Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/14/22

Area Forecast Discussion

National Weather Service Phoenix AZ

 527 PM MST Wed Jul 13 2022

.UPDATE...Updated Aviation Discussion.

.SYNOPSIS...
Above normal temperatures will prevail through at least early next
week with highs reaching 110 degrees or better across most lower
desert locations. Moisture should continue improving and spreading
westward resulting in steadily increased shower and thunderstorm
chances. Storms will be most prevalent and concentrated over higher
terrain areas, however there will be modest daily chance of rain
over the Arizona lower elevations.

&&

.DISCUSSION...
Strong subtropical high pressure ridging continues to be the
dominant SW Conus feature centered almost directly over the four
corners with expansive H5 heights near 595dm. A more pronounced
easterly wave has propagated west of the Baja peninsula this
afternoon albeit with a straggling trough axis still extended back
into southern AZ. Combined outflow and deeper layer southeast flow
has helped further moisten the atmospheric column overnight as
objective analysis indicates 10-12 g/kg boundary layer mixing ratios
spread into the central parts of the forecast area. However, 12Z
regional soundings and ACARS data shows the moisture profile not
completely continuous through the boundary layer, and lacking
optimal structure for more robust lower elevation thunderstorm
development.

While WV imagery depicts little in the way of an ascent mechanism or
support near the CWA, there is only minor notable negative influence
as MLCape grows above 500 J/kg through the southern parts of the
state. Somewhat drier air analyzed entering far eastern Arizona
should restrict the coverage and intensity of deep convection over
the White Mountains and eastern Rim. The greatest HREF probabilities
and conceptual approach highlights central and eastern Pima County
as most prolific for storm initiation and sustenance. DCape values
exceeding 1500 J/kg will support strong, organized outflow
boundaries with HREF probabilities of 35+ mph winds in excess of 50%
along a northward moving boundary crossing into the southern CWA.
Aside from the gusty winds, dense blowing dust potential will be the
other primary concern and impact, particularly along the I-8
corridor in Pinal and southern Maricopa counties. Given the slightly
better moisture profiles, isolated showers and/or storms developing
along and behind outflow boundaries within the Phoenix metro are
certainly feasible though required NBM POPs only peak around 15%.

On Thursday, overall moisture levels should improve a bit more and
expand westward via outflows and cycling of moisture around the anti-
cyclone, yet still lack a deeply mixed layer exceeding 10-11 g/kg
through the boundary layer. MLCApe will once again breach into a 500-
1000 J/kg range with minimal, yet still notable Cinh needed to be
overcome across lower elevations. In addition to the better quality
moisture, there are model indications of improved upper level
conditions with weak divergence aloft supporting organized
convection. Overall, HREF membership shows the possibility of more
robust storms Thursday initially favoring high terrain, but
progressing into the lower deserts more readily than the past
several days with multiple outflow boundaries and likelihood of
several boundary collisions initiating new storm development. While
the greatest impacts will once again be focused on gusty winds and
blowing dust, chances for heavy rainfall and localized flooding
begin increasing with better moisture profiles and slower storm
motion. NBM PoPs Thursday are now higher than other days, reaching
20-30% across south-central Arizona and 10-20% for southwest
Arizona.

Storm chances during the end of the week into next week will be at
least partially dependent on convective evolution the preceding day
and possibility of a detrimental convectively overturned atmosphere
or favorable pristine convective environment. Nevertheless, a fair
sampling of deterministic and ensemble models suggest either Friday
or Saturday will comprise a more classically active monsoon day with
a better defined inverted trough and jet maximum tracking through
the region. Along with these synoptic features, juxtaposed upper
divergence, better quality boundary layer moisture, and modest
instability with little inhibition may result in robust storms and
deep, converging outflows enveloping much of the forecast area. A
convectively active monsoon pattern may continue through early next
week given acceptable moisture profiles, however substantial day-to-
day variability may exist dependent on mesoscale influences.

Temperature will continue to trend in an above normal category
through the weekend with central high pressure H5 heights not
straying far from 595dm, or just above the climatological 90th
percentile for mid July. Mandated NBM maintains forecast highs
remain between 110F-114F across the lower deserts, solidly within
moderate HeatRisk thresholds, and just shy of High HeatRisk levels.
However, some modest ridge strengthening over the weekend along with
persistently warming overnight lows could result in localized high
and very high HeatRisk into SE California, and particularly the
Imperial Valley and city of El Centro. Also considering rising
dewpoints coincident with these temperatures, an Excessive Heat Watch
has been issued for a small area around El Centro for the possibility
of excessive threshold being reached. Some modest heat relief could
be in store next week as NBM guidance shows temperatures gradually
retreating to near normal by the middle of next week.

&&

.AVIATION...Updated at 0027Z.

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

Outflow boundaries from distant storms to the east and southeast
will be the main forecast concern this evening. These outflows are
expected to push through the metro area around 1-2Z. The probability
for greater than 30 kt outflow wind gusts is slightly higher than
yesterday at 30-50% with a general worst case peak gusts around 40
kts. An outflow from the south may also bring blowing dust to the
metro area. However, confidence is still too low to include BLDU in
any of the Phx area TAFs (except KIWA) at this point. Odds of storms
generating with the outflow remain slight (10-20%). Aside from
outflows, winds will tend to favor typical diurnal trends with
variability during transitions. Cloud bases will mostly remain aoa
12 kft with greater coverage during the evening and overnight hours.
An earlier-than-usual switch to westerly is anticipated on Thursday
(15-17Z) with some gustiness during the afternoon hours. As far as
TS chances on Thursday afternoon, they appear that they will be
somewhat greater than today (20-30%) along with even better chances
for gusty outflow winds/blowing dust. However, confidence is still
too low at this point to include anything more than a gusty wind
shift during the evening hours.


Southeast California/Southwest Arizona including KIPL and KBLH:
Winds at KIPL will favor an easterly to southeasterly component
while winds at KBLH will favor a southerly component through the
period. Light winds are expected through the morning hours with
afternoon breeziness gusting upwards of 15-20 kts at times,
especially at KBLH. Otherwise, expect FEW-SCT clouds aoa 15 kft.

&&

.FIRE WEATHER...
Daily shower and thunderstorm chances, generally 20-40% each day,
are expected over the Arizona high terrain through early next week,
while chances (10-30%) will expand westward over the lower deserts
through Friday. The main threats from the mainly afternoon/evening
thunderstorms will be strong outflow winds and lightning. Modest
moisture levels will keep minimum afternoon humidities mostly to
between 15-20% across the lower deserts to upwards of 25% over
higher terrain areas. Wetting rainfall chances will remain fairly
low with daily chances 5-15% for the lower deserts to upwards of 15-
25% over higher terrain areas. Winds will generally follow diurnal
patterns with some enhanced upslope afternoon breeziness common most
days. Above normal temperatures will persist through at least the
weekend with daily readings 3-6 degrees above normal.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Excessive Heat Watch from Friday morning through Sunday evening
     for CAZ563-566-567.

&&

$$

DISCUSSION...18/Kuhlman
AVIATION...Percha/Benedict
FIRE WEATHER...Kuhlman