Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/13/22

Area Forecast Discussion

National Weather Service Phoenix AZ

 354 PM MST Wed Jan 12 2022

.UPDATE...Updated 00z Aviation Discussion.


&&

.SYNOPSIS...
Dry weather, cloudy, and unusually warm temperatures will persist
through the remainder of this week. Briefly lower clouds and some
virga is likely Thursday night into Friday before a dry weather
system moves through and clears up the lower clouds. This weather
system will also bring breezy conditions Saturday. The weather
pattern will be essentially stalled through the weekend with a
slow moving weather system only wobbling towards the region early
next week.

&&

.DISCUSSION...
High clouds continue to spread over the area downstream of a
nearly stationary closed low well to the southwest, over the
eastern Pacific. Aircraft soundings out of Phoenix Sky Harbor show
a few degrees of warming through most of the tropospheric profile.
However, this may not fully translate to the surface due to
limited mixing with the persistent clouds. It was also a cooler
start this morning versus yesterday and temperatures midday are
roughly 5 degrees behind yesterday. Overall, NBM forecast highs
this afternoon are similar to yesterday, if not a degree or two
cooler, but we`ll see if Phoenix can actually reach 70F.

Satellite and objective analysis this afternoon depict a
progressive ridge moving in from the eastern Pacific, north of
the closed low, with the current center of the anticyclonic motion
over San Diego. Ensembles continue to push this ridge east,
traversing the local area through Thursday, with 500 mb heights
rising up to 585-587 dm (above the 95th climatological
percentile). This will result in further tropospheric warming
heading into Thursday. However, once again the high clouds will
still be present and may keep afternoon highs from reaching into
the mid-70s. The NBM probability of reaching 75F in Phoenix is
roughly 25% tomorrow and the following couple of days. Subsidence
from the ridge has already pushed drier air down toward the lower
troposphere, as evident in the aforementioned aircraft soundings,
which will likely have an effect on the precip chances in the
coming days.

In previous days` model runs, there was a lot of uncertainty in
the evolution of the closed low to the southwest, but CPC clusters
now show good consistency among global ensembles through at least
this weekend. The majority of members keep the closed low over
open waters, with a slow drift north and gradual weakening,
through this weekend. Variance in the ensemble spread grows
(lowering predictability) by early next week, but the ensemble
means depict the low opening into a weak low-amplitude shortwave
before absolving into the broader synoptic flow. What does this
all mean for the forecast? The answer, likely continued warm above
slightly above normal temperatures, plenty of high clouds, and
very minimal precip chances.

Precip chances have been falling with every forecast package with
12-hr NBM PoPs now under 10% each day, CWA-wide, through this
weekend. The best push of moisture from the southwest is expected
late-Thursday through Friday morning, with EPS and NAEFS mean
showing PWATs climbing upwards of 0.7-0.9" across southern AZ and
southern CA. However, one look at a vertical cross-section and it
is clear all the moisture will be mostly above 700 mb, with the
dry lower tropospheric layer still in place. The richest moisture
is expected to remain just south of the international border. So,
will likely see a lot of virga echoes on radar Thursday night
through Friday morning. A few very light showers reaching the
desert floors cannot be fully ruled out given the depth of the
moisture aloft, but nearly all ensemble members are dry (no
measurable rain) through Friday.

One feature that has not been mentioned yet is the low offshore
from the PacNW. This low is expected to quickly open up and
become positively tilted after moving inland Thursday and dig
southeast through the Great Basin and then Arizona later Friday.
The best PVA is expected to be removed from the local area, so
this shortwave is not anticipated to deliver much in the way of
forcing for precip generation. For the local area, this wave will
mostly flatten the ridge and significantly dry out the mid-
troposphere. GFS and NAM forecast soundings are showing 60-70C
dew point depressions in the midlevels following the passage of
the trough axis by Saturday. Perhaps the biggest sensible weather
impact from this trough will be a strong low and mid level
gradient developing on the backside of the trough. Latest
deterministic models are showing the potential for up 30-40 kt
northeasterly winds in the 850-700 mb layer over central AZ. With
the progressive nature of the shortwave, timing will dictate the
potential for winds to mix to the surface. Current timing has the
strongest winds overnight Friday into Saturday and then weakening
quickly through the day Saturday. So breezy conditions are
possible Saturday, with most global ensembles supporting potential
for 20-30 mph wind gusts after sunrise Saturday, especially
across south-central AZ.

&&

.AVIATION...Updated 2255Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation impacts expected through the TAF period. Winds of 8 kts
or less will favor diurnal trends through the period with extended
periods of light and variable likely. High clouds will persist AOA
25 kft through Thursday morning, with scattered coverage
developing down to 15 kft by Thursday evening.

&&

.FIRE WEATHER...
Friday through Tuesday:
Dry weather with warmer than normal temperatures are the most likely
outcome through early next week though a decaying weather
disturbance could yield a few isolated showers sometime early next
week. Wetting rains would not be expected. Minimum afternoon
humidity levels will generally fall into a 15-30% range following
fair to good overnight recovery around 25-60%. Winds will mostly be
light with only occasional gustiness over ridge tops and potential
enhancement of northerly gusts in western districts over the
weekend.

&&

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

$$

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