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Area Forecast Discussion (AFD)

Issued by San Diego, CA (SGX)

FXUS66 KSGX 211614

Area Forecast Discussion
National Weather Service San Diego CA
914 AM PDT Sat Sep 21 2019

Fair and warmer weather is expected this weekend, with limited 
night and morning low clouds and fog near the coast. Low pressure 
will develop south over California and Nevada on Monday, possibly 
with enough moisture and instability for a few showers or 
thunderstorms Tuesday and Wednesday. A much larger area of low 
pressure will develop over the West during the latter half of next
week, maintaining a chance for light showers over Southern 
California at times as the marine layer deepens well inland. 



Low clouds still linger along the immediate coast but are burning
off. 12Z KNKX sounding shows PW of 0.71 inch with inversion up to
850 mb. Expect a mostly sunny, dry day today with temperatures
several degrees warmer than Friday. Highs should reach the 90s in
some inland valley areas including much of the inland empire and
100 in a few desert locations. Forecast trends are on track and no
changes are necessary with the morning update. 


Marine stratus early this morning was patchy near the Coast and 
showing no signs of increasing through 2 AM PDT. Surface pressure 
gradients were weak and wind reports light early this morning.

Broad troughing prevalent over the West will pull east, allowing 
heights to rise and the atmosphere to warm over SoCal. This trend 
will be brief as more toughing fills in from the west and NW. A few 
more mid-level clouds could get pulled north on Sunday and Monday 
ahead of these incoming systems, but generally skies will be fair 
and temperatures near to a bit above average.

Confidence lowers beyond Monday as a closed low forms over the Lower 
Colorado River Valley. Model solutions vary with this feature, but 
the favored track steers most of the moisture well to our east 
initially. Most model solutions show the low meandering over far NW 
MX through Wed until sagging westerlies farther north draw it NE 
across AZ/NM. Before the low departs, some easterly flow and 
associated moisture around the north side of the low could spark 
some shower/thunderstorm activity, particularly over our 
mts/deserts. Some of this could drift west of the mts as it weakens. 
Low POPS are in the forecast Tue-Wed for this possibility. 

As a larger, longwave trough digs over the West Thu-Sat, and the 
compact upper low moves NE, stronger onshore flow will build the 
marine layer. Moisture could be sufficient for periods of light 
rainfall at times along and west of the mts into next weekend. The 
ECMWF solution looks aggressive with this precip beginning on Thu 
and continuing through next weekend so fcst POPS are low and trimmed 
temporally for this extended period with climatology in mind.  Along 
with the clouds and moisture, expect daytime temperatures to be well 
below average after Wednesday.  

211515Z...Coast...Patchy low clouds with bases 1000-1500 ft MSL 
continuing to linger along the coast. Scatter out expected 16-17Z. 
Otherwise, mostly clear with unrestricted vis through this evening. 
Patchy low clouds may redevelop after 06Z Sunday with bases near 
1000 ft MSL and will be confined to the immediate coast. Low 
confidence in cigs impacting coastal TAF sites overnight. 

Valleys/Mountains/Deserts...Clear with unrestricted vis through 
Sunday morning. 


No hazardous marine weather expected through Wednesday.


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