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AGUS76 KRSA 301515
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
830 AM PDT Tue Apr 30 2024

...LIGHT PRECIP POSSIBLE OVER FAR NORTH INTO THURSDAY AS SYSTEMS
BRUSH BY TO THE NORTH...

...PRECIP POSSIBLE LATER FRIDAY INTO THE WEEKEND BUT UNCERTAINTY IN
DETAILS ESPECIALLY THE SRN EXTENT OF PRECIP...

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

Upper level ridge over the Central Eastern Pacific (centered around
150W) with a trough over the NW U.S.. A disturbance moving into the
Pac NW this morning then digging into the Great Basin tonight into
Wednesday morning and another disturbance entering the Pac NW
Wednesday night and into the Great Basin Thursday.  These
disturbances will brush by the far north portion of the region for
periods of light precip possible over the Srn OR Cascades and far NW
CA coast and Nrn NV today through Thursday.  Precip amounts expected
to be generally around a tenth of an inch or less each day but up to
around a quarter of an inch possible over the Srn OR Cascades and
Wednesday and Thursday. Freezing levels generally around 3000-5000
ft over Srn OR and far NW CA and around 5500-7500 ft over Nrn NV
today rising to around 7000 ft and higher Wednesday afternoon and
dropping to around 5500 ft over Srn OR Cascades on Thursday morning.

Weak ridging over the region early Friday in between systems as the
trough over Nrn Great Basin shifts to the east and an upper level
low pressure system approaches the NW Coast.  There is model and
ensemble member variability with the timing track and strength of
this system for lower confidence in precip amounts and areas
(especially the southern extent of precip) and timing for late
Friday into the weekend. The det 06Z GFS is farther south with the
low off the Nrn CA coast Saturday morning and moving through Central
CA and into Srn NV Sunday. The det 00z EC has the low off the Pac NW
coast Saturday morning and brings it inland through the Pac NW and
Nrn CA Saturday afternoon into Sunday. The 24 hr QPF 50th percentile
clusters ending 00Z Sunday show a range of solutions from cluster 3
22% of members (Canadian 5% and GFS 17% and EC 32%) showing only
light precip over NW CA coast and Srn OR Cascades to Cluster 4 21%
of the members (canadian 35%, GFS 20% and EC 16%) to precip spread
across Srn OR and Nrn CA and even into the South Bay Area with
amount up 1-2 inches along the Nrn CA coast and 0.75-1.5 inches for
the Shasta Basin and Nrn Sierra and Srn OR Cascades.  The forecast
mainly uses a combination of the NBM and WPC for Friday into the
weekend. Precip may start as early as Friday afternoon over the NW
CA coast and Srn OR Cascades and increase and spread south and east
into Nrn NV and possibly Central CA Friday night into Saturday.
Precip tapers off Saturday night into Sunday. Highest precip amounts
(around 1-1.75 inches) expected over the NW CA coast and Srn OR
Cascades and Nrn Sierra.  Freezing levels will vary with the exact
track of the low and are currently forecast to drop to 3000-5000 ft
over Nrn CA Saturday and around 5000-7000 ft over Central CA and Nrn
NV Saturday night and rising on Sunday.


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



Osborne

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