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AGUS76 KRSA 201427

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

730 AM PDT Wed Mar 20 2024



...A LOW PRESSURE SYSTEM WILL RETURN WET WEATHER TO THE REGION 

FRIDAY AND OVER THE WEEKEND...

...A SHORTWAVE INTO THE PACNW MONDAY TO BRING ADDITIONAL PRECIP 

CHANCES TO NRN CA/SRN OR...



.METEOROLOGICAL CONDITIONS (SHORT TERM: WED AM - SAT AM)...



A ridge of high pressure remains situated over the western U.S. this 

morning as a shortwave offshore approaches the PacNW. A pair of 

upper lows also reside to the north and west of the trough. The 

shortwave will continue to move to the northeast the rest of this 

morning traveling inland through OR/WA this afternoon and evening. 

This may result in a few light showers over nw CA. As the shortwave 

progresses inland, the two upper lows offshore will merge in the 

Gulf of Alaska just west of BC this evening. The system will then 

gradually head to the south offshore of the PacNW on Thursday as the 

ridge continues to bring dry conditions to the region. Initial 

showers from this next system are expected to reach the north coast 

late Thursday night before more moderate precip spreads across nrn 

CA Friday morning and afternoon along with a cold front. At that 

time the surface/upper low will have arrived just west of OR before 

shifting back in a northerly direction Friday evening as the front 

continues to sweep across CA. This will allow precip to spread into 

central CA and across the Sierra as well Friday evening. At the end 

of the short term, the core of the low is still forecast to remain 

offshore as the front passes Point Conception with the bulk of the 

precip now focused across the Sierra.



The morning forecast was a combination of the latest NBM and WPC 

guidance. The majority of the precip in the near term is expected on 

Friday with only isolated light showers today/tomorrow. Highest 

precip amounts across the Sierra, Shasta, and over the Smith 

Basin/Kings Range area. QPF through 12z Sat: 0.75-1.75" 

Sierra/Shasta, 1-2" Smith Basin/Kings Range (0.75-1.50" rest of 

north coast), 0.20-0.80" Bay Area/central coast, 0.10-0.75" down the 

valleys, and a few hundredths to a tenth of so just south of Point 

Conception. 



Freezing levels 6-8 kft across nrn CA through Thursday and 8+ kft 

elsewhere before the cold front lowers levels from nw to se into the 

weekend. By Saturday morning, freezing levels 3.5-4.5 kft north of I-

80 and 4.5-7 kft south to Point Conception.





.METEOROLOGICAL CONDITIONS (LONG TERM: SAT AM - TUE AM)...



Trofing over the northeast Pacific is forecast to continue the wet 

and cool conditions into the long term window as an upper-level 

cutoff approaches the Pacific Northwest coast on Saturday and moves 

onshore into Sunday. The broader trof axis is forecast to shift 

inland on Sunday and Monday as s/wv activity embedded in the base of 

the broader trof results in pockets of northwesterly pva over 

California, extending shower activity into early next week. 



The heaviest 24-hour period looks to be 12Z Saturday to 12Z Sunday, 

with over an inch forecast for the North Coast (Smith Basin) and 

0.50 to 0.75 inches forecast for the Central to North Coast and the 

crest of the Sierra. Lighter amounts (trace to 0.25 inches) are 

forecast for the Sacramento, San Joaquin, and Southern California 

Coast. Shower activity will linger into next week with amounts 

generally <0.25 inches on Monday and tapering off into Tuesday 

morning. Freezing levels are forecast to start the period at 3,500 

feet in the northwest and 6,000 feet in the south on Sunday before 

rising to 4,000 feet in the north and 10,000 feet in the south on 

Tuesday. 





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







AS/CH



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