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AGUS76 KRSA 031430

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

730 AM PDT Fri May 3 2024



...COOLER TEMPS WITH WIDESPREAD PRECIP OVER NRN CA/SRN OR THIS 

AFTERNOON/TONIGHT BEFORE SPREADING ACROSS THE REGION SAT (ISOLATED T-

STORMS SAT OVER NRN CA) AND DIMINISHING INTO SUN AS A LOW MOVES 

THROUGH...

...LIGHT SHOWERS OVER THE NRN PORTION OF THE REGION MON AS A 

DISTURBANCE PASSES TO THE NORTH FOLLOWED BY DRYING CONDITIONS THE 

REST OF THE PERIOD AS HIGH PRESSURE TAKES OVER...



.METEOROLOGICAL CONDITIONS (FRI AM - THU AM)...



A large surface and upper low reside over the Gulf of Alaska this 

morning as a tropical moisture plume of 1-1.25" PW stretches from 

just offshore of the PacNW to north of the Hawaiian Islands ahead of 

the surface low's cold front. Over land, some weak ridging is 

building into the west coast as a trough moves through northern NV. 

The low will quickly approach into this afternoon bringing precip to 

nw CA as the moisture plume travels south along the northern CA 

coast. The cold front will gradually move across CA from nw to se 

tonight and through Saturday spreading precip inland across the 

state and to the south into central CA along with the moisture 

plume. Models have this moisture traversing the SF Bay Area tomorrow 

morning before reaching Point Conception in the afternoon. Behind 

the front/moisture, the upper low will begin to push inland around 

the CA/OR border Saturday afternoon carrying precip further across 

NV. The core of the low is then progged to head eastward across 

northern CA with the core of the low stretched across CA/NV by the 

evening. This may result in some isolated thunderstorms across nrn 

CA on Saturday. As the low moves inland up north, the moisture plume 

will continue to travel to the south passing coastal srn CA 

overnight Saturday before exiting into Baja Sunday morning. Precip 

will gradually diminish across the region Saturday evening into 

Sunday morning with showers now more concentrated over NV as the low 

moves through. The system will then exit the region Sunday evening.

 

The bulk of the precip for the next 6 days is expected with this 

first system later today through Saturday. Models are in relatively 

good agreement on the highest precip totals occurring along the 

north coast and across the northern Sierra. QPF clusters for the 24 

hrs ending Saturday afternoon are only split into 2 groupings with 

80% of the ensembles in cluster 1. Cluster 2 contains none of the 

ECMWF or CMC members but is comprised of 67% of the GFS ensembles. 

The main differences are over the north coast and the 

northern/central Sierra where over half of the GFS ensembles favor 

heavier precip compared to the ECMWF and CMC. Cluster two has at 

least an inch more across the north coast and 0.50-1" more over the 

northern/central Sierra compared to cluster 1. After Saturday 

afternoon, precip will become focused across the Sierra and nrn NV 

with lingering showers for much of the rest of CA. Today's QPF was a 

blend of the morning WPC guidance and the latest NBM. The result was 

about a 0.10-0.30" decrease for a good portion of northern CA/NV and 

central CA for today through Sunday. QPF 12z Fri-12z Mon: 1.50-3" 

north coast, 0.75-2.50" Sierra, 1-2" Shasta, 0.25-1" Greater Bay 

Area, 0.30-1" rest of nrn CA and down the valleys (1-1.50" 

foothills), and a few hundredths to 0.10" or so for coastal soCal 

(0.10-0.50" in the hills).



This low will act to cool temperatures down to 10-20 deg F below 

seasonal normals with over 20 deg below normal for nw CA starting 

tomorrow and lasting through Sunday. Freezing levels will also lower 

from nw to se starting at 7.5-12 kft today dropping to 3-7.5 kft 

north of I-80 Saturday morning and spreading to 2.5-6.5 kft north of 

Point Conception by Sunday morning. Freezing levels will then 

rebound as the low exits the region throughout Sunday.



Some weak ridging will then move over CA/NV into Monday drying out 

most of the region. Some light showers possible over the northern 

CA/NV borders and into srn OR as another system approaches the 

PacNW. Troughing will then dig into northern CA/NV Monday afternoon 

continuing shower potential for those areas into early Tuesday. 

Afterwards, high pressure will build into the eastern Pacific 

keeping the region dry and bringing temperatures back up closer to 

normal. QPF in the extended is all expected on Monday as that trough 

digs into the northern portion of the region. Forecast was mainly 

the latest NBM coming out to 0.25-0.60" over the Cascades, 0.10-

0.50" over the Smith Basin, and generally a few hundredths to a 

tenth of an inch elsewhere along nrn CA/NV.



Freezing levels Monday onward about 3.5-8 kft north of I-80 and 8-14 

kft to the south with higher freezing levels spreading across the 

state mid week. Expecting most of CA to be above 8 kft by Tuesday 

evening and up to 14 kft along the soCal coast with only ne CA 

and nrn NV down to 5-7.5 kft.





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







AS



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