FXUS65 KPSR 191231
Area Forecast Discussion
National Weather Service Phoenix AZ
531 AM MST Mon Feb 19 2018
.UPDATE...Updated Aviation and Fire Weather discussions.
Temperatures will cool drastically today and Tuesday as
a low pressure system drops southward through the Great Basin and
into the Desert Southwest. Winds will become very breezy today
with light rain and snow chances for the higher terrain through
early Tuesday morning. In the wake of the low pressure system,
very cool weather will persist only warming back to near average
late this weekend.
An upper level trough continues to dive southward this morning
into the Great Basin and is currently bringing rain and snow
showers across the West Coast. As this feature continues to move
southward throughout the day, pressure gradients will continue to
tighten ramping up the southwesterly flow across the desert
southwest. This has already advected a slug of moisture into our
area with PWs at 0.78 inches in Tucson's 00Z sounding, up roughly
0.4 inches from 24 hours ago.
The prominent orographic lift along with the higher moisture has
allowed weakly convective showers to generate over the higher
terrain north and east of Phoenix. Tucson's sounding indicates
roughly 100 J/kg of mixed layer CAPE while model analysis suggests
similar vales are currently being observed over Gila County.
Given that moisture and the strong southwesterly flow (i.e.
orographic lift) will remain fairly steady through this afternoon,
expecting showers to continue for the higher terrain until
moisture shuts off behind the front early Tuesday morning.
The associated surface front with the aforementioned trough is
currently stretched across southern Nevada but will continue to
race down towards our CWA this morning. Models indicate this front
will rip through Blythe around 8am this morning and into the
Phoenix metro this afternoon/evening. While the front is expected
to be dry for lower elevations, we are expecting some very
breezy/windy conditions with it. Consequently, we have a wind
advisory for portions of SE California and also for the higher
terrain of Gila County. For the Phoenix area, winds will not quite
be at advisory criteria but gusts up to 30 mph could be realized.
Winds are forecast to quickly settle down by late Monday night.
Behind the front, colder and much drier air will begin flooding
into our area. By Tuesday afternoon, 850 mb temperatures will only
be around 1-2 C over Phoenix which would translate into highs in
the mid-50s! This is despite the fact that skies will be crystal
clear under the late February sun. Believe it or not, this could
match or best the coldest day so far this winter which was 57
degrees observed on December 21st. Temperatures are forecast to
plummet Tuesday night after sunset with widespread 30s expected by
Wednesday morning in the lower deserts. In fact, the coldest
lower desert locations could briefly drop into the upper 20s
during this period!
This long wave trough is forecast to stick around through at
least Friday. However, the warm February sun will undoubtedly
modify this airmass on both Wednesday and Thursday bringing a bit
of warming each day. Yet another shortwave will rotate through
this tough come Friday which looks to be relatively cold in
nature but will not be packing much in the way of moisture. PWs
are forecast to be around 0.5 inches at best but strong PVA
forcing may accompany this trough if indeed it comes to fruition.
Really, the main impact would be some breezy conditions along with
some light snowfall above 4000 ft. However, there are still model
disagreements with the ECMWF & GEFS offering a much drier
solution than the GFS.
Quasi-zonal flow develops for the weekend and possibly into early
next week bringing tranquil weather. This pattern would allow
temperatures to gradually rise back to near normal while winds stay
South-Central Arizona including KPHX, KIWA, and KSDL:
Abundant low-level moisture is resulting in CIGS generally in a
4-6k ft range across the Phoenix area. The stratocu will lift and
eventually dissipate this afternoon as drier air overspreads the
area behind a cold front. Further to the north and east, scattered
showers will persist through most of the day across the Mogollon
Rim and there is a slight chance of a shower backbuilding towards
The other aviation weather concern will be the windy conditions
with gusts to 30 kt likely at KPHX. Southwesterly winds early this
morning will veer to westerly later this morning. Winds will
gradually subside tonight, though it is likely that the westerly
flow will persist through at least 10z Tuesday.
