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AGUS76 KRSA 281515

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

815 AM PDT Thu Mar 28 2024



...LINGERING SHOWERS AND ISOLATED TSTORMS TODAY AS A COLD 

FRONT CONTINUES TO MOVE THROUGH CA/NV...

...A LARGE SURFACE/UPPER LOW WILL TRAVEL ALONG THE COAST FRIDAY INTO 

THE WEEKEND BRINGING WIDESPREAD PRECIP AND ISOLATED TSTORMS...



.METEOROLOGICAL CONDITIONS (SHORT TERM: THU AM - SUN AM)...



A surface/upper low sits just offshore of the PacNW with a troughing 

pattern over much of the west coast. A cold front continues to 

gradually push through CA and NV this morning resulting in scattered 

showers across the region. Lightning detection is also picking up 

some activity over ne NV and along the north coast. The moisture 

plume has pushed south of the Bay Area still right around the cold 

front near Point Conception as TPW imagery shows 0.75-1" PW of 

moisture from Point Conception out to the Pacific. The cold front 

and moisture plume brought widespread precipitation to 

northern/central CA yesterday and last night with observations 

reporting totals of 1-3" in some of the higher spots for the past 24 

hrs. The front will continue to gradually move southeast the rest of 

today and along with the pattern overhead will produce scattered 

showers. There also remains chances of thunderstorms for parts of 

nrn CA and NV the rest of today.



This afternoon, another surface low and upper trough will form off 

the back side of the main low before heading for CA. Precip will 

ease this evening as the front dissipates with scattered showers 

still across parts of nrn CA as the low approaches. The upper 

shortwave will deepen forming a closed low just above the surface 

low by early Friday morning. The low will pull another plume of 0.75-

1" PW moisture from the southwest. The system will then reach the 

coast by mid morning providing another surge of precipitation into 

the afternoon this time more focused across the Bay Area/Central 

Coast then eventually soCal. There is still some disagreement on how 

close the low will get to the coast therefore impacting the QPF for 

Friday particularly for the Bay Area/Central Coast. 24 hr QPF 

clusters ending Friday afternoon remain split into 3 groupings and 

along similar lines as yesterday. The closer the system gets to the 

coast the higher the precip amounts and the further inland more 

moderate precip will spread. Totals in the ensemble clusters range 

from 0.10-0.50" (cluster 2 36%) to 0.50-1.50" (cluster 3 21%). The 

presence of the low may again result in isolated thunderstorms for 

these areas on Friday.



Once the low reaches the coast, it will begin to travel southward 

still just offshore the rest of Friday and into Saturday as the 

system draws moisture into the srn CA coast. At this time, the bulk 

of the precip will shift focus to Point Conception through to the 

southern Sierra and southward. The core of the large vertically 

stacked system will be just west of the Bay Area early Saturday 

while the moisture plume travels south across the soCal coast. The 

low will continue to head to the south the rest of Saturday dropping 

precipitation across the region along with isolated thunderstorms. 

For Saturday, the main focus of heavier precip will be across the 

Transverse Range and coastal soCal. There is some uncertainty on 

amounts particularly for coastal areas from LA to San Diego. QPF 

clusters ending Saturday afternoon are split into 3 groups (39%, 

39%, 22%). All three agree on at least an inch for much of the 

aforementioned areas, but cluster 3 is the wettest containing over 

half of the GFS ensemble members on the order of more widespread 

amounts of 1.50-2" for coastal areas. Individual 24 hr ensemble 

members between the GFS/ECMWF ending Sunday morning vary from as 

little as under 0.50" to over 3" over San Diego. Actual amounts will 

depend on the positioning of the low and the timing/movement of both 

the low and the moisture plume. The degree of potential orographic 

enhancement across the Transverse Range may also result in higher 

precip than currently forecast.



The center of the low is forecast to pass south of Point Conception 

overnight Saturday with a secondary low forming somewhere over NV 

and a burst of energy sliding through the PacNW. This will result in 

additional precip across NV and parts of central CA overnight into 

Sunday. In summation, a surface/upper low will travel along the CA 

coast drawing moisture into srn CA and resulting in widespread 

precip across the region for much of the short term period. Heaviest 

precip will be focused across the Transverse Range/coastal soCal as 

well as the central coast mountains and across the Sierra. QPF 

through 12z Sun: 1-2.50" CA coast from Sonoma to San Diego, 2-4" 

Transverse Range, 2-3.50" central coast mountains, 1.50-3" Sierra, 

0.75"-1.75" most of the rest of nrn CA, 0.50-1.25" down the valleys, 

and 0.10-0.50" for ne/se CA.



Freezing levels 3.5-5 kft north of I-80 and 4-11 kft to the south 

today with lower freezing levels spreading across the region into 

Friday. Mid Friday morning, expecting freezing levels 3.5-6.5 kft 

north of Point Conception and 5.5-10.5 kft to the south. Most of the 

region will be below 6 kft by Saturday morning with the entire 

region down to 4.5-6.5 kft at the end of the period as the low takes 

over.





.METEOROLOGICAL CONDITIONS (LONG TERM: SUN AM - WED AM)...



The period will begin with one area of low pressure just south of 

Point Conception starting to swing to the east toward the coast near 

the CA/MX border. A secondary low pressure will be making its way 

east of UT/NV border near Wendover. Both of these features will be 

the focal point of precip mainly on Sunday across coastal southern 

CA and in a deformation zone along the I-80 corridor of northern NV 

with amounts generally from 0.25- to 0.75-inch. Freezing levels will 

generally be from 4000- to 6000-feet mainly north to south. Then 

into early next week...the pattern will evolve to one where the upr 

trof moving inland will become positively tilted...while over the 

eastern Pacific an upr ridge will become nudge inland over the 

Pacific Northwest and northern CA. This will generate drier north to 

northeast flow across the west coast as PW values over the region 

drop below 0.50-inch. Freezing levels will also rebound across the 

area and reach 10000- to 12500-feet on Tuesday as the high pressure 

builds.





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







AS/Kozlowski



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