textproduct: NWS Phoenix

UPDATE...Updated 18z Aviation Discussion

KEY MESSAGES

- Elevated flows will continue on the Salt and Gila rivers through at least the middle of the week due to 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/

Early morning WV imagery shows a compact, cyclonic circulation propagating south through Sonora while high pressure ridging builds into the SW Conus. In the northern stream, a progressive wave was breaking onshore over the Pacific NW/SW Canada aiding in the intensification and inland push of the aforementioned high pressure ridge to the south. This configuration will support large scale subsidence and surface pressure rises across the region while innocuous, low amplitude features settle over northern Mexico in the next 72 hours. The enhanced pressure gradient will support some gusty morning east winds across ridge tops and terrain gaps in south- central Arizona the next couple days. This is a very typical weather pattern for the season, and forecast wind speeds do not appear particularly unusual. Otherwise, H5 heights will hover in a 580- 585dm range which is slightly above average for early/mid November. Ensemble numerical spread remains quite narrow resulting in excellent confidence of high temperatures 2F-5F above normal with morning lows slightly more anomalous.

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 1700Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns under clear skies can be expected throughout the TAF period. Winds will generally remain out of the east 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 throughout the TAF period. At KIPL, winds will be light and variable through early this evening before shifting to a light westerly component during the late evening/overnight period. At KBLH, winds will generally fluctuate between a light northeasterly and northwesterly direction.

FIRE WEATHER

Dry conditions will prevail across the region through the majority of the week with some enhanced morning ridge top and terrain gap breeziness the next couple days. 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.