Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/30/21
Area Forecast Discussion
National Weather Service Phoenix AZ
427 PM MST Tue Jun 29 2021
.UPDATE...Updated Aviation Discussion.
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.SYNOPSIS...
Scattered showers and thunderstorms will be common around the region
throughout the week as monsoon moisture steadily increases. Strong
winds and localized blowing dust will be the main impacts for most
lower desert communities. However, a transition to a heavier
rainfall threat may materialize during the latter half of the week,
particularly for wildfire burn areas. Temperature should hover
slightly below normal coincident with the moisture increase.
Thunderstorm activity may wane somewhat early next week while
temperatures increase as the monsoon pattern temporarily realigns.
&&
.DISCUSSION
Latest water vapor imagery and RAP streamline analysis clearly
trace out the flow around a well-defined inverted trough across
southern NM. This is resulting in stronger than normal northerly
winds across Arizona. Within this stronger mid-level speed max, a
complex of showers and thunderstorms developed this morning across
NW Arizona in an area characterized by steep mid-level lapse
rates and colder air aloft. Some of this activity drifted into
northern Maricopa County this afternoon, but subsequently fizzled
out.
Hi-Res CAMs including the HREF have struggled so far today and
generally failed to initialize the placement of the morning
convection. During situations like this, it is generally prudent
to rely more on the HRRR, which has captured the storms currently
along the Mogollon Rim. Latest ACARS from Phoenix indicates PWATs
have increased to near 1.2 inches. Combined with cooler air aloft,
this is yielding MLCAPE between 500 and 1000 J/kg. CIN is only
negligible, which will promote at least isolated thunderstorm
development later today, assuming an outflow boundary from the
aforementioned Rim convection reaches the Valley.
Did not deviate much from the NBM PoP for tonight, which
indicates a widespread 30 percent. Mesoanalysis indicates DCAPE
around 1500 J/kg and consequently, the strongest storms will be
capable of producing wind gusts to 50 mph, and areas of blowing
dust.
&&
.PREVIOUS DISCUSSION...
Outflows, Gulf surges, and the outer influences of Enrique should
begin a marked increase in total column moisture content Wednesday
with forecast soundings indicating 11-12 g/kg mixing ratios in the
lower levels. Still, a persistent dry northerly flow towards the top
of the boundary layer may continue to create a negative influence on
realizing full convective potential at lower elevations. The
moistening will also result in reduced lapse rates and lower overall
instability measures while the inhibition remains. Favorable ascent
will still be present juxtaposed with sufficient DCape to create
another day of multiple outflow boundaries. Given better moisture
profiles and modestly weaker inhibition, convection may be most
expansive Wednesday evening versus other days this week with a flood
threat added to the wind and dust threat. CAMs still do not present
a resounding indication or better confidence of more extensive
storms and forecast soundings don`t depict the telltale signs of
convective overturning suggesting more isold/sct coverage.
The Conus pattern will undergo an adjustment period towards the end
of the week with the strong northern ridging shifting eastward into
the northern plains. During this transition, the inverted trough
along the international border will eject into the East Pacific
while subtropical Gulf of Mexico ridging retrogrades into the
Southwest. The local flow pattern will gradually become more
subsident incorporating some drier westerly winds aloft early next
week. However, lingering moisture will allow terrain forced storms
to percolate most days though the trend will be towards less chance
of maintenance into lower deserts with time. Conceivably, there
could be a certain day with a better defined shortwave or jet streak
to enhance lift and allow storms to persist across a greater
majority of the CWA. Pinpointing any specific day this far in
advance is impossible and POPs mostly resolve back towards a
climatology type forecast by the end of the forecast period.
&&
.AVIATION...Updated at 2330Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
There are uncertainties regarding winds and thunderstorms the
next few hours. While westerly winds have become predominate at
all TAF sites, there is a northerly/northeasterly outflow boundary
moving towards the area. Timing the arrival and potential wind
strength is unclear but the most certain outcome of this boundary
is for a northeasterly wind switch at KSDL and KDVT within the
next hour or so. If speeds are weak, the boundary may wash out
over the metro and not impact any other sites, allowing the
westerly winds to continue. If the boundary is strong, between
15-25 kts, or is reinforced by new convection, expect the boundary
to propagate through all TAF sites between 01/02Z. For later this
evening, if convection forms due east, there could be additional
outflows from that direction. The chances for convection within
the general area is between 30-50% favoring the higher terrain
east of Phoenix, with lower chances (10-15%) for storms over any
given terminal. Easterly winds will prevail through the night with
a few hours of a westerly wind anticipated again tomorrow afternoon.
If trends for isolated convection today continue, conditions for
more widespread thunderstorms may become more ripe Wednesday
afternoon and evening.
Southeast California/Southwest Arizona including KIPL and KBLH:
Southerly to southeasterly winds are anticipated at both sites with
speeds primarily between 8-12 kts. However, there is a low chance
(10-15%) that distant convection could send outflows through the
area, either from the north and/or south, late tonight. Conditions
seem too dry for any storms in the area but occasional dense cloud
cover may pass overhead.
&&
.FIRE WEATHER...
Friday through Tuesday:
Thunderstorms with gusty, erratic winds and localized heavy rainfall
will be common over eastern districts through the weekend with lower
chances in western districts. On most afternoons, there will be at
least a 50% chance of storms with similar chances of wetting rains.
The threat for flash flooding on already burned area will also
exist. Moisture levels will peak during the middle and end of the
week with minimum afternoon humidity values mostly in a 20-40% range
and good overnight recovery in a 30-60% range. Somewhat drier
conditions will return early next week with storm chances lowering,
albeit still present each afternoon over higher terrain of eastern
districts. Aside from the influence of thunderstorms, winds will
follow the typical upslope/drainage diurnal trends.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...MO
AVIATION...AD
FIRE WEATHER...MO/Hirsch