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AGUS76 KRSA 121938

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

1240 PM PDT Fri Apr 12 2024



...WEEKEND STORM SYSTEM ON TAP WILL BRING COOLER/WETTER CONDITIONS...

...DRYING INTO NEXT WEEK WITH TEMPS RETURNING MORE SEASONABLE...



.METEOROLOGICAL CONDITIONS (SHORT TERM: FRI PM - MON AM)...



Already seeing a couple lines of precip fire this morning in the 

area of diffluence ahead of the main upr low off the CA coast 

crossing 130W at the latitude around Point Arena. The first is over 

the Trinity Alps...while the second a bit more interesting from 

Butte county toward the north-northeast with embedded convection and 

numerous lightning strikes. Precip associated with the frontal 

boundaries will begin to affect coastal areas of northern and 

central CA overnight into Saturday...and then spreading inland and 

southward as the area of low pressure reaches the coast near the SF 

Bay Area and pinwheels several disturbances around the cyclonic 

flow...which will serve as focal points for developing precip. The 

upr low will move inland on Sunday and finally east of the area 

either late Sunday or early Monday with precip tapering off through 

the day. Over the next 72 hours...the best precip amounts are 

expected across the higher terrain of northern/central CA with 0.75- 

to 1.50-inches and some localized amounts closer to 2.00-inches over 

the western portion of the Shasta Lake drainage where favorable 

upslope flow occurs...and the Big Sur coast down to the Santa Ynez 

mountains where a couple of the stronger disturbances rotating 

through the area will cross.



Freezing levels will drop through Saturday as the cooler airmass 

filters in across the area bottoming out late Saturday or early 

Sunday from about 3500- to 6500-feet across CA (lowest northern and 

central CA)...and then about 5500- to 7500-feet for NV.





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



Forecast remains on track with no real changes to the afternoon 

update. An upper low exiting the region on Monday will bring some 

lingering scattered showers in the morning. Conditions will dry out 

in the afternoon as the system continues to move into the four 

corners and an upper ridge builds into the eastern Pacific. High 

pressure will slide into the west coast early next week as another 

low travels south across BC. Differences between the models remain 

on the trajectory of that low with the ECMWF still taking the system 

on a more easterly path while the GFS has more of a southerly 

component. Some of the GFS ensembles take the system closer to the 

northern regional border than the det run as do a few of the ECMWF 

members. Regardless, models agree that any resulting precip would be 

fairly minimal. Not more than stray shower or two over the northern 

regional border. QPF for the extended is still only some scattered 

instances of a few hundredths of an inch or so with dry conditions 

for the rest of CA/NV through Wednesday.



Freezing levels starting at 5.5-7 kft over eastern CA and NV as the 

low exits rising from west to east once high pressure moves in. 

Tuesday, expecting most of the region to be at 8-12.5 kft. The 

northern low may lower levels along the northern regional border 

down to 7-8 kft while the rest of the region rises to 9-14 kft N to 

S into Wednesday.





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







Kozlowski/AS



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