NWS Phoenix, AZ wrote its last area forecast discussion before the first event at Apr 30, 5:36 PM MST, 6 hours 24 minutes earlier.
Area forecast discussion, Apr 30, 5:36 PM MST, 6 hours 24 minutes before
Area Forecast Discussion
National Weather Service Phoenix AZ
536 PM MST Sun Apr 30 2023
.UPDATE...Updated Aviation discussion.
&&
.SYNOPSIS...
Temperatures several degrees above normal will continue through
Monday and then gradually cool into a below normal category later
in the week in response to a strong low pressure system
meandering along the California coast. With the approach of this
system, breezy conditions are likely most days through the week,
with the strongest winds Monday afternoon and evening.
Temperatures should moderate back closer to the seasonal normal by
the weekend. Despite the introduction of this low pressure
system, a continuation of dry weather should be expected.
&&
.DISCUSSION...
Phoenix has officially hit 100F for the first time this year,
with 500mb ridging overhead and centered over eastern AZ this
afternoon. A first 100F+ day on April 30th this is right around
normal. The normal first 100F+ day for Phoenix is May 2nd.
Phoenix could also reach the daily record high if the NBM forecast
of 102F is realized (see Climate section). Elsewhere,
temperatures are expected to top out in the low-100s, with light
winds and cirrus spreading over the area downstream from a subtle
shortwave passing over SoCal. These highs will result in moderate
HeatRisk, posing a risk of heat-related health impacts for those
sensitive to the heat.
Heading into this coming workweek the ridge will continue to slide
east toward the Plains as a large scale omega block pattern takes
hold with a low on either side of the ridge, one over the
northeast CONUS and another over the California coast. As the west
coast low progresses down the coast and heights fall across the
Desert Southwest, temperatures will begin ta gradual decline.
Winds will also pick up as the pressure gradient tightens across
the area. Under a blocking pattern, breezy conditions are
expected for much of the week as the general pattern persists.
Strongest winds are still being advertised on Monday, and more
specifically Monday afternoon through the evening. EPS and NAEFS
have the greatest wind anomalies on Monday, especially across
Southwest AZ, with an unusually strong southerly wind anticipated.
Spring wind events are more commonly characterized by breezy
westerlies. Despite the strong positive anomalies, wind magnitude
forecast mostly remain under advisory thresholds in AZ. Gusts will
mostly be in the 25-35 mph range. This will still create periods
of critical fire weather conditions however, with the addition low
humidity and very dry fine fuels. Stronger downsloping westerly
winds are anticipated in Southeast CA Monday afternoon and
evening, specifically Imperial County, where gusts up to 40-50 mph
are anticipated. Wind Advisories have been issued for parts of
western Imperial County, including the Imperial Valley. The winds
Monday will also be capable of generating areas of blowing dust.
Ensemble members continue in excellent agreement pulling vorticity
and lower heights inland during the middle and latter half of the
week. The consistency among membership is actually quite surprising
given this is evolving from a blocking situation, and portends a
brief period of below normal temperatures across the CWA. NBM
spreads have narrowed further and its now very conceivable that much
of the forecast area does not even eclipse the 80F mark on Thursday.
Moisture profiles still look to be very limited as the cold core
translates inland (less than 5 g/kg) though there could be enough
moist upslope and vorticity forced ascent to yield a couple light
showers Thursday. Otherwise, modest height rises should spread into
the region during the end of the week as the blocking pattern
attempts to realign resulting in temperatures moderating back
towards the seasonal normal. There is some uncertainty on how
quickly this occurs, but the overall trend is towards warming
atmospheric profiles over the weekend.
&&
.AVIATION...Updated at 0036Z.
South-Central Arizona including KPHX, KIWA, KSDL, KDVT:
Diurnal, down-valley flow is anticipated tonight and tomorrow
morning. Winds will strengthen Monday afternoon as the pressure
gradient tightens ahead of a deepening low pressure system off the
west coast. Peak gusts in the afternoon and early evening will
likely (70%) reach 30 kt in many spots, before subsiding during
the late evening. Meanwhile, easterly winds in the morning will
gradually veer throughout the day, ultimately reaching west-
southwesterly in the afternoon. Consequently, this will result in
a 2-4 hour window of breezy, southerly crosswinds at KPHX, during
the late morning and early afternoon.
Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will strengthen Monday afternoon as the pressure gradient
tightens ahead of a deepening low pressure system off the west
coast. Peak gusts in the afternoon and early evening will likely
(80%) reach 35-40 kt at KIPL, before subsiding during the late
evening. Somewhat lighter winds are anticipated at KBLH. The windy
conditions may also generate areas of blowing dust with reduced
visibilities, particularly at KIPL.
&&
.FIRE WEATHER...
Dry conditions with above normal temperature will continue the next
couple days with a gradual cooling into the middle of the week. This
transition will result in breezy conditions through the week,
with the strongest winds impacting all districts Monday afternoon
and evening. Wind gusts up to 25-35 mph will be common in Arizona
districts Monday, with up to 40-50 mph in parts of Southeast
California. With minimum afternoon humidity levels falling near
10%, poor to fair overnight recovery of 15-35%, and dry fuels,
critical thresholds still appear likely. The Fire Weather Watch
has been upgraded to a Red Flag Warning for most AZ districts. As
temperatures cool to during the middle of the week, modest
improvements in humidity levels should occur with afternoon
readings falling into a 10-25% range and overnight recovery
improving into a 40-70% range. Occasionally breezy afternoon
upslope winds should persist into the middle and end of the week
resulting in some localized elevated fire danger.
&&
.HYDROLOGY...Updated 253 PM MST 4/30/2023
Salt: Increased flow from Granite Reef Dam has prompted a renewed
Warning for the stretch from Granite Reef to Tempe Town Lake through
Tuesday evening. This is due to flow sufficient to inundate the
normally dry river bed including unbridged crossings, gravel mining
operations, and homeless encampments.
Gila: Flow in the Gila River continues to travel downstream through
Yuma County as water releases from Painted Rock Dam continue.
Releases from Painted Rock Dam remain above 3000 cfs. Continued
releases from the dam will lead to inundation of downstream
unbridged river crossings through Yuma County. Several unbridged
roads in Yuma County have already reportedly been closed due to
flooding. Flood warnings remain in effect downstream of Painted Rock
Dam to the Colorado River. The latest USGS gauge observation along
the Gila River near Dateland recorded a depth around 8.3 feet,
which is above action stage (8 feet). The latest forecast from the
CBRFC indicates that flow in the river will remain above action
stage through at least the next week. The USGS gauge closer to the
town of Yuma, near Dome, began responding today and still rising,
with a current flow height of 16.5 feet (Action stage is at 20
feet). Thus, Flood Warnings along the Gila River have been
extended in time and will remain in effect through at least May
7th.
&&
.CLIMATE...
Record high temperatures:
Date Phoenix Yuma El Centro
---- ------- ---- ---------
Apr 30 102 in 1943 103 in 1943 104 in 2021
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Red Flag Warning from 11 AM to 8 PM MST Monday for AZZ132.
CA...Wind Advisory from 11 AM Monday to 5 AM PDT Tuesday for CAZ562.
Wind Advisory from 2 PM to 11 PM PDT Monday for CAZ563-566-567.
&&
DISCUSSION...Benedict/18
AVIATION...Hirsch
FIRE WEATHER...Benedict/18
HYDROLOGY...Benedict/AJ
CLIMATE...18