935
AGUS76 KRSA 221333
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
635 AM PDT Tue Apr 22 2025

...SCATTERED PRECIP NEAR THE CA/OR BORDER TODAY INTO WED...
...COOLER AND BROADER SYSTEM IMPACTS THE REGION THU THROUGH SUN...

.METEOROLOGICAL CONDITIONS (TUE AM - MON AM)...

A weak positively tilted s/wv trof currently resides over the
Pacific Northwest back to just off the OR coast this
morning...tracking to the southeast toward northern CA. This feature
is expected to generate enough forcing for scattered showers
primarily over the Shasta Lake drainage up toward the Northeast CA
Plateau both today and then again on Wednesday as the overall system
swings across northern CA and then shifts northeast toward the
northern Rockies.

Then into Thursday through the upcoming weekend...a slow moving
negatively tilted longer wave upr trof will make its way toward the
west coast before eventually forming a cutoff upr low over northern
CA later Friday into Saturday and then shifting eastward across the
Great Basin on Sunday. Given this late season system...the 22/00Z
deterministic models are actually in reasonable agreement this
morning (much better than the previous few model cycles) in the
evolution of this system across the area. Initially on
Thursday...look for scattered showers to develop over the Trinity
Alps and the southern Cascades...in an area of diffluence aloft.
Then by Friday...the axis of the upr trof reaches the west coast
with a broader area of scattered showers encompassing northern and
central CA and portions of northern/western NV. For the
weekend...the upr low is anticipated to be pretty much overhead
northern CA...which should bring for an interesting day of precip.
With the cold air aloft in the core of the system...and any daytime
heating...could see numerous showers and probably even some t-storms
develops in the afternoon and early evening hours. Freezing levels
near the core of the system look to drop down to 4000- to 5000-feet
or so. Finally by Sunday...the slow moving system will shift off
toward the east across the Great Basin...with the best opportunity
for precip affecting the Humboldt River basin.


QPF graphics are available at www.cnrfc.noaa.gov/qpf.php



Kozlowski

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