Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 301643

Area Forecast Discussion
National Weather Service Phoenix AZ
943 AM MST THU JUN 30 2016

Plentiful monsoonal moisture will bring continued chances for
showers and thunderstorms through at least Friday. Due to the
increased moisture and cloud cover, high temperatures will fall with
some locations dropping below 100 degrees today and Friday. There
will be a return to drier southwest flow aloft over the weekend and
into early next week which will limit thunderstorms to higher terrain
areas east of Phoenix by Sunday. High temperatures will steadily
climb late this week and early next week as the atmosphere becomes


A variety of cyclonic circulations evident in satellite imagery this
morning. Some of these include one centered near Lake Mead, another
over southern AZ, and another over southern Baja. These are in
between troughing to our west and ridging centered over northwest
Mexico and the interior western states. Radar imagery also indicates
a circulation (likely an MCV from last night) centered near the
Maricopa/Yavapai border. Otherwise, there is a lot of debris
cloudiness covering most of AZ and Sonora. Near and west of the Lower
Colorado River Valley. The vast majority of radar echoes this morning
are weak showers associated with the aforementioned circulations.
However, isolated stronger activity has developed over Mohave County
where there has been less cloudiness. For our area, anticipating
strongest convection to be over southwest AZ (mainly La Paz County)
where surface heating will be better and there will be some steering
flow advecting storms southwestward from Yavapai/Mohave Counties.
Further west, there is good moisture and RAP depicts very high CAPE
with decreasing CIN later this afternoon. May need to increase PoPs
in these areas. Meanwhile over south-central AZ, thinking shower
activity will be isolated to scattered the whole day but with only
isolated stronger storms (more likely over higher terrain). However,
with such high PWAT values, the showers will be very efficient rain


A complex situation is ongoing across eastern Arizona and northern
Mexico with multiple mesoscale features and broad upper level
support. A very weak (but still relevant) upper level jet max is
situated across the Baja northward into central Arizona. To the right
of this jet is an area of difluence over southern Arizona which
continues to aid in shower and thunderstorm develop early this
morning. At least three distinct MCVs can be seen within radar
imagery between Phoenix and Tucson. An inverted trough or even a weak
closed mid level circulation also resides over northern Sonora
Mexico. In the near term there remains enough mid level instability,
low level foci, and upper level difluence to support persistent
shower and thunderstorm development. Hi-res model data overall have
been all over the place with what to expect the rest of tonight, but
it seems likely enough the current activity will persist for several
more hours.

Given all this current activity, widespread cloud cover will likely
persist through much of the day. Due to the cloud cover, it is
difficult to determine whether this afternoon and evening will be
extremely active. We start to lose some upper level support as flow
aloft becomes less difluent, but the inverted trough over northern
Sonora is shown to move into far southeastern Arizona by this
evening. Moisture levels will continue to increase through tonight as
1000-700mb mixing ratios increase toward 12 g/kg as the inverted
trough inches northward. Very moist mid levels should result in
mostly cloudy skies through at least the south-central Arizona
deserts and possibly as far west of the Lower Colorado River Valley.
This should keep instability levels fairly low. Another inhibiting
factor for any stronger thunderstorm activity will be the warming
aloft that is forecast and rather weak mid level lapse rates. Taking
all these factors into account, this afternoon and evening will still likely
see scattered to even numerous showers east of the Colorado River,
but overall thunderstorm activity may be dampened due to the lower

Tonight into early Friday may continue to be quite active at least
across eastern Arizona as the mid level circulation tracks across
Tucson by around midnight and then into east-central Arizona by 12Z
Friday morning. The weak upper level jet max will also move into
central Arizona by 12Z Friday providing additional support. The
combination of the mid level circulation and the jet max will likely
provide enough for showers and thunderstorms to last through tonight
mainly east of Phoenix.

During the day Friday, a drying upper level westerly flow overtakes
most of Arizona likely scouring out any mid and upper level
cloudiness by late morning. Ample low level and sufficient mid level
moisture will still be present for Friday afternoon for us to likely
see another day of scattered showers and thunderstorms, mainly from
Phoenix eastward. There is some doubt to how much activity will be
across the lower deserts as a southwesterly steering flow of 10-20kts
will keep most high terrain storms off the lower deserts.

The drying westerly flow will persist through this weekend into early
next week with most lingering lower desert moisture mixing out on
Saturday and completely being scoured out on Sunday. We should still
see some isolated to scattered high terrain storms on Saturday, but
activity will stay confined to areas east of Phoenix. By Monday,
1000-700mb mixing ratios drop to below 8 g/kg which is even likely
too low for any high terrain storms. This flow looks to persist
through Tuesday and possibly into next Wednesday before the high
shifts far enough north into New Mexico to bring a moist
southeasterly flow back to our region.

Forecast temperatures during the period start out below normal for
areas over Arizona through Friday due to the increased moisture and
extensive cloud cover. Once the drying takes place this weekend,
temperatures will be on the rebound with near normal highs by Sunday.
Monday through Wednesday should see temperatures climb to above
normal levels, but at this point it does not look like excessive heat
will be a big concern.


South-Central Arizona including KPHX, KIWA, and KSDL:
Today feels more like a day that should be in August...not late June.
Deep monsoon moisture surface with various embedded disturbances will
continue to circulate through south-central AZ, supporting periods of
BKN-OVC CIGS generally 8-10kft. Given the significant increase in
moisture and some rainfall over the Phoenix area overnight, some
lower SCT decks around nearby terrain/foothills cannot be ruled out.
The stronger thunderstorm activity ended overnight, with showers and
an isolated lightning strike or two possible through midday. Winds
should maintain headings with some slight variants off of east
through midday.

Confidence in the forecast beyond midday degrades significantly.
Conceptually, storm activity should be rather diminished today as the
atmosphere is well mixed and worked over from last evenings storm
activity. Usually a busy aftn/evening/overnight is followed by a
less busy aftn/evening the next day. However, any sky clearing and
solar heating of the moisture-rich atmosphere could allow for
shower/thunder development into the evening again. For now, left the
aftn/even rush periods with at least VCSH mention to introduce some
mention of weather in the terminal airspace and elevated easterly
breezes, potentially from outflow winds from nearby/on-going storms.

Southeast California/Southwest Arizona including KIPL and KBLH:
South to southeasterly headings to persist for the next 24 hours,
with some afternoon gustiness possible for KBLH. SCT to BKN clouds
will develop on and off through the day, with thicker clouds possible
towards the afternoon and evening hours. Bulk of the thunderstorm
activity should stay east of the river and across Arizona again
today, but thunderstorm outflow winds and a few pulse thundershowers
near KBLH are possible later this afternoon and evening.

Aviation discussion not updated for amended TAFs.


Saturday through Wednesday...
Enhanced humidities and storm chances will continue on Saturday
before trending downward, with minimum humidities in the lower
deserts ranging from 20-30 percent on Saturday to 10-20 percent on
Wednesday. Similarly, overnight recoveries will also be trending
downward as we start to dry out this weekend. Thunderstorm chances
on Saturday will be greatest north, east, and southeast of Phoenix.
Sunday through Wednesday, thunderstorm chances will greatly decrease
and be confined to the higher terrain of south-central AZ. Apart
from strong erratic winds associated with thunderstorms, winds will
primarily have a southerly component in southeast California and
southwest Arizona through the period with some afternoon gustiness
up to 20 mph. Over south-central Arizona, winds will following
typical upslope and downslope directions with winds around 5 to 15


Spotter activation is not expected.




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