Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Phoenix Arizona
845 PM MST Tuesday Mar 31 2015
Synopsis... the high pressure ridge that has been anchored over the
Desert Southwest will begin to break down...and begin a slow decline
in the warm temperatures the area has seen along with an increase in
dry westerly winds...but no chance for rain.
Some afternoon showers and thunderstorms associated with a low
pressure system in Mexico were present in extreme east and Southeast
Arizona during the afternoon but have since died down. Skies across
the region are mostly clear. Phoenix Sky Harbor Airport once again
set a new record today with 95 degrees above the old record of 94 degrees.
Today should be the last in the streak of 95 plus temperatures for the
Phoenix area as the ridge begins to break down. A Pacific trough
dropping into the Desert Southwest over the next few days will break
the heat somewhat with temperatures dropping to near 90 by the weekend in
Phoenix. By early next week another...stronger...system will develop
over the Pacific region and should help drop temperatures down
further...into the middle 80s by midweek.
Forecast was in great shape and no changes were needed other than
Previous discussion... scattered showers are beginning to develop
across eastern Arizona this afternoon in an area of anomalously high
/95th percentile for the end of March/...and in an area of weak
isentropic ascent associated with a weak trough over central Sonora. Storms
are primarily located along the highest peaks although a few isolated
showers appear to be drifting toward extreme eastern Gila County.
Meanwhile across the lower deserts of south- central Arizona and
southeast California...skies are mostly clear and temperatures are well into
the lower 90s as of 20z.
Isolated showers will dissipate quickly this evening with the loss of
daytime heating and as subsidence behind the departing trough takes
hold over eastern Arizona. In the wake of this upper trough...drier
air will begin to move into the area on Wednesday...with a
reinforcing shot of drier air Thursday and Friday courtesy of another
shortwave trough moving through the Great Basin. The combination of
dry air and breezy winds will result in elevated fire weather
conditions on Thursday...although widespread critical thresholds
should not be realized. Winds will be strongest down the lower
Colorado River valley on Thursday although latest hi-res WRF models
and other hi-res datasets suggest wind speeds will remain below Wind
Advisory criteria. The trough will also serve to cool down
temperatures ever so slightly...bringing them more into line with
climatological normals for early April. Late week temperatures will
fall into the middle/upper 80s by Thursday/Friday...with a rebound into
the lower 90s expected through the weekend.
After the late week shortwave clears the region...broad trough
heights/southwesterly flow remain over much of the western Continental U.S.
Through early next week. Operational GFS/European model (ecmwf) solutions advertise
a large shortwave moving off the Pacific late Sunday/early
Monday...however their ensemble (gefs/naefs/ecens) counterparts do
little to inspire confidence in the evolution of that system.
Broadbrush forecast will hold through the weekend and into early
next week of continued dry conditions and slightly above-climatology
Record highs this week...
City March 31
Phoenix 94 in 2012/2004/1989
Yuma 100 in 2011
south-central Arizona including kphx...kiwa...and ksdl...and
southeast California and southwest Arizona including kipl and kblh...
A weak weather disturbance will move across northern Arizona today...
bringing gusty afternoon/evening southwest to west winds across the
region. Strongest winds are expected late afternoon to early
evening...when gusts up to 24 kts are possible. Otherwise expect
only occasional periods of high cloudiness.
Aviation discussion not updated for amended tafs.
..gusty northwest winds and very low humidity area-wide Thursday
afternoon for marginal fire weather conditions...
Thursday through Monday...
A series of weather disturbances will move across the western states
mainly north of Arizona for enhanced afternoon breezes each day. However
one stronger disturbance will move farther south across northern Arizona
Thursday generating gusty north to northwest winds 15 to 25 miles per hour with
gusts to 30 miles per hour. A significantly drier airmass from the north will
also sweep across the region. Marginal fire weather conditions are
expected Thursday especially along the lower Colorado River valley as
well as the ridgetops of southern Gila County. Otherwise...breezy
conditions are forecast each afternoon with minimum relative
humidities in the 5 to 10 percent range. Overnight recovery should be
fair...except for the breezy/windy period Thursday night. Afternoon
temperatures will remain 8 to 10 degrees above normal.
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