Forecast Discussion for PSR NWS Office
000
FXUS65 KPSR 270521
AFDPSR
Area Forecast Discussion
National Weather Service Phoenix AZ
1021 PM MST Tue May 26 2020
.UPDATE...
Updated Aviation section.
&&
.SYNOPSIS...
With strong high pressure building into the region, temperatures
will warm substantially the remainder of the week. Readings during
much of the latter half of the week will fall just short of record
levels and around 10 degrees above normal. Slightly cooler, but
still above average temperatures are likely early next week as an
area of low pressure slowly moves towards the west coast.
&&
.DISCUSSION...
Afternoon WV imagery and objective analysis depicts a strengthening
anti-cyclone across the Los Angeles basin as the flow pattern over
the eastern Pacific and southern Conus become increasingly blocked.
H5 heights currently near 588dm will intensify through the
remainder of the week as a result of negative height anomaly
comprising the western portion of the omega block growing in
magnitude and amplification. Multi-model forecast spread is quite
narrow the next couple days as this ridge and associated thermal
bubble slowly migrates inland towards the forecast area yielding
temperatures close to 10F above normal by Thursday afternoon.
By Friday, more pronounced high pressure ridging with H5 heights
near 594dm will become centered over eastern Arizona providing the
hottest weather of the year so far. While this type of height
anomaly is only 1-2 normalized standard deviations above normal,
NAEFS percentiles show these forecasts briefly eclipsing the 99th
percentile. Similarly, NAEFS H8-H7 thermal profiles suggest readings
above the 95th percentile Friday although only falling closer to the
90th percentile on surrounding days. Investigation of forecast BUFR
soundings reveals H8 temperatures peaking around 30C Friday/Saturday
during the climax of this heat event (rule of thumb is 850mb temps
30C=high temp of 110F in Phoenix).
The primary east Pacific circulation center will lift towards the
central California coast over the weekend breaking over the ridge
axis and nudging the high pressure center eastward into New Mexico
and west Texas. While height falls will be sufficient to cool the
western CWA several degrees, temperatures will continue to hover at
excessive heat thresholds through south-central Arizona. Warnings
may be extended through Sunday in the Phoenix metro should higher
height/thermal profiles persist, and mid/high level clouds and
moisture not become an influence.
As this aforementioned wave sweeps northwest of the area over the
weekend, the juxtaposition of a weak jet segment propagating into
Arizona and moisture leaking westward up the Rio Grande Valley will
result in the potential for deeper convection across higher terrain
areas of eastern Arizona. Well mixed 5 g/kg moisture profile along
with steep lapse rates would support some very limited instability
towards far eastern Gila County and isolated thunderstorm
development. Larger T/Td spreads would suggest very little rainfall,
but mostly just winds and lightning. Activity may be more modulated
by upper level support given the very modest instability, so its
difficult to determine the more favored day during the Fri-Sun time
frame.
Ensemble spread grows more significantly during the first part of
next week with shortwave energy filling back into a mean trough
position through the east Pacific basin. However, there is enough
evidence that height falls will be large enough to erode the
excessive heat with temperatures retreating closer to normal.
Whether this means a wave opening and lifting northwest of the
forecast area (dry and breezy outcome) or a more closed feature
meandering directly through the CWA (more unsettled/stormy outcome)
remains to be seen.
&&
.AVIATION...Updated at 0520Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A ridge of high pressure will keep winds aloft relatively light
and favor familiar diurnal surface wind patterns through
Wednesday evening. The southern end of a weather system passing to
the north will lead to somewhat stronger surface winds Wednesday
afternoon than what we had Tuesday with frequent gusts of
15-20kts. Otherwise, skies will be clear.
Southeast California/Southwest Arizona including KIPL and KBLH:
A ridge of high pressure will keep winds aloft relatively light
and favor familiar diurnal warm season surface wind patterns
through Wednesday. The southern end of a weather system passing to
the north will lead to somewhat stronger surface winds Wednesday
afternoon than what we had Tuesday with frequent gusts of
15-20kts (later onset for the Imperial Valley). Otherwise, skies
will be clear.
&&
.FIRE WEATHER...
Friday through Tuesday:
Much above normal temperatures late this week will only cool
slightly early next week with afternoon highs 5-10 degrees warmer
than average. Although the majority of the area will remain dry,
there is a slight chance of an isolated thunderstorm in eastern Gila
County Saturday afternoon albeit with little to no accompanying
rainfall. Minimum afternoon humidity levels will fall to around 10%
this week, then potentially closer to 15% next week. Overnight
recovery will mostly fall in a 20-35% range. Winds will be somewhat
more gusty Sunday and Monday, though well below critical thresholds.
Nevertheless, fire danger will remain heightened with the prolonged
period of very hot, dry weather.
&&
.CLIMATE...
Record highs this week:
Date Phoenix Yuma
---- ------- ----
May 27 111 in 1983 114 in 1951
May 28 113 in 1984 116 in 1983
May 29 112 in 1910 115 in 1984
May 30 114 in 1910 120 in 1910
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning from 10 AM Wednesday to 8 PM MST Saturday
for AZZ534-537>556-559>561.
Excessive Heat Warning from 10 AM Wednesday to 8 PM MST Friday
for AZZ530>533-535-536.
CA...Excessive Heat Warning from 10 AM Wednesday to 8 PM PDT Friday
for CAZ561>570.
&&
$$
DISCUSSION...MO
AVIATION...AJ
FIRE WEATHER...MO
CLIMATE...MO
NWS PSR Office Area Forecast Discussion
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