Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 181801
HMDRSA

Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
930 AM PST Sun Feb 18 2018

...SYSTEM TO BRING LIGHT PRECIP AND VERY COLD AIRMASS THROUGH
MONDAY...
...SECOND SYSTEM EXPECTED THURSDAY...

.METEOROLOGICAL CONDITIONS (SUN AM - SAT AM)...

A surface front dropped south into the region overnight, bringing
showers to the North Coast and Upper Klamath, along with portions of
Northern NV. Precip continues this morning, spreading towards the I-
5 corridor and Nrn Sac Valley. Expect precip to shift into the
Sierra during the afternoon hours, generally bypassing the remainder
of the Sac Valley. A minor uptick in intensity is expected this
evening as a vort max moves over the Nrn/Central Sierra, though
overall QPF amounts are expected to remain low. As the upper low
digs southward overnight, we could see some light precip along the
coast down to the Santa Cruz Mtns, as well as into the Southern
Sierra. By Monday morning, some light showers are also possible over
portions of Srn CA, especially the North slopes of the San Gabriel
and San Bernadino Mtns.

The biggest impact from this system is expected to be the cold
temperatures and low snow. While overall snow amounts should be low
over CA due to limited moisture availability, the very cold airmass
brought in with the trough should bring snow levels down to the
coldest seen this year. Can`t rule out a dusting over the Santa Cruz
Mtns, with freezing levels down to 2000-2500 ft Monday morning, and
foothill snow with levels as low as 500-1000 ft over the Northern
and Central Sierra. In the valley, which is not expecting precip,
temperatures are expected to drop below freezing Monday and Tuesday
mornings.

Expect drying by Tuesday as the upper trough moves off to the east.
By Wednesday, an upper low moving down the west coast *may* bring
some light precip to coastal areas through the day. Models are
waffling on how far offshore the upper low remains, which will make
the difference between showers and dry conditions. Moisture is again
limited during this time, so even the wettest solution brings less
than a third of an inch to any given coastal location.

A final system during the forecast period is expected to drop
southward late Wed into Thursday. The EC has been tracking this
system for the last few days, while the GFS has just bitten off on
the moist solution in the last few runs. This takes the form of
another inside slider, taking a very similar track and coverage
pattern as today`s system. Precip could move southward through
Northern CA during the day Thursday, moving into the Central and Srn
Sierra into early Friday, then bringing light showers to Srn CA
Friday morning. Expect this system to eject eastward Friday
afternoon, leaving dry conditions behind. Details are still
uncertain, but this system also has the potential to tap into very
cold temperatures, keeping the work week well below normal.


.HYDROLOGICAL CONDITIONS...

With cold temperatures in the forecast, runoff is expected to remain
minimal.

All forecast points are expected to remain below monitor levels for
the next five days.


More information on the CNRFC website at www.cnrfc.noaa.gov

JM/CN

$$



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