Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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FXUS66 KHNX 232122

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
222 PM PDT Mon Apr 23 2018

Above normal temperatures and dry conditions will continue for the
next few days as high pressure dominates. There will be slight
chances for afternoon showers and thunderstorms for the higher
elevations of the Sierra Nevada beginning Wednesday into the
weekend as a low pressure system moves into northern California.
The main system impacts will be increased winds and clouds for
all other areas as the system moves through the region.


Current temperatures are already in the upper 80s across most of
the SJV and a few 90s in the Kern desert per the latest 20z
surface observations. Weak ridging that was keeping things quiet
weather-wise is currently giving way to more broad ridging that
will increase the synoptic warming over the region. By tomorrow
high temperatures in the low to mid 90s across the SJV will be
the rule rather than the exception and will continue on Wednesday.
The broad ridging over the western third of the country will be
bounded by low pressure systems on both the west and east sides of
the ridging developing an omega block.

Guidance unfortunately does not do the best in blocky patterns
and typically suffers in the temporal department. With a block in
place it has been my experience to add at least a day to the model
solution timing as the guidance tries to keep things moving in a
normal fashion even though the atmosphere flow is being impeded.
This forecasters confidence is not the highest in the longer term
due to this issue. Current thinking would suggest that due to the
block the Pacific system currently progged to move into central
California will in fact move further north than plotted. Even a
deviation of 100 miles northward would create a difference in not
only forecasted temperatures but also winds speeds and
precipitation chances. I have opted to keep the forecasted slight
chance of thunderstorms for the higher elevations of the Sierra
Nevada mainly near the Yosemite National Park area in the forecast
as even a slight mid-level cooling/moistening by a system passing
through northern California would create enough instability for
convective initiation with the relatively warm mountain surfaces.
Orographic lifting would also be present with a westerly flow to
the south of the low completing the convection ingredient tri-
fecta. Timing may still need to be pushed back if the system gets
held up west of the region by the block which seems likely to be
the case. As time goes outward during this forecast so does my
confidence. In other words we need to wait and see what happens
the next couple of days to better make forecast decisions out past
the Wednesday time frame. But, in the mean time enjoy the nice,
albeit a bit on the warm side, weather we will have over the next
few days.


VFR conditions will prevail across the Central CA Interior during
the next 24 hours.





The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit for additional information
an/or to provide feedback.


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