Debris Flow and Flood in California, November 28 to 30, 2018

Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
448 PM PST Tue Nov 27 2018

...Updated Air Quality Section...

.SYNOPSIS...
A return to wet weather is expected from Fresno County northward
by this evening and will spread southward by Wednesday. Expect
heavy snow in the higher elevations of the Sierra Nevada Wednesday
night into Thursday and moderate to heavy rain at times elsewhere.
Possible flash flood and mudslides across the foothills from
Fresno County northward. Unsettled conditions will continue
through the weekend.

&&

.DISCUSSION...
A rather grey day as clouds from a storm over Northern California
invaded the district today. The passing cloud cover inhibited the
burn off of the ground fog as haze lingered across the valley
today. Even with the grey skies, temperatures across the area have
managed to warm slightly above values observed on Monday
afternoon. Having Central California ahead of the cold front that
will drop into the area late tonight, we've been observing
conditions in the warm sector that have placed us above seasonal
normals. Yet, once the cold front reaches Central California, cold
air will advance into the region along with unsettled weather.
Currently, regional Doppler radar imagery has the precipitation
over Northern California and extending south to around the
Stockton area. The current timing for precipitation to reach
Central California is still set for late tonight with the bulk of
the rain and high elevation snow arriving early Wednesday morning.
While this first storm has the potential of providing the district
with wetting precipitation, the second storm right behind the
first will threaten the Central California Interior with
significant rain and snow amounts.

Winter Weather Watches in the form of possible Flash Flooding and
Heavy Snow and have been posted for the foothills and higher
terrain of the Sierra Nevada, respectively. Thursday will be the
focus of the hazardous weather event with possible flooding as
early as Wednesday afternoon. Will monitor the Ferguson Fire Burn
Scar as even minor flooding can cause problems due to the lack of
water infiltration into the ground and enhanced runoff. While
flooding will be a problem over Mariposa County (Ferguson area)
the trajectory of the Winter storm will enhanced precipitation
production over the foothill area as far south as Balch Camp (in
Fresno County) or even Dunlap. In addition, the same storm has the
potential of producing from one to two feet of snow across the
Sierra Nevada (especially above 7000 feet) on Thursday as the bulk
of moisture slams into the mountain range. Will keep the current
Winter Storm Watch in effect for heavy mountain snow centered
around Thursday when models show the best potential for high snow
accumuation.

Once the weak disturbance pushes through the area on Wednesday,
model show the introduction of a strong jet max driving into
Central California on Thursday. Jet dynamics will be the main
forcing factor for the production of significant precipitation
across the district on Thursday. Presently, model precipitation
rates at the 3 hour interval could reach above 1.00 inch over the
mountains and near a quarter of an inch across the valley. If
these rates can be sustained for even just 12 hours, serious
hydrologic concerns can arise for much of Central California.
Based on good model run to run consensus, confidence in a
significant winter storm with higher precipitation rates is high
for the Thursday event. Except for Monday, cyclonic flow over the
West Coast will keep unsettled conditions ongoing for much of the
forecast period as precipitation lingers through at least next
Tuesday (or Wednesday).

&&

.AVIATION...
Local IFR ceilings and visibilities likely in the San Joaquin Valley
until 00Z Wednesday. Otherwise, VFR/MVFR conditions will prevail
this afternoon. Rain and Sierra Nevada higher terrain snow possible
between 00Z and 06Z Wednesday from Fresno County northward.
Precipitation spreading south through the remainder of the district
overnight.

&&

.AIR QUALITY ISSUES...
On Wednesday November 28 2018...Fireplace/Wood Stove Burning Status
is: No Burning Unless Registered in Fresno... Kern... Kings...
Madera... Merced 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 Watch from Wednesday evening through late Thursday
night CAZ096-097.

Flash Flood Watch from Wednesday morning through Friday morning
CAZ093.

&&

public/avn/fw...Molina
synopsis...Molina

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