textproduct: NWS Phoenix

UPDATE

Updated 06Z Aviation Discussion.

KEY MESSAGES

- Temperatures will gradually warm through the weekend with lower desert highs reaching the upper 90s to near 100 degrees following comfortable morning readings.

- 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 Friday/

Early afternoon 500mb analysis reveals broad troughing continuing to sit over the Desert Southwest, while a more potent disturbance provides some late season snow to parts of Wyoming and Montana. Unlike our northern neighbors, the weak troughing over our forecast area lacks moisture and energy, so dry and tranquil conditions will continue through the end of the work week. The negative height anomalies associated with this pattern has helped keep temperatures at or below normal since the beginning of this week, and even though we have seen readings climb over the past few days, no significant warmup is expected so afternoon highs today and Friday will remain right around normal. Lower desert highs will range in the middle to upper 90s, while higher elevation locations will see values more in the 70s and 80s. No weather related travel impacts are anticipated if you are planning to start this Memorial Day Weekend a little early.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Over the weekend, low amplitude shortwave ridging will temporarily build into the SW Conus in response to deepening troughing entering the eastern Pacific. The full NAEFS suite continues to exhibit minimal spread in the H5 height pattern with a 582-585dm levels settling over the CWA. As such, confidence is very good that temperatures will warm several more degrees into a slightly above normal range, but certainly nothing particularly unusual for this time of year. Early next week, the ridge axis shifts east into New Mexico with a strong subtropical jet punching into northern Mexico. The resulting flow pattern will become deeply meridional allowing the import of marginally better moisture profiles, although likely no more than 5 g/kg within the boundary layer.

This type of transition season pattern is not uncommon for the SW Conus (especially during developing El Nino episodes - e.g. 2023 and 2015), however the intensity of this shortwave and associated subtropical jet are unusually strong. General pattern recognition continues to suggest robust jet forced ascent and cooling aloft surging into south-central Arizona early next week. Ensemble membership indicates some minor uncertainty in timing, intensity, and moisture availability, though the overwhelming preponderance of model output highlights Monday afternoon and evening as the most opportune time frame where deep mountain convection over the eastern CWA would be supported. Given the likely thermodynamic profiles, minimal actual rainfall may be common with this convection, but rather numerous dry lightning strikes and gusty outflow winds would be the more likely outcome. Should this evolution come to fruition, the greatest concern would be wildfire starts in remote high terrain areas. The passage of stronger troughing north of the forecast area midweek could help increase winds which could exacerbate fire weather issues, though larger ensemble spread yields lower forecast confidence during this time frame at the end of the forecast period.

AVIATION

Updated at 0505Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns will exist through the TAF period under mostly clear skies. Winds will generally follow their typical diurnal tendencies with speeds aob 10 kt.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected during the next 24 hours under mostly clear skies. At KIPL, current SW'rly winds will go SE around sunrise tomorrow morning with wind speeds staying aob 10 kt through the period. AT KBLH, current SW'rly winds will go southerly during the overnight period. Wind speeds will remain aob 10 kt through tomorrow morning with speeds increasing during the afternoon and evening hours, with some occasional gusts into the upper teens.

FIRE WEATHER

Temperatures will remain in a slightly above normal category through early next week with dry conditions over the majority of the districts. Minimum afternoon humidity levels will fall into a 5-15% range this week with a modest increase in moisture resulting in levels increasing closer to 10-20% over the weekend. This moisture increase along with an incoming weather disturbance may lead to a slight chance for afternoon/evening storms and lightning strikes over high terrain of eastern districts. Little to no rainfall would be expected with this activity resulting in a heightened threat for new wildfire starts, particularly Monday afternoon. Poor to fair overnight recovery of 20-40% will only improve slightly over the weekend. 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.

PSR WATCHES/WARNINGS/ADVISORIES

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