Damaging Wind in Arizona, February 21, 2019

Area Forecast Discussion
National Weather Service Phoenix AZ
1054 AM MST Thu Feb 21 2019

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
A major winter storm will affect the region today with valley
rain and mountain snow becoming widespread by mid to late morning,
continuing off and on through tonight before tapering off from
west to east Friday. Precipitation will be best east of the Lower
Colorado River Valley. Significant accumulating snow can be
expected for elevations above 3000 feet with very heavy snow above
4000 feet. Otherwise, expect much below normal temperatures
through Saturday before a slow warming trend starts. A return to
dry conditions are forecast into next week with temperatures
gradually warming back to near normals by late next week.

&&

.DISCUSSION...

Forecasts look to be on track this morning for what still looks like
the most significant winter storm the region has seen since 2010.
Precip began early this morning, with current rainfall totals across
our CWA ranging from less than 0.05 inch over Yuma County up to as
much as 0.50 inch over extreme northern and northeast Maricopa
County. Precip is falling as snow at elevations as low as 2500 feet,
with accumulating snow being reported as low as 3000 feet, which is
in line with current forecasts. Latest HRRR and WRF high-res models
continue to show an upramp in precip rates this afternoon/evening as
the main upper low center approaches the region, and winds aloft
increase. Given an expected increase in mid-level instability
(MUCAPES rising into the 200-500 J/KG range), slight chances for
thunderstorms have been added to the gridded forecasts. These
embedded heavier showers/thunderstorms could produce brief locally
moderate-heavy rainfall/snowfall, which will likely impact the
evening commute and produce localized flows in washes/small streams.
Needless to say, significant travel impacts can be expected,
especially for anyone trying to travel north and east out of the
greater Phoenix area. Just as a side note, the high reached 86F at
Sky Harbor on this day in 2016, which set a record for the date.

.PREVIOUS DISCUSSION...
The strongest weather system of the winter season and likely of
the past few winters is beginning to affect the Desert Southwest
early this morning. A deep trough is currently being carved out
across the Southwestern U.S. with the trough center over Nevada.
Further deepening is anticipated over the next 12-18 hours as the
center of the trough shifts southward over southern California.
The positioning of this impressive late winter trough will provide
a nearly perfect scenario for heavy snow across the high terrain
of Arizona. As stated in previous discussions, upper level
dynamics and low level upslope forcing will be quite strong and
persistent over the majority of Arizona this morning through much
of tonight.

Current objective analysis shows light rain and snow becoming more
widespread over southern California and the northwestern 3/4 of
Arizona. As the atmosphere saturates from the top down and
forcing increases, rain and snow will increase in intensity later
this morning for much of Arizona. Little has changed with the
current forecast package with high QPF amounts still shown over
all but southwest Arizona and southeast California. The best
timeframe for moderate to possibly heavy rain and snow over the
eastern half of Arizona looks to be this afternoon and evening
with the heaviest precipitation shifting southeastward into
southeast Arizona by sunrise Friday. The highest impacts will
obviously be the heavy snow across elevations above 3500-4000
feet. Snow levels continue to be a bit difficult to handle with
initial levels around 3000 ft early this morning and gradually
rising to around 4000 ft this afternoon before dropping back down
again on Friday. Snow accumulations are still likely to occur down
to around 3000 ft early this morning and on Friday, changing over
to rain below 4000 ft between 18Z today and 12Z Friday.
Elevations around 4000 ft and above should stay mostly snow
during the bulk of the event with accumulations above 1 foot,
possibly as much as 30" over the highest peaks in the Mazatzal
and Superstition Mountains and across far eastern Gila County.
Total rainfall of 1-1.5" is likely for lower elevation areas from
central Phoenix and to the north and east. This will likely lead
to some localized flooding of washes, but no Flood Watches should
be needed.

The trough will finally begin shifting east through Arizona and
Utah on Friday with the cold core moving over the area. At this
time, the main forcing will push to the east into New Mexico, but
steep lapse rates under the cold core and forcing from a strong PV
anomaly over central Arizona will aid in scattered rain and snow
showers from Phoenix eastward Friday afternoon into the early
evening. The colder air with the trough will lower snow levels
closer to 3000 ft again and with the convective nature of the
showers we can't rule out rain mixing with snow or graupel as low
as 1500-2000 ft elevation. Drier air will quickly work in from
the west later Friday with skies becoming mostly clear for the
lower deserts by late Friday evening. After chilly daytime
temperatures mostly in the 40s to around 50 for the lower deserts,
overnight lows into Saturday morning should again end up around
freezing. The coldest desert spots may dip into the upper 20s to
around 30 degrees.

