Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 301151

Area Forecast Discussion
National Weather Service Phoenix AZ
451 AM MST Thu Nov 30 2023

.Update...Updated Aviation

An unsettled weather pattern will persist across the region over
the next couple days allowing another weather disturbance to move
through later today into early Friday. As a result, widespread
showers and a few isolated thunderstorms are expected to impact
south-central and eastern Arizona from as early as this evening
through early Friday morning. Much cooler temperatures will also
be seen over the area starting today with readings failing to
reach normals through at least Saturday. Starting Sunday and
through at least the first half of next week, high pressure will
build over the region leading to a strong warming trend and
above normal temperatures by next Tuesday.


The first of two weather systems is currently moving through the
region, but limited moisture has kept any measurable
precipitation confined to the Arizona high country. This compact
shortwave trough is providing a good deal of dynamics for
precipitation development due to its shift toward a negative tilt,
but it was an overall miss for our area as it`s already beginning
to move into western New Mexico.

The weather pattern over the Southwestern U.S. will stay primed
for more precipitation chances already by this evening as a second
shortwave trough is quickly diving southeastward just off the
California coast. The latest model runs continue with the recent
optimistic rain chances for our area with guidance increasing
moisture further with forecast PWATs now peaking around 0.75", or
near 200% of normal late this evening. Modest low level
southwesterly upslope flow will combine with a fairly strong PV
anomaly moving through the area tonight, and these forcing
mechanisms will be enough for shower development later today
initially just west of the Phoenix area. The 00Z HREF and the
latest HRRR show widespread shower development, and likely even
some isolated thunderstorms, during the latter half of the evening
through the overnight hours focused over south-central Arizona.
Given the very weak instability of 100-200 J/kg of CAPE, any
thunderstorms are likely to be weak, but we can`t rule out one or
two storms that last long enough to provide some brief gusty winds
due to the forecast 30-45 kts of 0-6km Bulk Shear. Forecast
rainfall amounts have risen slightly from what we were seeing
yesterday with around 0.25" on average in the Phoenix area to
upwards of around 0.5" across the higher terrain east of Phoenix.

As the forcing begins to wain after sunrise Friday, the shower
activity should mostly move east of Phoenix with some isolated to
scattered showers persisting into afternoon hours over the
eastern Arizona high terrain. The potential for any snow or mixed
precipitation tonight into Friday is not a big concern for our
area given snow levels stay at around 6000-6500 feet.

Temperatures will continue to drop off over the next couple days
with highs only in the low to mid 60s on Friday under gradual
clearing skies. Chilly overnight temperatures will also settle
into the area starting Friday night with readings dipping well
into the 40s areawide to as cold as the mid 30s for the rural
lower desert valley locations. As drier air continues to filter
into the region this weekend, the coldest night is likely to be
Saturday night with lows in the mid 30s to low 40s. There is also
some potential for localized freezing temperatures Sunday morning
for locations like Globe and San Carlos, and portions of La Paz

By Sunday, a strong ridge building to our west is expected to
begin to move into our region. As this occurs through early next
week, H5 heights are likely to rise to near 580dm which will
provide for a significant warming trend. The latest NBM forecast
temperatures show highs reaching normal on Monday and then easily
into the mid 70s Tuesday, before peaking in the mid to upper 70s
next Wednesday. Ensemble guidance heavily favors this strong ridge
impacting our region for the majority of next week with only a
gradual cooling trend likely late next week into the following


.AVIATION...Updated at 1150Z.

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

Rainfall along with low ceilings tonight through tomorrow morning
will be the main aviation concerns during the forecast period. VFR
conditions are anticipated through the early evening hours with
winds following a typical diurnal pattern. Showers will start to
move over the metro area starting as early as 03Z, with the
heaviest rain likely occurring between 05-09Z. The majority of
shower will likely be east of the area by 09Z, but a few
lingering showers are possible (20-30%) through the remainder of
the period. As the precipitation pushes closer towards metro
terminals, ceilings will be on the decline, potentially (30-50%)
reaching MVFR levels as early as 05-06Z. MVFR conditions will
continue to be possible through the remainder of the period, but
cloud bases will begin to slowly rise after 12Z.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation concerns are expected during the forecast period.
Winds at IPL will be out of the W through the period, with some
occasional gusts upwards of 20 kts during the afternoon. At BLH,
winds will contain a more SW`rly component with some isolated
afternoon gusts there as well. Mid and upper level clouds will be
present this morning before a FEW cumulus develop across the
region this afternoon with the lowest bases around 5-7 kft.


Unsettled weather conditions will be seen through Friday as
a weather disturbance moves through the region. Moisture will
increase today, especially across southern Arizona before
widespread showers and isolated thunderstorms become likely this
evening across south-central Arizona and then over eastern Arizona
tonight. Wetting rain chances are now very good (70-80%) across
the eastern districts tonight. For Friday, rain chances will
linger mainly over the eastern Arizona high terrain. MinRHs above
35-40% are expected today and Friday, while temperatures fall to
below normal. Winds through the event will remain fairly light,
but some daytime breeziness with gusts to around 20 mph can be
expected today. By late in the weekend into the first half of
next week, high pressure and drying conditions will take over
leading to a return of above normal temperatures by around Monday
and MinRHs dropping to between 20-30% as early as Sunday.




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