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AGUS76 KRSA 221457

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

800 AM PDT Fri Mar 22 2024



...SPRING CONDITIONS TURNING MORE UNSETTLED INTO NEXT WEEK...



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



The pattern shift is well underway from a quieter spring-like regime 

to unsettled and cooler conditions as the upr ridge along the west 

coast shifts a bit farther inland...and upr troffing over the 

northeast Pacific makes its way toward the region. Radar imagery 

already showing the leading edge of precip making its way onshore 

along the north coast from the CA/OR border down to about Cape 

Mendocino...while precip gauges since 22/12Z show anywhere from 0.25-

to 0.50-inch (local to 0.75-inch over the King Range) falling along 

the immediate coast. This feature will slowly make its way across 

the region...while individual disturbances making their way through 

the cyclonic flow aloft carves out a broad upr trof across the 

western US all the way downstream to the Rocky Mountain states. 

Finally by early next week...the core of the system along the west 

coast located over western OR will dive south-southeast before 

kicking inland pretty much along the US/MX border...allowing for 

broad anti-cyclonic flow to set up over the eastern Pacific and 

west coast on Monday.



Widespread precip is anticipated with this system...spreading across 

much of CA and NV through the weekend...with the deserts of 

southeast CA looking the least favorable for measurable amounts. 

Greatest totals are expected along coastal locations from the upper 

portions of the Russian River basin northward to the Smith River 

basin...and then inland over the Shasta Lake drainage down across 

much of the Sierra with 1.00- to 3.00-inches. Across the rest of the 

coast from the lower Russian River basin to the CA/MX border...look 

for amounts to generally range between 0.50- and 1.50-inches. 

Central Valley locations will see anywhere from 0.25- to 0.75-inch. 

As the cooler airmass moves in with this system...look for freezing 

levels to drop...bottoming out early Sunday as the core of the 

system moves over the area. Currently...freezing levels are from 

7000-feet northwest to 10500-feet southeast...and about 8000- to 

9000-feet along the I-80 corridor. Early Sunday...these will have 

fallen to about 3500-feet northwest and 5000- to 6000-feet 

southeast (about 4000- to 4500-feet along I-80).





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



Light lingering showers on Monday, mainly across nrn CA/srn OR/nrn 

NV, as one system exits and a weak front/upper shortwave moves into 

the PacNW. Not expecting more than a few hundredths to a tenth of an 

inch or so for most locations with 0.10-0.25" locally around parts 

of the north coast and a bit higher over the crest of the Cascades. 

Models have the next system approaching Tuesday from the Gulf of 

Alaska as a surface/upper low while some brief ridging builds in 

over the west coast. Some uncertainty for Tuesday on how widespread 

any lingering showers will be. Some ensemble members are essentially 

dry while others show potential for more widespread 0.25-0.50" at 

least of precip. Initial showers from the low are forecast to arrive 

later in the day and in the overnight period. Given the uncertainty, 

went mainly with the latest NBM and blended in a little of the 

morning WPC guidance along the north coast. This amounts to 0.10-

0.25" for most of the north coast and 0.25-0.50" over the Smith 

Basin. Showers in the official forecast mostly limited to areas west 

of I-5 and over ne NV.



The low will continue to approach the PacNW from the Gulf of Alaska 

into Wednesday sending a front towards nrn CA. Det models show more 

moderate/locally heavy precip spreading across northern CA Weds 

morning before moving across the interior and into central CA some 

time in the afternoon. There are some timing and positional 

differences regarding the system between the models and amongst the 

ensembles that are making for some uncertainty in the precip. 

Looking at the 24 hr QPF clusters ending 00z Thurs, ensembles are 

split into 3 clusters at 50%, 32%, and 18%. Cluster 1 is mainly 

composed of the GFS/ECMWF members showing more moderate precip along 

the north coast and lighter showers reaching the central Sierra and 

Bay Area. Cluster 2 contains 85% of the CMC ensembles and is slower 

timing wise confining precip to the nrn CA coast and into Shasta. 

Cluster 3 is the quickest taking precip across most of the Sierra 

and into the central coast. For now, the official forecast is closer 

to cluster 1 taking precip into the Bay Area in the afternoon 

spreading further across the state in the evening/overnight. The 

majority of the QPF in the extended is expected on day 6 (Weds into 

Thurs) with the highest amounts along the north coast, over Shasta, 

and across the Sierra. QPF for Weds: 1-2" north coast (locally 2-

2.5" Smith Basin/Kings Range), 1-1.75" Shasta, 0.75-1.75" Sierra, 

and 0.10-0.75" Bay Area/central coast/down the valleys (locally 

closer to 1" in the foothills. Not expecting precip to make it south 

of Point Conception.



Freezing levels Monday 4.5-7.5 kft n to s across the region rising 

across southern areas Tuesday up to 6-9 kft south of I-80. Higher 

freezing levels will spread with the brief ridging up to 5.5-8.5 kft 

north of I-80 and 8.5-11 kft to the south by Weds am. The 

approaching low and front will lower freezing levels nw to se the 

rest of the period down to 3-4.5 kft north of I-80 and 4-7 kft from 

I-80 to Point Conception.





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







Kozlowski/AS



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