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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
100 PM PDT Wed Mar 22 2023

...LINGERING SHOWERS THE REST OF TODAY WITH ISOLATED THUNDERSTORMS 
IN THE AFTERNOON/EVENING...
...LIGHT PRECIP OVER NRN CA/NV AND SRN OR LATE WEEK INTO THE WEEKEND 
AS A COUPLE TROUGHS MOVE INTO THE PACNW...
...NEXT SYSTEM WITH WIDESPREAD PRECIP POTENTIAL EXPECTED EARLY NEXT 
WEEK, DETAILS STILL FUZZY...

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

Over the past 6 hours the majority of the additional precipitation 
that has fallen has been across the coastal mountains from Monterey 
County southward at about 0.30" to just under an inch. The surface 
low has slowly moved southward earlier this morning and now lies 
just west of the northern Monterey Bay. This low continues to rotate 
scattered showers into central/southern CA along with isolated 
thunderstorms. Lightning detection has picked up strikes/flashes 
along the soCal coast over the past few hours. Expect scattered 
showers and isolated thunderstorms to continue the rest of the 
afternoon/evening as the low heads inland and dissipates. Best 
chances for thunderstorm activity remain over coastal soCal and the 
SJ valley. The trough overhead will gradually swing through the 
region this afternoon and evening while a weak embedded shortwave 
heads into the PacNW. This will keep scattered showers across much 
of the region through early Thursday morning. Most of the additional 
precipitation expected will again be across the soCal coastal 
mountains at another 0.25-0.75" before tomorrow morning (locally 
higher amounts where thunderstorms develop). Only minor changes in 
the QPF compared to this morning, but there is some uncertainty 
given that at least some of the remaining precipitation from this 
system will be convective.

The upper trough will enter the Four Corners Thursday morning as the 
next one approaches the PacNW along with a cold front. The front is 
forecast to arrive at the north coast in the afternoon bringing 
moderate showers to the north coast. Lingering influence from the 
exiting previous trough will also keep scattered showers across much 
of CA/NV the rest of Thursday. The PacNW trough will move inland 
through WA/OR Thursday evening and reach ID early Friday morning. 
The next shortwave will then slide into the PacNW just behind that 
one the rest of Friday. By then, only expecting light precip around 
the CA/OR border and northern NV for the remainder of the near term. 
Highest precip amounts for Thursday and Friday are still expected 
along the north coast and over the soOR Cascades. QPF amounts have 
not changed much since this morning. Amounts are as follows: 0.50-
1.25" along the north coast, 1-1.40" over the soOR Cascades, 0.10-
0.75" across the Sierra (S to N), and generally less than a tenth of 
an inch elsewhere.

Temperatures will remain below normal in the near term by roughly 10 
to 20 deg F resulting in lower freezing levels persisting. Freezing 
levels are forecast around 3-5.5 kft through most of tomorrow before 
lowering across norCal and rising over soCal. Levels early Friday 
morning and are expected at 1-3 kft north of I-80, 3-5.5 kft from I-
80 to Point Conception, and 5.5-6.5 kft to the south. These numbers 
will fluctuate a bit between troughs but ultimately lower again into 
early Saturday at under 1 kft across northern CA to 3 kft along I-
80, 3-5 kft I-80 to Point Conception, and 5-7.5 kft to the south.


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

One s/wv trof over the Pacific Northwest will dig toward the Great 
Basin before exiting to the east across the central Rockies. This 
will bring generally light precip to areas near the CA/OR border and 
inland over northern NV on Saturday. There may be just enough lift 
and moisture to squeeze out some light precip across the crest of 
the Sierra as well. Then in terms of another disturbance dropping 
south out of the Gulf of Alaska into the cyclonic flow aloft along 
the west coast...precip will be on the increase on Monday. 22/12Z 
models did slow down just a bit in terms of timing the system toward 
the region...but so far the latest WPCQPF and 22/13Z NBM doesn/t 
reflect this trend. As a result...blended the two camps into the Day 
6 forecast periods. This does trim a bit of precip from northern CA 
as compared to the previous forecast.