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AGUS76 KRSA 031413

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

715 AM PDT Wed Apr 3 2024



...WARM AND DRY AIRMASS MOVING OUT...

...COOLER AND UNSETTLED CONDITIONS INTO EARLY NEXT WEEK...



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



The upr ridge over the region yesterday has been displaced 

downstream of the area...now aligned from near the CA/MX border 

northeast across the intermountain west up into central Canada. The 

polar s/wv trof has moved out of the Gulf of Alaska...and is diving 

down the coastal waters of the west coast. This has switched the 

overall flow pattern to onshore southwesterly aloft. Through 

today...look for two focal areas of precip mainly developing this 

afternoon and increasing during the evening hours as an area of 

diffluence aloft and a mid-level vort max brings a band of precip 

setting up from the eastern portion of the Shasta Lake drainage up 

across the northeast CA Plateau and portions of the upper Klamath 

River basin...where totals through tomorrow morning will range from 

0.25- to 0.75-inch with some localized amounts reaching 1.00-inch. 

Also...with upslope flow over the northern/central Sierra...expect 

orographic precip to be on the increase mainly down to the Merced 

River basin. Totals in this area will generally range from 0.10- to 

0.33-inch with some localized amounts approaching 0.50-inch. 



Into Thursday...the s/wv trof will carve out cyclonic flow aloft 

across much of the west coast with the core of the system 

approaching the SF Bay Area and shifting inland overnight into 

early Friday. This should bring the best precip to areas between the 

Russian River basin down to the Big Sur coast...and then inland over 

much of the Sierra (heaviest from the Tuolumne River basin to the 

Kings River basin). Also...on the downstream side of the upr trof 

axis...models have been hinting at a band of precip setting up from 

north-central NV back toward the west-central portion of the state. 

Look for totals in these areas to range from 0.25- to 0.75-inch with 

some localized amounts over the southern Sierra around 1.00-inch.



Finally...by Friday into early Saturday the upr trof will have dug 

far enough south with the base of the feature dragging a ribbon of 

mid-level vorticity across coastal southern CA with the best onshore 

westerly flow bringing upslope conditions to areas between southwest 

San Bernardino county down to the CA/MX border with totals generally 

from 0.25- to 0.50-inch and some localized totals nearing 0.75-inch. 

As the system moves inland...precip will be tapering off over 

northern/western locations becoming much more scattered.



Freezing levels are starting the day with the leading edge of the 

cooler air on the doorstep. Other than being down near 6500-feet 

from the Smith River basin northeast to the upper Klamath River 

basin...the rest of the region is still generally from 9000- to 

12500-feet from northwest to southeast across the area. As the 

colder airmass ushers in behind the frontal boundary...look for 

freezing levels to plummet with unseasonably cold temperatures 

encompassing the region by Friday. Freezing levels will bottom out 

later Friday morning as the core of the system moves overhead...down 

to a range of 2000- to 5000-feet from northwest to southeast.  





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



Unsettled weather is forecast to continue into the weekend as a s/wv 

will dig southward over California on saturday before moving out of 

the region early next week. Models differ on exact phase, timing, 

and location of the wave, leading to uncertainty in the specific 

placement and magnitude of precipitation accumulations. EC keeps the 

s/wv and upper level cutoff further west, producing higher 

precipitation accumulations over the Sierra on Sunday while the GFS 

is earlier and further east. While models continue disagree in the 

specifics of the weekend disturbance, accumulations remain 

relatively light with up to or just above a tenth of an inch over 

the Smith basin on Saturday, <0.10 inches over the northern/central 

California mountains on Sunday, and a few hundredths over southern 

California on Monday. Ridging is forecast to build once the s/wv 

moves further inland leading to warmer and drier weather early next 

week. 



Freezing levels will begin the forecast period relatively low under 

the troffing (2,600 feet across the north rising to 4,000 feet over 

the south). Ridging will raise freezing levels to above 9,000 feet 

across California and 5,000 feet across Nevada by Tuesday morning 

next week. 





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







Kozlowski/CH



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