Severe Thunderstorm Warning 95, NWS Phoenix, AZ

857 
WWUS55 KPSR 130817
SVSPSR

Severe Weather Statement
National Weather Service Phoenix AZ
117 AM PDT SAT OCT 13 2018

CAC065-130830-
/O.CON.KPSR.SV.W.0095.000000T0000Z-181013T0830Z/
Riverside CA-
117 AM PDT SAT OCT 13 2018

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 130 AM PDT
FOR RIVERSIDE COUNTY...

At 117 AM PDT, a severe thunderstorm was located 8 miles northeast of
Cottonwood Visitor, or 13 miles north of Chiriaco Summit, moving 
northeast at 25 mph. The storm has been holding together and still 
has good potential to produce large hail.

HAZARD...60 mph wind gusts and quarter size hail.

SOURCE...Radar indicated.

IMPACT...Hail damage to vehicles is expected. Expect wind damage to 
         roofs, siding, and trees.

Locations impacted include...
Chiriaco Summit and Cottonwood Visitor. 

This includes CA Interstate 10 between mile markers 74 and 89.
 
PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 3386 11554 3359 11572 3366 11595 3394 11592
TIME...MOT...LOC 0817Z 206DEG 23KT 3386 11571 

HAIL...1.00IN
WIND...60MPH
 
$$

CB

038 
WWUS55 KPSR 130824
SVSPSR

Severe Weather Statement
National Weather Service Phoenix AZ
124 AM PDT SAT OCT 13 2018

CAC065-130833-
/O.EXP.KPSR.SV.W.0095.000000T0000Z-181013T0830Z/
Riverside CA-
124 AM PDT SAT OCT 13 2018

...THE SEVERE THUNDERSTORM WARNING FOR RIVERSIDE COUNTY WILL EXPIRE
AT 130 AM PDT...
                
The storm which prompted the warning has weakened below severe
limits, and no longer poses an immediate threat to life or property.
Therefore, the warning will be allowed to expire.

LAT...LON 3386 11554 3359 11572 3366 11595 3394 11592
TIME...MOT...LOC 0823Z 206DEG 23KT 3388 11570 

$$

CB

Area Forecast Discussion
National Weather Service Phoenix AZ
818 PM MST Fri Oct 12 2018

.UPDATE...Updated discussion and aviation discussion

&&

.SYNOPSIS...
An upper low will move through the region bringing scattered to
numerous showers and isolated thunderstorms starting in southeast
California later tonight and spreading eastward to Arizona
tomorrow. Shower activity will become more isolated and confined
to the higher terrain of central and eastern Arizona Monday
through Thursday. Temperatures will remain below normal.

&&

.DISCUSSION...

A strong upper level low is currently sitting off the coast of
Southern California this evening and is forecast to move inland
tonight. As it does so, lift generated from the system will
trigger elevated convection in SE California starting 04-06Z this
evening. Thunderstorms and showers will then slowly move eastward
through Saturday morning as the upper level low pushes inland.
The latest HREF indicates convection and showers could begin in
the Phoenix area late Saturday morning. Storm motion is expected
to be relatively fast but training of storms will create a risk of
flash flooding. The forecast remains on track for tonight/Saturday
and no changes were made.

&&

.PREVIOUS DISCUSSION...
Rest of today through Sunday...Shower activity associated with
moisture from the outer fringes of what was TS Sergio continues
to taper off across south central Arizona, with mostly dry
conditions expected by late this afternoon/early evening. Very
isolated showers and possibly even a thunderstorm or two over
western Arizona will be possible this afternoon with enough
daytime heating and forcing from terrain, but chances are very
low.