The trough finally exits well to the east by Saturday morning with
dry westerly zonal flow taking over through Monday. Temperatures
will be slow to recover this weekend with highs still only in the
low to mid 50s Saturday over the Arizona deserts to around 60 in
the western deserts. Overnight lows Saturday night will again be
quite chilly, likely only a couple degree improvement over the
previous night's near freezing temperatures. Models are now
leaning to a bit quicker of a warm-up next week with a weak ridge
building across the Western U.S. Tuesday into Wednesday. This
should allow highs to climb to around 70 degrees by Wednesday and
into the lower to middle 70s for the end of next week.

&&

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

Weather impacts abound as a weather system moves through the
terminal area. First, there will be periods of light to moderate rain
through at least tonight and likely well into Friday. During this
time, ceilings will continue to remain low, likely below 5k feet
and at times 2-3k feet. Ceilings at or below 1k feet are also
possible for short periods of time. Visibility will also be
reduced during any showers. The winds will be tricky during the
rest of the morning and afternoon as strong gusts upwards of 25
kts will prevail for the next several hours. The winds will slowly
transition out of the southeast towards a more southerly
direction creating strong crosswinds at most terminals by the late
morning/early afternoon. There is uncertainty as to whether or
not the winds will become westerly but a westerly shift makes
sense as a stronger wave of showers moves into the terminal area.

Southeast California/Southwest Arizona including KIPL and KBLH:

The winter weather storm will create some aviation problems for
the terminal area, primarily with strong westerly winds with gusts
upwards of 25 kts. Scattered showers will also prevail through
much of the late morning and afternoon. However, the overall
weather should improve slowly through the day into the afternoon.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Saturday through Wednesday: A strong winter storm will exit to the
east Friday night resulting in a drying and gradual warming trend
for the weekend into the middle of next week. Despite nearly
constant warming each day, highs will remain below normals through
next Tuesday although they will climb into mid to upper 60s over the
warmer lower deserts. Warmer deserts will finally approach normal
and reach the low 70s by next Wednesday. Humidity levels will remain
elevated through the period with drier deserts still mostly above 20
percent each day. Winds will tend to be on the light side during the
five day period.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Winter Storm Warning until 5 PM MST Friday for AZZ545-557-558-
     560>563.

CA...Winter Weather Advisory until 10 PM PST this evening for CAZ560.

&&

DISCUSSION...Percha/Kuhlman
AVIATION...Deems
FIRE WEATHER...CB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1225 PM MST THU FEB 21 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1220 PM     HAIL             4 NW WADDELL            33.64N 112.44W
02/21/2019  E0.25 INCH       MARICOPA           AZ   PUBLIC

&&

MP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1228 PM MST THU FEB 21 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1220 PM     HAIL             2 NNW WADDELL           33.64N 112.41W
02/21/2019  E0.70 INCH       MARICOPA           AZ   PUBLIC

            1/2 HAIL FOR 1-2 MINUTES.

&&

MP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1238 PM MST THU FEB 21 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1228 PM     HAIL             4 NW WADDELL            33.64N 112.44W
02/21/2019  E0.25 INCH       MARICOPA           AZ   TRAINED SPOTTER

            PEA SIZED HAIL NEAR BELL RD. AND CITRUS RD.
            ENOUGH ACCUMULATION TO JUST START COVERING
            THE GROUND.

&&

AJ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1240 PM MST THU FEB 21 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1231 PM     HAIL             3 SW BEARDSLEY          33.65N 112.42W
02/21/2019  E0.25 INCH       MARICOPA           AZ   TRAINED SPOTTER

            HAIL WITH LARGEST STONES UP TO HALF AN INCH
            IN DIAMETER OCCURRED NEAR LOOP 303 AND BELL
            RD. ENOUGH ACCUMULATION TO START COVERING
            THE GROUND.

&&

AJ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1243 PM MST THU FEB 21 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1240 PM     HAIL             4 WNW WADDELL           33.64N 112.45W
02/21/2019  E0.25 INCH       MARICOPA           AZ   PUBLIC

            1/4 HAIL COVERING THE GROUND.

&&

MP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1245 PM MST THU FEB 21 2019

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1235 PM     HAIL             1 N WADDELL             33.62N 112.39W
02/21/2019  E0.25 INCH       MARICOPA           AZ   PUBLIC

&&

MP