Excessive Heat Warning 2, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
300 AM MST Thu Jun 13 2019

.SYNOPSIS...
Excessive heat conditions will remain an issue through today with
afternoon high temperatures at or just over 110 degrees for the
lower deserts. A low pressure system approaching from the northwest
will slowly move through the region Friday and Saturday bringing
some relief with cooler temperatures by Friday, but very dry
conditions will continue to prevail. Near to slightly below normal
temperatures are then anticipated this weekend into next week.

&&

.DISCUSSION...
Strong high pressure continues across southern Arizona early this
morning; latest 00z plots showed 500mb heights around 593dm across
the lower deserts into far SE California. Yesterday, 850mb temps ran
in the ballpark of 30C across the lower deserts and many locations
exceeded 110 degrees; Phoenix topped out at 112, Yuma and Blythe
hit 114 and Imperial reached 115. Guidance remains very consistent
in calling for the ridge to slowly weaken and shift to the east
today as an open wave low pressure trof approaches Arizona from the
west. Heights aloft will fall but 850mb temps will stay near 30C
over portions of south-central Arizona and only fall to around 28C
over far southwest Arizona. NAEFS percentiles for 850mb temps today
put much of the lower deserts above the 90th percentile and given
dry air and increased mixing we can expect another very hot day
especially over south central Arizona. Phoenix is forecast to hit
112 again today although that would be 2 degrees below the record of
114.

Given the potential for one more very hot day, the Excessive Heat
Warning remains in effect through 8 pm for much of the lower
deserts, extending as far west as portions of eastern Riverside
County. We even added much of Yuma County into the warning as well,
including the community of Yuma itself. One other issue for today -
as the trof approaches winds will increase and we can expect rather
breezy conditions during the afternoon and into the evening.
Combined with single digit RH and hot temperatures, fire danger will
be elevated. At this time, it appears we will still be a bit below
red flag criteria but the FWF has been headlined for the increased
fire danger. Only location where winds will meet advisory are in the
favored far southwest corner of Imperial County; a Wind Advisory has
been issued that will run from 4 pm this afternoon through 8 am
on Friday.

On Friday as the upper trof settles into the desert southwest and
Arizona, 850mb temps lower to around 23-25C across the lower deserts
and accordingly high temperatures fall sharply. Phoenix looks to see
a high around 104 on Friday with similar temperatures across the
lower deserts into far southeast California. Less wind will occur
Friday so no advisory issues, and fire danger will decrease a bit.

For most of the forecast period, this weekend into the middle of
next week, we can expect dry but cooler conditions as the influence
of a pair of low pressure trofs will keep highs suppressed and near
seasonal normals. No significant winds are expected but locally
breezy south to southwest winds are likely during the afternoon
hours on many of the days. Phoenix can expect highs in the 103-104
ballpark for most of the period with the warmest lower deserts
struggling to reach 105.

&&

.AVIATION...Updated at 0500 UTC.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No major aviation weather concerns for the rest of tonight. Light
westerly winds will become easterly across the terminal area
(around 9-10Z for KPHX). There may be some slantwise visibility
issues for acft on eastward take-offs/approaches tomorrow morning
due to nearby fires. Vis in the terminal area should be fine.
Otherwise, still expecting strong westerly winds by early
afternoon for the area due to an approaching front. Gusts 15-25
kts will be common from the early afternoon through at least
sunset.

Southeast California/Southwest Arizona including KIPL and KBLH:

Some strong westerly winds with gusts upwards of 20 kts are still
expected for the next few hours before waning late tonight.
Stronger gusts upwards of 25-30 kts will resume by tomorrow
afternoon. Wind directions will primarily remain westerly although
there may be a slight southerly direction component for KBLH at
times early Friday morning.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday:
Several weak low pressure systems will sweep through the region
this weekend and early next week bringing temperatures back to
near seasonal average. However, very dry conditions will also
prevail with afternoon humidity values generally falling to around
10-15% following only poor to fair overnight recovery. Very
typical afternoon upslope breeziness (gusts mainly in the teens)
should settle into the region during the weekend and persist into
early next week with afternoon winds favoring the south to
southwest.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST today for AZZ530-533-
     534-537>544-546-548>556-559.

     Excessive Heat Warning 11 AM until 8 PM MST today for AZZ531-532-
     536.

CA...Excessive Heat Warning until 8 PM PDT today for CAZ569-570.

     Wind Advisory 4 PM PDT today until 8 AM PDT Friday for CAZ562.

&&

DISCUSSION...CB
AVIATION..Deems
FIRE WEATHER...Hernandez