National Weather Service Raw Text Product

265 
FXUS65 KPSR 150522
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1022 PM MST Fri Jul 14 2023

.Update...Updated Aviation

&&

.SYNOPSIS...
A strong subtropical ridge will continue to dominate the Desert 
Southwest through at least early next week, allowing near record to 
record temperatures to prevail. An Excessive Heat Warning is in 
effect through Wednesday, as widespread Major HeatRisk increases 
to Extreme HeatRisk this weekend. Isolated shower and thunderstorm
chances the next couple days will be confined to higher terrain 
areas of eastern and southeastern Arizona with increasing chances
expected to extend into the south-central Arizona lower deserts 
by early next week.

&&

.DISCUSSION...
Heat is the number one weather-related killer in the United 
States. It is important to not only acknowledge this, but also 
have mitigation plans for the heat as this historic heat wave 
continues. Everyone is susceptible to this magnitude of heat and 
should take it seriously. Take proper precautions by staying 
hydrated and protecting yourself and family from the heat. Limit 
time outdoors and find adequate cooling. You can find a map of 
cooling centers and hydration stations around Maricopa County at 
hrn.azmag.gov/#/map. As we head into the weekend with 
unprecedented temperatures, highs in the 115-120 degree range and
lows in the mid-80s to mid-90s, nearly all lower desert/valley 
locations will experience Major HeatRisk while most populated 
areas, including Phoenix, Yuma, and El Centro, will experience 
Extreme HeatRisk. For many, the high temperatures this weekend 
will be the hottest ever experienced and on top of that the 
overnight relief will be minimal. 

Phoenix Sky Harbor reached 110F before noon today, bringing the 
consecutive 110+ day count to 15 days. Now only 3 days from tying 
the record streak of 18 days and 4 days from the outright record. 
With 115+ F in the forecast for Phoenix through the middle of next
week, the record is expected to be tied on Monday. Driving this 
intense and long-lasting heat is a very strong, near record 
strength, H5 high pressure. Currently the high is building between
LA and San Francisco, CA. A sounding from Edwards AFB this 
morning measured a 597dm 500mb height. Further strengthening of 
this high is expected this weekend, with the heights pushing 
599-600dm based on grand ensemble mean. The greatest 500mb height 
sampled in AZ is 601.5dm over Flagstaff back in 1989. Forecast 
heights do dip slightly after Monday, as the high pressure 
repositions eastward toward the AZ/NM border region, but only to 
around 596-598dm. Suffice to say, the heatwave will continue. The
Excessive Heat Warning was extended another day, through Wednesday
for most areas.

A rain shower or thunderstorm would be a great at mitigating the 
afternoon heat. Unfortunately, the atmosphere is drying through 
this weekend (PWATs falling down to around 1") and a couple 
perturbation waves rounding the high pressure are expected to stay
mostly south of the international border, moving west through 
northern Sonora and the Baja Peninsula. With the high pressure 
sliding east late this weekend into early next week, this will 
likely allow moisture to gradually creep back northward into at 
least southern Arizona, raising dew points back into the 50s 
across the lower deserts. NBM PoPs for Monday afternoon/evening 
across eastern and southern Arizona have increased over the past 
several runs, now showing PoPs of 20-30% in the Phoenix area 
Monday evening. Even though moisture still looks to be rather 
marginal with PWATs of around 1.3" and low level mixing ratios of 
maybe 8-9 g/kg in the Phoenix area, and weak northeasterly 
steering flow may be present to help storms that develop over the 
mountains to continue into the lower deserts. Frankly, the NBM 
PoPs on Monday may be a bit too optimistic given the amount of 
subsidence that is still likely to be present under the high and 
the fact the forecast CAPEs barely top 500 J/kg. Models do agree 
the high center will eventually shift somewhere to the east 
northeast of Arizona, near the Four Corners, by the middle of next
week which will at least give some opportunity for marginal 
moisture to stick around, but ensembles aren't really pointing at 
good quality moisture that we would likely need to really break 
this heatwave. Still, the setup toward next weekend resembles more
of a traditional monsoon setup. It just may take a few days under
the synoptic regime for storms to really begin threatening the 
lower deserts.

&&

.AVIATION...Updated at 0520Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Tranquil conditions are expected to continue going forward through
tomorrow. Some uncertainty remains regarding the usual E'rly shift
at Sky Harbor tonight/tomorrow morning, but typical diurnal 
trends are expected at the remaining terminal sites. W winds will 
take over across the region by mid-morning. Besides a FEW high 
clouds, skies will be mostly clear overnight

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are anticipated during the TAF period, with
FEW high clouds over the region overnight. Light S/SW winds will
shift out of the SE over the next few hours at IPL. At BLH, SW
winds will become more S'rly during the nighttime hours. 


&&

.FIRE WEATHER...

Extreme temperatures are expected through the weekend, as lower 
desert high temperatures push 112-120 degrees. Overnight relief 
will be limited with lows only falling to the mid-80s to mid-90s. 
Moisture levels will be dropping the next few days as drier air 
returns this weekend, with afternoon MinRHs mainly between 10-20%,
and overnight recoveries near 25-45%. Throughout the afternoon to
early evening hours the next couple days, a chance for high 
terrain thunderstorms exists. However, limited precipitation is 
expected with any activity so the chance for wetting rains remains
below 10%. As a result, there is at least a minor threat for dry 
lightning. Winds will tend to follow typical diurnal and terrain 
influences, with occasional afternoon wind gusts up to 20-25 mph.
There is some indication that moisture will increase early next 
week with more optimal flow out of the east resulting in better
chances for showers and thunderstorms by Monday. Temperatures will
remain hot and above normal next week, but should also slowly
decrease throughout next week. Overall humidity levels will remain
fairly stable for at least the first half of next week with 
MinRHs mostly in a 15-20% range over the lower deserts to 20-25% 
in higher terrain areas.

&&

.CLIMATE...
...RECORD HIGH TEMPERATURES...

         ...PHOENIX...   ...YUMA...   ...EL CENTRO...

July 14    116 (2003)    118 (1936)     119 (1936) 
July 15    117 (1998)    116 (1998)     116 (2019) 
July 16    118 (1925)    116 (1960)     119 (1936) 
July 17    116 (2005)    117 (2005)     121 (2005)
July 18    115 (1989)    117 (1960)     117 (2009)
July 19    116 (1989)    115 (2000)     117 (1978)

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Wednesday for AZZ530>544-
     546-548>551-553>555-559.

     Excessive Heat Warning until 8 PM MST Monday for AZZ545-547-552-
     560-561.

     Excessive Heat Warning from 10 AM Saturday to 8 PM MST Sunday 
     for AZZ556>558-562-563.

CA...Excessive Heat Warning until 8 PM PDT Wednesday for CAZ560>570.

&&

$$

DISCUSSION...Benedict/Kuhlman
AVIATION...RW
FIRE WEATHER...Kuhlman 
CLIMATE...Kuhlman