523 
FXUS65 KPSR 211216 AAA
AFDPSR

Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
515 AM MST Wed Mar 21 2018

.UPDATE...Updated aviation and fire weather discussions.

&&

.SYNOPSIS...
High pressure aloft will continue to bring warmer temperatures 
with readings peaking Thursday in the mid 80s to around 90 
degrees. Thereafter, a weather system will pass through the region
bringing a chance of showers late Thursday into Friday. Cooler 
conditions can be anticipated in the wake of this system Friday 
afternoon through early next week. 

&&

.DISCUSSION...
A weakening upper level low off the California coast will open up
later today as a second low dives southward out of the northern
Pacific. As this occurs, a weak sub-tropical jet and modest
atmospheric river will combine with the merging Pacific lows
tonight into Thursday. Over the Desert Southwest, heights aloft
will continue to rise through tonight as ridging amplifies over 
the region northward through the Rockies. This will lead to
further warming, but with increasing cloudiness as upper level 
moisture peels off from the atmospheric river to our west. Highs 
today will easily reach into the middle 80s areawide while 
increased cloudiness and lowering heights to our west on Thursday
will lower highs over southeast California. Elsewhere on 
Thursday, highs will again reach at least into the middle 80s, 
possibly even topping 90 in the Phoenix area.

The bulk of the atmospheric river moisture will get fed through
central California into southern Nevada through Thursday with less
and less moisture available as it progresses eastward Thursday
night. There will still be sufficient moisture for at least
scattered showers developing across southeast California by late
Thursday afternoon and then into south-central Arizona Thursday 
night as a weak cold front pushes through the area. Upper level 
dynamics will overall be weak and continue to weaken as the 
shortwave trough progresses through northern Arizona Friday 
morning. Rainfall amounts over the deserts will again be light 
with some places seeing a few hundredths while some high terrain 
spots could top a tenth of an inch.

Some shower activity may linger across the high terrain east of
Phoenix through mid morning Friday, but the shortwave quickly 
exits the region by around noon. Temperatures Friday will drop 
behind the weak cold front, but highs should still end up a couple
degrees above seasonal normals as skies become mostly sunny 
during the afternoon.

This weekend still looks to be dry, but another weakening low 
pressure trough will approach from the northwest keeping
temperatures near normal. Winds should also be on the breezy side
as the system slowly approaches, but skies should still remain 
mostly clear. Though model spread increases into early next week, 
model consensus shows the approaching trough digging southward 
into the Desert Southwest and potentially becoming closed off 
through the middle of next week. Even if this trough would sit 
over our region for a couple days, rain chances will still be 
fairly low due to the likely low amount of system moisture. 
Forecast temperatures do lower starting Sunday and stay slightly 
below normal through early next week, but this is highly 
dependent on the closed low affecting the region.

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

High pressure aloft will gradually shift east over the next 24 hours 
allowing variable amounts of mid and high cloud to spread across the 
deserts and affect the TAF sites. Expect SCT to BKN decks today 
mostly AOA 20k feet with FEW-SCT decks 15-18k feet at times. Clouds 
to thicken and bases to lower later today and tonight, especially 
over the western deserts. Winds will be rather light especially in 
the greater Phoenix area, where we can expect winds to favor typical 
diurnal tendencies. No real aviation concerns at the terminals for 
the next 24 hours.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Friday through Tuesday...A fast moving weather disturbance will 
bring cooler high temperatures Friday along with isolated to 
scattered showers east of the lower Colorado River Valley. Best rain 
chances will be over higher terrain areas north and east of Phoenix. 
Expect high temperatures to drop to near seasonal normals. Humidity 
will be a bit elevated with minimum RH values over the deserts 
mostly 20 percent and higher. Dry southwest flow aloft on Saturday 
will keep skies partly sunny and temperatures will remain near 
seasonal normals. A large area of low pressure will gradually 
develop over the southwestern states Sunday into early next week; 
little if any rain is expected but temperatures will cool with highs 
falling into the low to mid 70s each day over the deserts. Humidity 
levels stay mostly in the teens each day across the deserts. 
Relatively light west wind are expected Friday afternoon; after that 
winds will increase and become rather breezy during afternoon and 
early evening hours each day, favoring the west to northwest.

&&

.SPOTTER INFORMATION STATEMENT... 
Spotters should follow standard reporting procedures.

&&

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

$$

DISCUSSION...Kuhlman
AVIATION...CB
FIRE WEATHER...CB