Southeast California/Southwest Arizona including KIPL and KBLH:
Main aviation weather impact will be the windy conditions behind a
cold front. Gusts to 30-35 kt will be possible, particularly at
KIPL. Otherwise, there is some potential for blowing dust and
associated reductions in visibility through late this afternoon.
Latest model guidance continues to indicate that winds will
Aviation Discussion not updated for amended TAFs.
Wednesday through Sunday:
A series of low pressure systems will move through the Desert
Southwest through the weekend. This will help to reinforce the
below normal temperatures across the region, while there will only
be a slight chance of precipitation with the system Friday and
Friday night. Below normal RHs are also expected particularly
Wednesday, though winds will remain below critical thresholds
through the period. A warming trend is likely by Sunday, though
temperature will remain below average.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
AZ...Wind Advisory from 11 AM this morning to 9 PM MST this evening
CA...Wind Advisory until 8 PM PST this evening for CAZ560-562-566.
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FXUS65 KTWC 191000
Area Forecast Discussion
National Weather Service Tucson AZ
300 AM MST Mon Feb 19 2018
.SYNOPSIS...Winter like conditions arrives to southeast Arizona this
week as a couple of weather systems will bring gusty winds, valley
rain and mountain snow into Tuesday. Freezing temperatures return to
the lower elevations Tuesday night into Wednesday morning from
mainly Tucson east and south. Temperatures will remain below normal
through the end the week with another chance of showers Friday.
.DISCUSSION...An active week coming up, especially the first couple
of days. Moisture in place over the region will be acted upon by an
approaching and deepening upper level trough today producing
scattered showers across the area, mainly from eastern Pima county
eastward. Also, the approach of this strong trough will generate
rather strong winds this afternoon with sustained speeds generally
20-35 mph and gusts in to 35-45 mph range with the strongest winds
east of Tucson and also over the mountains where gusts into the 50s
The trough will drive a cold front across the area this evening with
the passage in the Tucson area around 6-8 pm then moving east from
there. With the associated strong cold air advection snow levels
will fall rapidly this evening with scattered showers about and as is
typical around here, the precipitation will be winding down as the
snow levels fall into the lower elevations so the snow amount
forecast in the 5-7000 ft range a bit tricky tonight. At those
elevations an inch or two is possible (including Oracle) while above
that the longer duration of potential snowfall will allow for higher
amounts and thus the reason for the Winter Weather Advisory above
Tuesday the bulk of the moisture and dynamics associated with the
deep western U.S. trough will be shifting east into New Mexico along
with the fast moving front. Thus any lingering showers over eastern
portions of the area will be quickly winding down. Even with abundant
sunshine, the cold air mass that will be in place will hold
afternoon high temperatures 15-20 degrees colder than average for mid
February. This cold and drying air mass along with clear skies
Tuesday night will lead to rather cold temperatures Wednesday
morning with sub-freezing temperatures likely from Tucson east and
Beyond that, remaining cooler than average through the remainder of
the week with dry weather at least through Thursday. Models keep
waffling on the idea of a significant trough moving across the area
later Friday leading to fairly low confidence in the forecast that
day. At this time I adjusted pops up a bit and temps down several
degrees as this has a similar look to what todays system looked like
in the model world several days ago. Still plenty of time to adjust
further in the colder and wetter direction if needed.
.AVIATION...Valid thru 20/12Z.
SCT-BKN cloud layers with ceilings generally between 4-8k ft. SCT
valley SHRA/mountain SHSN mainly from KTUS south and east. Brief
MVFR conditions possible in/near SHRA/SHSN. SFC wind S-SW at 8-12
kts this morning. Speeds will increase late in the morning to 18-28
kts with a few gusts of 35 to 40 kts. The strongest speeds are
expected at the KALK/KFHU/KDUG terminals. W-SW winds of 10-15 kts
will then occur overnight into early Tuesday morning. Aviation
discussion not updated for TAF amendments.
