Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 231726
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Fri Feb 23 2018

...MAINLY LIGHT PRECIP IN THE NORTH THROUGH THE END OF THE WEEK THEN
MORE WIDESPREAD MAINLY LIGHT PRECIP FIRST HALF OF NEXT WEEK...

.METEOROLOGICAL CONDITIONS (SHORT TERM: FRI AM - SUN NIGHT)...

Aside from a few showers in SW CA, it appears precip has essentially
ended over the region as an upper trough moves into NV.  Could see a
few additional light showers over the southern Sierra and eastern NV
today with little accumulation expected.  Expect yet another system
to move in from the NW and bring light precip to mainly far northern
CA, southern OR, and northern and central NV tonight through Sat
night with freezing levels 2000-4000 ft.  Sun into Sun night, expect
a stronger system to approach from the north.  This should bring
light amounts to northern CA/NV and southern OR by late Sun night,
with more moderate amounts for the far north coast and southern OR
Cascades.  Expect freezing levels around 1000-3000 ft.


.METEOROLOGICAL CONDITIONS (LONG TERM: MON AM - THU AM)...

With the upr ridge continuing to reside over the eastern Pacific
near 150W...the door will be open to cooler systems dropping down
the west coast toward CA and NV. Models in reasonable agreement with
the next in a series of systems diving in from the north on Monday.
The trajectory of this s/wv trof is either right along or just
outside of the west coast...which will allow the system to draw in
some Pacific moisture. PW values just ahead of the cold front will
reach near 0.50-inch. Precip will shift from areas near and north of
the I-80 corridor early on Monday to central and southern sections
later on Monday. Freezing levels will drop somewhere between 1000-
and 3000-feet for the northern half of the area and for the southern
half of the area generally from 3000- to 5000-feet. This system will
then exit the area to the east on Tuesday.

Beyond this system...the forecast become a bit more mottled as the
models are struggling a bit with a s/wv trof moving through the
Pacific Northwest late Tuesday into Wednesday and then a potential
stronger s/wv trof dropping south along the west coast on Thursday.
With the Wednesday system...the 23/00Z GFS is a bit faster bringing
light precip to the far northern portions of the region...while the
23/00Z EC lags a bit on the timing. Then...the bigger differences
show up with the Thursday system. The EC continues to show a cold
upr low dropping south toward the region...but instead of keeping
this feature offshore for a longer period of time (yesterday/s
thinking)...the EC shifts the upr low inland near the CA/OR border
now. The 23/00Z GFS completely dropped the idea of an upr low. So
right now...confidence is rather low with the Thursday into Friday
system.


.HYDROLOGICAL CONDITIONS...

Hydrologic response over the past 24 hours has been minimal for many
rivers in the CNRFC domain due to low snow lines and fairly light
precipitation. The precip expected Sun/Mon will result in only minor
rises, focused mainly along the northern coast of CA.  All river
forecast locations are expected to stay well below monitor levels
through the forecast period.


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

KL/DRK/BW

$$



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