Scientific Forecaster Discussion
fxus65 kpsr 281621
Area forecast discussion
National Weather Service Phoenix Arizona
920 am MST Tue Mar 28 2017
a Pacific front will affect the region today with gusty winds and
patchy blowing dust. The strongest winds will continue over portions
of southwest Arizona and southeast California before weakening this
evening. A few showers and thunderstorms are also possible across
high terrain areas of central Arizona. Otherwise, high pressure will
redevelop across the region Wednesday and Thursday ahead of another
weather system moving into the Desert Southwest over the weekend.
the main core of a Stout pv anomaly has sunk into far SW New Mexico
this morning with an objectively analyzed -24c 500 mb cold core situated
in Southeast Arizona. In fact, 12z ktwc sounding sampled an impressive 12dm 500 mb
height fall while -23c fell within the lowest 10th percentile for
the end of March (quite interesting as just a week ago we were
constantly talking about temperatures aloft near record levels).
Meanwhile, regional radar and satellite imagery indicate another
weaker vorticity center over eastern Arizona descending into the trough
base. This feature should tap residual midlevel moisture and pockets
of SBCAPE through srn Gila County to invigorate sct showers/storms
/552 am MST Tue Mar 28 2017/
models indicate the highest amounts of low level moisture, and
subsequently instability, will remain to our east today in Gila
County. Most models have a few hundred j/kg of cape materializing
there this afternoon, which in combination with the westerly upslope
flow, should be enough to initiate convective shower activity with a
chance of a weak thunderstorm. Some model solutions indicate light
precipitation could form over far eastern portions of Maricopa
County today as well.
The trough shifts off to our east late in the day on Tuesday which
should help weaken winds dramatically Tuesday evening and diminish
any chance of precipitation in Gila County by early Wednesday
morning. Beyond this, a transient ridge builds in which will help
warm temperatures across our entire County Warning Area with highs reaching the
upper 80s by Thursday.
Models show yet another trough diving down from the Pacific
northwest and into our area on Friday. This will cause a rather
sharp cooling trend Friday with highs at least 10 degrees cooler
than Thursday. This transition to a cooler airmass will
subsequently increase pressure gradients and drive another round
of windy conditions, especially out in southeast California and the
Colorado River Basin. Although at this point, they do not look as
strong as what we will be experiencing on Tuesday. As with our
current trough, the best chance of precipitation will remain in
Gila County with amounts remaining rather light.
All major global circulation models agree that this trough will
linger through Saturday but major differences arise beyond that.
Because of this, there is very low confidence in the forecast for
early next week as each one of the models has their own unique
solution. For now, have gone with a blended approach and have kept
temperatures near seasonal normals.
south-central Arizona including kphx, kiwa, and ksdl:
west-northwesterly flow will strengthen this afternoon with gusts
reaching 20 to 25 kt. Meanwhile, latest guidance indicates that
isolated showers will develop across the higher terrain, but will
remain well north and east of Phoenix. This evening, winds will
subside with a shift to downslope easterly more likely at kiwa
than at kphx.
Southeast California/southwest Arizona including kipl and kblh:
winds will remain the primary aviation weather impact. Gusts to
30-35 kt will be possible at kblh but somewhat weaker at kipl.
Improving conditions are expected this evening at both sites as
high pressure builds in and the stronger winds abate.
Aviation discussion not updated for amended tafs.
Thursday through monday:
the weather pattern will remain relatively active across the Desert
Southwest through early next week, though in general precipitation
is not expected. Only exception will be in the higher terrain well
north and east of Phoenix. Main weather impact will be breezy to
windy conditions, which are expected to redevelop Thursday and
Friday as the next low pressure system moves through the region.
With rhs generally remaining below 15 percent, elevated fire danger
will again be a possibility for a few hours across southeastern
California, particularly Thursday afternoon. Thereafter, the low
pressure system will likely move through Arizona Saturday, bringing
below normal temperatures along with a general decrease in wind and
an increase in moisture. High pressure will follow for Sunday and
Monday, resulting in a warming trend and a return to above normal
temperatures. Otherwise, little to no changes were needed in the
morning update to capture hourly trends.
Spotter information statement...
spotters should follow reporting procedures with criteria reports
Arizona...red flag warning from noon today to 7 PM MST this evening for
Wind Advisory until 7 PM MST this evening for azz020-021-026.
California...red flag warning from noon today to 7 PM PDT this evening for
Wind Advisory until 7 PM PDT this evening for caz031.
Wind Advisory until 4 PM PDT this afternoon for caz030-032-033.
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