What forecasters said that day
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Phoenix, AZ wrote its last area forecast discussion before the first event at Jul 10, 4:15 PM MST, 1 hour earlier.
Area forecast discussion, Jul 10, 4:15 PM MST, 1 hour before
Area Forecast Discussion
National Weather Service Phoenix AZ
415 PM MST Tue Jul 10 2018
.SYNOPSIS...
Monsoon moisture levels will continue to remain high enough this
week to cause isolated to scattered thunderstorms daily across
most of the region. The best chances for more widespread storms
will be Tuesday afternoon through Wednesday afternoon, with
chances decreasing for the second half of this week before
increasing again later this weekend. Temperatures will generally
end up slightly below normal over Arizona with readings closer to
normal across southeast California.
&&
.DISCUSSION...
A slow-moving upper-level disturbance that is currently centered
over western Arizona is helping trigger isolated to scattered
thunderstorm activity this afternoon over portions of southeast
California and just south and east of the Phoenix metro. The
first area of thunderstorms over southeast California is west of
the easterly wave where better dynamic forcing in the form of
positive differential vorticity advection is interacting with
stronger instability (2000+ J/kg of CAPE) where temperatures have
warmed up into the upper 90s. Although DCAPE values are near 1000
J/kg, terrain and weak westerly shear aloft should help mute the
potential for gusty outflows. Excessive rainfall will be a greater
threat given the weak steering flow and precipitable water values
between 1.5-1.9 inches, but these storms have shown some movement
to the west with its outflows to generally keep radar estimates
below an inch. Hi-res models show this activity will continue
over the next few hours before weakening by early evening.
The second area of thunderstorms is ongoing south and east of the
Phoenix metro from convective outflows associated with convection
that developed earlier this afternoon and morning across
southeast Arizona. An outflow boundary associated with the
strongest cell near the Maricopa-Pinal County border just west of
Gila County is causing wind gusts up to 40-50 mph that is causing
blowing dust in Pinal County and southeastern portions of
Maricopa County that will eventually include southeast portions of
the Phoenix metro along I-10. Visibilities below a quarter mile
will be possible over Pinal County, with higher visibilities at or
above a quarter mile into the Phoenix metro. Another area of
blowing dust is pushing west into Maricopa on Highway 238. Thus,
we have added blowing dust for Pinal County and the southeast
Phoenix metro back into the forecast grids for the next few hours.
However, we do not expect widespread dust this afternoon and
early evening for most of the Phoenix metro. Strong to borderline
severe wind gusts up to 50 mph will be possible but DCAPE values
below 700 J/kg should help limit them too much beyond that.
Although the persistent cloud cover that had blanketed the
Phoenix metro most of the day is clearing to some extent to allow
us to reach convective temperatures in the mid 90s, aircraft
soundings still show a weak midlevel stable layer. Thus, any new
thunderstorm activity that develops along the outflows should
generally be short-lived into the Phoenix metro in agreement with
the broader hi-res model suite except for areas where terrain is
able to cause additional lift. Although gusty winds to 40 mph will
be possible, excessive rainfall capable of producing up to 1 inch
of rain per hour and nuisance-type flooding will be the primary
threat for the strongest cells over the higher terrain east of
Phoenix. Any cells that are able to slow down a bit over the
higher terrain or rain over areas that received heavy rainfall
yesterday could cause some flash flooding, though it is not
expected to be significant at this time. Most hi-res models are
in broad agreement that thunderstorm activity will generally wane
during the evening hours. There are a few models (like the NAM
Nest) that are showing evening and overnight development over
southwest Arizona in closer proximity to the midlevel low, so we
have accounted for that slight possibility in the forecast.
However, this will be largely tied to the evolution of convection
over the next few hours and whether or not a low-level jet is able
to develop, which currently seems unlikely.
Moisture levels and flow aloft change very little tomorrow, but
the upper-level disturbance should move further to the west.
Global models still depict a decent amount of convection most of
the region tomorrow, but hi-res models have quite a bit of
variability with most keeping activity over the higher terrain
north and east of Phoenix primarily over Gila County. Similar to
today, the shear and flow aloft will be weak with less than 10
knots of steering flow. Precipitable water values should also
still be 2-3 standardized anomalies above normal, so heavy
rainfall capable of producing flash flooding will be a threat.
However, greater daytime warming tomorrow with high temperatures
about 5 degrees warmer will also support higher CAPE and DCAPE
values that should allow for a greater threat of strong to severe
wind gusts and blowing dust. We will have to see what happens with
this afternoon and evening's activity before making a better
judgment on the priority of threats tomorrow.
A drying trend still seems fairly likely starting Wednesday
night, lasting through Friday as GEFS PWATs drop towards 1.2
inches. The European shows less drying, but both show the flow
turning a bit more southerly to maybe even southwesterly for a
brief time. We have continued to lowered PoPs for Thursday and
Friday due to the potential drying, favoring best chances across
the high terrain of eastern Arizona. Temperatures should get a
boost both days as moisture levels drop, but highs should stick
around normal levels.
Beyond Friday, model agreement between the GFS and ECMWF is fairly
poor, with GFS being quite a bit drier. However, both models do
show a weak easterly wave/inverted trough at some point this
weekend, with Sunday or early next week looking a bit more likely
than Saturday, which will probably remain fairly dry. Although
this trough should in turn bring higher moisture levels and more
favorable dynamics, it is not as defined as the one that moved
through over the past few days and there is some indication that
the midlevel ridge may rebuild enough over the region to dampen it
out to some extent. Regardless, temperatures should remain near or
slightly below normal which will definitely be welcome to most.
