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AGUS76 KRSA 181522

HMDRSA



Hydrometeorological Discussion

National Weather Service / California Nevada RFC / Sacramento CA

830 AM PDT Mon Mar 18 2024





...UPPER LOW WILL BRING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS 

TODAY AND TUESDAY MAINLY OVER SRN SIERRA AND SRN CA AND SRN NV...

...PRECIP OVER SRN OR AND NRN CA THURSDAY AND SPREADING SOUTH INTO 

CENTRAL CA AND EAST INTO NRN NV FRIDAY AND INTO SRN CA AND NV 

SATURDAY...



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



Upper level low centered near CA/AZ border this morning and expected 

to move west into Srn CA during the day then shift back east 

into Arizona tonight into Tuesday and off into New Mexico Wednesday. 

Meanwhile ridge of high pressure continues over Pac NW and into Nrn 

CA and Nrn Nv today and shifts south into Tuesday and east on 

Wednesday as an upper level low approaches the Pac NW coast. 

Scattered showers and isolated thunderstorms today over Srn CA and 

Srn NV and along the Srn Sierra. HREF shows a probability of 20-40% 

of half an inch or more of precip in an hour this afternoon into 

early evening over Srn CA and a 10-15% chance of an inch or more in 

an hour over SW San Bernardino and Orange and Western Riverside and 

San Diego Counties this afternoon into early evening. Precipitation 

amounts will be variable with the convection but generally a 

hundredth or two to around a quarter of an inch will local amounts 

to around a half of an inch possible.  Showers possible in the 

Shasta Basin and along the Sierra and over Srn Ca (mainly over 

higher terrain) and Srn NV on Tuesday and tapering off on Wednesday 

as the pattern begins to shift. Precipitation amounts will be 

variable with the convection but generally a hundredth or two to 

around a tenth of an inch will local amounts up to a half of an inch 

possible. Freezing levels around 8000 ft and higher through 

Wednesday. 



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



A surface/upper low are on track to approach the region late this 

week impacting the region through the weekend. Timing has slowed 

down since yesterday with showers now not expected to arrive until 

late Thursday night or Friday. The det GFS is currently slower than 

the ECMWF holding off on bringing in showers until Friday afternoon 

while the ECMWF is showing earlier Friday morning. There is also a 

variety of arrival times amongst the ensembles ranging from Thursday 

morning to Friday evening. Disagreement exists on the pattern as 

well with the slower GFS showing a larger surface/upper low just 

west of OR Saturday morning as the ECMWF begins to move the smaller 

system inland. Either way, showers are expected to spread across 

nrn/cntrl CA and srn OR on Saturday as the system digs across the 

western U.S. The low will remain overhead the rest of the extended 

allowing showers to persist into Sunday. 



Best precip amounts are expected along the north coast, over Shasta, 

and across the Sierra. The forecast was mainly a combination of the 

latest NBM and WPC guidance. QPF for the extended: 1-2.50" north 

coast/Shasta, 1-2.80" Sierra, 0.40-1.25" Bay Area/central coast, 

0.10-0.75" down the valleys, and a few hundredths to a couple tenths 

along coastal soCal. Freezing levels 7-9 kft north of I-80 into 

Friday and 9-10.5 kft to the south. The approaching low will lower 

freezing levels nw to se down to 4.5-6 kft north of I-80 and 5.5-11 

kft to the south early Saturday. This downward trend will continue 

the rest of the long term reaching 3.5-4.5 kft north of I-80 and 4-

7.5 kft to the south early Sunday.



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







Osborne/AS



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