Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/19/21

Area Forecast Discussion

National Weather Service Phoenix AZ

 420 PM MST Thu Mar 18 2021

.UPDATE...00Z Aviation Discussion.


&&

.SYNOPSIS...
Warmer than normal temperatures will prevail into the weekend before
a quick moving weather disturbance cools readings back towards the
seasonal average early next week. Any precipitation associated with
this weather system should be relegated to higher terrain locations
of northern and eastern Arizona. A secondary weather system may
affect the region during the middle of next week acting to reinforce
the seasonally normal temperatures, and potentially leading to some
light showers in eastern Arizona.

&&

.DISCUSSION...
A large cold core circulation was spinning nearly stationary over
the East Pacific basin acting to enhance ridging through the SW
Conus with objective analysis indicating H5 heights now pushing
above 576dm. Late morning aircraft soundings shows marked warming
through the lower troposphere since yesterday resulting in high
temperatures this afternoon some 5F-10F warmer. Only weak winds
trapped in an unusually shallow boundary layer preclude readings
getting even warmer today. Although heights aloft will be peaking in
the next 24 hours, additional minor warming through the atmospheric
column along with increased mixing depths will allow for a few more
degrees tacked onto high temperatures Friday and Saturday. Ensemble
and multi-model spread is extremely narrow in this time frame
yielding excellent forecast confidence of widespread lower elevation
afternoon readings in the middle 80s under mostly sunny skies.

Later in the weekend, the aforementioned Pacific low will become
sheared eastward into the northern Rockies while absorbing a piece
of central Pacific jet energy. The resulting flow pattern will
feature a highly elongated, positively tilted trough axis descending
south from the Great Basin. With only minimal ensemble uncertainty,
this configuration should have very little available moisture while
promoting upstream surface pressure rises and low level dry air
surging into the forecast area. While its conceivable this trough
could have enough cold air to squeeze out some light precipitation
over higher terrain of eastern Arizona, the signal is fairly weak
and each model iteration seemingly reduces POPs with this system in
Arizona. Locally breezy conditions are the most likely impact from
this disturbance though the weaker nature to the pattern should
limit speeds well below advisory criteria.

A second and potentially a third shortwave trough may affect the
region to some degree during the middle and end of next week
respectively. Model spread remains fairly high with respect to the
depth and track of these waves; and modeling clusters are clearly
falling into two physics camps. An increasing number of ensemble
members depict a more progressive system mostly passing through the
Four Corners area into New Mexico (highly concentrated in GEFS and
CMC membership). However, there remains a notable number of members
(nearly all EPS) indicating potential for a quasi-closed low diving
southward through Arizona in response to NE Pacific ridging poking
east into western Canada creating a blocking type pattern. If any
realistic precipitation chances were to occur, the slower closed low
solution would need to come to fruition. Given the current
progressive pattern and little evidence in extended forecasts of
large scale blocking prior to this midweek system, the deeper closed
EPS flavor seems a less likely outcome and POPs have been limited to
the far eastern CWA and muted towards the ensemble majority.
Regardless, temperatures should be kept in check near the seasonal
average with prevailing northwest flow.

&&

.AVIATION...Updated at 2320Z.

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

No major weather issues will exist through the TAF period under
periods of high cirrus decks. Diurnal directional tendencies
should occur around the typical times with speeds under 8 kts.
Extended periods of nearly calm or variable winds will exist given
the weak pressure gradient.

&&

.FIRE WEATHER...
Sunday through Thursday:
Cooler temperatures near the seasonal normal are likely next week as
a couple weather disturbance move through the region.  Most
districts should remain dry with moisture fairly limited, though
some isolated wetting precipitation may be possible over far eastern
districts during the middle of the week. Breezy afternoon conditions
will be common with gusts reaching 20-30 mph. Minimum afternoon
humidity levels will fall generally in a 10-20% range though higher
elevations will fall closer to 20-30%. Overnight recovery should
only be fair in a 25-50% range.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

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

$$

DISCUSSION...MO/Kuhlman
AVIATION...Feldkircher/MO
FIRE WEATHER...MO/Kuhlman