textproduct: NWS Phoenix

KEY MESSAGES

- Elevated flows will continue on the Salt and Gila rivers through at least early next 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 next week.

SHORT TERM /TODAY THROUGH MONDAY/

Current 500 mb RAP analysis places the center of an upper low over Sonora early this afternoon, with notable height packing along its western periphery, resulting in a northerly jet streak stretching from over the Lower CO River southward over the northern Baja. To the north of this upper low, midlevel ridging is apparent stretching from off the CA Coast inland over the Great Basin, allowing positive H5 height anomalies to nudge into the forecast area this weekend as the upper low departs to the south. Higher momentum air began to mix down to the surface this morning for portions of the western deserts, along the Lower CO River Valley, resulting in breezy north winds with gusts upwards of 20-30 mph observed and locally as much as 35 mph. Further east across South-Central AZ, winds are generally lighter at the surface and more so driven by a northeasterly SLP gradient which has developed as a result of this pattern, with relatively high surface pressure established over the Colorado Plateau (11.72 mb gradient observed between Snowflake and KPHX at 12Z this morning). Gradients will relax through the rest of the weekend but are expected to persist into early next week such that wind directions across the forecast area continue to favor northeast.

Rising midlevel heights and a rather quick response in thermal profiles will result in warmer temperatures over the weekend into early next week. Ensemble mean H5 heights will reach a 581-585 dam range, between the 55th and 80th percentile of climatology for this time of year. Despite the positive midlevel height anomalies and warming midlevel thermal profiles, ensemble mean 850-700 mb temperatures will still remain generally in a 30th-60th percentile of climatology range (850 mb temperatures between 12C-16C). However, downslope flow off the Colorado Plateau and some adiabatic compression will ensure surface temperatures remain seasonably warm, with latest NBM highs today through Monday in the lower to middle 80s across the lower deserts (warmer out west), between 2F-5F above daily normals.

LONG TERM /TUESDAY through FRIDAY/

Hemispheric pattern amplification driven by an unusually early season sudden stratospheric warming (SSW) event will be the main story for the latter half of next week with large ensemble forecast spread persisting. For much of the week, northern stream jet energy will settle over southern Canada while weak low amplitude waves in the southern stream remain sequestered over northern Mexico. As a result, subsident ridging with nearly steady midtropospheric heights will define the pattern over the SW Conus yielding high confidence of a very tranquil, near persistence forecast carrying on from early in the week. By the end of the week, effects from disruption of the polar vortex will be manifested in poleward retrogressive ridging while deep negative height anomalies descending equatorward over the NE Conus and East Pacific. However, the specifics regarding depth, positioning, and evolution of features within the greater synoptic pattern remain highly uncertain. Recent operational models peel a notable shortwave from the east Pacific trough towards the SW Conus/northern Mexico late in the week, however this type of solution is not consistent among NAEFS and EPS members. Given the amplification phase, wide ensemble spread and large run-to-run variations are likely the next several days resulting in low forecast confidence for next weekend.

AVIATION

Updated at 1710Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns under mostly clear skies can be expected throughout the TAF period. Easterly winds will speeds generally aob 10 kts will prevail throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns under clear skies can be expected throughout the TAF period. Winds will generally fluctuate out of a north to northwest direction with speeds generally under 12 kts.

FIRE WEATHER

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