Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 151542

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PDT Sun Apr 15 2018


Special Note: This will be the last HMD of the 2017-2018 winter
operational season. The next issuance of this product will be
October 15 2018 unless conditions warrant a special issuance.


The upr low spinning over the Gulf of Alaska has started to dive
toward the southeast with WV/IR imagery showing the primary
circulation spinning near 47N/136W this morning. Blended TPW imagery
shows a fairly narrow plume of moisture entrained into the system
just ahead of the cold front located just off the northwest CA
coast. Trimble IWV sensors just north of Eureka indicate values
hovering right around 0.75-inch intersecting the coast.

Models continue in reasonable agreement with the progression of this
system across the region with precip increasing along the north
coast this morning...beginning to spread inland and southward as the
cold front moves in from the northwest. Best precip will associated
with the cold front and will be focused along the coast from Cape
Mendocino northward and inland over the Shasta Lake drainage down
across the northern Sierra to approximately Lake Tahoe. Freezing
levels will start today close to 5000-feet over far northwest
CA...9000-feet along the I-80 corridor...and greater than 10000-feet
for central and southern CA into southern NV.

As the cold front continues to progress inland and to the south on
Monday...the cooler airmass will settle in across the region with
the story for tomorrow being the potential for convective precip
becoming a bit more dominant. The upr trof axis will begin to shift
inland late morning and be overhead across northern/central CA
during the afternoon hours...which looks to be ideal for the
development of scattered showers and thunderstorms. Freezing levels
will plummet with the passage of the cold front and the cooler
airmass from the northwest settling in across the area. Near the
CA/OR border freezing levels will drop to near 2000-feet...along the
I-80 corridor down across central CA 3000- to 4000-feet...and 4500-
to 6000-feet for southern CA inland toward far southern NV.

A brief break from the precip will occur across most areas on
Tuesday as a weak transitory upr ridge slides overhead from the
west. The next system moving east along 50N will dive southeast
toward the north coast on Wednesday...and be located just west of
Cape Mendocino during the afternoon hours. Models are in a bit
better agreement with the timing and trajectory with this system as
compared to earlier model runs. Precip will spread from WNW to ESE
from Wednesday into Thursday as the upr low crosses overhead near
Sacramento early Thursday and then moves across central NV during
the daytime hours before exiting to the east and reaching the Four
Corners area Friday morning. Precip will taper off for Day 6 into
the following weekend. Freezing levels near the core of the system
will drop between 3500- and 5000-feet...before rebounding behind the


The Truckee River at Truckee remains at flood stage threshold due to
continued release from Lake Tahoe. All other locations in the CNRFC
forecast area are below monitor stage and are forecast to remain so
through the 5-day forecast window. Runoff production from watersheds
is generally in recession throughout the CNRFC forecast area.
Increases in river flows are generally the result of either
reservoir regulation or snowmelt.

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



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