Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/20/23

Area Forecast Discussion

National Weather Service Phoenix AZ

 450 PM MST Tue Sep 19 2023

.UPDATE...00Z Aviation Discussion.

&&

.SYNOPSIS...
Mostly tranquil weather will continue through at least the beginning
of next week as rain chances remain minimal. Temperatures will
slowly cool, eventually reaching slightly below normal levels during
the latter half of the week. Some locally enhanced breeziness
Wednesday and Thursday will be the only notable weather impact.
Otherwise, some modest warming is likely to occur early next week as
high pressure builds back into the area.

&&

.DISCUSSION...
An innocuous upper level low spinning west of the southern
California coast was beginning to eject eastward in response to more
vigorous shortwave energy digging into the Pacific NW. The
associated trough axis through the East Pacific has been pinched and
realigned in a more E-W fashion further strengthening a downstream
westerly jet streak punching through northern Arizona. In fact, the
u-wind component anomaly above the 90th percentile for this time of
year has continued to depress subtropical ridging with H5 heights
closer to 585dm this afternoon. Morning in-situ ACARS sounding data
already showed boundary layer temperatures a couple degrees cooler
than Monday, and over the next few days, temperatures will continue
cooling a few more degrees retreating from near to slightly below
normal levels.

Over the next 48 hours, the aforementioned Pacific NW shortwave will
dig and intensify over the Great Basin while absorbing the weaker
wave currently along the California coast. While height falls across
the forecast area will not be tremendous, the enhancement of zonal
wind energy crossing the coast range should be exacerbated by a
deepening marine layer and tightened thermal/pressure gradient. NBM
probabilities for advisory type winds across far SW Imperial County
have increased greater than 75% for both Wednesday and Thursday
evening. Conceivably, some mountain rotors and hydraulic jumps could
pull stronger winds farther inland, but latest model output only
modestly supports this idea. On Thursday, the enhanced breeziness
will become more widespread extending through south-central Arizona
with the strongest gusts focused over higher terrain locations.
Regardless, forecast wind speeds into Arizona look to remain below
advisory criteria.

The unseasonably strong Great Basin negative PV anomaly will eject
into the central/northern plains over the weekend allowing
midtropospheric heights to rebound as some form of ridging returns
to the region. Given that a blocking regime will become established
over the Upper Midwest/Canada, more credence probably should be
given to more amplified ensemble members though the overall ensemble
spread is not overwhelming. While some warming should be expected
early next week, height rises may not be pronounced as renewed
upstream Pacific troughing could quickly erode the high pressure
ridge.

&&

.AVIATION...Updated at 2350Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are expected through the forecast period.
Generally light and diurnal tendencies will prevail, however the
easterly shift this evening will be slightly earlier than normal.
A period of southerly crosswinds will occur early tomorrow
afternoon before a slightly elevated westerly component takes
hold. Increasing mid to high level clouds are anticipated this
evening through late tomorrow morning.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected through the TAF package, besides
some afternoon breeziness tomorrow. West to northwest winds at
KIPL may see a period of variable winds overnight before elevated
west winds take hold tomorrow afternoon, with gusts between
20-25kts expected. At KBLH, winds will vary between a southerly to
southwesterly component and gust near 20 kts tomorrow afternoon.
FEW to SCT mid to high level clouds will pass over the terminals
throughout the period.

&&

.FIRE WEATHER...
Quiet weather conditions will continue through early next week as
wetting rainfall chances remain negligible. Temperatures will
steadily cool through the week falling slightly below the seasonal
normal. Afternoon humidity values will mostly fall into the teens,
although some higher terrain areas may remain above 20%. Fair to
good overnight recoveries of 30-60% will be common though there will
be a tendency towards increased dryness in lower elevations and
better recovery over mountainous areas. For the majority of the
time, winds will remain light with just some local upslope
breeziness, however enhanced wind gusts will start to become more
widespread Wednesday and Thursday. The strongest winds Wednesday
will be confined to western Imperial County, then spreading east
Thursday resulting in a localized elevated fire danger.

&&

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

$$

DISCUSSION...18/Lojero
AVIATION...Leffel
FIRE WEATHER...18