...LINGERING SHOWERS TODAY AND POSSIBLY A FEW THUNDERSTORMS OVER
SRN CA, THE SIERRA, AND NV AS A LOW CONTINUES TO MOVE THROUGH...
...DRY CONDITIONS AND WARMING TEMPERATURES FOR MOST OF THE WEEKEND
BEFORE ADDITIONAL SHOWER ACTIVITY IS POSSIBLE FOR NRN CA EARLY NEXT
WEEK...

.METEOROLOGICAL CONDITIONS (FRI AM - THU AM)...

Yesterday's upper low has opened up into a trough now stretched from
ID to the Pacific offshore of Baja. Surface analysis has a cold
front through central CA nw NV into ID as well with showers on radar
along I-80 over nrn NV. A few convective showers offshore of srn CA
can be seen on radar as well. Observations over coastal srn CA again
exceeded the forecast as another 0.30" to over 1.50" for some areas
was reported over the past 24 hours. The rest of the region saw
about 0.10-1". Expect scattered showers to continue today over srn
CA, across the Sierra, and into NV as a secondary low forms off the
current trough over srn CA later today. Small chance of additional
thunderstorms over srn CA, the Sierra, and srn NV as well. That low
then looks to head into the Desert Southwest tonight/early Saturday
with high pressure building in behind it returning dry conditions
for most of the weekend. One more day of widespread below normal
temperatures before gradually warming back up to seasonal normals
from west to east as that ridge moves in starting tomorrow. For the
rest of the current system, scattered amounts of 0.10" or less and
up to 0.25-0.50" or so under heavier convective cells.

Models continue to diverge on the overall pattern after this ridge.
Both the GFS and the ECMWF do show another low approaching from the
Gulf of Alaska, but differ on the timing and trajectory of this next
system. The ECMWF has the low moving into the PacNW late Sunday into
Monday bringing some showers into the north coast and along the OR
border into Tuesday. The GFS carries this same system southeastward
into northern CA about 24 hours later. The GFS then shows the low
stretching out into a trough into Wednesday with a small upper low
around Cape Mendocino and another low offshore near 140W by early
Thursday. The ECMWF, however, after that first low exits into the I
ntermountain West, predicts some transitional ridging overhead the
rest of the forecast period while a much larger surface/upper low
spins offshore around 140W. Taking a look at the 500 mb height
ensemble clusters shows good agreement of a low somewhere around the
PacNW or nrn CA Monday afternoon. The CMC and the ECMWF strongly
favor a more northerly position compared to the GEFS. The four
clusters shown begin to diverge for Tuesday afternoon with various
degrees of troughing in different positions across the west. Cluster
2 shows that weak ridging the det ECMWF predicts and unsurprisingly
is mainly comprised of members from the ECMWF ensemble. Things don't
get much closer together after that either. Bottom line, there is a
great deal of uncertainty in the forecast beyond tomorrow as models
disagree on the pattern and timing. Ensemble 24 hour QPF members
over Arcata continue to show a spread of 0" to over 1" for early
next week. The official forecast was a blend of WPC and the NBM for
this time period which is leaning closer to the ECMWF solution, but
confidence in this is very low. For now showing 0.10-0.50"+ along
the north coast and 0.10" or less generally along the rest of the
CA/OR border.

Freezing levels will rise behind the low as it exits back up to 10-
13 kft across CA by mid Saturday morning. What happens after that
will strongly depend on what the 500 mb height pattern ends up being.

Please Note: This product may NOT be routinely updated.
Please refer to the following product issued by the CNRFC
www.cnrfc.noaa.gov/Daily-Briefing for a graphical summary of
weather and hydrologic conditions.