506
AGUS76 KRSA 091429
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
730 AM PDT Thu May 9 2024

...WARMING THROUGHOUT THE WEEK AND OVER THE WEEKEND AS HIGH PRESSURE
BUILDS OFFSHORE...
...GENERALLY DRY CONDITIONS ASIDE FROM ISOLATED SHOWERS/T-STORMS
OVER NV THURS AND THE SIERRA/NV FRI/SUN/MON AFTNS/EVES...

.METEOROLOGICAL CONDITIONS (THU AM - WED AM)...

An elongated low is oriented ne to sw from NE all the way through
southern CA this morning as an upper ridge resides over the eastern
Pacific just offshore. The core of the upper low will continue to
progress back west towards the region the rest of today pushing the
ridge further offshore of CA with the northern end wrapping around
the low into the PacNW. The result will be both warming temperatures
and dry conditions for most of CA with continued below normal temps
for NV and se CA along with chances of isolated showers and
thunderstorms (mainly for E NV) in the afternoon/evening. This setup
will remain in place for Friday as well with the offshore ridge
bringing temperatures across nrn and cntrl CA 5-15 deg F above
seasonal normals while most of NV remains below normal due to the
upper low. The presence of the low will also generate additional
chances of showers and thunderstorms for the cntrl/srn Sierra and
much of NV.

On Saturday, the low will shift its trajectory and begin to head
eastward taking the core of the system into the Four Corners in the
morning. This will replace the more moist mid level air with dryer
flow from the offshore ridge as it is allowed to build into CA and
nrn NV. The intrusion of high pressure will allow for higher
temperatures to spread further across the region with most locations
above normal. While the ridge moves over land, models have an upper
low moving into the Gulf of Alaska sending a trough towards the
PacNW while a weaker low develops under the ridge just west of CA.
The PacNW trough will move through to the north throughout the day
Sunday sending some mid-level moisture and instability across the
CA/NV borders and over the Sierra. This may result in some isolated
showers and thunderstorms in the afternoon/evening. The trough will
exit the PacNW into ID/MT Monday morning. There is some uncertainty
after that as ensembles disagree on the 500 mb height pattern Monday
afternoon. The det GFS/ECMWF and some of the ensembles have an upper
low just sw of Point Conception with an upper ridge to the northwest
over the eastern Pacific. About 60% of the GFS/ECMWF/CMC ensembles
do not show the low offshore or have it weak enough to not make much
of a difference beyond cooling temperatures along the coast. The
GFS/ECMWF have this low along with the exiting system to our north
generating some mid-level moisture/instability over the Sierra as
well as parts of NV/nrn CA. This does creep into the NBM which
generates some precip over the Sierra Monday afternoon/evening,
isolated thunderstorms also possible. Should the low develop, it
looks to move to the south offshore of the srn CA coast into Tuesday
allowing the upper ridge to sneak back in closer to the west coast.
This will keep cooler conditions for central/srn coastal CA while
above normal temperatures by at least 5-15 deg F remain for the rest
of the region.

QPF over the next 6 days is fairly minimal the result of some
afternoon/evening convective showers/isolated thunderstorms
today/tomorrow and then again Sunday/Monday. Totals are forecast at
generally a tenth of an inch or less across the Sierra and parts of
NV with locally higher amounts possible should thunderstorms
develop. Freezing levels will continue to rise from west to east the
rest of the week up to 9.5-12 kft this afternoon with most of the
region above 10 kft by tomorrow afternoon. Levels then generally 10-
12.5 kft over the weekend rising to 11-13.5 kft early/mid next week.


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



AS

$$