Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/20/22

Area Forecast Discussion

National Weather Service Phoenix AZ

 1238 PM MST Sat Feb 19 2022


.SYNOPSIS...
Very warm temperatures and dry conditions will continue through
Sunday. Highs this weekend will reach the upper 70s to low 80s
across the lower deserts. More unsettled weather is likely
starting early next week with a weather system bringing increased
winds, cooler temperatures, and a chance of rain. Snow levels will
decrease leading to a risk of high elevation snow showers as
well.

&&

.DISCUSSION...
High pressure remains in control over the desert southwest with
clear skies and light winds for most locations today. The airmass
has warmed considerably compared to yesterday, with surface-700 mb
temperatures roughly 2-5C warmer according to the latest ACARS
soundings. This will lead to increased surface high temperatures
today with the NBM showing readings mostly in the 75-82 F range.
The probability of reaching 80 F has increased to around 40% for
Phoenix. With the synoptic height pattern remaining relatively
unchanged into Sunday, temperatures are forecast to be similar to,
if not a few degrees warmer. However, Sunday is expected to be
cloudier, with high clouds streaming in from the compact low
working its way down the west coast. This could slightly insulate
morning temperatures and inhibit daytime solar heating.

Conditions will begin to deteriorate heading into next week in
response to the previously mentioned cut off low ejecting inland
over Arizona. This feature will be filling in on approach and will
be quite moisture starved in the lower levels, leading to
essentially no risk of precipitation. However, cloud cover will
thicken and lower, which will result in high temperatures dropping
5-10 F from Sunday`s readings. Global ensembles continue to come
into better agreement with respect to the pattern evolution
Tuesday through Thursday, as a second and much colder trough digs
into the region. As it does so it will absorb the remnants of the
compact cut off low and partially phase the northern and southern
jet streams. This should put Arizona in a favorable location for
dynamically induced lift and will help to compensate for what is
otherwise a fairly dry system. Forecast PWAT will only be around
0.5-0.6" at the peak.

This system will have multiple impacts. Considering the wind
potential, this will focus on Tuesday and Wednesday. A robust west
to southwest oriented pressure gradient will significantly
increase the wind speed. Winds at all lower levels will be
anomalous, but particularly so above 850 hPa. ECMWF EFI is
highlighting widespread values of 0.6 to 0.8, with values
approaching 1 just north of the CWA for the higher elevation
areas. SOT values have increased since yesterday, indicating a
greater fraction of the ensemble members forecasting a more
unusualwind event may occur. As of now, the potential exists for
wind gusts of 25-35 mph across most of the lower deserts, with
higher values possible near Imperial and the high terrain areas.

Another impact of this system will be the rapid decrease of
temperature and anomalously cool conditions beginning Wednesday.
500mb heights will fall into the mid 540s under the coolest
portion of the trough, with 850 mb temperatures decreasing to
around -1C. This will be enough to knock highs down into the upper
50s to near 60F in the valleys, with low temperatures in the mid
30s to near 40F. Some typically cooler areas away from the city
center may locally observe frost or freeze conditions.

Precipitation is also expected with this storm. WPC clusters now
show a robust signal for mostly dry weather except for Tuesday
night through Thursday morning, when PoPs rise considerably. The
odds of at least some measurable precipitation is near 60-70% for
Phoenix now, with a 25-35% chance for southeast California and
southwest Arizona. NBM probabilities show about a 25% chance of
exceeding a quarter inch in the Phoenix area. A few sporadic
ensemble members maintain the possibility of heavier totals, but
this seems unlikely for now. It won`t just be rain with this storm
system, snow is also possible for some locations. Snow levels
will decline to 3000-4000` on Wednesday, suggesting that a
transition to snow may occur for portions of JTNP and Gila County.
Totals are not expected to be heavy, but the highest elevation
locations may see a few inches.

Towards the tail end of next week WPC clusters are in good
agreement that storm conditions will diminish, but less certain
with respect to how this happens. Roughly half of solutions bring
a return of the ridge, with the other half showing some variation
of weak troughing returning. None of these cases result in much
precipitation.





&&

.AVIATION...Updated at 1705Z.

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

No significant weather issues will exist through Sunday afternoon
with only a modest increase in cirrus decks late in the period.
Winds in the Phoenix area will maintain an easterly direction much
longer than usual this afternoon, only briefly obtaining a light
west to northwest drift during the early evening. A W/NW component
will be preferred at SE CA terminals for the bulk of the period
though variability will be common. For the vast majority of the
time, wind speeds will remain below 10kt.

&&

.FIRE WEATHER...
Monday through Friday:
A weather system will approach and move through the region during
the early through middle of the week, cooling temperatures back to
normal Monday and then several degrees below normal into the middle
part of the week. This system will also lead to increased winds
during the first half of the week, with 30-40 mph gusts anticipated
for many areas. Precipitation chances increase beginning as early as
Tuesday, with the best chances in South- Central AZ Wednesday into
Thursday. There will also be potential for accumulating snow at
higher elevations like Joshua Tree NP and southern Gila county.
Minimum humidities increase into a 20-30% range by Tuesday with
overnight recoveries through the middle of the week upwards of 60-
80%. Drier air returns through Thursday and into the end of the
week, as minimum humidities fall back to around 10-20%.

&&

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

$$

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