Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 271920
AFDSGX

Area Forecast Discussion...UPDATED
National Weather Service San Diego CA
959 AM PST Mon Feb 27 2017

UPDATED TO ADD SMALL CRAFT ADVISORY FOR THE INNER WATERS TODAY

.SYNOPSIS...
a low pressure trough aloft will pull a deep Pacific moist layer
across portions of Southern California today into tonight creating
widespread moderate to locally heavy rainfall. The heaviest
rainfall potential exists for San Diego County. Some snow will fall
on the higher mountain peaks as well. Strong westerly winds will
accompany the rain and snow in the higher mountains. Slightly warmer
for Tuesday. Then dry with a warming trend for Wednesday through
Friday with periods of weak offshore flow. A little cooler for next
weekend.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

...Moderate to heavy rainfall looking likely today for southern San
Diego County and across far northern Baja CA...

A flash Flood Watch is in effect through this evening for San Diego
County. Based on satellite imagery, the deep moisture plume remains
on track to move across the International Border area later today.
This will bring an extended period of moderate to heavy rainfall and
possible flooding. The greatest concern continues to be for the
areas of Southern San Diego County, including the Tijuana River
Valley.

Winds in the mountains this morning have been in the 25 to 35 MPH
range with peak gusts near 45 MPH. A Wind Advisory remain in
effect for the mountains through 10 AM Tuesday.

The 12Z Miramar sounding was saturated from the sfc through 13K FT
with a PW of 1.03 inch. Model projections keep San Diego County in
this plume exceeding one inch through 06Z, before moving south.

From previous discussion...

A trough of low pressure moving southward along the California
coast will draw moisture northward into far southern California
from a plume of subtropical moisture directed into northern Baja.
Lighter precipitation early this morning may intensify for late
this morning through early this evening with the most significant
rainfall across northern Baja extending northward into southern
and central San Diego County and possibly into western Riverside
County. Showers will decrease from the northwest late tonight and
end early Tuesday.

Greatest rainfall totals north of the border are expected across
southern and central San Diego County. Through tonight...rainfall
across central and southern San Diego County is expected to range
from around one inch near the coast to 2 to 3 inches in the
mountains with amounts decreasing towards the northwest.

Urban and small stream flooding is expected across portions of the
coastal...valley...and mountains areas below 5000 feet in San
Diego County with isolated flash flooding possible. The rainfall
could cause a rise in the San Diego River sufficient to flood low
water crossings through Fashion Valley for late this evening
through late tonight.

...Amended 1452Z...

Snow levels near 5400 feet early this morning...will rise to 6000
feet for this afternoon...then decrease to 4000-4500 feet late
tonight. A few inches of snowfall early this morning...with total
snowfall of 3 to 6 inches through late evening...with isolated
snowfall to 8 inches on the highest peaks.

Strengthening onshore flow will bring strong gusty west winds
in the mountains and the northern Coachella Valley into Tuesday
morning. Strongest winds are expected through late tonight with
west winds 25 to 35 mph with gusts to 55 mph...and with isolated
gusts to 65 mph at times in the most wind-prone areas. Strongest
winds are expected near mountain ridge tops onto the desert slopes
of the mountains and in the northern Coachella Valley below the
San Gorgonio Pass. The strongest gusts through 3 AM were 63 mph
at Whitewater in the northern Coachella Valley...and 62 mph at
Volcan Mountain in the San Diego County Mountains.

Continued cool today...then drying and slight warming for Tuesday.
For Wednesday through Friday...high pressure aloft off the
California coast and surface high pressure over the Great Basin
will bring dry weather with a warming trend with periods of weak
offshore flow. A little cooler with weak onshore flow for next
week with a return of coastal low clouds fog possible Saturday
night into Sunday morning.

&&

.AVIATION...
271640Z...Low CIGS in San Diego County through 03Z Tuesday with
OVC003-006 and vis 1-2 miles in rain and fog. Slightly higher CIGS
farther north in ORA, RIV and SBD Counties this morning with BKN-
OVC015-030, lowering to OVC010-020 this afternoon as rain spreads
north. Strong south winds 15-25kt at KSAN through 23Z with higher
gusts.

Mountains obscured in clouds/fog/pcpn. Strong winds in the mountains
and desert slopes with strong up/down drafts and llws over and east
of the mountains. Desert areas to have BKN-OVC030-060 with periods
of light rain. Vis mostly unrestricted.

&&

.MARINE...Updated
A Small Craft Advisory is in effect for the Inner Waters through 9
AM Tuesday. Strong south to southwest winds of 15-30 kt are likely
over the Inner Waters today ahead of a cold front. The winds will
shift westerly late this afternoon with the passage of the cold
front.

In the Outer Waters, a Small Craft Advisory will be in effect for
gusty northwest winds from 9 PM today through 9 AM Tuesday.

&&

.SKYWARN...
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Winter Weather Advisory from 8 AM this morning to 10 PM PST this
     evening for Riverside County Mountains.

     Wind Advisory until 10 AM PST Tuesday for Riverside County
     Mountains-San Bernardino County Mountains-San Diego County
     Mountains-San Gorgonio Pass Near Banning.

     Flash Flood Watch from 8 AM PST this morning through this
     evening for San Diego County Coastal Areas-San Diego County
     Mountains-San Diego County Valleys.

PZ...Small Craft Advisory for winds from 9 PM this evening to 9 AM
     PST Tuesday for Waters from San Mateo point to the Mexican Border
     Extending 30 to 60 nm out including San Clemente Island.

     Small Craft Advisory until 9 AM PST Tuesday for Coastal Waters
     from San Mateo Point to the Mexican Border and out to 30 nm.

&&

$$

PUBLIC...JAD/17
AVIATION/MARINE...Moede


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