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AGUS76 KRSA 101423

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

725 AM PDT Wed Apr 10 2024



...DRY AND WARM THE NEXT COUPLE DAYS...

...LOW PRESSURE WILL BRING COOLER AND WETTER CONDITIONS THIS 

WEEKEND...



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



The upr ridge axis is pretty much aligned along the west coast this 

morning...and this feature is expected to shift inland across the 

intermountain west by tomorrow. This will bring dry conditions and 

warm above average temperatures to the region with anomalies 

anywhere from plus 5- to plus 15-degF. As the high pressure moves 

inland...a deep upr low over the Gulf of Alaska will begin to drop 

south-southeast along the west coast...promising to bring a change 

to the overall pattern that will be cooler and unsettled for Friday 

into the weekend. Models continue to hint at a couple areas of 

scattered precip developing Thursday afternoon...the first over the 

crest of the southern Sierra and the second near and above Shasta 

Dam. 



Although the overall transition of the pattern for the end of the 

week is looking likely...the details with the upr low still vary 

quite a bit amongst the most recent models. At 12/12Z (Friday 

morning)...the deterministic models all show the primary circulation 

nearing 30N as it moves southward...but the 10/00Z CMC is just 

outside of 130W...the EC is closer to 133W...and the GFS is the 

farthest west at 135W. This will impact how much precip reaches the 

west coast with the initial cold front and the moisture plume (PW 

near or just above 0.75-inch) entrained ahead of this boundary. 

Farther west solutions keep the majority of the moisture offshore 

with the boundary...and resulting precip on Friday is limited. On 

the other hand...the farther east solutions are spreading the 

moisture and frontal boundary across CA with widespread precip 

moving across northern/central portions of the state. Given the low 

confidence...forecast represents a blend of the previous issuance 

and the latest 10/12Z NBM. This would result in totals generally 

between 0.25- and 0.50-inch across coastal northern/central CA and 

the Sierra focused on the central portion of the range. 



Freezing levels will start near or above 10000-feet with the upr 

ridge moving overhead today into tomorrow...and then show more of 

an east-to-west gradient with the upr low settling near or just off 

the central CA coast late Friday into early Thursday. NV and 

southern CA will range from 9000- to 11500-feet...the Sierra will 

range from 6000-feet north to 9000-feet south...and northern/central 

CA coastal areas will be between 5000- and 7000-feet.





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



Uncertainties surrounding the timing and track of the upper low 

persist through the weekend with the EC moving the low inland faster 

than the GFS. Additionally, the EC focuses the heaviest 

precipitation over the central Sierra whereas the GFS takes a more 

southern track, taps into more eastern Pacific moisture, and funnels 

stronger southerly moisture transport into the western Transverse 

mountains. This solution in the GFS leads to nearly 2.5 inches over 

Santa Barbara county. The differences in timing are leading to large 

spread in precipitation accumulations from 12Z Sunday to 12Z Monday 

with the EC moving the upper low inland to the Inter-Mountain West, 

resulting in limited shower activity over CA, whereas the GFS has 

the upper low lingering near Point Conception. Due to these 

differences in the propagation of the upper low inland, the EC is 

forecasting a few hundredths of an inch across a majority of CA (up 

to 0.15 inches over the Central Sierra and the mountains of San 

Diego), while the GFS is suggesting 1.25 inches over Santa Barbara 

county. Upper ridging is forecast to build behind the upper low as 

it moves inland resulting in a return to warmer and drier conditions 

by Tuesday next week. 



Given the large spread across a majority of models, morning 

forecasts followed the guidance of the NBM and WPC. 72-hour QPF 

places the highest accumulations of >1.00 inch over the southern 

Sierra, central Coast, and western Transverse Range. Forecasts will 

continue to update as guidance begins to converge on a solution.



Freezing levels are forecast to lower as the upper low moves inland, 

dropping to below 4,000 feet along the coast and above 10,000 feet 

over Nevada on Saturday. Freezing levels will begin to rise again on 

Tuesday as ridging returns to the region, reaching >11,000 feet over 

the south and >5,000 feet over the north. 





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







Kozlowski/CH



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