Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 190900

Area Forecast Discussion
National Weather Service Phoenix AZ
200 AM MST Fri Apr 19 2019

After fairly hot temperatures today, readings will cool somewhat
over the weekend yet still remain slightly above the seasonal
average. The weather system bringing these cooler temperatures will
also yield breezy conditions during the afternoon hours this
weekend. A warming trend will commence next week with some lower
elevation communities possibly flirting with 100 degrees during the
latter half of the week.


With a ridge axis objectively analyzed directly over south-central
Arizona early this morning, a more innocuous low pressure system was
propagating towards the southern California coast while a deeper
kicker trough was descending towards the Pacific NW. Regional 00Z H5
heights were sampled at 585dm and H8 temperatures solidly in a 20C-
25C range. While the ridge axis will be dampened and dislodged
eastward by the initial southern California wave, deep mixing and
excellent insolation will yield the warmest day of the year.

One caveat may be a glancing blow of higher clouds spilling
northeast from the subtropics, though the majority of model output
suggests the bulk of this cloud cover remaining south of the
forecast area. Regardless, several lower elevation areas may flirt
with the 100F threshold though guidance spread is quite narrow and
supportive of falling just short for most locations. While not that
unusual for this time of year, several degrees short of record
territory, and a far cry from temperatures the region will
experience in the coming months, caution still should be taken for
those working or recreating outdoors during peak heating.

The initial wave will lift through the four corners as the deeper
Pacific NW trough digs towards the SW Conus over the weekend and
through early next week. Gradual H5 height falls and steady cooling
of the boundary layer will progressively cool temperatures over the
region, yet with afternoon highs only falling near or slightly above
average. As is typical this time of year, this system will be quite
moisture starved with the only realistic chance of rain showers over
higher terrain of northern and eastern Arizona in association with
the cold core aloft and a backdoor cold front. The more notable
feature will be breezy afternoon conditions resulting from the
tightened pressure gradient ahead of this system. Current modeling
indicates nothing that unusual for late April with H8-H7 winds only
in a 20-30kt range limiting the overall gust potential. One
exception may be through SE california where stronger terrain
induces sundowner winds could be an issue over the weekend.

The early week trough will only slowly eject eastward through the
middle of next week as the system becomes largely disassociated from
the northern stream jet influence. Operational and ensemble spread
grows increasingly during the middle and latter half of the week
with a majority of GEFS members holding lower heights into the SW
Conus into Wednesday while CMC member are much more aggressive in
pushing the system east and re-building heights over the forecast
area. As a result, have delayed the onset of more substantial warming
into Thursday and Friday; and even then, there is rather notable
uncertainty with respect to how amplified and persistent the
trailing ridge can become.


.AVIATION...Updated at 0540 UTC.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
With no aviation concerns during the period, expect light and
variable to light winds favoring diurnal trends through early Friday
morning. Wind speeds will be mostly under 7kt with isolated periods
of higher speeds under 10kt. For Friday afternoon, expect atypical
wind directions favoring southeasterly to southerly directions.
Skies will be mostly clear with SKC to FEW cirrus through the period.

Southeast California/Southwest Arizona including KIPL and KBLH:
There are no aviation weather concerns during the period. Expect
light winds with diurnal tendencies along with periods of light
and variable winds through most of the period. Late in the period
moderate westerly and southwesterly winds near 7-10kt will develop
at KIPL and KBLH respectively. Otherwise, skies will be mostly clear
with occasional FEW-SCT cirrus passing through the region.

Aviation Discussion not updated for amended TAFs.


Sunday through Thursday:
An elevated fire threat will exist Sunday as a dry weather
disturbance results in afternoon wind gusts 20-25 mph over most of
the districts. This will be coincident with humidity levels falling
into the teens and fine fuels becoming more cured with recent hot
weather. Weather conditions for the remainder of next week will be
very typical for late April with the usual afternoon upslope
gustiness, relatively light overnight winds, afternoon humidity
levels falling into the single digits and teens, and fair to good
overnight recovery. Weather conditions for prescribed burning
activity look very good during the Tuesday-Friday time frame.


Spotter activation is not expected for the next 7 days.





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