Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PDT Thu Mar 23 2017

...WET PATTERN NEXT FEW DAYS...

.24 HOUR PRECIPITATION TOTALS (ENDING MAR 23 AT 500 AM PDT)...

A frontal system brought precip to the region yesterday, heaviest
over the Sierra Nevada and eastern NV. Over the Smith basin, around
0.3-0.6" fell, with 0.10-.25" over the Eel R Basin. Amounts dropped
off over the Russian/Napa to less than 0.1", but intensified again
over the Santa Cruz and Santa Lucia Mtns, where 0.3-0.6" was
reported. Isolated spots in the transverse ranges of Southern CA,
and the San Diego County mtns measured up to 0.5" as well, while the
rest of the SoCal coasts and Valleys picked up under 0.1".

The Shasta Basin reported around 0.3-0.6", with up to 0.8" along the
east side. Over the Northern and Central Sierra, amounts ranged from
0.5-1", with up to 1.3" in some areas. The Southern Sierra measured
around 0.25-0.5" precip. East of the crest, around 0.25" fell.
Eastern NV around the Ruby Mtns reported 0.5-1" precip.


.METEOROLOGICAL CONDITIONS (SHORT TERM: THU AM - SUN AM)...

An upper-level trough axis is now pushing east of the region.  Light
showers continue for areas such as SW CA, the Grapevine area, and
the ern half of NV.  Expect this activity to diminish today.

Meanwhile, expect moisture and isentropic lift to begin increasing
over the north coast by this afternoon.  This timeframe should mark
the onset of light precip on the north coast, with precip spreading
inland this evening.  As the cold front nears and forcing aloft
increases, expect the potential for areas of heavy precip in nrn CA
coastal areas, the nrn Sierra, and the Shasta drainage tonight
through Fri.  As precip pushes south and east Fri night, forcing and
moisture are expected to diminish, leading to diminishing precip
rates as well.  Precip should end by Sat night.  Freezing levels in
the Sierra should start 5000-10000 ft and lower to 5000-7000 ft.


.METEOROLOGICAL CONDITIONS (LONG TERM: SUN AM - WED AM)...

Sunday begins with a frontal system approaching the North Coast,
with a fairly broad blob of moisture (pwat~1.2") sitting off the
coast. An upper trough moving through CA/NV on Sunday and Monday
will propel this front through the region, and bring cooler
temperatures as well. Model agreement isn`t great with respect
towards timing, with the EC bringing the front inland about 6-12
hours earlier than the GFS, Sunday afternoon rather than late Sunday
night. Additionally, the 00Z and 06Z GFS runs brought a stronger
vort max through the coast and Northern Sierra timed with the
frontal passage, resulting in heavier precip for those areas on
Monday. Took a middle of the ground approach for now, though hedging
a little closer towards the timing of the EC as it was more in line
with the Canadian.

Expect the focus to shift to Nevada on Tuesday as the upper trough
moves through, with the precip winding down across the board by
Wednesday morning. Freezing levels during this time period are
expected to start out around 6000-ft near the OR/CA border, and
around 8000-ft over the Sierra. Expect cold air along the front to
quickly lower them on Monday to around 4000-ft near the OR/CA
border, and around 6000-ft over the Sierra.


.HYDROLOGICAL CONDITIONS...

A series of storm systems and current reservoir releases are
expected to maintain moderate to high flows on many California and
Nevada rivers and streams into next week.  The Humboldt river in
Nevada can expect stages to remain above floods levels into next
week at least.  Numerous stages are currently above or forecast to
rise above monitor levels across the northern half of California and
Nevada through the weekend.


More information on the CNRFC website at http://www.cnrfc.noaa.gov

JM/KL/JM/AM

$$



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