Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 181614

Area Forecast Discussion
National Weather Service San Diego CA
930 AM PDT Mon Jun 18 2018

The low pressure trough over the West will weaken today, with areas
of low clouds very slowly clearing west of the mountains along with
continued below normal temperatures regionwide. High pressure aloft
will build Tuesday through Friday and result in a return to hot
weather in the deserts and some of the inland valleys, especially
starting Wednesday. The night and morning low clouds will be more
patchy. Slight cooling will occur over the weekend as the high
weakens. Otherwise, dry conditions will prevail the rest of this
week and early next week.



Skies were mostly cloudy west of the mountains, with early
clearing over most of southern San Diego County. The 5 AM NKX
sounding showed an inversion around 3700 feet MSL that was 10 deg C
strong. However, the clouds were generally thinner than previous
days, so better clearing will occur today, even though it will still
be slow over Orange County and parts of the Inland Empire. We will
have highs 5-10 deg F below normal in most areas today, though less
at the coast where temps are usually cool in June.

The biggest weather impact this week will be the desert and far
inland valley heat, especially Wednesday through Friday. As the
upper low over the West gradually weakens and lifts northeast
towards the northern Rockies/northern Plains Tuesday, we will have a
high pressure ridge forming just off the southern California coast,
with the high shifting east to So-Cal/southwest Arizona Wed/Thu.
As would be expected at this time of year, the high will bring hot
weather inland, with temps at seasonal levels Tuesday, then 5-10 deg
F above seasonal levels Wednesday through Friday for most inland
areas. This means 110-114 deg F in the lower deserts, which is near
or just below critical levels. The humidity will be low, both at the
surface and aloft, so nighttime minimum temps will mostly be in the
70s, except a few 80s in thermal belts. For now, no excessive heat
watch will be issued for the deserts, but we will watch this
closely, and if it appears 115 deg F temps will occur beyond just a
few localities, we will definitely consider a watch. As the upper
high shifts south of the US-Mexico border this weekend due to an
upper low diving south across the Rockies and eastern parts of the
Great Basin, that should bring a few degrees of cooling inland.
Monsoonal moisture stays well to the southeast through at least
early next week.


181540Z...Coast/Valleys/Coastal Mountain Slopes...Low clouds
beginning to clear, with a SCT layer around 2500 ft MSL and BKN-OVC
layer 3500-4000 ft MSL and tops to 4500 ft MSL. All layers should be
mostly SCT  by 18Z. Low clouds should begin to redevelop along the
coast between 03Z and 06Z Tue, with bases 1500-2000 ft MSL. Clouds
expected to increase in coverage overnight. Areas of reduced VIS are
likely where clouds and terrain intersect.

Desert Mountain Slopes/Deserts...Mostly clear with unrestricted VIS
through tonight. Gusty northwest winds will continue to weaken today.


West northwest winds gusting near 20 kt will develop this afternoon
and evening. Otherwise, no hazardous marine weather is expected
through Friday.


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





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