212
FXUS65 KPSR 221751
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1051 AM MST Sat Jun 22 2024

.UPDATE...Updated 18Z Aviation Discussion.

&&

.SYNOPSIS...
Thunderstorm chances and coverage will continue to increase this
weekend, with today anticipated to be the more active across
south-central Arizona relative to yesterday. Daily thunderstorm
chances will continue through early next week, but become more
confined to the higher terrain areas. Temperatures will continue
to run several degrees above normal, although the warming trend
through the middle of next week is becoming more muted, resulting
in mostly Moderate HeatRisk.

&&

.DISCUSSION...
The upper level pattern continues to usher in mostly higher clouds
early this morning from the remnants of former tropical cyclone
Alberto, as the general center of this feature moves offshore of
the far southern Baja Peninsula early this morning. A strong
ridging feature centered over the Lower Mississippi River Valley
is the main source of steering flow, which is bringing in these
increased moisture levels and clouds into southern to southeastern
Arizona.

The latest MRMS radar indicates areas of light showers/virga
across southern Arizona, with even a few embedded convective
showers that are propagating into the southwestern Yuma and
southern Maricopa Counties. Upon further model analysis, there is
a weak inverted trough circulating around the ridge feature at the
700-500 mb levels, resulting in the initiation of these showers.
Hi-res models suggest these light showers/isolated convection to
persist into the morning hours and continue to stream further
northward, ahead of more robust convection that is already
evident on MRMS that is currently centered over the northeast
reaches of the Gulf of California.

These current events, along with PWAT`s continuing to increase
upwards of 1.60"-1.90" are anticipated to result in a more active
day across the region. While cloud cover may inhibit the
thermodynamic potential (HREF ensemble means generally 500-1000
J/kg) a bit, the aforementioned shortwave should aid in overcoming
this deficit. Additionally, steering flow will be much weaker due
to the stronger influence of the ridge to the east, resulting in
more favorable outflow propagation into the lower deserts this
afternoon/evening. As such, hi-res models show a decent signal of
storms that initiate in the higher terrain early this afternoon,
with chances for thunderstorms increasing going into this evening
across the lower deserts of south-central Arizona, marking the
first legitimate chances to see thunderstorm activity across the
metro for the monsoon. Chances for showers and storms are
forecasted around 40-60% (20-30%) for the higher terrain (lower
deserts) of southcentral AZ this afternoon and evening. While
thunderstorms may be nice to see, the usual threats/impacts will
continue to be a possibility across south-central and evening into
western/southwestern AZ today and into tonight. HREF
probabilities of 35 mph wind gusts around 50-70% across the
Phoenix metro and reaching further westward into Yuma and La Paz
Counties at around 30-50% going into the overnight hours. Thus,
the severe potential (55+ mph) is seemingly lower relative to the
past few days, which shouldn`t come as too much of a surprise due
to the higher moisture levels and the resultant DCAPE`s around
1000-1200 J/kg. With these storms/outflows, blowing dust will
continue to be a threat/impact as the outflows roll in from the
north and (especially) east/southeast. It should be worth
mentioning as well, that with higher moisture levels and weak
steering flow, any localized downpours could cause some localized
flood potential for today (some hi-res hourly QPF output upwards
of 0.75"-1.00").

Looking past today, Sunday is looking like a less active day, as
seen in the extended hi-res guidance. While another weak vort max
looks to rotate around the ridge once again, steering flow looks
less favorable as model soundings show more southerly to
southwesterly mean flow in the low to mid-levels, which would
limit chances to mostly higher terrain. As mentioned previously,
despite the well above normal moisture levels over the weekend, the
convective coverage on Sunday will be dependent on how the activity
pans out today, as it is not that common to get widespread
activity on back to back days. However, similar threats of
locally heavy downpours and gusty winds will continue to be a
threat for any storms that develop on Sunday as well.

Looking towards next week, the ridging over central CONUS will
slowly retrograde further westward, resulting in mid-level heights
to build into the 594-597 dam range by the middle of the week. As
such, temperatures near normal over the weekend will warm several
degrees going through early and into the middle of next week.
However, one noticeable difference with the latest ensemble suite
is that there is seemingly slight changes in ridge positioning,
resulting in slightly cooler temperatures. Thus, the current
forecast is calling for primarily Moderate HeatRisk across the
region, with NBM probabilities showing lower likelihoods of
excessive heat (i.e. Major to Extreme HeatRisk) developing during
this period. Looking past the middle of the week, ensemble
clustering showing longwave troughing moving into the Pacific
Northwest, resulting a pretty noticeable weakening of the ridging
entrenched across the Desert Southwest. However, there are timing
and depth differences, resulting in increasing uncertainties in
temperature trends across the region going into late next week.

Elevated moisture levels will continue through next week, with
daily thunderstorm chances anticipated to continue as well.
However, as PWAT`s wane back below 1.50" by the middle of the
week, chances for any lower desert activity drops off
precipitously past Monday (current forecast of 10-20%). Unless
the ridge positioning and steering flow are ideal on any given day,
convective activity will be become more confined to the higher
terrain areas going through the end of the week.

&&

.AVIATION...Updated at 1750Z.

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

Winds during much of the TAF period are expected to contain an
SE/E`rly component, outside of some brief moments of variability.
Confidence in SHRA and TS activity over terminal locations has
decreased since the last forecast package, but rainfall over or
in the vicinity of TAF sites cannot be completely ruled this
afternoon and evening. The potential of seeing strong outflow
winds associated with convective activity remains but has
decreased, with chances of seeing winds exceed 30 kts now between
30-50% (50-70% 12 hours ago). Potential outflows will be
dependent on where convective development occurs and how
widespread it becomes, and due to the above-mentioned uncertainty,
confidence regarding timing and strength of these features is
low. Future amendments are likely to be needed if more widespread
convection is realized. BKN to occasionally over OVC skies will
prevail through this evening, with the lowest bases around 10k ft.


Southeast California/Southwest Arizona including KIPL and KBLH:

Winds at IPL are expected to be out of the SE through the TAF
period, with BLH favoring more of a S`rly/SSW`rly component. Both
terminals will see afternoon and early evening gusts between
20-25 kts before winds calm through the nighttime hours. Mostly
clear skies, with a FEW clouds around 10-12k ft, will prevail
through tonight before cloud coverage begins to increase early
Sunday morning.

&&

.FIRE WEATHER...
Moisture will continue to increase across the region through the
weekend, bringing daily chances for afternoon thunderstorms, with
the best chances expected across the higher terrain areas of
south-central AZ. Best chances for thunderstorms across the lower
deserts of south-central to western/southwestern AZ will be
today. MinRH values this afternoon will range between 35-45%
across the far eastern districts to between 15-25% across the
western districts. MinRH values will remain elevated going into
early next week before slowly drying into the middle of the week.
Winds will follow their typical daily tendencies, with gusty
outflows from any thunderstorm activity anticipated over the next
several days. High pressure is expected to strengthen over the
region by early to middle of next week leading to even hotter
temperatures along with slightly drier conditions.

&&

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

$$

DISCUSSION...Young
AVIATION...RW
FIRE WEATHER...Young/Lojero