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Office: PSR

FXUS65 KPSR 192004
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
104 PM MST Sun Aug 19 2018


.SYNOPSIS...
Above normal temperatures are expected across the region on
Sunday and Monday as high pressure remains centered over Arizona.
Highs over the lower deserts will approach 110 degrees with some
spots over southeast California a few degrees warmer. Moisture
returns to the region by Tuesday morning to increase thunderstorm
chances through the rest of next week with temperatures decreasing
back closer to normal.

&&

.DISCUSSION...
Satellite imagery this afternoon shows scattered cumulus over the
higher terrain of the Desert Southwest while dry northerly flow
advects across the region. This is in response to an upper level
high which is centered just to our west over Southern California.
The dry northerly flow is apparent in our 12Z sounding taken from
Phoenix this morning with RH values generally less than 5% above
500 mb! Not surprisingly, nearly all the 1.53 inches of PW
recorded in today's sounding is in the lower half of the
atmosphere (1000-500 mb) with the majority of the CAPE in the
lower elevations and little (< 500 J/kg) along the Mogollon Rim.

Looking at mesoscale models, only isolated activity is expected
in the higher terrain this afternoon. Whatever does form will have
a light NW steering flow which is certainly not conducive to
lower elevation convective activity. A few CAMs show light
activity from Mohave and Yavapai Counties weakening as it moves
into La Paz and Maricopa late this afternoon. This looks
reasonable as outflows will likely be far too weak to break the
convective cap that remains over the lower elevations. Otherwise,
all other areas should remain dry. Besides this, temperatures
will be very warm, about 5 degrees above normal, with highs just
below 110 for Phoenix and likely exceeding that in SE California.

Monday will be a transition day as the aforementioned upper level
high drifts east and our flow patterns shifts to the southeast.
An increase in moisture near Tucson may be enough to generate
storms and an outflow to our SE. This could possibly bring some
dust toward Phoenix but chances of an outflow making it this far
north on Monday are low. By late Monday night into Tuesday
morning, models show a shortwave moving through and bringing a
pronounced increase in moisture. It is not clear whether this wave
will be enough to generate convective activity but the NAM and
GFS do show some precipitation falling in south-central and
southwest AZ Tuesday morning. For now, have bumped up PoPs
slightly for the Tuesday morning timeframe but is something we'll
need to watch.

Depending on how Tuesday morning shakes out, at least scattered
thunderstorm activity is expected to resume during the afternoon.
The ridge will continue to push farther east into west Texas as
well to support relatively strong southeasterly flow aloft that
may increase shear to 20-30 knots for Tuesday. Therefore, storms
that develop may be more organized and stronger than usual,
capable of producing damaging winds and blowing dust.

We will likely see a shortwave or two rotating around the ridge at
some point between Wednesday and Thursday. This wave may have
some connection with a vorticity tail that breaks off from the
trough over the eastern two-thirds of the U.S. as a front pushes
into the Southern Plains. However, it is too difficult to pinpoint
whether these waves will occur with maximum daytime heating or
not. These shortwaves may also be convectively reinforced by MCVs
over Mexico that push into the region to complicate the forecast
further.

Beyond the middle of next week, the GFS continues to merge towards
the ECMWF in keeping the ridge centered to our east which places the
region in a persistent southeasterly flow aloft. This would
support continued below normal temperatures and at least isolated
thunderstorm activity over the lower deserts with greater
coverage over higher terrain Friday and Saturday. At the current
moment, it is difficult to pick out a specific day or two for the
most elevated thunderstorm chances beyond Wednesday, but it does
appear that at least lower grade monsoon thunderstorm activity
will persist into the weekend.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:

Much drier air will move into the region today, which will
essentially turn off the Monsoon for a day across much of Arizona.
No aviation weather impacts are anticipated at the terminals while
diurnally driven winds dominate.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather impacts expected. Diurnal winds and mainly clear
skies will prevail at both KIPL and KBLH through at least Monday
morning.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...

Tuesday through Saturday:

An increase in available moisture during the first half of next week
brings a chance of thunderstorms back to the lower deserts in
addition to increasing minimum relative humidity values back above
20 percent over the lower deserts. The best chances for storms
across the entire region currently appears to be on Tuesday, but
thunderstorms will be possible over higher terrain locations
nearly each afternoon next week. Wind speeds will be typical for
mid-summer with the usual afternoon breezes. Temperatures will
remain slightly above normal through the extended period.

