Area Forecast Discussion
Issued by NWS Phoenix, AZ

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS65 KPSR 192106 AAE

Area Forecast Discussion...UPDATED
National Weather Service Phoenix AZ
206 PM MST Mon Mar 19 2018

Temperatures will steadily warm through the week with highs
reaching the mid to upper 80s by Thursday. A weaker weather
system moves in late Thursday into Friday bringing our next
chance for showers although rainfall amounts look meager. Cooler
and drier conditions will follow this system with near normal
temperatures expected Friday through the weekend.



Latest satellite imagery shows scattered high clouds moving
across our CWA this afternoon that are associated with an upper
level low that is currently parked out over the Eastern Pacific
near 140 W. These clouds are riding along a 90 kt jet over a
weakly amplified ridge. Near the surface, temperatures have warmed
into the 70s this afternoon while dew points have plummeted into
the low teens as dry air filters into our region. Winds continue
to stay light with most locations at or below 10 mph.

The aforementioned upper level low will continue to remain
stationary over the Eastern Pacific through at least midweek. As
it does, models project that the downstream flow will become more
amplified through the week positioning the Desert SW under a
ridge of high pressure. This will allow 500 mb heights to
gradually build from 568 dm today to around 581 dm on Thursday
with very little spread between the models. As one could expect,
this will translate into temperatures warming through the week
with highs pushing the upper 80s by Thursday afternoon. Believe it
or not, there is even a chance Phoenix could see it`s first 90
degree reading of 2018 on Thursday. For climatological
perspective, the first 90 degree day typically occurs in Phoenix
on March 31st (1981-2010 average) but has occurred as early as Feb
17 (2016)! Needless to say, we are approaching that time of year
when a strong ridge of high pressure can push our temperatures
over the 90 degree mark.

The upper level low that is forecast to remain stationary over the
Eastern Pacific through midweek will finally eject inland by
Thursday as it joins up with a larger longwave trough. With this
trough will come a considerable amount of high level clouds and
is one reason why we may not see 90 degree readings on Thursday.
As with nearly all troughs that move through our area, temperature
gradients will induce pressure gradients that will increase winds
over our area. However, as it stands right now, Thursday is not
looking particularly windy but gust 20-25 mph in the afternoon
will likely be realized. By late Thursday, PWs over our area will
approach an inch thanks to a strong SW flow. This combined with
positive vorticity advection will bring a chance of precipitation
to CA on Thursday night and to the Phoenix metro on Friday
morning. Unfortunately, the best dynamics may be just to our north
which would limit precipitation amounts over our area. The latest
GEFS has QPF amounts around 0.05 for both Phoenix and Yuma.

After this trough swings through, dry air will filter into the
region with H5 heights staying suppressed through our extended
forecast. This will translate into pleasant late March weather
with highs in the upper 70s under mostly sunny skies.


South-Central Arizona including KPHX, KIWA, and KSDL and
Southeast California/Southwest Arizona including KIPL and KBLH:

High pressure will remain in control through our TAF period
bringing light winds that follow typical diurnal tendencies. FEW
to SCT high clouds (20+ kft) will move over the TAF sites the
next 24 hours with a FEW mid level clouds (~10 kft) arriving in CA
late Tuesday morning. No other aviation concern.

Aviation Discussion not updated for amended TAFs.


Wednesday through Sunday...
Expect warm and dry conditions ahead of a weather system that will
pass across the region Thursday into Friday with drier air returning
by the end of the week. The weather system on Thursday will bring a
chance of light rain from SE CA to AZ. Unseasonably warm daytime
highs increase to the mid 80s by Wednesday - with upper 80s expected
in south-central Arizona - and then drop back down into the upper
70s to low 80s by Friday. Min RH`s of 12-20% Wednesday are expected
to spike up to the 18-28% with Thursday`s system. Drier air will
spread in over the weekend, dropping minimum RH values into the 12-
17% range. Breezy southwesterly winds gusting in excess of 25kt from
SE CA to SW AZ are also expected with Thursday`s system. Otherwise
winds will be rather light and favoring typical diurnal tendencies
mostly favoring west to northwest during afternoon hours. Generally
fair overnight recoveries should improve to fair to good by
Wednesday night and Thursday night.


Spotters should follow standard reporting procedures.




FIRE WEATHER...Sawtelle/CB is the U.S. government's official web portal to all federal, state and local government web resources and services.