CNRFC Hydrometeorological Discussion
Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
130 PM PDT Mon Mar 20 2023
...SCATTERED SHOWERS MAINLY OVER THE HIGHER TERRAIN AND OVER SRN CA
TAPER OFF THIS AFTERNOON AND EVENING...
...COOLER SYSTEM TONIGHT INTO WEDNESDAY WITH THE BULK OF PRECIP
ALONG THE I-80 CORRIDOR AND SOUTH...
...ANOTHER SYSTEM BRINGS PRECIP MAINLY TO SRN OR AND NRN CA AND NV
AND DOWN ALONG THE SIERRA THURSDAY INTO SATURDAY...
.METEOROLOGICAL CONDITIONS (SHORT TERM: MON PM - THU AM)...
No major changes to the afternoon forecast with the biggest changes
increasing amounts along the transverse range around 0.25-5 inches.
Isolate to Scattered showers mainly over Srn CA and along the Sierra
and over NV this afternoon and evening as one system exits to the
east an a cooler low pressure system approaches the west coast. The
colder upper level low and surface low along with associated trough
offshore of the CA coast (around 130W 37N) early Tuesday morning.
This system taps into a main subtropical moisture plume (about 1.3
inch) and streams it into Srn CA tonight into Tuesday morning.
Weaker moisture plume (Around an inch) moves along the Srn CA coast
Tuesday afternoon into the evening. The deterministic models in
better agreement with the low center just off the coast of the Bay
Area by noon Tuesday and then weakens and moves to the SE and inland
over the S Bay Area and into Central CA Wednesday and into NV
Wednesday night. Precip will increase along the Central and Srn CA
coast later tonight and continue into Tuesday. Northern CA,
especially the Russian and Napa basins and the east slope of the
coastal range will increase precip with the low along the Bay Area
coast Tuesday afternoon and evening. Precip will become more showery
Tuesday night into Wednesday night with upper level trough moving
through the region. The majority of the precip with this colder
system is expected around the I-80 corridor and south. Freezing
levels around 2500-3500ft near ORCA border and 3500-5500ft over the
Sierra and 5000-8000ft over Srn CA Tuesday morning and remain around
3000-5000ft Tuesday afternoon-Wednesday. Precip amounts Monday
night-Wednesday night generally are 2-6 inches across the transverse
Mtns (except up to 7.5 inches along the San Gabriel into San
Bernardino and into San Diego Cty Mtns and and 2-4 inches for the
Srn Sierra and Santa Cruz Mtns and Big Sur coast and 1-2 inches for
the Central Sierra and 0.75-1.5 inch for the Russian and Napa Basins
and east side of Coastal Range/west side Sac Valley and Nrn Sierra
and 0.25-1.25 over Nevada and Central Valley.
.METEOROLOGICAL CONDITIONS (LONG TERM: THU AM - SUN AM)...
Forecast remains on track with no major updates to the afternoon
forecast package. Lingering showers across the region on Thursday
due to the remnants of a surface/upper low impacting CA earlier this
week. The next upper trough will then approach the PacNW arriving in
the late afternoon/early evening. The southern end of the system
will scrape the CA/OR and northern NV borders through early Friday
morning bringing light precip along the CA/OR border and over nrn
NV. There is some disagreement between the models later Friday.
Though both show another burst of energy sliding down the backside
of the trough, the ECMWF has a deeper system that penetrates into
northern CA Friday night while the GFS is more shallow. This results
in precip spreading further to the south into nrn CA/NV Friday night
in the ECMWF solution compared to the GFS. The 12z ECMWF then
deepens this system Saturday morning until it engulfs the entire
region result in additional scattered light precip. The overall
pattern in the GFS is still a trough, but the system that moved
through the PacNW does not expand to the south as the ECMWF
predicts. This is creating QPF differences between the models for
Friday through Saturday with the ECMWF about 0.10-0.20" or so wetter
than the GFS in general, and about 0.50-0.75" wetter along the north
coast. Either way, additional light scattered showers are expected
on Saturday while the next surface/upper low approaches from the
Gulf of Alaska Saturday night into Sunday. Precip from this next
system is not expected during the current forecast period.
For the forecast, mainly stuck with WPC again resulting in only
minor changes from this morning's QPF. QPF 12z Thurs to 12z Sun is
as follows: 0.50-1.25" north coast (S to N), 0.75" to just over 1"
for the soOR Cascades, 0.25-0.50" for the northern Sierra, 0.10-
0.25" central Sierra/Shasta, and generally 0.10" or less elsewhere
across northern/central CA. Freezing levels to start out at roughly
3-4.5 kft for most of the region early Thursday. Levels will rise
over the se portion of the region and lower to the nw Thursday night
reaching 1-3.5 kft north of I-80 and 3-7.5 kft to the south early
Friday morning. Freezing levels will further decrease into Saturday
at under 500 ft along the CA/OR border and up to 5 kft by Point
Conception. These will fluctuate the rest of Saturday but lower back
down overnight.
|