&&
.AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL:
Expect mostly light winds favoring the east and southeast and the
westerly shifts as well. With rain showers in the vicinity and a
slight chance of afternoon thunderstorms, winds in the vicinity of
any storms that do develop will be variable and gusty along with
a slight chance of blowing dust and reduced visibilities. The
confidence in blowing dust or thunderstorms is too low to include
in the TAFs at this time. Skies will be partly to mostly cloudy
with BKN mid to high level clouds from 10-22Kft.
Southeast California/Southwest Arizona including KIPL and KBLH:
Expect periodic chances of rain showers and isolated thunderstorms through
the period. Moderate winds will favor the south and northeast at
KBLH, and southeast and westerly directions at KIPL. Wind gusts of
27 to 32mph can also be expected closer to storms. Expect SCT to
occasionally BKN cloud decks from 11-20kft.
Aviation Discussion not updated for amended TAFs.&&
&&
.FIRE WEATHER...
Friday through Tuesday:
Slightly drier, low grade Monsoon conditions will prevail through
monday with better storm chances returning on Tuesday. Expect min RH
values to fall to the mid to upper teens to mid to upper 20 percent
range across the region. In addition to any gusty thunderstorm
winds, expect mostly light and variable to normal diurnal wind
patterns. Overnight recovery will be fair to good.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters may be needed late this afternoon and evening.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
DISCUSSION...Hopper/Kuhlman
AVIATION...Sawtelle
FIRE WEATHER...Sawtelle
In the hours before
Special weather statement, Jul 10, 3:38 PM MST, 1 hour 37 minutes before
Special Weather Statement
National Weather Service Phoenix AZ
338 PM MST TUE JUL 10 2018
AZZ547-549-552-555>558-102330-
Fountain Hills/East Mesa AZ-Tonto Basin AZ-Mazatzal Mountains AZ-
Apache Junction/Gold Canyon AZ-Superior AZ-Rio Verde/Salt River AZ-
Pinal/Superstition Mountains AZ-
338 PM MST TUE JUL 10 2018
...SIGNIFICANT WEATHER ADVISORY FOR GILA...MARICOPA AND PINAL
COUNTIES UNTIL 430 PM MST...
At 338 PM MST, Doppler radar was tracking a strong thunderstorm 7
miles north of Queen Valley, or 12 miles northwest of Superior,
moving northwest at 15 mph.
Winds in excess of 40 mph will be possible with this storm
especially over Apache and Roosevelt Lakes.
Locations impacted include...
Roosevelt, Saguaro Lake, Queen Valley, Canyon Lake, Superstition
Mountains, Tonto National Monument, Roosevelt Dam, Lost Dutchman
State Park, Apache Lake, Salt River Tubing Recreation Area, Gold Camp
and Tortilla Flat.
This includes the following highways...
AZ Route 87 between mile markers 195 and 196.
AZ Route 188 between mile markers 241 and 247.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If on or near Apache or Roosevelt Lakes, get out of the water and
move indoors or inside a vehicle. Remember, lightning can strike out
to 10 miles from the parent thunderstorm. If you can hear thunder,
you are close enough to be struck by lightning. Move to safe shelter
now! Do not be caught on the water in a thunderstorm.
&&
LAT...LON 3338 11109 3327 11132 3359 11162 3373 11111
TIME...MOT...LOC 2238Z 154DEG 13KT 3341 11127
18
Special weather statement, Jul 10, 4:04 PM MST, 1 hour 11 minutes before
Special Weather Statement
National Weather Service Phoenix AZ
404 PM MST TUE JUL 10 2018
AZZ538-539-559-102345-
Sonoran Desert Natl Monument AZ-Tonopah Desert AZ-Gila Bend AZ-
404 PM MST TUE JUL 10 2018
...SIGNIFICANT WEATHER ADVISORY FOR MARICOPA COUNTY UNTIL 445 PM
MST...
At 404 PM MST, Doppler radar was tracking a strong thunderstorm near
Bosque, or 9 miles southeast of Gila Bend, moving north at 10 mph.
Wind gusts up to 50 mph will be possible with this storm.
Locations impacted include...
Gila Bend, Estrella, Bosque, Cotton Center and Sonoran National
Monument.
This includes the following highways...
AZ Interstate 8 between mile markers 117 and 135.
AZ Route 238 between mile markers 1 and 25.
AZ Route 85 between mile markers 120 and 132.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3274 11243 3276 11269 3312 11274 3310 11235
TIME...MOT...LOC 2304Z 188DEG 8KT 3288 11255
18
Special weather statement, Jul 10, 4:16 PM MST, 59 minutes before
Special Weather Statement
National Weather Service Phoenix AZ
416 PM MST TUE JUL 10 2018
AZZ548-551-553-102345-
Northwest Pinal County AZ-East Valley AZ-
Southeast Valley/Queen Creek AZ-
416 PM MST TUE JUL 10 2018
...SIGNIFICANT WEATHER ADVISORY FOR MARICOPA AND PINAL COUNTIES UNTIL
445 PM MST...
At 416 PM MST, Doppler radar was tracking a strong thunderstorm near
Seville, or near Sun Lakes. This storm was nearly stationary.
Wind gusts up to 50 mph will be possible with this storm.
Locations impacted include...
Chandler, Gilbert, Sun Lakes, Queen Creek, Chandler Heights,
Tumbleweed Park, San Tan Village Mall, Seville, Santan and Higley.
This includes the following highways...
AZ Route 87 between mile markers 153 and 165.
AZ Route 202 between mile markers 39 and 48.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.
&&
LAT...LON 3317 11166 3312 11180 3326 11192 3334 11172
TIME...MOT...LOC 2316Z 153DEG 4KT 3323 11177
18
Local storm report, Jul 10, 4:30 PM MST, 45 minutes before
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