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AGUS76 KRSA 121433

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

735 AM PDT Fri Apr 12 2024



...COOLER AND UNSETTLED CONDITIONS THROUGH THE WEEKEND...

...DRYING WITH SOME WARMING INTO NEXT WEEK...



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



The pattern transition is well underway with yesterday being the 

peak of the warm above normal temperatures across the region as high 

pressure along the west coast shifted inland with the upr ridge axis 

moving downstream toward the Rocky Mountain states. The cool area of 

low pressure dropping south-southeast out of the Gulf of Alaska is 

crossing 30N just outside of 130W with an initial frontal boundary 

stretched from the northern CA coastal waters back toward the 

southwest and then another cold front closer to the primary 

circulation with the coldest airmass behind this boundary. Through 

much of Friday...precip scattered precip will develop in the 

diffluent area in the northeast quad of the upr low close to the 

CA/OR border and across the northern/central Sierra with southwest 

upslope flow. The main precip band should remain near or just off 

the immediate coast...finally starting to shift inland as the upr 

low approaches the coast near the SF Bay Area. The best precip 

through Saturday at 12Z will be from the upper portions of the Eel 

River basin southward across the Russian River basin...Santa Cruz 

Mountains...and Big Sur coast. Also with flow around the upr low 

being from the south-southeast through the Sacramento Valley...look 

for some upslope conditions to develop over the western portion of 

the Shasta Lake drainage and northwest side of the Sacramento Valley 

near Clear and Cottonwood Creeks.



Saturday looks to have the most impacts from the incoming system as 

the circulation moves onshore and pinwheels individual disturbances 

through the primary cyclonic flow. Best precip looks to fall all the 

way from the upper Klamath River basin down across northern and 

central CA...and then portions of the transverse mountains between 

Santa Barbara and Los Angeles counties. Look for general totals of 

0.50- to 1.00-inch with some localized higher amounts approaching 

2.00-inches where favorable dynamics or upslope flow exist.



Finally...into Sunday...the system will make its way east of the 

area toward the 4-Corners region. Best precip will fall across 

northeast CA and northwest NV where a deformation axis sets up and a 

secondary area near Point Conception as a disturbance rounds the 

base of the overall system. Otherwise...the trend will be downward 

in terms of precip coverage and intensity.



Freezing levels peaked yesterday with the most notable decrease this 

morning closer to the primary circulation from northwest CA up 

toward the crest of the southern OR Cascades (6000- to 7500-feet). 

Elsewhere...freezing levels are generally from 8500- to 11500-feet 

from northwest to southeast across the region. The cooler airmass 

will filter across CA on Saturday and then NV on Sunday. For CA 

these will bottom out between 3500- and 6500-feet (lowest for 

northern CA)...and about 5500- to 7000-feet across NV. 





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



Lingering showers over soCal and NV Monday morning as an upper low 

continues to exit the region into AZ/UT. Only expecting a few 

hundredths of an inch or so of additional precipitation before 

conditions dry out across the region. High pressure will build into 

the eastern Pacific behind the low pushing inland as the prior 

system moves further into the Four Corners. At the same time, 

another low will move through BC towards the PacNW. Once the weekend 

low moves out of the region, high pressure will take over keeping 

dry conditions across CA/NV later Monday and Tuesday. There is some 

disagreement on the path of the low coming out of Canada early next 

week. The GFS is taking the system on a more southerly trajectory 

into eastern WA, OR, and ID Tuesday while the ECMWF moves the system 

eastward into MT. By early Wednesday morning, the GFS has the core 

of the low over northern MT into ID with the backside of the system 

stretched across ID just north of the NV border while the ECMWF has 

the low over ND. The result is the GFS predicting some light showers 

reaching nrn NV while the ECMWF does not. A handful of the ECMWF 

ensembles show some showers as well as the GFS members. In any case, 

whatever path the low takes it is not expected to produce any 

significant precip over the region. Bottom line, light lingering 

showers early Monday over srn CA and NV as a low exits to the east 

followed by mostly dry conditions the rest of the extended. 



The morning forecast was mainly WPC guidance with a little of the 

latest NBM. Three day totals are not more than some scattered 

instances of less than a tenth of an inch. 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 8-11.5 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 9-13.5 kft N to S into Wednesday.





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







Kozlowski/AS



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