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Hydrometeorological Discussion
Issued by NWS California-Nevada RFC
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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
730 AM PDT Fri Apr 19 2024

...WARM AND GENERALLY DRY INTO MONDAY ASIDE FROM ISOLATED
SHOWERS/TSTORMS FOR THE CNTRL/SRN SIERRA THIS AFTN/EVE...
...CHANCE OF PRECIP MID TO LATE WEEK AS A LOW APPROACHES THE CA
COAST...

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

Generally dry conditions across the region today as a ridge passes
across the west coast. An embedded shortwave moving through soCal
later today may result in some isolated showers/thunderstorms over
the central/southern Sierra in the afternoon/evening. Dry conditions
will persist into the weekend as the area remains under high
pressure. A surface low and upper trough will approach the PacNW
Saturday from the Gulf of Alaska before moving through WA in the
afternoon/evening. A few stray showers may reach the CA border, but
otherwise precip is forecast to remain far to the north. Behind that
low, high pressure will move into the eastern Pacific centered west
of the PacNW for Sunday. This will keep the area dry the rest of the
weekend and through Monday.

Uncertainty grows as we get deeper into next week due to model
differences. The GFS/ECMWF generally agree that two lows will
approach on Tuesday, one offshore of BC coming from the Gulf of
Alaska and another approaching from west of CA. The models have
these systems in different positions relative to each other as well
as differences in timing. The ECMWF has the northern low reaching
the BC coast Tuesday afternoon while the GFS has the same low just a
bit further offshore and closer to WA/OR. In spite of these
differences, both models are predicting some light showers across
nrn CA/NV for Tuesday. The other difference comes with the low west
of CA. Both models have the low shifting to the south towards soCal
on Tuesday, but the GFS speeds up the systems arrival across coastal
soCal to mid Weds morning while the ECMWF still has it much further
out to sea. In fact, the ECMWF does not have the low arriving until
Thursday morning while the GFS already carries the now open trough
into AZ with another system dropping in from the nw. The CMC is on
the slower side as well more in line with the ECMWF, but still with
some differences. Looking at the ensembles, timing varies from
Tuesday to Thursday on the arrival of precip from the southern most
low. Either way, this system is not expected to produce significant
amounts of precipitation. Will keep an eye on the models over the
weekend and hopefully they will come into better agreement.

As for temperatures, expecting afternoon highs to be 5-15 deg F
above normal away from the coast through Monday. Temperatures will
then lower from west to east early to mid week as the low
approaches. Timing of the cool down will depend on when the low
arrives, but when it does expecting afternoon highs down to 5-10 deg
F below normal for most of CA. Freezing levels 8-12 kft N to S
through Sat am rising to 8.5-13 kft Sat afternoon with higher
freezing levels spreading northward throughout the rest of the
weekend. Freezing levels to then lower mid week down to 7-10.5 kft
then 6-10 kft depending again on the timing of the next low.


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



AS

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National Weather Service Weather Forecast Office
