Flood in Arizona, February 22, 2019

Area Forecast Discussion
National Weather Service Phoenix AZ
945 AM MST Fri Feb 22 2019

.SYNOPSIS...
A major winter storm will continue to bring scattered valley rain
and accumulating snow above 3000 feet to central Arizona through
this afternoon. An isolated thunderstorm will also be possible this
afternoon over the lower deserts of Maricopa and Pinal Counties as
the upper level low passes overhead. Drier conditions with gradually
warming temperatures will sweep into the region this weekend and
next week.

&&

.DISCUSSION...
A deep PV anomaly has propagated into far SW Arizona this morning
while the stream of more pronounced isentropic ascent and
midtropospheric frontogentical forcing has shifted into SE Arizona.
While moist southwest flow persists around and east of the Phoenix
area immediately ahead of the trough axis, much lighter
precipitation rates have been observed more removed from the
stronger forcing mechanism. However, objective analysis and regional
12Z sounding data still shows a large lobe of extremely cold air (-
30C at H5) and very steep lapse rates (8 C/km in the H5-H7 layer)
poised to pass through the eastern half of the CWA. Though breaks in
cloud cover will be few and far between, all high resolution output
suggests enough sfc heating to support convective showers and a few
embedded thunderstorms this afternoon. 100-200 J/kg of SBCape are
already analyzed near the cold core, and feel even only modest
warming with temperatures reaching the upper 40s will result in low
topped storms (current tropopause is below 20K ft, so storms can't
go that high). Main changes made this morning were to expire the
Winter Weather Advisory for points west of I-17, but extend the same
Advisory a few more hours to the east where light snow continues.
Very well need to extend the Warning in parts of Gila County into
this evening more closely associated with the trough passage.

&&

.PREVIOUS DISCUSSION...
/505 AM MST Fri Feb 22 2019/
Although we are seeing a downtrend in shower activity right now,
we do expect that isolated to scattered convection will redevelop
this afternoon over the lower deserts of Maricopa and Pinal
Counties as the cold core of the upper level low passes overhead.
Most hi-res models show this activity passing over the Phoenix
metro between 1 and 6 PM before pushing south and east of the
metro by the evening hours. Forecast soundings do show some modest
surface-based instability of at least 100-300 J/kg of CAPE this
afternoon with 30-40 knot shear in place, so at least a few
thunderstorms capable of producing small hail or graupel will once
again be possible similar to yesterday. Strong wind gusts will be
possible as well, but winds should be sub-severe. The isolated to
scattered nature of the convection may allow for very brief heavy
downpours, but in general rainfall amounts this afternoon should
average below a tenth of an inch with locally heavy amounts up to
a quarter inch. Some of the stronger cells could briefly drop the
freezing level low enough to allow snow levels to fall as low as
2000 feet elevations, but the timing of this cellular activity in
mid-afternoon will probably favor graupel or hail.

Snowfall will continue to occur at or above 3000-3500 feet this
afternoon with some convective enhancement possible. However,
amounts this afternoon should average around 1-2 inches with
locally heavy amounts up to 4 inches. This activity will continue
into the evening hours in Gila County, but snowfall rates should
drop and as mentioned previously, we should be able to expire the
Winter Storm Warning on time at 5 PM MST. If a brief extension for
a few hours is needed for a few locations, the day shift will
evaluate that and extend it for those locations at that time.
Snowfall amounts of over 2 feet are still expected over the
highest peaks and travel is still highly discouraged across the
region, with more road closures possible today.

Drier air will quickly work in from the west this evening with
skies becoming mostly clear for the lower deserts by late Friday
evening. Freezing temperatures will once again be a possibility in
normally colder locations across the lower deserts. 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. Due to recently issuing a Freeze Watch
for freezing temperatures over the lower deserts on Wednesday
morning, we have elected to not issue another Freeze Watch for
this event. In general, temperatures should be very similar or
about a degree warmer than they were on Wednesday morning.

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 Tuesday with
high clouds keeping temperatures around 70 degrees on Wednesday
before warming into the mid 70s by Thursday and Friday.

