Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
356 am MST Sat Jul 30 2016
a humid airmass will be in place over the Desert Southwest this
weekend and much of next week. The moisture availability, as well as
some weather disturbances, will make for an active period of weather
over the region. All typical hazards associated with the monsoon
season including strong damaging winds, blowing dust, lightning, and
localized flooding will be in play.
today through Sunday...
runoff over portions of southwest Maricopa County continues.
Surprisingly, Waterman wash has not trended down yet. Will probably
need to extend the areal Flood Warning. Storm activity hasn't ended
for the night as there is a batch of activity over southern Mohave
and northern La Paz counties going early this morning. This activity
originated over southern Nevada (apparently aided by a weak wave in
the westerlies). Through propagation toward Richer moisture as well
as interaction with outflow from earlier storms over our area, the
storms have tracked southward. Hrrr has been trending toward a
continued southerly expansion of convection over La Paz and Yuma
counties the rest of the morning. Earlier runs had it dissipating
closer to northern La Paz. Big question for today is how much cin
will there be. Typically after and active night, there tends to be
too much cin (even if there is a lot of cape). However, much of our
area only got outflow winds and no rain - especially southwest Arizona and
southeast California. Latest rap and 06z NAM and GFS all depict areas of
breakable cin this afternoon - even over south-central Arizona deserts
though there are also areas that have higher cin (greatest toward
yuma). With another active day over the higher terrain of central AZ,
anticipate that there is still a chance for storms over the valley
floors. Went above guidance for southwest Arizona and southeast California. Model
cape not looking quite as good Sunday but still good enough for
storms. If today winds up being a down day, then Sunday will be
looking better. Temps today will be lower everywhere. Trends for
Sunday of course will depend upon today's activity. But, temps look
to be below normal east of the lower Colorado River valley.
Monday through Friday...
deep moisture remains over the region through at least Wednesday.
Models depict easterly waves/inverted troughs passing by or through -
especially Tuesday into Thursday where an inverted trough/upper low
tracks right through Arizona. Hard to hang one's hat on that
scenario but it's entirely possible. End result is that storm chances
continue. GFS depicts some decline of moisture beginning Thursday
while the European model (ecmwf) hangs on to it as it is slower to eject the low.
Temps are near to below normal through Wednesday before climbing some
late in the week - most noticeably over south-central Arizona.
south-central Arizona including kphx, kiwa, and ksdl:
westerly winds to prevail through the late afternoon hours with
stronger winds (sustained speeds as high as 12 kts) during the mid-
late afternoon hours today.
Latest high-res computer models are now in much better agreement on
the idea that thunderstorms developing over the higher terrain east
of Phoenix, at least sending strong outflow winds this evening into
the greater Phoenix area during the 01z-02z hours. This will likely
affecting all of the phx area taf sites with even a decent chance for
the storms themselves affecting one or more of the taf sites. Wind
speeds of at least 25 kts, with gusts as high as 35 kts look likely,
with even stronger speeds possible along with blowing dust reducing
visibilities. Heavy downpours and even small hail are possible if
thunderstorms do actually reach the terminal(s). Winds will become
light easterly later this evening, once the storms move through.
Southeast California/southwest Arizona including kipl and kblh:
should be another quiet taf period at kipl, with little chance of
any isolated showers or storms, and winds remaining from a
Winds will continue to favor southerly directions and wind speeds at
kblh through this evening, with stronger winds during the late
afternoon/evening hours. There is fairly high confidence that
outflows from thunderstorms over south-central Arizona will affect kblh
for a time later this evening, with winds becoming gusty from an
easterly direction along with some blowing dust possible.
Aviation discussion not updated for amended tafs.
Monday through Friday...
deep southerly to southeasterly flow aloft is expected to push
copious amounts of monsoon moisture into the region, resulting in
scattered to numerous thunderstorms Monday through Wednesday with
good to excellent chances for at least some wetting rains and locally
gusty winds. The combination of considerable cloudiness and rainfall
will also keep temperatures below normal during this period, and
humidities above normal. A shift to more westerly winds aloft is
then expected to gradually reduce moisture levels, and chances for
wetting rains during the Thursday-Friday period, while allowing
temperatures to return to near-normal levels. Minimum humidities in
the 25-45 percent range in the Monday-Wednesday period to drop into
the 20-35 percent range by Friday, with good-excellent overnight
recoveries. Outside of thunderstorms, winds to mainly follow typical
Spotter information statement...
spotter activation is possible this evening and Saturday.
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