Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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FXUS66 KHNX 221117

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
417 AM PDT Thu Mar 22 2018

Continued atmospheric river influence over the area through
Friday morning. A brief break from the precipitation will take
place on Friday afternoon and into Saturday morning. Then chances
for light precipitation will increase by late afternoon Saturday
as a low pressure system moves through the region. Ridging will
then begin to move into the area on Monday bringing warmer
temperatures and drying conditions well into the middle of
next week.


Both an interesting and somewhat difficult forecast situation
today as we continue to have the atmospheric river moving over
the area bringing continued bouts of precipitation. There will be
breaks in the train of moisture such as what is currently
occurring as can be seen on both current infrared satellite and
radar data. The southwest to northeast orientated axis of
moisture (that term reminds me of the description of World War I
participant every time I say it) currently is draped over the
northern parts of the CWA from about Fresno County northward with
a slow northward progression. This is actually a good thing as it
gives Kern and Tulare Counties a break from the continued
precipitation and keeps the possibility of flooding lower. Some
areas of overnight fog have developed in the Kern County desert
areas with the damp conditions.

Now the interesting part of this forecast is that later today the
axis of moisture will once again push southward with cooler air to
the north behind it and model sounding data shows decent (for this
area) low level (0-1km) storm relative helicity values from
80-110 m2/s2 indicating the directional shear present at the lower
levels this afternoon. Winds at the surface will be southeasterly
with more southwesterly winds as you go further aloft. The SPC
currently has the northern central parts of our CWA marked as
marginal in the day one convective outlook. CAPE could definitely
be better but between 21z and 00z Friday there seems to be ample
instability, this along with plenty of moisture and with jet
dynamics helping to supply lift coupled with the aforementioned
shear there is the possibility of isolated thunderstorms which may
begin to spin, heck, a weak tornado or two would not be
completely out of the question. Just like our neighboring area to
the north found out yesterday. Now here is where things can get
dicey, not just because of the tornado possibility either, with
the development of thunderstorms rainfall could be heavy at times
with these storms and could very quickly create flooding issues
with already very wet soils present. So if thunderstorms do
materialize, it would need to be monitored very careful in these
areas for flood potential, especially if any of the storms moves
over a burn scar area. The thunderstorms also could create small
hail and gusty winds but with the very moist tropical-like airmass
(pwats around 1-1.5 inches) the hail threat will be somewhat
minimized. Any thunderstorms could produce deadly cloud to ground
lightning so if thunder roars, go indoors.

Even without the thunderstorms the expected rainfall and very
high elevation mountain snows with this atmospheric river pattern
will still continue to bring decent precipitation amounts. Another
quarter to around one inch is still expected in the SJV. The
foothill areas will see around an inch to around 3 inches of
additional precipitation. The higher elevations will see from
about 3 inches to about 4 inches more with this storm. The highest
elevations could still see another 2 feet or so of snow in some

By Friday morning the main atmospheric river portion of this storm
will have moved southeast of the CWA. But the parent low pressure
system sitting just off of the coast of Oregon will begin to move
southward on Saturday bringing another increase in precipitation
chances and cooler temperatures. The timing of this system does
not look to be in favor of convection at this time. However, if
this system slows in any manner, Sunday may see the potential for
some thunder activity, especially with the very damp
soils/moisture and the instability present with this cold low
pressure system. As the trough moves east to southeastward out of
the region, ridging will begin to move over the west coast
bringing a return to warmer temperatures and allowing things to
dry out well into the middle of next week.


Mountain obscuration due to clouds/precipitation in the Sierra
Nevada and Tehachapi Range. Thunderstorms are possible between 18z
today and 00z Friday. Otherwise, MVFR/IFR conditions in low ceilings
and precipitation will prevail for 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 high.

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


.HNX Watches/Warnings/Advisories...
Winter Storm Warning until 11 PM PDT this evening ABOVE 8000

Flash Flood Watch through this evening CAZ093>097.



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