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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 181035 AAA

Area Forecast Discussion
National Weather Service San Diego CA
334 AM PDT Sat May 18 2019

A weak ridge aloft will bring dry and warmer weather today. It will 
turn cooler and breezy again on Sunday as a cold front approaches 
and moves onshore. Showers are expected, and even an isolated 
thunderstorm or two is possible. The snow level will lower enough 
for several inches of snow to accumulate over the higher mountains, 
and winds will become quite gusty into the deserts. Continued breezy 
and cool on Monday with showers ending early over San Diego County. 
Another large, cold trough develops over the West by Tuesday and 
slowly weakens through Friday. It will maintain strong onshore flow, 
with below normal temperatures, a deep marine layer, and a chance 
for more light precipitation midweek. 



Skies were mostly clear early this morning. Satellite imagery showed 
some patchy high clouds approaching from the west though. Wind 
reports were mostly light.

We remain in a very active weather pattern for May. A strong Polar 
jet across the EastPac will once again supply several rounds of 
shortwave energy this week, that are destined to dig south over the 
Western U.S. as a sharp ridge reasserts itself along 140W. This 
anomalous jet position for late Spring keeps the western U.S. in a 
cool and unsettled pattern through the coming week, and perhaps even 
into the Memorial Day Weekend.

In the near is shaping up nicely. Some patchy low 
clouds may develop along the San Diego County Coast by dawn, but 
generally skies will be fair today and it will be a bit warmer. 

For Sunday, some of that jet energy will be digging south toward 
SoCal, pushing a cold front over the coastal waters and onshore 
during the day with increasing westerly winds and showers. Models 
show sufficient CAPE, and good jet positioning for a small 
thunderstorm threat over the coastal waters in the morning, then 
transitioning inland to the higher mountains and deserts later in 
the day due to the potential for strong sfc heating beneath sharp 
mid-level cooling destabilizing the atmosphere there. 

Rainfall amounts are expected to be one-quarter inch or less along 
the Coast, to one-half to one-and-one-half inches in the mountains 
where upslope flow and a threat for heavier convective showers 
exists later in the day. Several inches of snow could accumulate 
above 6500-7000FT in the San Bernardino and San Jacinto Mts and 
strong and gusty westerly winds will develop Sunday afternoon and 
evening in the mts/deserts. A Wind Advisory will likley be needed 
and perhaps even a Winter Weather Advisory if QPF remains on track. 

Look for a break later on Monday, but by Tuesday more energy and 
cold air are already carving out a broad trough over the PacNW bound 
for SoCal. The enhanced onshore flow and marine layer generated by 
this system once again threatens accumulating precip along and west 
of the mts for the midweek period, along with much below normal 
temperatures. How far below? Looks like 15-20F for the Valleys, Mts, 
and deserts. Marine influence will keep the coast closer to about 5F 
below normal. 

Looking ahead to the upcoming holiday weekend...The operational and 
ensemble means for the ECMWF/GFS still favor a trough over the SW. 
It looks weaker with less cold air, so the weather may be dry with 
temps closer to average.


181000Z...Coast/Valleys...A mostly clear sky will prevail with a low 
threat of patchy low stratus cloudiness with bases of 2500 ft MSL. 
However, no signs of stratus development so favoring VFR. Cloudiness 
will increase tonight ahead of the next system which will spread 
-SHRA into the area from NW to SE after about 14Z Sunday.

Mountains/Deserts...VFR will prevail. NW winds will increase late 
this afternoon/evening with gusts to around 20 kt.


West winds will be on the increase again over the waters late 
morning on Sunday with gusts of 20-25 kt forecast, increasing 
further Sunday night-Monday when gusts could reach 30 kt. Windy 
conditions will continue through Wednesday. A Small Craft Advisory 
will be needed.


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