Areal Flood Warning 21, NWS Phoenix, AZ

Area Forecast Discussion
National Weather Service Phoenix AZ
551 AM MST Fri Nov 29 2019

Updated 12Z aviation discussion.

.SYNOPSIS...
Widespread rain will taper off from west to east this morning with
lingering shower activity this afternoon and tonight over portions
of south-central Arizona. Snow levels will drop rapidly from west to
east today and a Winter Storm Warning remains in effect above 4500
feet over much of Arizona. Expect much cooler high temperatures
today with readings peaking the 50s on the deserts. Warmer and drier
conditions are expected during weekend as high pressure builds
across the Rockies. Another low pressure system will bring a chance
of rain to the region midweek.

&&

.DISCUSSION...
A north-south oriented cold front was located over western Maricopa
County as of this writing with a narrow band of intense rainfall.
While there is CAPE, the updrafts have been relatively shallow and
thus there has been little to no lightning. But, with the strong
environmental winds and convective mixing, cannot rule out brief
severe level gusts. There is an outside possibility of a brief and
weak non-supercell tornado embedded within the line at any point.
Meanwhile, rainfall rates have exceeded half an inch in 30 minutes.
Stream gauges and law enforcement have reported flash flooding in
various locations spanning eastern Riverside, Imperial, La Paz,
Yuma, and Maricopa Counties since late yesterday afternoon. In
addition to the frontal zone lift, there is ongoing rainfall west of
there due to QG forcing associated with PVA and jet energy rounding
the bottom of the trough. Very strong southerly winds have
accompanied the approach of the front with peak gusts of 40-50 knots
over the metro area. Behind the front, winds have been much weaker.

Scattered showers have developed ahead of the front over northeast
Maricopa (including metro Phoenix) with amounts generally under one
tenth of an inch so far. With the passage of the front and the QG
forcing, there will be much more to come this morning.
Anticipate the front to reach Sky Harbor by about 4 am. Including
the main batch of follow-on showers behind the more intense band,
much of the precip for metro Phoenix should be over by roughly 9 am.
Most of the precip over our higher terrain zones east of Phoenix
will finish a few hours later. However, CAMs indicate some isolated
instability showers in the afternoon (including metro Phoenix).
Including precip since midnight, anticipate another 0.5 - 1.0 inch
for much of metro Phoenix and even 1 - 1.5 in some spots. Anticipate
there will be ongoing runoff after the precip is over - especially
over the higher terrain. Thus have kept the Flash Flood Watch (FFA)
going until 5 pm. For southwest Arizona, the precip should be coming
to an end by the time the Watch expires (5 am) and locations that
have already had flooding will should start to recede. Thus, have
not extended the FFA for that area. For the Winter Storm Warnings,
will allow the Joshua Tree National Park portion to expire at 5 am
MST. For our other area (mainly southern Gila County above 4500ft),
snow levels will continue to fall through the morning and afternoon.
Storm total snow amounts will vary from 1-5 inches between 4500-5500
ft and 5-12 inches above 5500 ft (not a lot of territory above that
elevation within our forecast area).

In the wake of the low pressure system, a ridge will migrate
eastward across the Desert Southwest Saturday and amplify across the
Rockies Sunday. GEFS indicates mid-level heights will remain above
average through early next week, which will translate into above
normal temperatures Monday and Tuesday. There is increasing
likelihood another trough will impact the region during the midweek
period. Both the GEFS and ECMWF-E suggest the potential for another
0.5-1.0 inch of rain. However, thicknesses point to a warm system
with above normal snow levels.

&&

.AVIATION...Updated at 1251Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

The very strong southerly winds that were occurring earlier this
morning have switched to westerly and diminished as the sfc cold
front has moved across the greater PHX area. Westerly winds are
expected to continue into the evening hours with some afternoon
gustiness likely. The moderate-heavy rain and MVFR CIGS that are now
occurring at all of the PHX area terminals will likely continue
until mid-morning, with this rain diminishing and CIGS gradually
improving during the late morning/afternoon hours. Skies are then
expected to clear overnight will more typical diurnal easterly
drainage winds returning. There is an outside chance for some patch
fog early Saturday morning, but confidence is too low at this point
to include fog in the TAFs at this time.

Southeast California/Southwest Arizona including KIPL and KBLH:

Gradual clearing is expected today at both KIPL and KBLH as the
weather system that brought the rain to the region moves off to the
east. Westerly winds to continue at both TAF sites today with some
afternoon gustiness, with these winds diminishing overnight. There
is an outside chance for some patch fog early Saturday morning, but
confidence is too low at this point to include fog in the TAFs at
this time.

&&

.FIRE WEATHER...
Saturday through Wednesday: Below normal temperatures Saturday will
warm to near normal by Monday under slow drying conditions and light
winds. Moisture levels should remain fairly elevated through early
next week with minimum RH values mostly above 35 percent. The next
low pressure system then looks to approach from the west late
Tuesday into Wednesday bringing increased moisture, rain chances,
and breezy conditions later Wednesday

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flash Flood Watch through this afternoon for AZZ534-537>563.

     Wind Advisory until 4 AM MST early this morning for AZZ534-
537>544-546-548>551-553>555-559.

     Wind Advisory until 9 AM MST this morning for AZZ545-547-552-
556>558-560>563.

     Winter Storm Warning until midnight MST tonight for AZZ557-558-
    563.

     Flash Flood Watch until 5 AM MST early this morning for
AZZ530>533-535-536.

CA...Flash Flood Watch until 4 AM PST early this morning for CAZ569.

     Winter Storm Warning until 4 AM PST early this morning for
CAZ560.

     Wind Advisory until 3 PM PST this afternoon for CAZ560.

&&

DISCUSSION...AJ/Hirsch
AVIATION...Percha
FIRE WEATHER...Kuhlman

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
513 AM MST FRI NOV 29 2019

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

0400 AM     TSTM WND GST     5 SE DEER VALLEY        33.63N 112.05W
11/29/2019  E50 MPH          MARICOPA           AZ   TRAINED SPOTTER

            HEAVY RAINFALL AS WELL.

&&

MP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE PHOENIX AZ
529 AM MST FRI NOV 29 2019

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

0400 AM     TSTM WND DMG     5 SSE DEER VALLEY       33.61N 112.08W
11/29/2019                   MARICOPA           AZ   BROADCAST MEDIA

            SEVERAL TREES DOWN ALONG THUNDERBIRD RD
            BETWEEN 7TH AVE AND 3RD ST.

&&

MP

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