337 
FXUS65 KPSR 191719
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
1019 AM MST Thu Dec 19 2024

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Record to near record high temperatures are expected through
Friday before a slight decrease in temperatures is likely starting
this weekend. The dry conditions and well above normal
temperatures will continue through early next week until a mostly
dry weather system arrives around Christmas Day. The weather
during the latter half of next week may be a little bit more 
unsettled, but overall dry conditions are likely to persist with
daytime highs running a few degrees above normal.

&&

.DISCUSSION...
An unseasonably strong high pressure ridge is now positioned over
much of the Western U.S., including the Desert Southwest. As H5 
heights remain near 585dm today into Friday, record to near record
highs are forecast for our area. Most lower desert locales are 
expected to top out in the upper 70s through Friday with much of 
the Phoenix area likely reaching or even topping 80 degrees. 
Daily records at KPHX are likely to be tied or broken today and 
Friday before temperatures begin to drop off slightly starting 
this weekend as the high pressure ridge gets tamped down a bit 
from a shortwave trough tracking across northern Nevada into 
Idaho. Skies will remain mostly clear into the weekend before some
increased higher level cloudiness starts to impact the region by 
Sunday. 

The influence of the high pressure ridge will start to wain by
early next week as the Aleutian Low shifts more southward just 
off the coast of California. This will allow for a more active 
weather pattern setting up over the eastern Pacific, affecting 
much of the Pacific Northwest and California through much of next
week. For our region, this weather pattern will gradually push 
out the unseasonably warm high pressure ridge, but we are not 
expecting any atmospheric rivers (AR) to reach our area. The first
AR hitting portions of Califonria on Saturday will largely push 
most of the moisture into the Great Basin leaving us with some 
higher clouds by Sunday. A second AR Sunday will essentially 
follow the first's path, while a third late Monday into Tuesday is
likely to be a bit farther south into central California. For our
region, the first two will largely go unnoticed with temperatures
still reaching into the mid 70s through early next week with only
some periodic high clouds. Guidance is still showing a stronger 
shortwave trough accompanying the third AR, likely at least 
passing through the northern portion of our region on Christmas 
Day. So far model guidance has not been showing very widespread 
precipitation chances for our region on Christmas, but there very 
well could be some shower activity that ends up affecting the
Arizona high country. The trajectory of the system doesn't bode 
well for any good boundary layer moisture return, so it's quite 
doubtful the lower deserts would see any precipitation. 
Temperatures should also turn cooler with the passage of the 
weather system as highs are forecast to drop into the upper 60s to
around 70 degrees across the lower deserts starting Christmas 
Day.

&&

.AVIATION...Updated at 1719Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns are expected through the TAF
period. Light east winds are expected through most of the TAF
period, with moderate confidence in a brief TEMPO westerly shift
late this afternoon/evening. Periods of light and variable winds 
are expected at the terminals. SKC/FEW250 will prevail through 
most of the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected through the next
24 hours. Overall wind speeds will remain light aob 7 kts, with 
the wind directions fluctuating between the west and north and 
with extended periods of variable to nearly calm conditions.

&&

.FIRE WEATHER...
No weather changes are expected through the weekend with dry 
conditions and well above normal temperatures persisting over the
region. Expect overall light winds the next few days, but with 
some breezy easterly winds mainly in the morning across the 
eastern Arizona higher terrain. Low humidities are forecast over 
the next several days with MinRHs in the teens across the lower 
deserts to around 20% over higher terrain areas. The weather
pattern next week is likely to become a bit more active, but with
any weather systems again mostly bypassing the region just to the
north. However, expect a gradual cooldown in temperatures during
the latter half of next week and a slight rise in moisture levels.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Kuhlman
AVIATION...Smith/Benedict
FIRE WEATHER...Kuhlman