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CNRFC Hydrometeorological Discussion

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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
1150 AM PST Wed Nov 30 2022

...LATEST SYSTEM MOVING IN TODAY INTO TOMORROW...
...FOLLOW-UP SYSTEM AFFECTS THE REGION THIS WEEKEND...

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

For the incoming system affecting the region later today through 
much of Thursday...changes to the afternoon forecast issuance were 
minor to incorporate the 30/12Z models. Satellite imagery shows the 
primary mid-level circulate spinning just west of Vancouver Island 
near 50N/130W...while the sfc cold front is already moving inland 
across the Pacific Northwest back to the southwest along the coast 
near the CA/OR border. Radar imagery shows a line of echoes making 
its way over far northwest CA up toward the crest of the southern OR 
Cascades. So far in the current 6-hour period ending 01/00Z...precip 
gauges have shown some bucket tips with anywhere from a couple 
hundredths of an inch up to just over 0.10-inch over the Smith River 
basin. Look for precip to increase and spread southward and inland 
into tomorrow as the cold front traverses the region and the s/wv 
trof axis moves toward the coast...maybe just a tad faster 
progressing south and east compared to previous thinking.

Precip will taper off across central and southern areas as the s/wv 
trof moves off toward the east late Thursday into early Friday...and 
the cold front dissipates along with the moisture plume dropping 
south of the CA/MX border. Attention next turns to a system dropping 
out of the Gulf of Alaska toward the northeast Pacific...expected to 
impact the region for the upcoming weekend. For Friday...it now 
appears the core of the system will remain far enough offshore 
outside of 130W...allowing the cold front and associated precip to 
align more north-to-south. Through Saturday 12Z...precip will remain 
offshore...keeping much of Day 3 dry across the region. 


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

Forecast remains on track this afternoon. Models continue to show 
that disorganized surface low and moisture stream aiming at the 
central coast on Saturday along with the larger surface and upper 
low approaching from the northwest. They also remain consistent in 
delaying the onset of precip over nw CA from the larger system until 
Saturday evening. There is still some slight disagreement on QPF, 
but the fact that the 12z models kept the additional surface feature 
is encouraging. Central CA will see precip from the west southwest 
on Saturday before re-enforcements arrive from the larger low in the 
evening. Precip will continue on Sunday with the main focus across 
the northern/central Sierra as the moisture plume to the south 
weakens and the core of the upper low begins to move inland. 
Lingering showers likely on Monday as well, though the bulk of the 
precip is forecast for Saturday/Sunday.

QPF overall has increased since this morning as models come into 
better agreement, particularly over the Sierra. Precip amounts for 
days 4-6 are as follows: 0.50-1.50+" along the CA coast north of 
Point Conception, 1.25-3.50+" across the Sierra, 0.60-1.00" near 
Shasta, and 0.25-1.10" down the valley. Amounts taper off to the 
south and east with SE CA not expected to see any precip. Given the 
cold nature of this system many higher elevation areas will 
experience much of this precip as snow. For snowfall amounts and any 
watches, warnings, or advisories please check with the local 
forecast offices.

Freezing levels are forecast to fall below 2 kft early Saturday 
across ne CA and northern NV. Levels will come up a bit in the 
evening to 3-6 kft north of I-80 and 6-9 kft to the south to Point 
Conception. Lower Freezing levels will spread southward Sunday as 
the upper low moves inland. Most areas north of Point Conception 
will be under 5.5 kft and down to just under 2.5 kft near the 
northern boarder Monday.