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Hydrometeorological Discussion
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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
1240 PM PDT Fri Apr 12 2024

...WEEKEND STORM SYSTEM ON TAP WILL BRING COOLER/WETTER CONDITIONS...
...DRYING INTO NEXT WEEK WITH TEMPS RETURNING MORE SEASONABLE...

.METEOROLOGICAL CONDITIONS (SHORT TERM: FRI PM - MON AM)...

Already seeing a couple lines of precip fire this morning in the
area of diffluence ahead of the main upr low off the CA coast
crossing 130W at the latitude around Point Arena. The first is over
the Trinity Alps...while the second a bit more interesting from
Butte county toward the north-northeast with embedded convection and
numerous lightning strikes. Precip associated with the frontal
boundaries will begin to affect coastal areas of northern and
central CA overnight into Saturday...and then spreading inland and
southward as the area of low pressure reaches the coast near the SF
Bay Area and pinwheels several disturbances around the cyclonic
flow...which will serve as focal points for developing precip. The
upr low will move inland on Sunday and finally east of the area
either late Sunday or early Monday with precip tapering off through
the day. Over the next 72 hours...the best precip amounts are
expected across the higher terrain of northern/central CA with 0.75-
to 1.50-inches and some localized amounts closer to 2.00-inches over
the western portion of the Shasta Lake drainage where favorable
upslope flow occurs...and the Big Sur coast down to the Santa Ynez
mountains where a couple of the stronger disturbances rotating
through the area will cross.

Freezing levels will drop through Saturday as the cooler airmass
filters in across the area bottoming out late Saturday or early
Sunday from about 3500- to 6500-feet across CA (lowest northern and
central CA)...and then about 5500- to 7500-feet for NV.


.METEOROLOGICAL CONDITIONS (LONG TERM: MON AM - THU AM)...

Forecast remains on track with no real changes to the afternoon
update. An upper low exiting the region on Monday will bring some
lingering scattered showers in the morning. Conditions will dry out
in the afternoon as the system continues to move into the four
corners and an upper ridge builds into the eastern Pacific. High
pressure will slide into the west coast early next week as another
low travels south across BC. Differences between the models remain
on the trajectory of that low with the ECMWF still taking the system
on a more easterly path while the GFS has more of a southerly
component. Some of the GFS ensembles take the system closer to the
northern regional border than the det run as do a few of the ECMWF
members. Regardless, models agree that any resulting precip would be
fairly minimal. Not more than stray shower or two over the northern
regional border. QPF for the extended is still only some scattered
instances of a few hundredths of an inch or so with dry conditions
for the rest of CA/NV through Wednesday.

Freezing levels starting at 5.5-7 kft over eastern CA and NV as the
low exits rising from west to east once high pressure moves in.
Tuesday, expecting most of the region to be at 8-12.5 kft. The
northern low may lower levels along the northern regional border
down to 7-8 kft while the rest of the region rises to 9-14 kft N to
S into Wednesday.


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



Kozlowski/AS

$$
National Weather Service Weather Forecast Office
