textproduct: NWS Phoenix

UPDATE...Updated 00z Aviation Discussion

KEY MESSAGES

- Temperatures will hover near to slightly above normal through early next before modest cooling arrives.

- Dry conditions will prevail through early next week with typical afternoon breeziness.

- A slight chance of thunderstorms will exist over the eastern Arizona high terrain early next week, albeit with limited rainfall potential.

SHORT TERM /TODAY THROUGH SUNDAY/

A split jet regime continues to evolve over the Eastern Pacific and onshore along the West Coast of North America. A broad area of midlevel anticyclonic flow offshore and cyclonic curvature over West-Central CONUS is evident in water vapor imagery and 500 mb RAP analysis early this afternoon. Within the broader flow, a few shortwaves are present, one embedded in the northern stream currently centered over South Dakota, and another, weaker disturbance associated with the subtropical jet sliding eastward over Baja California. As a result of this setup, primarily the weaker southern system near the Desert Southwest, the forecast area remains under negative height anomalies. However, clear skies and intense daytime insolation typical of late May are likely to result in near normal lower desert highs in the middle to upper 90s today, despite the negative height anomalies aloft.

Over the next 36-48 hours, negative height anomalies will shift into the Southern Plains, with a transient shortwave ridge building over the Southwest US over the weekend. Ensemble mean H5 heights are forecast to peak between 581-583 dam on Sunday, supporting warming temperatures over the weekend, with highs near 100F for some of the warmest spots across the lower deserts on Sunday. Otherwise, anticipate dry and tranquil conditions with only modest afternoon breeziness through the weekend.

LONG TERM /MONDAY THROUGH THURSDAY/

The first half of next week will be characterized by height falls over the SW Conus as strong troughing entering the Pacific NW and Great Basin combines with a weak shortwave and enhanced subtropical jet propagating across southern California/northwest Mexico. A brief period of deeply meridional flow should import marginally better moisture profiles into the eastern parts of the forecast area, however models continue to indicate no more than 5 g/kg within the boundary layer. The intensity of this shortwave and associated subtropical jet are unusually strong for this time of year, and pattern recognition suggests robust jet forced ascent and increased moisture interacting with the cooling aloft and steepening lapse rates over the higher terrain of eastern Arizona Monday afternoon. While instability will likely be limited, deep mountain convection should develop over parts of southern Gila County, though thermodynamic profiles indicate a substantial amount of evaporation which would favor dry lightning strikes and gusty outflow winds versus accumulating rainfall. Assuming this evolution come to fruition, the greatest concern would be wildfire starts in remote high terrain areas.

Forecast confidence deteriorates towards the middle of next week in response to a developing blocking pattern over the western hemisphere. Recent GFS and ECMWF operational iterations have sided more towards the majority of CMC ensemble members depicting a slow moving, closed circulation hovering over the Great Basin until the end of the week. However, GEFS members are surprisingly far more dispersive than their CMC counterparts with many members showing a far less intense and less cutoff negative height anomaly. Given the preference towards a blocking pattern, would favor the slower, more closed circulation outcome in this forecast which would be more apt to yield areas of stronger winds, albeit with more impactful speeds relegated to northern Arizona. That said, it would not be unexpected to see future automated NBM/WPC mandated forecasts advertise stronger wind gusts in the Wed-Thurs time frame once these ensemble blends converge on a similar pattern.

AVIATION

Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns under mostly clear skies can be expected throughout the TAF period. The overall wind pattern will follow the typical diurnal tendencies with speeds generally aob 10 kts, with some occasional afternoon gustiness in the mid to upper teens.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns under clear skies can be expected throughout the TAF period. At KIPL, winds will generally be out of the southeast, although a period of southwest winds may temporally materialize this evening. At KBLH, winds will generally be out of the south. Overall wind speeds will range between 5-12 kts, strongest during the afternoon and early evening hours.

FIRE WEATHER

Temperatures will remain in a slightly above normal category through early next week before slight cooling during the middle of the week. Minimum afternoon humidity levels will fall into a 10-20% range with poor to fair overnight recovery of 20-40% improving somewhat next week. A marginal increase in moisture early next week may lead to a slight chance for afternoon/evening storms and lightning strikes over high terrain of eastern districts. This would most likely occur Monday, and with little to no accumulating rainfall, the threat for new wildfire starts due to lightning strikes will be heightened. The typical afternoon spring upslope gustiness of 15-25 mph will be common through the period with the most pronounced gusts over eastern district high terrain and through the lower Colorado River valley during the middle of next week.

PSR WATCHES/WARNINGS/ADVISORIES

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