstorms will be possible
over the mountains. Another low pressure system will move into the
region by the middle of next week bringing cooler temperatures and
continuing the threat of possibly more widespread showers or
thunderstorms during the middle and end of the week.


Weak upper low off the norcal coast which brought isolated
mountain thunderstorms on Saturday drifting to the southwest
today. As a result...instability associated with the low is moving
southward as well. Therefore...only expecting a threat of showers
or thunderstorms over the northern Sierra today south of about
interstate 80. Overall airmass under upper level ridging will be
warming slightly today bringing up high temperatures to near
records for the date. The low then shifts inland towards the Socal
coast on Monday in response to a larger trough dropping out of the
Gulf of Alaska and into the eastern Pacific. With the forecast
area well north of the the Socal low...moister is fairly limited
but models show some increased instability over the mountains
Monday so isolated afternoon mountain thunderstorms are not out of
the question. Airmass remains very warm on Monday but may see
highs drop just a bit over Sunday highs. by Tuesday
afternoon...Gulf of Alaska through is forecast to dig in just off
the coast. Should see a few to several degrees of cooling as upper
flow becomes more onshore increasing marine influence.  Mid range
models in fairly good agreement in pivoting some sort of shortwave
out ahead of the trough bringing a threat of showers or
thunderstorms to most areas of the CWA afternoon and evening hours.
General idea of mid range models is to split the trough as it
moves inland into a close low off the socal coast and an open wave
over the Pacific Northwest. Models differ on details but agree on
showing enough instability and moisture over the North state to
warrant shower or thunderstorm threat most areas Wednesday. Daytime
temperatures continue to cool on Wednesday but at this time are
still forecast to remain above normal.


.Extended Discussion (Thursday through Sunday)

The longwave trough will dominate through the latter portion of
the week, keeping temperatures moderated. A closed low that moves
southward along the coast will be over northern Baja by Thursday.
However, the broad low will still provide instability over NorCal
and bring return flow moisture from an easterly direction with
thunderstorms looking like a pretty good bet Thursday. The low
will weaken and move to the east by Friday, but the longwave
trough will likely remain near the west coast with potential
showery activity through the weekend.      JClapp



VFR conditions next 24 hours. Afternoon isolated thunderstorms
will develop over the Sierra southward of Lake Tahoe. Light winds
will continue except in vicinity of thunderstorms.     JClapp


.STO Watches/Warnings/Advisories...

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