National Weather Service Forecast Discussion

Dicussion provided by the National Weather Service Forecast Office located in San Diego, California

000
FXUS66 KSGX 071555
AFDSGX

Area Forecast Discussion
National Weather Service San Diego CA
855 AM PDT Tue Apr 7 2020

.SYNOPSIS...
A low pressure system southwest of Point Conception will move
slowly toward the southeast and east, finally moving eastward and
out of the area on Saturday. Periods of showers will continue
into Friday with a slight chance of thunderstorms this afternoon
and again Wednesday afternoon. Saturday through Monday will be
mostly dry and a little warmer.

&&

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

Showers continue to move north-northeast across the area this
morning with the most widespread activity just off the San Diego
County coast. The morning sounding from KNKX shows precipitable
water of 0.84 inch, down only slightly from the 0.90 inch
yesterday afternoon. Weak instability developing this afternoon
will be sufficient for locally heavy showers and a slight chance
of thunderstorms.

Showers should decrease in coverage and intensity tonight as
instability decreases. All models are showing a somewhat narrow
band of precipitation wrapping around the east and north sides of
the low. Depending on where this sets up there could be moderate
rain over the deserts tonight into Wednesday morning, though at
this point it looks like it will remain east and north of our
forecast area.

The upper level low finally moves over the area on Wednesday. The
colder air near the center of the storm will bring snow levels
down to 4500-5000 ft. Greater instability is expected, especially
during the afternoon, increasing the threat of thunderstorms and
isolated heavy showers. Moisture decreases significantly which
will help limit rainfall amounts.

This low pressure system will remain centered over the
southwestern states for Thursday and Friday before weakening and
moving off to the east on Saturday. Periods of showers will
continue on Thursday and decrease on Friday.

The lowest high temperatures are expected on Wednesday and
Thursday with high temperatures for some inland areas 20 to 25
degrees below average. There will be a warming trend for Friday
through Monday but with high temperatures remaining below average.

&&

.AVIATION...
071530Z...Coast/Valleys/Mountains...Occasional -SHRA will continue
today and tonight with variable cigs 1000-3500 feet MSL, occasional
vis 1-4SM with higher terrain obscured at times. Lowest cigs/vis
during SHRA or +RA, as well as during isolated brief TSRA during the
afternoon. -SHSN will occur in the mountains mainly above 5500 feet
MSL. The rainy and snowy pattern will continue into tomorrow.

Deserts...BKN skies around 5000-1000 FT MSL with areas of -SHRA at
times. Best chances this afternoon and tonight where some ceilings
could fall to below 4000 feet MSL, and local vis could fall to 3-
5SM.

&&

.MARINE...
There is a slight chance of thunderstorms, mainly during this
afternoon and Wednesday afternoon. Otherwise, no hazardous marine
weather is expected through Saturday.

&&

.BEACHES...
There is a slight chance of thunderstorms producing lightning
strikes, mainly during this afternoon and Wednesday afternoon.

&&

.HYDROLOGY...
Through Friday, additional rainfall is expected to range from
around 1.5 inches near the coast to 2 to 4 inches in the mountains
with 1 to 1.5 inches across the high deserts and one half to one
inch in the lower deserts. There is also a slight chance of
thunderstorms for this afternoon and Wednesday afternoon.

A snow level near 6000 to 6500 feet today, will lower to 4500 to
5000 feet for late tonight through Wednesday night, then rise to
5000 to 5500 feet Thursday. In the mountains of San Bernardino and
Riverside Counties, additional snowfall of 3 to 6 inches is
expected from 4500 to 5500 feet, 6 to 12 inches from 5500 to 6500
feet, 12 to 24 inches from 6500 to 7500 feet, with greater than 24
inches on the highest peaks.

The potential for urban and small stream flooding will continue
today and Wednesday along with the possibility of isolated flash
flood flooding with thunderstorms or where showers track
repeatedly across the same area. Low water crossings along the
San Diego River in Fashion Valley will experience minor flooding
through at least Wednesday as the river is forecast to remain
above monitor stage.

&&

.SKYWARN...
Skywarn activation may be requested this afternoon.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...Flash Flood Watch through Wednesday evening for Apple and
     Lucerne Valleys-Coachella Valley-Orange County Coastal
     Areas-Orange County Inland Areas-Riverside County Mountains-
     San Bernardino County Mountains-San Bernardino and
     Riverside County Valleys-The Inland Empire-San Diego County
     Coastal Areas-San Diego County Deserts-San Diego County
     Mountains-San Diego County Valleys-San Gorgonio Pass Near
     Banning-Santa Ana Mountains and Foothills.

     Winter Storm Warning until 5 AM PDT Thursday for Riverside
     County Mountains-San Bernardino County Mountains.

PZ...NONE.
&&

$$

PUBLIC...SS
HYDROLOGY...SS/17
AVIATION/MARINE/BEACHES...APR

NWS SGX Office Area Forecast Discussion