.FIRE WEATHER...Scattered valley rain and mountain snow showers
will continue into Tuesday morning as a couple of weather systems
track through the southwest. Dry conditions and well below normal
temperatures will then occur Tuesday into Friday morning, with a few
showers possible Friday afternoon. 20-ft southwest winds will be
gusty this afternoon, generally 20-30 mph with gusts up to 40 mph.
Wind speeds will generally remain less than 15 mph Tuesday and
Wednesday. Slightly elevated west or southwest winds may then occur
late in the work week.
Winter Weather Advisory until 5 AM MST Tuesday for AZZ510.
Wind Advisory from noon today to 11 PM MST this evening for
Winter Weather Advisory until 11 PM MST this evening for AZZ511-
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FXUS65 KFGZ 191206
Area Forecast Discussion
National Weather Service Flagstaff AZ
505 AM MST Mon Feb 19 2018
.SYNOPSIS...Expect very windy and colder conditions today, with
areas of rain and snow through the evening. Very cold temperatures
are expected tonight and Tuesday, with some warming on Wednesday. A
chance of rain and snow, along with another cooling trend, arrives
again on Thursday and Friday.
.DISCUSSION...Numerous upslope bands of rain and snow pellets have
developed from about Williams, all the way to the White Mtns this
morning. This most intense bands are producing lightning and as much
as a quarter inch of liquid in an hour or two. Actual snow has been
tough to come by as pre-frontal snow levels are high and most frozen
precipitation has been in pellet form. Some of the more intense
bands are coating the ground with snow pellets, but not much depth.
As the front approaches, snow levels will fall and saturation depth
should increase. A few hours of intense precipitation are likely
along the front, this is when most areas will see the accumulation.
The front will slow down a bit and encounter deeper moisture along
the eastern Mogollon Rim and White Mtns, this will prolong the
precipitation in these areas.
The other story is wind, most areas will see Advisory or Warning
gusts today, decreasing rapidly from west to east behind the front
Very cold and dry air will move in tonight and Tuesday, with most
precipitation coming to an end.
Current models keep an active storm track in our area, with chances
for rain and snow returning Thursday and Friday. Some moderation is
likley over the weekend.
.AVIATION...For the 12Z Package...Strong southwest winds will
persist through the day today ahead of an approaching cold front.
Most areas will be 15-25 kts gusting near 40 kts. The strongest
winds will be north and east of KFLG at 30-35 kts with gusts around
55 kts. Rain and mountain snow showers with MVFR conditions will
continue to expand in coverage over the mountainous terrain through
the morning and persist through this afternoon. Expect isolated IFR
conditions in snow and blowing snow in mountainous areas above 6kft
MSL. Showers will decrease with conditions improving west to east
aft 00Z. Aviation discussion not updated for TAF amendments.
.FIRE WEATHER...A strong low pressure system and cold front will
move through the area through Tuesday bringing much colder and
unsettled weather. Expect strong southwest winds today gusting near
50 mph for most areas, with the strongest winds gusting 60+ mph east
of Flagstaff to the New Mexico border. Rain and mountain snow
showers will continue through this evening before tapering off from
west to east. The most snow accumulation is forecast along the
Mogollon Rim and White Mountains. Dry and much colder weather will
follow for Tuesday.
Wednesday through Friday...A cold and unsettled weather pattern will
remain over Arizona with a chance for additional precipitation
returning on Thursday and Friday.
Wind Advisory until 5 PM MST this afternoon for AZZ006>008-038.
High Wind Warning from 7 AM until 5 PM MST this afternoon for AZZ005-
Wind Advisory until 7 AM MST this morning for AZZ005-009>014-039-040.
Winter Storm Warning above 6500 feet until 5 AM MST Tuesday for
Winter Weather Advisory above 6500 feet until 11 PM MST this evening
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