Scientific Forecaster Discussion
fxus65 kpsr 142052
Area forecast discussion
National Weather Service Phoenix Arizona
150 PM MST Mon Oct 14 2019
very typical mid October mundane, yet pleasant weather will persist
across the region this week. Temperatures will warm somewhat through
the middle of the week with Lower Desert communities reaching back
towards the mid 90s. A fast moving, dry weather system will force
temperature back down around the seasonal average by the weekend.
a positively tilted shortwave was descending towards western Arizona
this afternoon though with the bulk of the midlevel cold core
remaining over northern Arizona and height falls minimal, synoptic
scale ascent appears rather limited. However, this wave was inducing
moist southerly flow through the h9-800 mb layer advecting modest
moisture into south-central Arizona from the Gulf of California.
Visible satellite presentation suggests some pockets of brief
vertical development, albeit likely capped by a warm inhibitive
layer just above 700 mb resulting in merely a congestive cu field.
While an isolated shower is possible through this evening within the
corridor of better moisture, there is little model support for more
organized activity and areal coverage would not be expected to
The lingering moisture may lead to some overnight strato-cu decks in
a 800 mb-700 mb layer, but the positive tilt nature of the passing trough
should allow stronger subsidence and rapid clearing to envelop the
forecast area by sunrise Tuesday. Height rises and shortwave ridging
will spread into the SW conus during the remainder of the day and
become most pronounced Wednesday with 500 mb heights peaking in a 586-
588dm range. Confidence is excellent that afternoon highs Wednesday
will reach back into the middle 90s at lower elevations - though
well short of record levels for mid October (phx Oct 16th record
high is 101f), this could be the last day of mid 90s around the
Phoenix area until next Spring (albeit with lower confidence as
abnormal warmth may return next week).
The progressive hemispheric pattern will force another fast moving,
low amplitude shortwave from the east Pacific into the Great Basin
during the latter half of the week. Other than a period of somewhat
stronger afternoon winds Thursday, the only other evidence of this
system will be temperatures retreating back into the upper 80s for
lower elevation communities (i.E. Very near normal for mid october).
Far more forecast uncertainty exists later in the weekend as a
trailing, and deeper Pacific trough will dig and amplify through the
western and central conus. A large majority of operational and
ensemble members support a more Continental trajectory with
amplification not occurring until the waves passes into the central
rockies. Almost no ensemble member indicates precipitation potential
with this system, and only a minority now would support more
significant cooling and breezier conditions.
Aviation...updated at 1745z
South-central Arizona including kphx, kiwa, ksdl, and kdvt:
cumulus clouds will increase this afternoon, with few to scattered
coverage expected and bases ranging between 5-10k feet. Overall
don't have much confidence in cigs at the terminals this afternoon
or evening. A few weak showers will be possible west and south of
Phoenix this afternoon and evening, but they are not expected to
impact any area terminals. A few clouds may linger overnight.
Winds will generally follow typical diurnal tendencies with
speeds less than 10kt, but may become more variable in nature at
times if showers do form closer to the Metro area.
Southeast California/southwest Arizona including kipl and kblh:
low-level clouds have increased generally near and east of the
lower Colorado River valley this morning, with primarily scattered
coverage and bases near 3-4k feet. With diurnal heating, clouds
should rise to ~6 kft by the afternoon. Winds will remain light
and variable through Monday morning at both terminals. With a
surface low near Yuma, kipl will likely switch northwest in the
afternoon, while kblh shifts towards the S, both with speeds
around 7 kts or less. Look for skies to gradually clear during
the evening hours tonight, but may see a few low clouds linger
Aviation discussion not updated for amended tafs.
Thursday through monday:
dry weather will persist across all districts through the weekend as
temperatures hover not far from the seasonal average. Seasonably
breezy conditions may exist Thursday afternoon in association with a
passing weather disturbance yielding a slightly enhanced fire danger.
However, much lighter winds should prevail into the weekend with
just the typical upslope breezes. Afternoon minimum humidity levels
will generally fall into a 10-20% range following mostly fair
Spotter information statement...
spotters should follow Standard reporting procedures.