&&

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

Strong winter storm continues to slowly push east today, and will
result in widespread low CIGS this morning with partial clearing and
rising of the CIGs in the afternoon. CIGs at the TAF sites will
generally range from 2k to 4k feet through mid afternoon with
occasional CIGs down near 1k feet in scattered mainly light showers.
Winds to favor the east and by 16z or so expect wind to turn to the
southwest. From mid morning into afternoon, CIGs will climb slightly
but still typically range between 3k and 5k feet. Isolated
thunderstorms are possible in the afternoon but confidence a bit too
low to mention in the TAFs at this time. May see a few gusts during
the afternoon from the west/southwest. Expect significant clearing
from the west later this afternoon and into the evening hours with
just a few clouds 5-8k feet during the evening hours.

one last note: despite very high surface temp/dewpoint spreads we
don't expect significant fog issues due to the cloud cover and
associated lack of radiational cooling.

Southeast California/Southwest Arizona including KIPL and KBLH:

Strong winter storm continues to push to the east and should be
mainly focused over south-central Arizona during the day today, so
precip issues should be generally over at the TAF sites. Look for
lingering CIGs around 6-7k feet this morning at KIPL, and some down
between 4 and 5k feet at KBLH. Cloud decks should diminish to FEW or
SCT by late morning with generally clear skies by early evening.
Winds to favor the west to northwest, with some gusts over 20kt
likely during the afternoon hours.

Aviation Discussion not updated for amended TAFs.

&&

.FIRE WEATHER...
Sunday through Thursday:
Dry conditions are expected through the five day period, along with
a warming trend as high pressure starts to build into the area.
Initially high temperatures will be well below normal; desert highs
Sunday will be in the low to mid 60s and nearly 10 degrees below
normal. After that steady warming will occur with highs back into
the low 70s and near normal by Tuesday. Highs will be above normal
by Thursday with mid 70s highs. Humidity levels will stay elevated
each day, with the deserts typically running 20 to 30 percent each
day. Winds will also 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 this afternoon for AZZ545-
     557-558-560>563.

     Winter Weather Advisory until 11 AM MST this morning for AZZ541-
     547-552-556.

CA...None.

DISCUSSION...MO/Hopper/Percha/Kuhlman
AVIATION...CB
FIRE WEATHER...CB

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
840 AM MST FRI FEB 22 2019

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

0837 AM     SNOW             10 ESE CAREFREE         33.76N 111.77W
02/22/2019  E9.0 INCH        MARICOPA           AZ   PUBLIC

            PUBLIC REPORTS 9 INCHES OF SNOW NEAR
            PINNACLE PEAK.

&&

INS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
847 AM MST FRI FEB 22 2019

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

0846 AM     SNOW             3 NNE GLOBE             33.43N 110.77W
02/22/2019  E10.0 INCH       GILA               AZ   PUBLIC

&&

INS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
852 AM MST FRI FEB 22 2019

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

0852 AM     SNOW             7 SE CAREFREE           33.74N 111.84W
02/22/2019  E4.0 INCH        MARICOPA           AZ   PUBLIC

&&

INS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
857 AM MST FRI FEB 22 2019

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

0854 AM     SNOW             5 SSE NEW RIVER         33.85N 112.11W
02/22/2019  M0.3 INCH        MARICOPA           AZ   TRAINED SPOTTER

            SPOTTER REPORTS 0.25 INCHES OF SNOW IN
            ANTHEM.

&&

INS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1145 AM MST FRI FEB 22 2019

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

1143 AM     SNOW             7 SSE CAREFREE          33.73N 111.86W
02/22/2019  M2.5 INCH        MARICOPA           AZ   CO-OP OBSERVER

&&

MP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
1200 PM MST FRI FEB 22 2019

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

1155 AM     SNOW             3 ESE HARCUVAR          33.74N 113.61W
02/22/2019  E0.0 INCH        LA PAZ             AZ   TRAINED SPOTTER

            REPORT OF A TRACE OF SNOW AT THE BASE OF THE
            HARQUAHALA MOUNTAINS IN LA PAZ COUNTY.

&&

INS