Area Forecast Discussion
Issued by NWS Sacramento, CA

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FXUS66 KSTO 182214
AFDSTO

Area Forecast Discussion
National Weather Service Sacramento CA
314 PM PDT Thu Apr 18 2019

.SYNOPSIS...
Chance of showers and thunderstorms across Norcal late Friday
through Saturday as low pressure from the Pacific moves inland.
Continued warm on Friday, then significantly cooler Saturday before
warming again Sunday through mid week.

&&

.DISCUSSION...
Temps trending some 5 to 10 degrees warmer over most of the area
under clear skies, and are forecast to warm 10 to 15 degrees above
normal this afternoon, the warmest temps so far this year. Some high
cloudiness is approaching from the SW and will spread over the Srn
portion of the CWA overnite from the low vcnty 28N/130W, while high
cloudiness will increase on Fri ahead of the Ern Pac wx system that
is approaching the coast.

The warmth is due to a neutral to slightly positively-tilted
upper ridge over the Wrn States. The ridge axis will shift Ewd on
Fri ahead of upper trof approaching the coast. The trof won`t be
inside 130W until evening, so Fri will another warm day, although
maxes may cool just a bit over some locations due to thickening
clouds primarily and minor synoptic cooling late in the day.
Forecast CAPE and negative LI`s over the lee-side of the Coastal
Range suggest a chance of showers/storms late in the afternoon and
evening.

This approaching trof is forecast to develop into a broad 5H trof
and upper low over Norcal for Sat afternoon/evening that will give
most of our CWA north of I-80 and the Sierra a chance of
showers/storms. We extended the PoPs/Wx a little farther S in our
CWA, to near SAC. The combination of thicker cloud cover and showery
precip on Sat is expected to significantly cool temps some 12 to 19
degrees from Fri and cool temps back to several degrees below
normal. Fortunately, this wx system will be moving into/across the
Great Basin with dry wx and rebounding temps on Easter Sun. JHM

&&


.EXTENDED DISCUSSION (Monday THROUGH Thursday)

As the weekend system continues to push toward the Four Corners
region, mid-level heights will build as an upstream ridge
approaches. Expected heights should be around 1.5 to 2 standard
deviations above mid/late April climatology. This supports a
continued period of early Spring warmth with numbers around 10 to
15 degrees above climatology. Based on the trajectory of the
ridge, Tuesday and Wednesday should prove to be the warmest days
featuring Valley highs in the mid/upper 80s with mountain locales
hitting the low 60s. With projected lows across the mountains
being in the low 40s, some gradual decrease in the snowpack can be
expected each day. By Friday and into next weekend, deterministic
and ensemble guidance favor a broad upper trough approaching the
California coast. Difficult to identify any discernible impacts at
this point. However, increasing cloud cover across the state
supports a decrease in temperatures after a rather warm week. ~BRO

&&

.AVIATION...

Quiet weather continues for northern California with VFR
conditions and generally light winds forecast for the next 24
hours.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$


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