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CNRFC Hydrometeorological Discussion

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