&&

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

&&

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

$$

DISCUSSION...Wilson/Hopper
AVIATION...Kuhlman
FIRE WEATHER...Percha/Wilson/Hernandez

FXUS65 KPSR 192044 AAA
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
145 PM MST Sun Aug 19 2018

.UPDATE...Updated Aviation and Fire Weather Discussions...

.SYNOPSIS...
Above normal temperatures are expected across the region on
Sunday and Monday as high pressure remains centered over Arizona.
Highs over the lower deserts will approach 110 degrees with some
spots over southeast California a few degrees warmer. Moisture
returns to the region by Tuesday morning to increase thunderstorm
chances through the rest of next week with temperatures decreasing
back closer to normal.

&&

.DISCUSSION...
Satellite imagery this afternoon shows scattered cumulus over the
higher terrain of the Desert Southwest while dry northerly flow
advects across the region. This is in response to an upper level
high which is centered just to our west over Southern California.
The dry northerly flow is apparent in our 12Z sounding taken from
Phoenix this morning with RH values generally less than 5% above
500 mb! Not surprisingly, nearly all the 1.53 inches of PW
recorded in today's sounding is in the lower half of the
atmosphere (1000-500 mb) with the majority of the CAPE in the
lower elevations and little (< 500 J/kg) along the Mogollon Rim.

Looking at mesoscale models, only isolated activity is expected
in the higher terrain this afternoon. Whatever does form will have
a light NW steering flow which is certainly not conducive to
lower elevation convective activity. A few CAMs show light
activity from Mohave and Yavapai Counties weakening as it moves
into La Paz and Maricopa late this afternoon. This looks
reasonable as outflows will likely be far too weak to break the
convective cap that remains over the lower elevations. Otherwise,
all other areas should remain dry. Besides this, temperatures
will be very warm, about 5 degrees above normal, with highs just
below 110 for Phoenix and likely exceeding that in SE California.

Monday will be a transition day as the aforementioned upper level
high drifts east and our flow patterns shifts to the southeast.
An increase in moisture near Tucson may be enough to generate
storms and an outflow to our SE. This could possibly bring some
dust toward Phoenix but chances of an outflow making it this far
north on Monday are low. By late Monday night into Tuesday
morning, models show a shortwave moving through and bringing a
pronounced increase in moisture. It is not clear whether this wave
will be enough to generate convective activity but the NAM and
GFS do show some precipitation falling in south-central and
southwest AZ Tuesday morning. For now, have bumped up PoPs
slightly for the Tuesday morning timeframe but is something we'll
need to watch.

Depending on how Tuesday morning shakes out, at least scattered
thunderstorm activity is expected to resume during the afternoon.
The ridge will continue to push farther east into west Texas as
well to support relatively strong southeasterly flow aloft that
may increase shear to 20-30 knots for Tuesday. Therefore, storms
that develop may be more organized and stronger than usual,
capable of producing damaging winds and blowing dust.

We will likely see a shortwave or two rotating around the ridge at
some point between Wednesday and Thursday. This wave may have
some connection with a vorticity tail that breaks off from the
trough over the eastern two-thirds of the U.S. as a front pushes
into the Southern Plains. However, it is too difficult to pinpoint
whether these waves will occur with maximum daytime heating or
not. These shortwaves may also be convectively reinforced by MCVs
over Mexico that push into the region to complicate the forecast
further.

Beyond the middle of next week, the GFS continues to merge towards
the ECMWF in keeping the ridge centered to our east which places the
region in a persistent southeasterly flow aloft. This would
support continued below normal temperatures and at least isolated
thunderstorm activity over the lower deserts with greater
coverage over higher terrain Friday and Saturday. At the current
moment, it is difficult to pick out a specific day or two for the
most elevated thunderstorm chances beyond Wednesday, but it does
appear that at least lower grade monsoon thunderstorm activity
will persist into the weekend.

&&

.AVIATION...
South-Central Arizona including KPHX, KIWA, and KSDL:

Much drier air over the region today will keep convective activity
well away from the Phx area terminals, with just a few storms to
develop over the Rim County, White Mtns, and SE AZ. No aviation
weather impacts are anticipated at the terminals while diurnally
driven winds dominate.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather impacts expected. Winds to remain mainly
southeasterly at KIPL and southerly at KBLH, with a bit of gustiness
at KBLH on Monday afternoon.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...

