Area Forecast Discussion
Issued by NWS San Joaquin Valley, CA

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FXUS66 KHNX 201057

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
357 AM PDT Tue Mar 20 2018

Clouds will increase tonight with the approach of a storm over
the Eastern Pacific. This storm will bring substantial
precipitation to the district from late Tuesday through Thursday
along with very mild temperatures over the higher elevations.
Friday through Saturday will be dry and unseasonably cool.


A change in the weather over Central California is quickly
approaching from the Eastern Pacific as precipitation makes its
way onshore this morning. Water vapor satellite imagery is still
showing a well defined circulation between Hawaii and the West
Coast able to wrap moisture around it that is now headed for
California. Based on Blended precip-water imagery, the storm
headed for California is very much an Atmospheric River type with
the potential for very heavy precipitation rates. Regional Doppler
radars and satellite rain rate imagery indicates light rain
offshore that will push onshore sometime this morning. At the
present moment, will observe the atmosphere moisten today before
measurable precipitation begins over the Central California
Interior. Currently, timing of the onset for measurable
precipitation is set for after 11 AM PDT with heavier
precipitation occurring later today (5 PM PDT). Therefore, a
Winter Storm Warning has been posted for the Sierra Nevada above
8000 feet which is expected to start after 5 PM PDT early this
evening. Due to the fact that subtropical moisture will stream
into the region, the source of the moisture is from a warm region
which will keep snow levels at very high elevations during the
event. Furthermore, because of the precipitation potential of the
Atmospheric River event, a Flood Watch remains in effect for
Central California below the 8000 foot elevation level.

Model confidence remains high in developing an Atmospheric River
event across Southern and Central California during the Wednesday
and Thursday time frame. While models still showing some
uncertainty in the position of the upper low off the west coast
toward next Tuesday, that uncertainty is becoming minimal as they
all still lean toward shifting and consolidating a closed low
circulation some 800 miles West of San Francisco that will support
the eastward surge of subtropical moisture into the region. As
the upper low shifts eastward, it will push a strong +110 knot jet
onto the West Coast that will allow for a good surge of moisture
into the area later today. With the upper level circulation
consolidating, models show better dynamic lift developing on
Wednesday and into early Thursday. Therefore, while precipitation
will start today, the heaviest precipitation will occur on
Wednesday with the best dynamic lift. Furthermore, Model
Integrated Water Vapor Transport and Standardized Anomaly Analysis
still support the arrival of subtropical moisture into the region
later Today. Standardized Anomaly Analysis is almost off the
record with standard deviation values of up to 4 above
climatological normals. Observed and progged precip-water values
of an inch and above could reach the district on Wednesday.

Furthermore, Ensemble model precip-water return interval analysis
is showing this event as a 1 day in every 5 to 10 years which
makes it a not so common event. Therefore, confidence is high that
significant precipitation will reach the area around the mid-week
period before models place a stronger ridge pattern over the west
around next weekend. Therefore, before the ridge pattern, the
district will remain unsettled with precipitation potential
through at least the end of the week. Models show the cold front
finally pushing through California Thursday afternoon which will
help to diminish the generation of precipitation across the area.
While minor storm will continue to push through the region beyond
Thursday (over the weekend), the potential for precipitation
generation will not compare to the Atmospheric River event. By the
start of next week, models hint toward a developing ridge pattern
that may allow for a brief break in the weather.


Mountain obscuration due to clouds/precipitation in the Sierra
Nevada and Tehachapi Range after 21z today. 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 medium.

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


.HNX Watches/Warnings/Advisories...
Winter Storm Warning from 5 PM this evening to 11 PM PDT Thursday
ABOVE 8000 FEET FOR THE Sierra Nevada from Yosemite to Kings
Canyon and the Tulare County Mountains /CAZ096-097/.

Flash Flood Watch from Wednesday afternoon through Thursday
evening for the Foothills and higher elevations of the Sierra
Nevada along with the Kern County Mountains /CAZ093>097/.



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