Brawley, California Weather Forecast Discussion

724
FXUS65 KPSR 190553
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
1053 PM MST Thu Sep 18 2025
.UPDATE...Updated 06Z Aviation Discussion.
&&
.KEY MESSAGES...
- Lingering shower and thunderstorm chances will persist Friday with
activity mostly focused on Arizona terrain features.
- Near normal temperatures over the next couple of days should warm
into an above normal range this early next week with moderate
HeatRisk returning across the lower desert communities.
&&
.SHORT TERM /Today through Friday/...
Early afternoon WV imagery clearly depicts the remnant tropical
circulation spinning west of San Diego with 2 distinct vorticity
centers pivoting about the eastern periphery of the gyre. The
leading shortwave was lifting inland with a notable wing of
vorticity extending well eastward into Arizona while sweeping north,
and largely responsible for the elevated showers and storms across
south-central Arizona this morning. A trailing vorticity maximum was
evident SW of San Diego and will follow a similar trajectory lifting
into SE California this afternoon providing strong ascent mechanisms
in a highly difluent upper air pattern within the preferred left
front jet quadrant.
This favorable dynamic setup is juxtaposed with very anomalous
atmospheric moisture content as an expansive reservoir of 13-15 g/kg
mixing ratios have surged into the lower Colorado River valley and
adjacent areas. Objective analysis suggests total column PWATs
around 2", or around the 99th percentile of climatology though drier
midlevels sampled in satellite imagery was already punching into the
western CWA and will effectively begin to lower total moisture
content. However, this evolution will also allow for better
insolation and daytime instability while maintaining copious
boundary layer moisture such that MLCape 1000-1500 J/kg with minimal
CinH should be realized this afternoon. While exact positioning and
coverage of storms still remains somewhat uncertain, latest HREF
neighborhood probabilities suggests upwards of 50-70% chance of
storms with locally heavy rainfall across the entire western CWA.
Given the boundary layer moisture content below the freezing level
combined with ample instability should result in very robust,
efficient rainfall rates. Ensemble probability matched means
indicate a 30-50% of 1" accumulations with the expectation of some
localized areas exceeding 2" totals this afternoon and evening.
Unfortunately, convective evolution this evening and overnight
towards the eastern half of the CWA remains highly uncertain further
removed from the stronger forcing and more pronounced moisture axis.
Conceivably, convective complexes propagating eastward could
intercept some form of an outflow boundary emanating from higher
terrain convection over south-central Arizona forming renewed
convection during the evening and overnight. However, recent HRRR
iterations have largely been downplaying this scenario lifting
western CWA convection northward with the mean flow aloft while only
creating a limited outflow boundary emanating from higher terrain.
Nevertheless with dynamic structuring still favorable and anomalous
moisture still present over the region, any small perturbation could
spark showers and storms through the overnight and morning hours.
By Friday afternoon, better vorticity advective forcing will have
shifted well north of the area while some measure of anti-cylonic
ridging and warming aloft spreads into the forecast area. While
certainly not optimal considering a lack of forced ascent, boundary
layer mixing ratios of 12-13 g/kg will still be present resulting in
minimal inhibition and MLCape likely approaching 1000 J/kg. Deep SW
flow over any terrain escarpment will certainly be capable of
sparking deep convection through the areal coverage and ability for
convective elements to survive beyond immediate terrain areas is
highly uncertain. There is somewhat better agreement that more
pronounced subsidence will finally spread into the region Friday
night bringing a marked decrease in rainfall chances.
&&
.LONG TERM /Saturday through Wednesday/...
Model uncertainty will continue over the weekend into early next
week as models are having a difficult time resolving what will
happen with a cut-off low that is likely to form off the California
coast Friday into Saturday. Yesterday`s model runs had mostly
dismissed this cut-off low as it called for it stay well to our
west, but the latest trends indicate it may get quite close to
southern California Sunday into Monday. We are still expecting our
region to largely be under the influence of the subtropical ridge
this weekend with overall dry conditions, but if the low does creep
close enough to our area we may see some moisture return Sunday into
Monday. The NBM shows 10-20% rain chances for later Sunday into
Monday, but this seems overly optimistic given the amount of
moisture that is likely to be available. We tend to believe the
ridge will win out keeping the cut-off low far enough to the west
resulting in the bulk of our area staying dry through at least early
next week.
Temperatures will be trending upward this weekend into early next
week as the ridge builds in from the south, but with the model
trends of keeping the cut-off low closer forecast highs are
noticeably lower than what we saw 24 hours ago. Highs are currently
expected top out at around 100 degrees this weekend before pushing
closer to 105 degrees by around next Tuesday. The upper end of
guidance does still show the potential for record highs for Phoenix
next Tuesday and Wednesday, but that will only happen if the cut-off
low stays far enough to our west.
&&
.AVIATION...Updated at 0553Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary weather concern during the TAF period is the ongoing
isolated shower and storm activity, how long it goes on through
the overnight, and any additional shower and storm activity
tomorrow evening. Isolated shower and storms will continue over
the next few hours, with most activity expected to end around 08Z.
However, it could linger longer into the overnight hours. Dry
conditions are then expected through the remainder of the TAF
period. However, some additional shower and storm activity is
possible tomorrow evening but confidence is too low to include in
the TAFs at this time. Winds will go southeasterly after this
outflow moves through and then stay southeasterly through the
early afternoon prior to the usual westerly shift around 19-21Z.
Models hint at another outflow from the southeast tomorrow night,
around 03-04Z, which will make the shift to southeast earlier
than usual. Wind gusts into the 20-25kt range are expected with
the outflow boundaries, otherwise wind speeds will be aob 10 kt.
SCT- BKN clouds will clear out through the overnight hours with
SCT mid-level clouds hanging on through the rest of the TAF
period.
Southeast California/Southwest Arizona including KIPL and KBLH:
Winds at KIPL will be light and variable through the TAF period.
At KBLH, current NE`rly winds will become light and variable
around 08Z and continue into tomorrow afternoon before going
southerly during the afternoon and then westerly in the evening.
Speeds will be aob 10 kt through the period. Skies are clearing
out but FEW clouds with bases aoa 8 kft remain in the area. FEW
clouds with bases aoa 8 kft are expected again tomorrow afternoon.
&&
.FIRE WEATHER...
Abundant moisture with a weather system residing across western
portions of the region today will help to bring fairly widespread
showers and thunderstorms. Best chances will be across southeast
California and southwest Arizona where a Flood Watch will be in
effect for much of today. Rain chances will continue into Friday,
but mainly across the Arizona higher terrain. Humidities will be
elevated over the next couple of days with MinRHs mostly between 30-
40% before gradually lowering closer to 20% by Sunday. Outside of
any storms, winds will remain light over the next few days with
directions mostly following diurnal trends. High pressure should
settle back into the region over the weekend and into early next
week resulting in a warming trend and overall dry conditions.
&&
$$
SHORT TERM...18
LONG TERM...Kuhlman
AVIATION...Berislavich
FIRE WEATHER...Kuhlman

NWS PSR Office Area Forecast Discussion