Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
1015 am MST Friday Mar 14 2014
isolated showers and thunderstorms are expected today mainly across
the higher terrain north and east of Phoenix as an area of low
pressure moves eastward through Arizona. Warmer conditions will
return for the weekend as high pressure becomes reestablished across
the Desert Southwest. Above average temperatures will persist
through next week with no chance of precipitation.
positively tilted upper trough over Arizona this morning with the
main vorticity lobe centered over southwest Arizona. This has been
producing very weak showers over south-central Arizona and northern
Arizona. Positive vorticity advection and associated q forcing will is shifting to the
eastern half of Arizona and radar trends reflect this with echoes
over our forecast area moving out of metropolitan Phoenix and into Pinal
and Gila counties. Showers are weak and at best are only producing
sprinkles. Latest models are somewhat of a mixed bag on the quantitative precipitation forecast for
this afternoon. However...a majority depict more quantitative precipitation forecast this afternoon
than this morning but pretty much just for zone 24 not metropolitan
Phoenix. This is likely due to a combination of lingering q forcing
and some destabilization with surface heating and middle level cooling.
The hrrr is more generous for the Phoenix area as it develops
showers near the Maricopa/Yavapai border and tracks them south and
eastward such that northern and eastern portions would be preferred.
However the amounts...if any...will be quite light. Will make some
adjustments to the probability of precipitation this afternoon. Probability of precipitation drop off dramatically
this evening as the system continues moving eastward and surface
heating GOES away. More later.
Previous discussion /issued at 310 am MST Mar 14 2014/...
an area of low pressure continues to move eastward through Arizona this
morning. Latest infrared imagery shows widespread middle clouds with some
cooling tops across northern Arizona. Across south-central Arizona...isolated
light showers have been observed across the Phoenix area and where
it is not raining...latest radar imagery suggests that virga is
prevalent. At Deer Valley Airport...winds briefly gusted to 23 miles per hour
during a shower and additional isolated gusts as high as 35 miles per hour are
possible this morning. Meanwhile...stronger than normal winds along
with the clouds are resulting in relatively warm conditions. As of 3
am...the temperature at kphx has not dropped below 70 degrees.
Record warm minimum for today is 64 degrees which last occurred in
Main vorticity maximum evident on WV imagery near Blythe continues to pivot
cyclonically...which has slowed the eastward progression of the
trough. Consequently...latest hrrr indicates that areas of virga and
showers will backbuild across south-central Arizona and persist this
morning. Latest GPS-met at Tempe measured an ipw near 0.6 inches.
However...any rain that manages to reach the surface will likely not
amount to more than a hundredth of an inch. Global and mesoscale
models are in good agreement that showers will become more organized
later this morning and this afternoon once the atmosphere has an
opportunity to destabilize. Strongest qg forcing for ascent will
slide into eastern Arizona by late morning...though convective and
orographic effects will predominate instead. Showers will mainly be
confined to the higher terrain north and east of Phoenix and probability of precipitation
were raised to as high as 80 percent across a small portion of
eastern Gila County. Given the subsidence behind the trough
axis...activity will quickly dissipate with the loss of heating
Strong anticyclone in the eastern Pacific will slide eastward this
weekend with temperatures quickly rebounding into the middle 80s under
sunny skies. Breezy conditions will develop Saturday afternoon
behind the passage of a trough...particularly down the Colorado River
valley where gusts may reach as high as 30 miles per hour. Warmest day appears
to be Monday as somewhat of a return flow develops ahead of an
approaching trough dropping out of The Rockies. GFS/European model (ecmwf) have come
into much better agreement and indicate the trough will only brush
by The Four Corners or perhaps further east. Main impact across the
lower deserts will be slightly cooler temperatures
Tuesday-Wednesday. Thereafter...height rises will Herald additional
warming through late week...though high temperatures are expected to
remain well below records.
south-central Arizona including kphx...kiwa...and ksdl...
considerable cloudiness continues through most of today...with scattered
to broken decks around 12-14k feet through Friday early evening. Some
virga and light showers are possible though confidence is low
anything will impact the taf sites...so no mention in the area tafs
at this time. Variable gusty winds are possible with shower
development...but speeds should remain below 20 kts. Shower activity
will remain well to the north and east of area air fields by Friday
afternoon and evening.
Southeast California and southwest Arizona including kipl and kblh...
winds will generally favor west at kipl and north to northwest at kblh
following weak frontal passage...but speeds should mostly stay at or below
12kt next 24 hours. Otherwise...periodic middle/high clouds above 15k
will generally clear by Friday morning.
Aviation discussion not updated for amended tafs.
Sunday through Thursday...
high pressure will build eastward into the Desert Southwest bringing
a warming trend to the region through the weekend. Breezy conditions
are expected on Sunday as a weather system skirts by just to the
east of the region. Dry conditions will persist with mostly calm
zonal wind flow expected. Brief gusts on Tuesday along the lower
Colorado River valley are possible...though less than 20 miles per hour
expected. No mention of precipitation chances during this time
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