Heat Advisory 2, NWS San Diego, CA

Area Forecast Discussion
National Weather Service San Diego CA
849 AM PDT Fri Jul 6 2018

.SYNOPSIS...
Very hot weather today will result from a strong high pressure
ridge over the West. Moisture will increase from the southeast
will bring a small chance of thunderstorms in the mountains today
and a greater chance for the coming days through next week.
Temperatures will very gradually decrease over the weekend and
next week as the high weakens.

&&

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

Low clouds have become a thing of the past as high pressure aloft
has squashed the marine layer almost down to nothing. Areas of
offshore winds have begun in some foothills, with spots in San
Diego County gusting 25-30 mph. This offshore flow will compress
and dry out the air to boost the heating we will all feel today.
Today's temperatures are likely to break quite a few daily records
across the region and we should all find a place to stay cool.
Another wrinkle in our forecast today is the increasing moisture
at mid levels arriving from the southeast. We have a very small
chance of thunderstorms in the forecast for the mountains this
afternoon, but instability and depth of moisture are very marginal
today. Temperatures will decrease Saturday as the high aloft
relaxes a little and moisture from the east increases and boosts
humidity. Tonight we actually get a coastal eddy to develop, which
will help make the cooling trend noticeable near the coast on
Saturday. Farther inland temperatures will only decrease by a few
degrees. Chances for thunderstorms increase each day Saturday,
Sunday, Monday and Tuesday as the easterly flow continues to
funnel monsoon moisture into the region. A couple easterly waves
could add a bit of energy this weekend, and again Monday into
Tuesday, that could present a chance of thunderstorms west of the
mountains, and/or during nights and mornings. It's a bit of a
monsoon mess that will make it hard to pinpoint the timing and
location of thunderstorms. Right now the deepest moisture and
greater potential for heavy rain appears Monday into Wednesday.
With the greater cloud cover and humidity, temperatures will be
mercifully lower next week, but will continue above average and it
will feel muggy. There are some clues that moisture decreases
later next week for less chance of thunderstorms. Onshore flow
increases during the week, possibly opening the door for a marine
layer to develop and coastal clouds to reappear.

&&

.AVIATION...
061530Z...Small chance of patchy low clouds with bases 800-1000 ft
MSL near KSAN tonight and impacts at KSAN are unlikely. Otherwise
SCT clouds at/above 12000 ft MSL through Saturday morning. Gusty
easterly winds will produce weak to mdt up/downdrafts and LLWS over
and west of the mtns through this afternoon, but impacts at TAF
sites are doubtful. Slight chance of TSRA- over the mountains this
afternoon, with strong up/downdrafts and erratic, gusty surface
winds. CB bases 10000-12000 ft MSL layered to 30000 ft MSL.

&&

.MARINE...
No hazardous marine weather is expected through Tuesday.

&&

.BEACHES...
South swells from Post Tropical Cyclone Fabio will continue high
surf and dangerous rip currents along south and southwest-facing
beaches of Orange and northern San Diego Counties through tonight.
Surf peaks this morning with sets 5-7 ft. High surf and strong rip
and longshore currents will create extremely hazardous conditions
for swimmers at all So Cal beaches. A High Surf Advisory remains in
effect through 9 PM this evening.

&&

.FIRE WEATHER...
Strong high pressure aloft and weak offshore flow will bring very
hot weather inland from the beaches today with lowest inland
humidities of 5 to 10 percent today. Those low humidities combined
with gusty east winds to 30 mph will cause near critical fire
weather conditions for the coastal slopes of the mountains into
the inland valleys through midday. For this afternoon, mid level
monsoonal moisture will slowly increase with a slight chance of
thunderstorms with dry lightning and strong gusty winds. The
chance of thunderstorms increases Saturday, but with higher
humidity and a better chance of wetting rains.

&&

.CLIMATE...
Record high temperatures that could be tied or broken on today and
Saturday based on the current forecast high temperatures. Some record
high minimum temperatures are likely for tonight as well.

Friday...
Location         Forecast    Existing record
Newport Beach       89        80 in 1936
San Diego           91        84 in 1981
Vista               98        92 in 1981
Chula Vista         93        84 in 2014
Riverside          115       108 in 1907
Escondido          106       102 in 1940
El Cajon           111        96 in 1996
Ramona             110       100 in 2017
Alpine             107       104 in 1957
Campo              104       104 in 1976
Thermal            116       116 in 1954

Saturday...
Location         Forecast    Existing record
Newport Beach       86        79 in 1931
Vista               94        93 in 1984
Chula Vista         85        85 in 2011
El Cajon            98        97 in 1985
Ramona             102       102 in 2017

&&

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

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Heat Advisory until 9 PM PDT this evening for Riverside County
     Mountains-San Bernardino County Mountains-San Diego County
     Coastal Areas-San Diego County Mountains.

     Excessive Heat Warning until 9 PM PDT this evening for Apple and
     Lucerne Valleys-Coachella Valley-San Diego County Deserts-
     San Diego County Valleys-San Gorgonio Pass Near Banning-
     Santa Ana Mountains and Foothills.

     Excessive Heat Warning until 9 PM PDT Saturday for Orange County
     Inland Areas-San Bernardino and Riverside County Valleys-
     The Inland Empire.

     High Surf Advisory until 9 PM PDT this evening for Orange County
     Coastal Areas-San Diego County Coastal Areas.

     Heat Advisory until 9 PM PDT Saturday for Orange County Coastal
     Areas.

PZ...NONE.

&&

PUBLIC/FIRE/CLIMATE...MM/17
AVIATION/MARINE/BEACHES...PG