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AGUS76 KRSA 221454

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

800 AM PDT Mon Apr 22 2024



...MOSTLY DRY CONDITIONS TODAY ASIDE FROM SLIGHT CHANCE OF ISOLATED 

SHOWERS/TSTORMS OVER THE CNTRL SIERRA AND CNTRL NV

...ABOVE NORMAL TEMPERATURES AGAIN TODAY BEFORE COOLING KICKS OFF 

THE REST OF THE WEEK ALONG WITH A RETURN OF PRECIP CHANCES...



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



An upper ridge remains over the eastern Pacific as a weak surface 

low develops offshore of nrn CA. Ridging will keep the majority of 

the region dry today with continued above normal temperatures at 5-

15 deg F. The exception will be slight chances of isolated 

showers/thunderstorms over the central Sierra and eastward through 

central NV this afternoon/evening. The surface low will continue to 

form offshore overnight and throughout Tuesday potentially resulting 

in some scattered showers across nrn CA, the nrn/cntrl Sierra, and 

parts of n/w NV along with isolated thunderstorms in the 

afternoon/evening. The next system will then approach as an upper 

low coming from the west. Later Tuesday, the low will take a shift 

to the south headed towards soCal. There are still differences 

between the models on the timing of this next system's arrival. The 

GFS remains ahead of the ECMWF bringing the core of the system just 

offshore of Point Conception Weds afternoon while the ECMWF waits 

until the evening. The ECMWF also has the core of the system further 

to the south off the coast of Baja as troughing pushes inland across 

central/southern CA. In either case, this is expected to produce 

some precip Weds over the central Sierra and through central to ne 

NV along with isolated thunderstorms. Amounts expected to be about 

0.25-0.75" near the CA/NV border down to 0.10-0.30" across NV. Light 

scattered showers across other parts of nrn CA will also be possible 

as another system approaches from the nw.



Thursday morning, the upper low will move through srn CA exiting 

into AZ throughout the morning and into the afternoon. Models 

disagree on the exact timing. Meanwhile up north, a surface low will 

approach the PacNW with an upper trough overhead. The GFS is a bit 

quicker at the low arriving along the coast than the ECMWF and is 

also faster at the upper trough expanding across the west coast. 

Both models do show precip spreading across northern CA/NV in the 

afternoon and evening. The upper trough is then expected to dig 

further into the west spreading showers across CA/NV before shifting 

its trajectory eastward later Friday. It is at this point that 

models diverge again. 00z Saturday ensembles disagree on both the 

depth of the trough and its east/west position. The ECMWF this time 

is the quicker model with the axis of the trough along the eastern 

CA border while the GFS is more over CA/NV. By Saturday morning, the 

ECMWF has the back edge of the system almost fully out of the region 

while the GFS still has troughing covering most of CA. The main 

result is the ECMWF showing another system arriving along the north 

coast mid Saturday morning while the GFS does not. Precip forecast 

for the 24 hrs 12z Sat to 12z Sun out of the GFS is dry across nrn 

CA while the ECMWF shows as much as 0.50-1.25" along the north 

coast. Many of the ECMWF ensembles are on the drier side, leading to 

lower QPF out of the NBM compared to the det run. Went with a blend 

of the NBM and det guidance to show some limited showers over nrn CA 

for Saturday. All this to say uncertainty in the forecast for most 

of the week as models continue to disagree and have not been as 

consistent as one would hope run to run.



The majority of the precip is still expected in the extended on 

Thursday/Friday. Highest amounts along the north coast, over the srn 

OR Cascades, and the mountains of ne NV. QPF 12z Thurs-12z Sun: 0.40-

1" north coast/srn OR Cascades (up to 1.50" Smith Basin), 1-2" ne NV 

mountains, 0.10-0.50" rest of nrn CA/NV, and a few hundredths to a 

tenth of an inch for cntrl CA/w NV.



Additionally, this change in pattern starting tomorrow will act to 

cool conditions from west to east gradually throughout the week. By 

Friday, afternoon high temperatures are forecast to be 5-15 deg F 

below normal. Higher freezing levels will continue today at 10.5-

12.5 kft from n to s. Freezing levels to then lower mid week down to 

8-11.5 kft then 6-10.5 kft by Thursday reaching 4.5-6.5 kft north of 

I-80 and 6.5-11.5 kft to the south Friday morning. The quicker exit 

of the upper trough will allow levels to rebound over the weekend up 

to 6.5-9 kft north of I-80 and 8.5-10.5 kft to the south Saturday 

morning.





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







AS



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