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AGUS76 KRSA 311515

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

815 AM PDT Sun Mar 31 2024



...SCATTERED SHOWERS AND ISOLATED TSTORMS OVER SRN CA/NV THRU MON...

...DRYING FROM NW TO SE STARTING MON AS A RIDGE BUILDS INTO THE WEST 

COAST...

...NEXT SYSTEM ARRIVING MID-LATE WEEK RETURNING PRECIP CHANCES 

ACROSS MUCH OF THE REGION...



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



Over the past 24 hours srn CA has seen 1-3" of precip with amounts 

in the hills up to 4" thanks to a moisture plume and vertically 

stacked low that has been slowly traveling southward off the CA 

coast the past couple of days. The low now sits offshore of the srn 

CA coast with a weakening surface trough offshore and a second upper 

low over NV. This is resulting in thunderstorms being generated just 

off the coast of srn CA and convective showers over land mainly from 

LA County southward. The second upper low over NV is producing a 

line of showers near the I-80 corridor across nrn NV. The offshore 

low will continue to slowly journey to the south the rest of today 

as the NV upper low moves into UT. This will keep scattered showers 

going across much of NV as well as srn CA into the Sierra. The 

offshore low will also generate thunderstorms across srn CA/NV. By 

the evening, the system will have stretched into a long positively 

tilted trough from offshore of Baja all the way through MT/WY. This 

will allow for continued shower activity overnight. QPF for the rest 

of today is 0.30-1" for far southern CA over coastal San 

Diego/Riverside counties and 0.10-0.75" for the rest of the coast. 

Locally higher amounts possible under thunderstorms or heavy 

convective showers. HREF exceedance probabilities show 10-30% 

chances of 0.50"+/hr rain rates and just less than 10% chance of 

isolated 1"/hr rates for today. Difficult to pin down QPF when 

amounts are heavily dependent on potential thunderstorms. Even high 

res models are not generally good at predicting the location and 

timing of developing storms. For the rest of the region: 0.10-0.75" 

for the central/southern Sierra and NV mountains, and a few 

hundredths to a couple tenths elsewhere. Again, locally higher under 

any thunderstorms.



Monday morning, the system will begin to shift further inland 

becoming displaced by an upper ridge building into the west coast 

from the eastern Pacific. The ridge will act to dry conditions 

across much of the region while also raising temperatures to above 

normal for northern areas as well as freezing levels. The continued 

influence of the trough over seCA and NV will keep shower and 

isolated thunderstorm chances for much of Monday. The ridge will 

gradually take over the rest of the day spreading across CA/NV 

overnight and dominating the pattern for Tuesday. High pressure will 

keep the region dry on Tuesday and bring temperatures for nrn/cntrl 

CA 5-15 deg F above seasonal normals. 



The next system will approach into Wednesday from the Gulf of Alaska 

and begin to push the upper ridge further inland. Troughing will 

move in just offshore of the west coast Wednesday morning bringing 

some initial light showers into nw CA before spreading inland along 

the OR border the rest of the day and then southward into the Sierra 

in the evening/overnight. The trough will form a closed low 

overnight as well before the system begins to shift its trajectory 

eastward heading inland late Thursday morning into the afternoon. 

This will spread showers further south across central CA and inland 

into NV. The system will continue its inland journey on Friday as 

well keeping chances of showers going to end the work week. There 

are some differences between the models on the progression of this 

system, particularly on how quickly it moves through once it shifts 

its movement eastward. The ECMWF is slower holding the center of the 

system over NV early Saturday morning while the GFS already has the 

system into the Four Corners. Either way, precip produced by the 

trough is not expected to be significant as models only forecast 

about 0.25-0.50" or so PW overhead as the low/trough moves through. 

Highest precip amounts in the extended expected over the Sierra and 

over nrn CA/NV. QPF 12z Weds-12z Sat: 0.50-1.50" Sierra/Shasta, 0.25-

0.75" nrn CA/nrn NV (0.50-1.25" NV mountains), 0.10-0.50" along the 

CA coast, and a few hundredths to 0.30" down the valleys.



Freezing levels 5-7 kft the rest of the weekend then rising from nw 

to se as a ridge builds in Monday. Expecting 8.5-10.5 kft for the 

nrn CA coast early Monday before higher levels spread across the 

region the rest of the day. By Tues am, expecting 9.5-11 kft north 

of Point Conception and 7-9.5 kft for s/e CA/NV. Freezing levels 

lowering again mid/late week as the next system moves in. Thus am, 

freezing levels 2-5.5 kft north of I-80 and 4-11.5 kft to the south. 

Lower levels spreading across the region into Friday down to 2-3.5 

kft north of Point Conception across CA and 4-8.5 kft to the 

south/east. By the afternoon, expecting the entire region down to 

2.5-5.5 kft.





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







AS



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