Lightning Strike in Arizona, July 18, 2016

Area Forecast Discussion
National Weather Service Phoenix AZ
845 PM MST SUN JUL 17 2016

.SYNOPSIS...
An increase in clouds and humidity can be expected during the next
few days along with a slight chance of showers and thunderstorms,
mainly east of the Lower Colorado River Valley. High temperatures
will also be a bit cooler. Storm chances on the lower deserts will
be slight, with better chances over the higher terrain and over
southeast Arizona. During the latter half of the week, storm chances
will dwindle and temperatures will increase to above normal levels.

&&

.DISCUSSION...

Although we did finally see a return to more southerly flow aloft,
and a increase in mid-level moisture over south-central AZ,
convective activity has turned out to be virtually nonexistent over
our cwa this so far this afternoon/evening. The primary reason for
the lack of convection is likely due to the fact that a considerable
amount of debris cloudiness from thunderstorms over southeast
AZ/northern Mexico lingered over the region well into Sunday
afternoon, which limited daytime heating, with high only getting
into the upper 90-low 100 range over the lower deserts. The latest
high-res HRRR and RAP13 model runs are now showing more debris
clouds from storms, that are now firing over southeast AZ and along
the international border, moving northward across our cwa later
tonight and Monday morning, perhaps leading to a repeat of what we
saw today, with a cloudy morning once again limiting convective
development in the afternoon/evening. Thus, for the short term, have
reduced pops into the slight chance range for the rest of this
evening across the lower deserts of south-central AZ, and made some
minor adjustments to the hourly temp/wind/dewpoint grids.

&&

.PREVIOUS DISCUSSION...

Tonight...

A fairly complicated pattern with regards to precipitation in south
central AZ will develop later this afternoon and evening. It seems
that mid level disturbances are flying off the shelf so to speak,
and into southern AZ. One feature was noted this morning in weather
balloon data and later with sunlight, visible satellite imagery.
This feature was responsible for increased thunderstorm activity
between Gila Bend and the Mexican border at noon. Then there is
another large mid level circulation feature in northwest Mexico (an
MCV from last nights Sonora Mex convection) that is forecast by the
models to move into AZ just west of Tucson by 5 pm MST. The GFS
model is forecasting a couple of Omega field 500-300 mb bullseye
areas from Pinal County just north to Tucson, to portions of south
Central AZ just north of the Mexican Border this evening.

Therefore with increased moisture, and a couple of nearby dynamical
features, it would be best to increase chances for showers and
thunderstorms over our south central AZ zones, with the best chances
southwest and south of Phoenix. Diminishing showers are expected
after midnight partial clearing skies.

Monday...Much higher monsoon moisture will have spread over the
region by Monday afternoon. With the lack of any notable mid/upper
level disturbances, we will go with a standard low grade monsoon
forecast, i.e. slight chance of afternoon and evening thunderstorms
especially mountains east of Phoenix.

Tuesday...The easterly wave moving out of west Texas this evening
(Sunday) and into Chihuahua and Sonora Mexico is progged by the GFS
model to bodily move into southern Arizona by late Tuesday afternoon
and night. We have elevated the threat of precip slightly in south
central AZ Tuesday evening because of this feature.

Wednesday...Monsoon moisture will be still be entrenched over the
region. Again without any mid/upper level disturbances expected,
only a slight chance of showers and thunderstorms are forecast for
south central AZ.

Thursday through Sunday...monsoon moisture is forecast to thin a
little as drier air from New Mexico and Colorado mix over the area.
At the same time atmospheric height and thickness values increase
dramatically over the region, and if it weren't for remnant monsoon
moisture, afternoon temperatures be much higher. The driest areas
Thursday through Sunday will be southeast California where afternoon
temperatures at Imperial, El Centro, and Blythe will flatline at the
114 degree mark. Ouch!

&&

.AVIATION...

The lack of convective activity this evening over south-central AZ
means that the typical shift to easterly winds will likely not take
place until later tonight. We still could also see residual leftover
showers passing through Phoenix later tonight and on Monday morning
as leftover debris clouds from this evening's crop of thunderstorms
over southeast AZ/NW Mexico once again move across the region,
though shower intensity would most likely be light and impacts
minimal. Some clearing is likely by early Monday afternoon. There is
once again a slight chance for thunderstorms during the late
afternoon/early evening hours on Monday, but confidence is too low
to include in the tafs at this time.

Southeast California/Southwest Arizona including KIPL and KBLH:
Only moderate confidence in terminal forecasts through Monday
morning as thicker 15K-20K cigs spread into SE CA. While
virga/sprinkles may occur briefly, any thunderstorm activity should
remain well east of the area. Sfc winds will favor a southerly
direction (occasionally gusty at KBLH) and southeasterly at KIPL,
though a brief period of evening SW winds at KIPL will be possible
on Monday.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Wednesday through Sunday...
Moisture and relative humidity values will decrease very slightly
through the latter half of the week as high pressure tends to
strengthen and air temperatures climb back to into an above normal
range. Thunderstorm and wetting rain potential will generally be
limited to higher terrain locations north and east of Phoenix, with
better potential for outflow winds heading downhill into lower
elevations of central Arizona. Minimum relative humidity values in a
15 to 25 percent range during the middle of the week will fall to a
10 to 20 percent range by the end of the week. Overnight recovery
will be fair to good. Outside of winds near thunderstorms,
directions will favor an upslope component in the afternoon with
typical gustiness and light overnight drainage.

.SPOTTER INFORMATION STATEMENT...
Spotter activation is not expected.

&&

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

&&

Visit us on Facebook...Twitter...and at weather.gov/phoenix

DISCUSSION...Percha/Vasquez
AVIATION...Percha/MO
FIRE WEATHER...MO