Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/19/21
Area Forecast Discussion
National Weather Service Phoenix AZ
420 PM MST Sun Jul 18 2021
.UPDATE...
Updated Aviation
&&
.SYNOPSIS...
Abundant monsoon moisture will continue to bring daily chances for
at least isolated to scattered showers and thunderstorms across
south-central and eastern Arizona with a tendency to favor the
higher terrain of eastern Arizona, especially for the first half of
the week. Isolated storms are also possible over southwest Arizona
and southeast California. Near to below normal highs expected for
the first half of the week, then below normal by late in the week.
More scattered to widespread storms are possible for the second half
of next week and into the weekend. Storms will be capable of
producing both locally heavy rain, strong winds, and blowing dust.
&&
.DISCUSSION...
The H5 RAP and SPC mesoscale analysis shows the UL high centered
near the NV-CO border, barely just N of 4-Corners area. Fairly deep
and moist S-SE-E flow aloft was present from below H7 to H5 to H3. A
large zone of elevated H7-H5 mean RH>=70 (& 80-90)% extended from N
MX, SE-S-Cent AZ into W-NW AZ. SPC mesoscale analysis showed
elevated PW ranging from 1.7-1.8 S and W of Phoenix to near 1.5
near Phoenix which was ~0.4 too low compared to the 12Z Phx
sounding which had over 1.85. The 12Z Phx sounding also showed
small caps in the mid levels and fcst sfc CAPE of 1389 j/kg. The
Phx 12Z also featured above normal mean W of 12.5 g/kg, up from 11.6
gm/kg shown on the 00Z sounding. SPC confirmed fairly widespread
elevated CAPE (& CIN) from the upper 100s to low thousands j/kg with
more elevated forecast values into the 2-3K j/kg forecast for the
afternoon along the outskirts and surrounding the CWA. 8 mid to late
morning ACARS showed mean MUCAPE up to 1276 j/kg.
Sunday GOES imagery showed abundant mid-upper blow-off clouds
associated with a weak PVA disturbance and and an area of associated
modest thundershowers SE of Phx earlier today. These thundershowers
moved into N Pinal and the SSE CWA including far SE Phx outskirts
this morning with spotty modest rainfall. By midday METSAT showed
cloudy-mostly cloudy conditions and an MCV in the W-central CWA and
W half of the Phx valley with an area of light rain returns, while
mostly clear skies, and stronger heating, dominated the E half of
Phoenix and much of the E CWA. The expanding UL ridge was driving
small disturbances and supporting the very moist and unstable
conditions across the high country, while igniting early afternoon
Mogollon Rim convection/thunderstorms.
The HREF and later runs of the HRRR support E AZ isolated to
occasionally scattered convection moving into S. Gila Cty for the
late afternoon and early evening for a few hours before decaying as
they edge west. Then a second late night round of convection is
depicted that could give Phx or the N-E Valley a glancing blow of
late night storms tonight. It is also very bullish on a very
pronounced E-NE outflow moving through Phoenix late tonight and even
possibly holding together through La Paz county early this morning.
For the first half of the week the UL high moves very little. As a
result very moist and unstable conditions and diurnal convection
will persist through the region, especially for the higher terrain
with its orographic and upslope advantages. As a result the
preferred NBM POPs remain significant through the period near 30-40%
around Phoenix with slightly lower POPs even supported out W across
SW AZ and SE CA. Storms will be capable of producing both locally
heavy rain, strong winds, and blowing dust.
Clusters and ensembles are still signaling possible upticks in
moisture for the second half of the week and into the weekend. This
may be the result of a larger easterly wave disturbance moving in
from Texas into N-NW MX. Higher end WPC QPF has emerged along with
increased chances for scattered flash flooding. Max temperatures
appear to become quite moderated in and around Phoenix as below
normal highs look to favor the upper 90s by late this week and
possibly even the weekend.
&&
.AVIATION...Updated at 2320Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds should become more solidly SW across the metro early this
evening with storms building over mountains. Although NBM shows 30%
chance of storms and HREF output indicates a 40% chance of outflow
winds in excess of 30 kt, in situ observations show an environment
not very good for thunderstorm maintenance. Recent HRRR model runs
have backed off the forecast of storms in the metro while also
dialing back outflows and wind speeds. Kept a mention of an outflow
boundary and VCSH in this TAF package, though with low confidence.
While stronger wind gusts are more uncertain, some measure of
easterly winds should take hold by late evening. There is even a
chance that storms in far SW AZ push a reinforcing SE outflow into
the metro well after midnight. It is also possible (20% chance) a
few elevated showers develop into the metro early Monday morning.
Otherwise, winds should switch to west by early Monday afternoon
with the potential for a SE outflow Monday evening.
Southeast California/Southwest Arizona including KIPL and KBLH:
Under occasional passing mid/high clouds, southerly winds will be
favored at KBLH while E/SE directions at KIPL. Speeds will remain
fairly steady around 10kt with a few higher gusts. Some enhanced
winds due to long traveling outflows may be possible Monday morning
along with localized haze resulting from thick moisture increases.
NBM output shows 30% chance of morning showers at KBLH and 20% at
KIPL, but have not included any mention in this TAF package.
&&
.FIRE WEATHER...
Wednesday through Sunday:
Temperatures will generally be near to slightly below seasonal
averages through the period as monsoonal moisture remains in place
over the region. Storm activity is anticipated to spread as far west
as southeast California with most storms having good potential for
wetting rain (0.10" or more). Threats from storms will continue to
involve locally heavy rainfall and flash flooding along with strong
outflow winds and localized downbursts within storms. Significant
flooding may be experienced on previously burned areas of Gila
County, particularly during the second half of the week. Min RH
levels are expected to remain in the 20-30% range most areas (30-50%
higher terrain of south- central AZ). Max RH levels will be 35-60%
most places (60-90% higher terrain of south- central AZ). Apart from
thunderstorms, winds will favor familiar diurnal patterns.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Sawtelle
AVIATION...18
FIRE WEATHER...Sawtelle/Kuhlman