Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 042316
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
416 PM MST Mon Mar 4 2024

.Update...Updated Aviation

&&

.SYNOPSIS...
Tranquil weather has returned to the region and will persist through
the middle of the week with temperatures warming several degrees
above normal by Wednesday. A series of weak weather disturbances
will bring increasing chances of light rain Thursday into Friday as
temperature retreat to below normal levels. However, Warming and
drying conditions are in store for this weekend.

&&

.DISCUSSION...
Deep longwave troughing continues to engulf much of the western and
central Conus resulting in quasi-zonal flow across the Southwest.
With the most notable negative height anomalies lifting north into
southern Canada over the next 48 hours, local H5 heights should
increase closer to a 564-568 dm range allowing surface temperatures
to rebound slightly above the seasonal normal under a largely
subsident regime. Forecast confidence remains excellent through
Wednesday, however then begins to deteriorate markedly during the
latter half of the week with the passage of a positively tilted
trough with several embedded shortwaves.

A closed low currently situated near 41N 145W will initially be
influenced and dislodged by a strong 150+kt subtropical jet, then
become absorbed into the pre-existing western Conus mean troughing
pattern during the middle of the week. While the initial
configuration suggests a sharp, positively tilted feature heading
into southern California, ensembles are now more resolute in tapping
northern stream PV such that a much more expansive trough digs and
lingers into the Southwest. Moisture availability still remains the
greater limiting factor with respect to precipitation chances,
however models continue to trend towards better near saturation
through the entire column and around 5 g/kg mixing ratios through
the boundary layer coincident with periods of forced ascent.
Investigation of forecast BUFR soundings also indicates fairly steep
midlevel lapse rates advecting into south-central AZ with modest
instability (100-200 J/kg) potentially developing during peak
heating Thursday. As predicted in previous discussions, required NBM
POP and thunder initialization continue to increase while
temperature forecasts decrease given the synoptic pattern. It is
fully expected this trend will continue the next couple iterations,
although not to the extent of widespread rainfall, but certainly
more than just a few isolated showers.

Rather large discrepancies remain among ensemble membership Friday
associated with a more pronounced secondary shortwave digging into
the western periphery of the mean trough position. Even EPS and CMC
members which were less enthusiastic about this outcome have now
shifted towards this idea which would support an additional round of
isolated to scattered showers assuming sufficient moisture is
maintained within/near the cold core aloft. NBM output appears to be
lagging in identifying this scenario, and similar to the Thursday
pattern, would expect increasing POPs in future forecasts. As the
main trough finally exits the region Saturday, strong subsidence
will spread into the region while a rebound in midlevel heights will
result in rapidly warming temperatures. Ensemble clusters indicate
that the ridging across the Desert Southwest will be short lived as
the next progressive trough begins to impinge from the northwest.
However, there is the typical expected spread amongst the ensembles
as early as Sunday with the evolution of the upper level pattern,
thus confidence in temperature trends remain only moderate. Should
the troughing remain relatively weak (which is the current trend),
highs reaching into the 80s across the lower deserts is not an
unreasonable scenario for late this weekend into early next week.

&&

.AVIATION...Updated at 2315Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No aviation concerns are expected during the TAF period. Winds
will be light (generally aob 8 kts) and follow diurnal
tendencies. Low clouds are beginning to scatter out leading to
brief period of clearing before SCT high clouds move in late this
evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
No aviation concerns are expected during the TAF period. Winds at
IPL will contain a W`rly component through tomorrow, with perhaps
a few gusts this evening upwards of 20 kts. Winds at BLH will
contain a S`rly component before becoming more variable by
tonight. SCT high clouds will prevail over the region through
tomorrow evening.

&&

.FIRE WEATHER...
Winds continue to subside across the region with only higher terrain
gusty winds 50-60 mph in southwest Imperial County continue to
linger into the morning hours. Cooler temperatures today will
precede a quick warming trend through the middle of the week.
Daytime minimum relative humidity values will trend drier over the
next couple of days, with widespread 15-25% afternoon RHs by the
middle of the week. This will precede moistening conditions due to a
weak weather system late this week, where portions of the region may
receive some light rain accumulations Thursday into Friday.

&&

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

$$

DISCUSSION...18/Young
AVIATION...RW
FIRE WEATHER...Young


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