Flooding and Heavy Snow in California, November 21 to 22, 2018

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
344 PM PST Wed Nov 21 2018

.UPDATE...Updated air quality issues.

&&

.SYNOPSIS...A storm system will bring rain and high Sierra
snow to the district tonight. Much of Thanksgiving Day will
be dry except for a few showers in the mountains. Wet weather
could return to the region by the end of the week into the
first part of the weekend.

&&

.DISCUSSION...Rain...California's liquid gold...is making
inroads into the central California interior this afternoon.
After an extremely lengthy dry spell, the rain couldn't be
more welcome! Although ultimately good, the rain will be a
mixed blessing. Besides putting beneficial water into the
ground, the rain is finally cleansing the atmosphere of smoke
pollutants and will help extinguish wildfires over the northern
half of the state.  On the down side, the onset of rain will
produce slick driving conditions on roads where a thin layer of
surface oil has collected after weeks of dry weather. While rain
should readily percolate into the soil in most areas, it will
likely runoff in the vicinity of wildfire burn scars and bring a
threat of mudslides and rock slides to nearby locations. This
includes the Ferguson and Detwiler burn scars in Mariposa county
in addition to other smaller burn scars southward into the Tulare
county mountains. The debris flow threat will only be magnified if
rain falls heavily over a short time interval on those burn
areas. By and large the rain that occurs into Thanksgiving Day
should fall gently enough to minimize the threat of flash flooding
near the burn areas.

In the broader picture,  our well-advertised pattern change is
finally coming to fruition, thanks to a storm system currently
centered off the northern California coast. A westerly flow aloft
associated with this storm system will sweep a cold front and its
precipitation through the central California interior during the
next 12 hours. The lion's share of this precipitation should come
during the early part of tonight. Above 7000 feet, precip will be
in the form of snow and by the time it diminishes to flurries
Thanksgiving morning, a substantial snow accumulation, the first
of the season, will have fallen over the high Sierra. Other than
scattered residual showers over the mountains, low clouds will
linger through Thanksgiving Day in the usual upslope areas. The
sun will make an appearance elsewhere tomorrow and make for a
relatively quiet day, weatherwise, for holiday feasts. The lull
will linger through Thursday night, during which time skies will
be partly cloudy to clear. In cloud-free areas of the San Joaquin
Valley, patchy dense fog could form Thursday night.

A second cold front will approach the central California interior
Friday. Although the bulk of this front's moisture and dynamics
will remain north of our CWA, showers could pop up just about
anywhere in the post frontal environment mainly north of Kern
county Friday afternoon and evening. Upslope areas of our CWA
face the best chance of precipitation from this second cold front
Friday into Friday night. This includes the west slopes of the
Sierra and the north facing slopes of the Tehachapi mountains
which may otherwise be plagued by low clouds into the weekend.

The models are now slower building the Eastern Pacific ridge into
California this weekend than earlier runs. Instead, the GFS and
ECM maintain a northwesterly flow aloft over the CWA on Saturday.
The ECM forecasts a weak upper level disturbance embedded in this
flow to bring a renewed chance of precipitation to mainly the
upslope regions of the CWA during the first half of the weekend.
Although the GFS is comparatively dry, a northwesterly flow aloft
could certainly keep low clouds banked along valley facing slopes
through Saturday. Low clouds in other parts of the valley could
mitigate fog development Saturday morning and possibly Sunday
morning. Inevitably the EPAC ridge will build inland over the
state, so during the early part of next week, night and morning
fog might become more prolific in the San Joaquin Valley. Whatever
the case, fog could still become a travel setback for anyone
driving home from the holiday weekend Sunday morning. High
temperatures this holiday weekend will average close to normal
while nightly lows will run slightly above normal.

The weather pattern will take an active turn again by next
Wednesday. During the mid to later part of next week, the models
are in general agreement that another storm system may impact much
of the central California interior. The ECM in particular
suggests that the storm coming into central California by November
29th will be stronger and wetter than the current one, so stay
tuned.

On a final note, the National Weather Service San Joaquin Valley
wishes everyone safe travels this holiday weekend and a joyous
Thanksgiving!

&&

.AVIATION...
MVFR visibilities in areas of smoke and haze today. Gusty south to
southeasterly winds will be possible over the Sierra Nevada today
and through tonight. IFR conditions possible tonight in MCE, MER,
FAT, and VIS. Precipitation spreading from north to south across the
region. Light rain occuring MER, MCE by 21z, FAT by 01z, VIS by 03z,
and BFL by 06z. Mountain obscuration in precipitation.

&&

.AIR QUALITY ISSUES...
Please see SFOAQAHNX for an Air Quality Alert

On Thursday November 22 2018... Fireplace/Wood Stove
Burning Status is: No Burning For All in Fresno... Kern...
Kings... Sequoia National Park and Forest and Tulare
Counties. Further information is available at Valleyair.org

&&

.CERTAINTY...

The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.html for additional information
an/or to provide feedback.

&&

.HNX Watches/Warnings/Advisories...
Winter Storm Warning from 4 PM this afternoon to 8 AM PST
Thursday ABOVE 7000 FEET FOR THE CAZ096-097.

Flash Flood Watch from 4 PM PST this afternoon through Thursday
morning CAZ093-096.

&&

public...Durfee
avn/fw...Bollenbacher
synopsis...Durfee

weather.gov/hanford