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AGUS76 KRSA 261503

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

800 AM PDT Tue Mar 26 2024



...WET PATTERN RETURNS MID WEEK THROUGH THE COMING WEEKEND AS A 

PAIR OF LOWS IMPACT THE REGION...



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



An upper ridge currently resides over the eastern Pacific while some 

weak residual troughing generates light scattered showers across NV. 

The ridge will progress eastward the rest of today traveling through 

the west coast resulting in mostly dry conditions for CA as NV 

continues to see some light scattered showers. Behind the ridge, a 

large surface/upper low will approach from the Gulf of Alaska 

sending a cold front towards CA. This system will bring precip back 

to the region for the duration of the short term. Initial showers 

are expected to reach the north coast late Tuesday night with more 

moderate precip arriving Wednesday morning along with the main cold 

front. Precip will then spread inland along the CA/OR border and 

southward across the nrn CA coast the rest of the morning into the 

afternoon as the low slowly heads southeastward towards the PacNW 

coast. There are some timing differences regarding the movement of 

the cold front and how quickly precip will spread into central CA. 

The GFS is a bit slower not taking precip into the central coast 

until late Wednesday night while the ECMWF is closer to the late 

afternoon/early evening. Troughing from the low will begin to move 

onshore overnight slowly engulfing the western U.S. throughout the 

day Thursday allowing showers to continue across northern/central 

CA. By Thursday night, the surface/upper low will arrive just 

offshore of the PacNW coast while another surface low and upper 

shortwave develops on the back side of the low. This system will 

then head towards northern/central CA overnight providing another 

surge of precip. There are also some timing issues with that second 

wave with some model ensembles bringing in that precip overnight 

Thursday while others wait until later Friday.



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

Highest precip amounts are expected along the north coast, 

particularly over the Smith Basin, Shasta, and across the 

northern/central Sierra. QPF 12z Tues-12z Fri: 1-2.50" north coast 

(2.50-4" Smith Basin/Kings Range), 1-2.50" Shasta/nrn/cntrl Sierra, 

0.25-1" southern Sierra, 0.10-0.75" Bay Area/central coast, and 0.10-

0.50" down the valleys (higher towards the foothills). 



High pressure will increase freezing levels later today to 6-8.5 kft 

north of I-80 and 7-10 kft to the south. The approaching low will 

then lower levels back down from nw to se to 5.5-7.5 kft north of I-

80 Weds am and 7-11.5 kft to the south. This downward trend will 

continue the rest of the short term to 3-4.5 kft north of I-80 Thus 

am and 4.5-11 kft to the south with lower levels spreading across 

the state into Friday as well.





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



Fri morning, expect a slowly deepening low at the surface and aloft 

to slowly move east toward the northern CA coast before becoming 

nearly stationary.  Expect light warm-frontal precip to spread 

across much of northern CA and parts of northern NV Fri morning, 

with a heavier band of precipitation near a cold front moving into 

the region a bit later on Fri.  The low and associated frontal 

system are expected to drop south to southeast through Sat. While 

still not excellent, model agreement has improved a fair amount 

regarding this system compared to Monday's runs, and the faster 

solutions now dominate the deterministic runs and ensemble members. 

Totals of 1-2 inches are expected Fri through late Sat along the 

length of the Sierra and much of the coast from the upper Eel basin 

southward, except 2-3 inches on the Big Sur coast and favored 

portions of the transverse ranges of southern CA.  Expect freezing 

levels to start off around 4000-6000 ft for much of northern/central 

CA and 6000-9000 ft for southern CA as well as NV.  Behind the 

front, freezing levels are forecast to fall to around 4000-6000 ft 

across the region.



Expect showers to continue and very gradually wind down across the 

region Sun into Sun night as the parent low swings across the 

southern half of the region.  Additional totals of 0.5-1" are 

expected for the southern CA coastal areas and favored terrain of NE 

CA, with lighter amounts elsewhere.  Freezing levels should continue 

around 4000-6000 ft.  NBM guidance was favored for the extended-

range QPF.  Models favor an upper ridge building over northern CA 

for the first half of next week, with an overall drier pattern 

expected.





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







AS/Lerman



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