textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion

KEY MESSAGES

- Elevated flows will continue on the Salt and Gila rivers through at least the middle of the week due to upstream dam releases.

- Dry weather with occasional breeziness and temperatures near to slightly above the daily normals will be common through much of the week.

- Unsettled weather with increased chances of showers may return to the region over the weekend.

SHORT TERM /TODAY THROUGH TUESDAY/

Midlevel water vapor imagery depicts a compact cyclonic circulation continuing to meander over Northern Mexico, now gradually shifting eastward into Chihuahua early this afternoon underneath broad ridging to its north that stretches from the Southwest US and further inland into the Intermountain West. In between these features, dry, northeasterly flow aloft remains over AZ. Through at least the next few days, ensembles remain in excellent agreement that the overall pattern will be characterized by Pac NW troughing with strongly negative midlevel height anomalies sequestered offshore and broad downstream ridging. Relatively high surface pressure has already developed over the Four Corners region from this configuration, with latest WPC surface analysis indicating SLP values between 1025-1030 mb. The enhanced pressure gradient will support some gusty morning east/northeast winds across ridge tops and terrain gaps in south- central Arizona the next couple days.

The ridge will be dampened somewhat heading into midweek as a shortwave disturbance in the northern stream is advertised to eject eastward from the Pac NW offshore trough, however, this should result in little change in sensible weather conditions locally other than a period of passing high cirrus on Tuesday- Tuesday night. Fairly steady H5 heights aloft in a 580-585 dam range, near to slightly above average for this time of year, will allow for a continuation of seasonably warm conditions with temperatures around 2F-5F above daily normals. This translates to lower desert highs in the lower to middle 80s.

LONG TERM /Wednesday through Saturday/

An unusually early season sudden stratospheric warming (SSW) event will be the primary influence towards hemispheric pattern amplification this week featuring ridge retrogression poleward and deep negative height anomalies descending into the NE Conus and East Pacific. During the initial stages of this transition, strong subsident high pressure with nearly steady midtropospheric heights will be situated directly over Arizona yielding a high confidence forecast of a very tranquil, near persistence temperatures a couple degrees above normal. Late in the week, there is growing ensemble agreement that shortwave energy will detach from the larger East Pacific trough and progress towards the SW Conus/northern Mexico. However, significant spread persists regarding the timing of incoming negative height anomalies and jet energy that would influence regional weather. Given the evolution of this highly amplified and semi-blocked pattern, would generally prefer a solution towards the slower end of the ensemble envelope bringing heightened rainfall chances into the CWA Saturday/Sunday. Regardless, run-to-run variations are still likely the next several days with respect to details in timing and location of the best forcing resulting in limited forecast confidence.

AVIATION

Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns under clear skies can be expected throughout the TAF period. Outside of periods of VRB conditions, winds will generally favor an E'rly component throughout the period with speeds aob 10 kts.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns under clear skies can be expected during the next 24 hours. At KIPL, light westerly winds overnight into the morning will be flanked by periods of VRB conditions. At KBLH, winds will generally fluctuate between a light northeasterly and northwesterly directions.

FIRE WEATHER

Dry conditions and slightly above normal temperatures will prevail across the region through the majority of the week with periods of enhanced morning ridge top and terrain gap easterly breezes. Minimum afternoon humidity levels will primarily fall into a 20-30% range in western districts and 30-50% in eastern districts with a tendency for drying towards the middle/end of the week. This will follow fair to good overnight recovery in western districts and good to excellent levels in eastern districts. Outside of the early week breeziness, wind speeds will be light with directional tendencies towards a northerly or easterly component.

PSR WATCHES/WARNINGS/ADVISORIES

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