textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion

KEY MESSAGES

- Extreme Heat Warnings remain in effect for much of the area through 8pm tonight.

- Thunderstorm activity will remain limited to the Arizona high terrain and portions of Southeast Arizona through this weekend, with minimal activity today and Friday.

- Look for elevated, well above normal, MinTs this evening. These elevated MinTs will pose a risk for heat related illness. Those at greatest risk are infants and young children, adults over 65, people who are homeless, people who are overweight, people who overexert during work or exercise, and people who are physically ill or on certain medications.

SHORT TERM /TODAY THROUGH FRIDAY/

Current wv satellite imagery reveals a rather compact shortwave traversing the intermountain west and northern portions of the Great Basin, with the center of an anticyclone (now flattened by the shortwave to its north) still overhead and gradually sliding westward. With H5 heights aloft in a 594-597 dam range today, down from the broad area of 597-598 dam values observed yesterday, we can expect afternoon highs several degrees cooler than the record- breaking values we saw yesterday, though still well above normal for the time of year. The latest NBM continues to advertise lower desert highs in a 110-115F range, with better probabilities of seeing 115+F focused along the Lower Colorado River Valley and portions of Southeast CA. With temperatures remaining this hot, areas of Major HeatRisk still linger today across much of the area, and so Extreme Heat Warnings remain in effect through this evening. By Friday, the subtropical high will have migrated to the vicinity of the SoCal Coast, and so H5 heights will continue to fall, reaching a 592-595 dam range for the weekend. As such, expect afternoon highs to respond by falling into a 105-110 degree range Friday onward. Thermal profiles do not typically respond this quickly, though models have consistently depicted a surge of low level moisture spreading across South-Central AZ tonight, and with this moisture in place through much of the day Friday, temperatures will not respond as quickly to daytime heating as they would if it were drier.

The shortwave traversing the northern portions of the Great Basin today will act to increase winds aloft, bringing enhanced afternoon/evening breeziness to the region. Global guidance depicts a very subtle tightening of the pressure gradient at midlevels, with 700 mb flow increasing to 20-25 kts. Though this is not particularly impressive, deep mixing heights this time of year mean that this higher momentum air even in the midlevels can reach the surface, and so afternoon/early evening gusts to 25-30 mph will become quite common, with even higher gusts to 35 mph over the AZ high terrain. In combination with low humidity, anticipate locally elevated fire weather concerns due to this enhanced breeziness this afternoon into the evening.

Thunderstorm activity will be quite minimal over the state today and Friday. Subsidence from the proximity of the subtropical high will preclude the development of storms over much of the AZ high terrain today, and as the high slides westward over the SoCal coast Friday, there will be a a surge of low level moisture, but winds aloft shift out of the northwest, effectively drying out the midlevels. With this combination of factors, it is not surprising that the latest HREF reflectivity >40 dBZ paintball plot depicts very little development through Friday, except perhaps over the White Mountains and over southern Cochise County.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

The convective potential through the weekend will continue to be very limited as the upper-level flow pattern will remain unfavorable for any deep moisture influx. In fact, as the high settles over the southern CA coastline, the flow will turn out of the north, bringing drier air with PWATs dropping below one inch during the weekend. However, enough low-level moisture may still be present for some afternoon convection to materialize, mainly across the vicinity of the White Mountains and the southeastern third of AZ. Heading into next week, model guidance continues to show the high repositioning towards the Four Corners Region, especially by the middle of the week. This would result in a more favorable flow pattern for deeper moisture advection, with convective coverage on the increase across the higher terrain and foothills initially before chances increase across the lower deserts, more likely by the latter half of the week. Recent deterministic runs of the GFS and perhaps less apparent but present in the ECMWF suggest that an easterly wave may propagate through the forecast area Wednesday-Thursday, helping to increase moisture and act as a focus for convective initiation if the timing is right. The details are quite uncertain this far out, but the potential exists for some thunderstorm activity even further west spreading into Southwest AZ if this easterly wave comes to fruition.

Temperatures next week will moderate closer to mid-July normals as moisture gradually increases and H5 heights aloft fluctuate around 591 dam, near the climatological average for this time of year. As such, the latest NBM shows the upcoming workweek starting with continued lower desert highs in a 105-110 degree range, dropping into a 103-108 degree range by midweek.

AVIATION

Updated at 0505Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT: No major aviation concerns are expected during the TAF period under mostly clear skies. Winds will follow familiar diurnal patterns, with some occasional breeziness tonight and once again tomorrow afternoon. The usual E'rly shift at KPHX still appears uncertain, but if one were to occur, it will be relatively brief. Otherwise, W'rly winds will prevail through Friday evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected over the next 24 hours under mostly clear skies. Sustained winds at KBLH should remain relatively elevated through tomorrow afternoon evening, with a couple period of gusts, some occasionally occurring during the morning hours, and once again Friday afternoon. Weaker winds are anticipated at KIPL. Familiar diurnal patterns direction wise will prevail.

FIRE WEATHER

Above normal temperatures and dry conditions will persist through the weekend. Expect wind gusts between 20-25 mph into this evening across South Central Arizona. On Friday, gusts upwards of 20-25 mph will be mostly confined to the high terrain of the eastern districts. Afternoon minRHs will generally bottom out between 15-20% areawide Friday and Saturday. Tonight, periodic gulf surges will result in MaxRH values in excess of 50-70% for all zones except Joshua Tree National Park. Very minimal rain chances will exist through this weekend, with activity focused mainly across the eastern and southeastern third of AZ, with CWR <10%.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.