Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 211117

Area Forecast Discussion
National Weather Service San Diego CA
317 AM PST Tue Nov 21 2017

High pressure aloft will dominate the weather pattern through
Thanksgiving weekend. High temperatures will be 15 to 25 degrees
above average on Wednesday and Thanksgiving, with numerous daily
record highs forecast west of the mountains. A slow cooling trend
will begin Friday, but above average temperatures will continue
into early next week. It is increasingly likely that San Diego
will fail to record measurable rainfall in November for the first
time since 1980.



At 3 AM...A upper level ridge had seized control of the region
bringing warming below 850 mb. This, along with numerous cirrus
above 20,000 ft MSL streaming around the northern periphery of the
ridge was keeping temperatures 5-10 degrees warmer than this time
yesterday. Winds were predominantly light and variable from the
coast the the deserts.

Today will be the first day of a late season heat wave that will
impact the region through the Thanksgiving Holiday. A jump of 3-4
degrees C in the 850 mb temperatures today will allow afternoon
highs to climb 5-10 degrees from yesterdays readings. This will
bring upper 80s to the inland valleys and Coachella Valley and
upper 70s to the beaches and high desert. Widespread record
breaking temperatures are not anticipated today, though a few
sites like Ramona and Campo may have a punchers chance at a daily
record. Outside of the warmth, today will be defined by light
winds and decreasing high level clouds. Given the current IR
satellite, another colorful sunrise possible this morning.

Hard to add much value to the holiday forecast, as you would have
to be living under a rock not to know record breaking heat is on
the way. The ridge currently over the region should peak
Wednesday with 500 mb heights near 594 dm and 850 mb temperatures
around 22 degrees C west of the mountains. This will focus the
most intense warmth west of the mountains and make Southern
California the warmest place in the CONUS on Thanksgiving. Weak
offshore flow will accompany the heat Wednesday and on
Thanksgiving, bringing local wind gusts of 25-40 mph to the
coastal slopes, canyons, and passes. When combined with relative
humidity values in the low teens and single digits, these winds
will produce elevated fire weather concerns. Greatest uncertainty
in the forecast revolves around coastal temperatures, where a
battle between a light sea breeze and the weak offshore winds will
dictate afternoon high temperatures.

A slow cooling trend will begin over the weekend as the
aforementioned ridge weakens and shifts slowly to the southeast.
Despite this, temperatures will remain 5-15 degrees above average
Saturday and Sunday, with the most significant cooling anticipated
next Monday when a weak trough passes to our north. For those
seeking rain, there is very little to look forward to in the long
range as dry conditions are favored through the end of November.
There is a high likelihood that San Diego will fail to record
measurable rainfall in November for the first time since 1980.


211010Z...SCT-BKN clouds AOA FL200 and unrestricted vis through
Wednesday morning.


No hazardous marine weather is expected through Saturday.


Light Santa Ana winds (gusts 25-40 mph) will develop along the
coastal slopes and below the passes and canyons Wednesday and
linger into Thanksgiving. Falling relative humidity values and
unseasonably hot temperatures will accompany the winds. Though
Red Flag conditions are not expected, elevated fire weather
conditions will still occur, and any fires that start may spread
quickly. Areas of greatest concern include: locations below the
Cajon and Banning Passes, the canyons of the Santa Ana Mountains,
and the coastal slopes in San Diego County.


Skywarn activation will not be needed this week.




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