Wedneday through Sunday:

An increase in available moisture during the middle and end of the
upcoming workweek to keep chances of thunderstorms elevated over the
region, in addition to keeping minimum relative humidity values
above 20 percent over the lower deserts. The best chances for storms
across the entire region currently appears to be on Tuesday. Some
drying and a reduction in convective activity is possible for next
Saturday and Sunday. Wind speeds will be typical for mid-summer with
the usual afternoon breezes. Temperatures will remain nea-normal
through the entire period.

&&

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

&&

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

$$

DISCUSSION...Wilson/Hopper
AVIATION...Percha
FIRE WEATHER...Percha



Office: TWC FXUS65 KTWC 192123 AFDTWC Area Forecast Discussion National Weather Service Tucson AZ 223 PM MST Sun Aug 19 2018 .SYNOPSIS...Drier air and building high pressure will result in less thunderstorm activity with higher afternoon temperatures again Monday. As the high center returns to east of our area, deep moisture will return this week with a good chance of showers and thunderstorms by Tuesday or Wednesday. && .DISCUSSION...Warmer temperatures aloft will continue to hinder the development of thunderstorms today and again tomorrow as high pressure shifts over Arizona. Both the GFS and ECMWF showed the high pressure ridge becoming centered over the southern Plains by Wednesday. This more favorable position of the high will advect deeper moisture pooled south of the region back into the area as early as Tuesday. Thereafter, the return of daily showers and thunderstorms can be expected. Cooler high temperatures will also coincide with the moisture increase and subsequent upswing in thunderstorms. && .AVIATION...Valid through 21/00Z. FEW-SCT cloud bases around 8-12k ft AGL through the period. Isolated -TSRA/-SHRA through 20/03Z will generally be near the higher terrain south and east of KTUS. NWLY SFC wind will remain less than 12 kts through the evening before becoming light and terrain driven overnight and into Monday. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Isolated storms will favor the higher terrain east and south of Tucson this evening. The pattern gradually shifts early in the work week allowing for better coverage of showers and storms, especially by Wednesday. Terrain driven 20-ft winds persist at less than 15 mph, except for in and around thunderstorms where strong outflows may occur. && .TWC WATCHES/WARNINGS/ADVISORIES...None. && $$ Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
Office: FGZ FXUS65 KFGZ 192335 AFDFGZ Area Forecast Discussion National Weather Service Flagstaff AZ 435 PM MST Sun Aug 19 2018 .SYNOPSIS...Expect limited storm activity into Monday, with a significant moisture increase by Tuesday. The remainder of the week from Tuesday onward will feature moderate to high grade monsoon activity. && .DISCUSSION...Models continue to show the ridge of high pressure currently centered over California, beginning to slowly move back towards the Four Corners region over the next 24 hours. This will allow for isolated convection, as seen over western Yavapai county to continue into the evening hours. Smoke from fires in the Pacific Northwest is currently impacting parts of the Navajo Nation. This smoke is expected to decrease as the plume moves eastward into New Mexico due to the shifting center of the high pressure ridge. Moisture is expected to advect back into Arizona beginning on Monday, but is not anticipated to impact storm development in Northern Arizona until Tuesday. Dry and stable conditions are expected to persist through the day Monday, with an isolated shower or two possible during peak heating. Tuesday onward as moisture moves into the region from the Gulf of California expect an increase in afternoon showers and thunderstorms through the rest of the week, limiting high temperatures. && .AVIATION...For the 00Z package...Expect VFR condtions across northern Arizona for the next 24 hrs. Isolated -SHRA/-TSRA will continue over Yavapai County until around 02Z. ISOLD -SHRA/TSRA will develop after 18Z west of a KPGA-KSJN line. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...Isolated showers and thunderstorms over Yavapai County will end around dark this evening. Monday will see breezy south to southwest winds, and isolated to scattered showers and thunderstorms from the Kaibab Plateau to the White Mountains and southward. Moisture will push northward Monday night through Tuesday, with increasing chances for showers and thunderstorms. .Wednesday through Friday...Moisture will continue to increase across the district Wednesday and Friday, with an increase in convective activity across northern Arizona. && .FGZ WATCHES/WARNINGS/ADVISORIES...NONE. && $$ PUBLIC...Suk AVIATION...MAS FIRE WEATHER...MAS For Northern Arizona weather information visit weather.gov/flagstaff