Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 182221

Area Forecast Discussion
National Weather Service Phoenix AZ
321 PM MST Mon Mar 18 2019

Updated Aviation section.


Warm and dry conditions the next couple days will give way to more
clouds and rain chances as a weather disturbance crosses the area
Thursday. High temperatures in the lower to middle 80s over the
lower deserts will fall back into the 70s later this week before
slowly warming again over the weekend. Not all areas will see rain
this week; and even those who do should not expect much


A high amplitude, western Conus Omega block will only slowly
translate eastward into the center of the country throughout the
week with a pronounced, full latitudinal ridge axis shifting from
the Rockies into plains. The resulting flow pattern will allow the
western trough portion of the block to propagate into the Southwest
and yield a period of somewhat unsettled weather surrounding the
Thursday time frame. At least for the next 48 hours, dry conditions
and slightly warmer than average temperatures will prevail with only
a gradual increase in thicker high clouds.

Models remain consistent showing the PV anomaly and primary cold
core crossing into SE California Thursday morning, then slowly
ejecting past the four corners region by Friday afternoon. The
overall depth of the trough and magnitude of cold air is not
particularly unusual for the middle/end of March though the negative
tilt and divergent fields are quite favorable. Likely the greatest
limiting factor will be moisture flux and availability as the
current forecast trajectory remains disassociated from a more robust
subtropical feed. That said, there is notable differences among
recent operational GFS iterations and NAEFS means with respect to
total column PWATs and QPF over lower elevations. The 12Z GFS does
indicate a brief period of better theta-e frontal organization
collocated with a plume of 0.75 inch PWAT and 6 g/kg mixing ratios
while the majority of ensemble members aren`t nearly as bullish.
Would not be surprised if more ensemble members trend towards the
GFS, though even so lower elevation rainfall would be under 1/4
inch (and most areas little more than a few hundredths).

The best potential for precipitation looks to be Wednesday night at
lower elevations and during the daytime hours Thursday at higher
terrain in an upslope regime, as the best combination of upper level
dynamics and lower/mid level moisture advection come together. In
reality, the bulk of the precipitation should end up falling over
the northern half of Arizona, though all forecast models suggest
more light showers versus a shield of steady rainfall. Temperatures
will take a good dip on Thursday with highs falling back closer to
70 degrees. As the trough exits to the east on Friday, temperatures
will climb back into the middle/upper 70s. Shortwave ridging should
then take over into the weekend with highs approaching 80 degrees
over the warmest desert communities.


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

Expect light winds to prevail this afternoon through Tuesday
morning favoring downvalley/drainage patterns during the nighttime
and morning hours. Anticipate southeast directions to prevail
Tuesday afternoon over south-central Arizona with southerly
directions prevailing over southeast California and southwest AZ
(anticipate gusts of 15-20kts over the Lower Colorado River
Valley). No significant cloudiness but there will be FEW-SCT
altocumulus (bases AOA FL100) as well as some increasing cirrus
Tuesday afternoon.

Aviation Discussion not updated for amended TAFs.


Tuesday through Saturday:
A warm weather pattern will predominate through Wednesday before
a weather system moves through the area for the second half of the
week. Expect above normal highs to continue in the low-mid 80s
through Wednesday. Highs will then cool to the low-mid 70s by
Thursday with slight chances of precipitation moving into the
lower deserts and better chances expected for the the higher
elevations to the east and north where there is also a fair chance
of wetting rains. Min RH values in the mid to upper teens through
Wednesday will improve to greater than 20 percent beginning
Thursday. The next system will also bring breezy southerly winds
out west on Tuesday with gusty southwesterly winds spreading
throughout the region on Wednesday and lingering into Thursday.
Breezy conditions are expected again on Saturday as well. Good
overnight recovery will improve to excellent by Thursday.


Spotter activation is not expected.




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