Models are continuing to trend a bit wetter with rainfall totals
overnight over southeast California and into Arizona tomorrow as
an upper level low approaches from the west. Ahead of this
aforementioned low, plenty of moisture will be in place, with
PWATS generally between 1 and 1.5 inches. This combined with
enough dynamical lift from the approaching system, will allow
showers and thunderstorms to develop overnight into tomorrow.
Right now, the timing of showers and isolated storms looks to be
around 06Z (11 PM) across our far western CWA, near 09Z (2 AM)
across Imperial and Riverside counties, near 12Z (5 AM) near the
Colorado River Valley, near 15Z (8 AM) across La Paz and Yuma
county, near 18Z (11 AM) across western Maricopa County, and near
21Z (2 PM) across central Maricopa county eastward. Although most
of the activity should be shower-like, there is the potential for
some isolated convection with GEFS forecast mean CAPE values near
500 J/kg. In addition, there will be a pretty decent amount of
shear (GEFS mean is near 35 to 40 kts) in place to also support
some isolated stronger storms that will have the potential to
produce hail. Severe hail is not as likely because mid-level lapse
rates should remain below 7.5 degrees/km. Storm motion is
expected to be pretty fast, so flash flooding will be a little
less likely, but cannot be completely ruled out. The increased
cloud cover tomorrow, will lead to another day of below average
temperatures with highs ranging from the low 80s in southeast
California to the upper 60s/ low 70s across our eastern CWA.
Lingering showers will exist Sunday morning, primarily across our
eastern CWA before 15Z (8 AM). After 15Z the axis of the upper-
level low should be across eastern Arizona, with moist advection
occurring ahead. Thus, some moisture will linger across our far
eastern CWA and this combined with daytime heating and upslope
flow will lead to another chance of afternoon showers and isolated
convection across the higher terrain north and east of Phoenix.

Sunday night through Thursday...An upper trough and associated
cold front push southward through southeast California and Arizona
Sunday night and Monday. This will bring strong northerly winds
to southwest AZ and southeast CA...along with dry air. The upper
low deepens into a closed low centered over Arizona on Monday
afternoon where it lingers before weakening and shifting eastward
on Thursday. This keeps PoPs going over south-central AZ. But, due
to drier air in place, PoPs are only in the slight category.
Anticipate somewhat cooler temperatures on Monday (most noticeably
over our western areas despite mostly clear skies there). Very
gradual warming from there.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:

A Pacific weather system will move inland early Saturday and will
generate showers and thunderstorms over the terminals late
Saturday morning. Stronger thunderstorms that move over the
TAF sties will likely drop visibility temporarily, perhaps even
into the MVFR range. Right now, the best chances for storms look
to be in the 19 to 22Z time range although lingering thunderstorms
will be possible into the evening hours. As far as ceilings are
concerned, expect a redevelopment of clouds around 5 kft early
Saturday morning with BKN skies lasting into the afternoon. Winds
will stay out of the east tonight and early Saturday morning
before switching to a south southwesterly direction briefly in
the afternoon. Excluding strong thunderstorms, winds should be
rather light for Saturday.

Southeast California/Southwest Arizona including KIPL and KBLH:

An approaching Pacific weather system will trigger showers and
elevated convection tonight over the terminals which will provide
a several hour window of precipitation chances. If a heavier
shower moves over the airport tonight, expect a temporary drop in
visibility, possibly down into the MVFR range. A broken band of
precipitation will slowly move east tonight and should be out of
the terminals by the 12 to 15Z timeframe. Another round of
convection could develop Saturday afternoon but am much less
confident that these storms will reach the terminals. For now,
this has been excluded from the TAFs.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Monday through Friday:
Isolated showers may persist into the first half of next week for
the higher terrain north and east of Phoenix, but other locations
further west should remain dry. Minimum relative humidity values
across the lower deserts will range from 10-40 percent with the
driest conditions across the western deserts. A cold front will
push southward through southeast California and Arizona Monday.
This will bring strong northerly winds to southwest AZ and
southeast CA, with gusts to around 40 mph. Outside of Monday,
winds will generally remain below 20 mph. High temperatures will
stay well below normal especially across south-central Arizona
where deserts highs will stay mostly in the 70s.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

DISCUSSION...Wilson
PREVIOUS DISCUSSION...Hernandez/AJ
AVIATION...Wilson
FIRE WEATHER...Hernandez