776
AGUS76 KRSA 051430
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
730 AM PDT Sun May 5 2024

...SCATTERED SHOWERS & ISOLATED T-STORMS TODAY AS A SYSTEM EXITS THE
REGION FOLLOWED BY SHOWERS ALONG THE NRN CA/NV BORDERS MON INTO
TUES AS A DISTURBANCE MOVES THROUGH THE PNW...
...WARMING AND DRYING TREND BEGINS EARLY NEXT WEEK...

.METEOROLOGICAL CONDITIONS (SUN AM - SAT AM)...

Radar imagery capturing scattered showers this morning, mainly north
of I-80, as the upper low that began to move through nrn CA
yesterday enters NV. Most of CA saw at least some rain yesterday
between the upper low and the cold front/moisture plume. Highest
precip amounts over the past 24 hrs were across the northern/central
Sierra at 1" to just over 3" with about 0.50-1.25" across the rest
of northern/central CA. Several thunderstorms developed over nrn CA
yesterday afternoon/evening while the cold front/moisture plume
brought about 0.10-0.50" of precip to coastal soCal and 0.50-1.25"
in the mountains. Snow was also reported across much of the CA
mountainous areas.

The cold front and moisture plume will continue to progress to the
south this morning, exiting into Baja over the next few hours.
Meanwhile, the upper low will push further into NV allowing
scattered showers to persist along with chances of thunderstorms
over northern NV. The upper low will begin to exit to the east later
this afternoon and into the evening as high pressure builds into the
eastern Pacific/CA behind it. This will allow for conditions to dry
out for most of the region. The continued presence of the low today
will result in another day of far below normal afternoon high
temperatures by 10 to 25 deg F.

A weak disturbance will pass through the PacNW on Monday resulting
in chances of showers along the northern regional border through
Tuesday morning before joining with the current low to become a
larger system over the north central US. Over the eastern Pacific, a
stronger ridge will build keeping most of the rest of the region dry
into early next week and kicking off a gradual warming trend. The
pattern for the rest of the week will remain high pressure to the
west and low pressure to the northeast. The ridge will attempt to
push into CA throughout the week only to be battled back by
troughing from the larger upper low. This will result in some
moderation of the warming allowing interior CA and NV to remain
below normal while conditions rise to near/above normal for the
coast and into the Sacramento Valley. The large upper low over the
north central US will then split in two with the western edge
retrograding back towards the west coast into Thursday and kicking
the ridge offshore. Most ensembles are dry with the returning low,
but a handful show the potential for showers over the Sierra and
eastward into NV Thursday. For Friday, the low and ridge will battle
for positioning to determine the fate of the west. The 500mb height
clusters for 00z Saturday (Friday afternoon) are divided on how much
influence the low will ultimately have with the GFS members (like
its deterministic parent) more in favor of the low and the ECMWF the
ridge. The det GFS even shows some showers over the Sierra and
through to central NV Friday while the ECMWF is dry. This will
impact temperatures as well should the ridge push more into the
region, temperatures will be warmer than if the low is the more
dominant feature.

To summarize, continued scattered shower activity with isolated
thunderstorms and below normal temperatures today as a system exits
the region. Light showers along the northern regional border Monday
into Tuesday as a disturbance moves by to the north followed by a
warming and general drying trend the rest of the week with high
pressure to the west and low pressure to the east. Some uncertainty,
mainly for the end of the week into the coming weekend on how far
into the region and for how long a low will push in from the east.

Nearly all the QPF in the forecast is expected before Tuesday
morning. Today`s forecast was a blend of the morning WPC guidance
and the latest NBM. Highest amounts along the northern regional
border and into the srn OR Cascades with scattered showers of a few
hundredths to a tenth of an inch or so (higher amounts under
thunderstorms or heavier convective showers). QPF through Tues am:
075-1.60" srn OR Cascades, 0.10-0.75" Smith Basin, 0.10-0.50" nrn
CA/nrn NV borders (higher in the nrn NV mountains), and a few
hundredths to a couple tenths over the northern Sierra (scattered
showers possible across the rest of CA/NV).

Lower freezing levels hang around today at 3.5-6.5 kft north of
Point Conception before higher levels spread northward tomorrow.
Expecting freezing levels 4.5-9.5 kft north of I-80 Mon am and 7-13
kft to the south. Higher freezing levels will continue to spread
northward Tuesday staying generally above 7 kft through mid-week
(aside from the northern regional border at 4.5-6 kft). By Thurs
afternoon the entire region will be above 8 kft and up to 12.5 kft.


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



AS

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