textproduct: NWS Phoenix

UPDATE

Updated 06Z Aviation Discussion.

KEY MESSAGES

- Dry and tranquil conditions, along with near normal temperatures will continue through at least the middle of the week.

- Rain chances will return to portions of Arizona over the next few days, although focused primarily over foothill and high terrain areas.

- Lower desert rainfall chances will be heightened somewhat during the latter half of the week.

SHORT TERM /Today through Wednesday/

A seasonally strong trough was moving onshore in southern California early this afternoon with a jet streak translating downstream of the cold core forcing deamplification and lifting of the cyclonic circulation towards the Great Basin. However, jet forced ascent has combined with a narrow band of midlevel moisture to produce a small area of elevated convection along the lower Colorado River valley earlier today. This feature will continue to exit the forecast area by this evening although residual, elongated troughing will linger across southern California/Nevada. This will create a deeply meridional flow pattern over the next 72 hours capable of importing sheared vorticity centers from the south, as well as periodically better low level moisture profiles. H5 heights will remain nearly steady state in a 580-584dm range ensuring a continuation of near normal temperatures the next several days.

Both global and HREF modeling suggests a low amplitude vorticity center (likely convectively enhanced over northern Mexico) streaming into eastern Arizona Tuesday afternoon. Along with a small jet segment feeding into the right rear quadrant of the northern stream, ascent structure tapping marginally better moisture in SE Arizona will become very favorable for deep convective development over higher terrain locations. While lower elevations in the CWA will not initially have sufficient moisture for thunderstorm sustenance, gusty southeast outflow winds seem more likely, fostered by DCape values near 1500 J/kg allowing better boundary layer moisture to surge northwest through the forecast area. As a result, instability parameters will reach much higher levels Wednesday (i.e. MLCape 1000- 1500 J/kg), though stronger CinH and lack of a triggering mechanism may preclude more than isolated mountain storms as the region may fall under shortwave ridging and subsidence behind the Tuesday vorticity center exiting the region.

LONG TERM /Thursday through Sunday/

By the latter half of the week, the influence of the weakening southwestern low will all but disappear. The focus will shift toward the interplay between large scale troughing over the eastern Pacific/West Coast and the subtropical high over the Southern Plains and Northern Mexico. Global ensembles favor retrogression toward the Desert Southwest approaching the weekend. This evolution would not completely scour residual moisture immediately, so rain chances will likely linger into Thursday. Current PoPs show 30-50% chances for foothill and mountain areas and 10-30% probabilities for the South- Central Arizona deserts. Beyond that, persistent southwesterly flow would eventually dry us out enough to limit rain chances heading into the weekend. Another influx of moisture by the end of the seven day period may bring rain chances back once again, but max chances at this time only range between 20-30%. Even with the competing airmasses, regional temperatures will only fluctuate within a few degrees through the weekend. While the ridge keeps another shortwave from progressing toward the region, as mentioned previously, in return, the large scale troughing to our west will keep the high from becoming too amplified, preventing any further discussion of abnormal heat, at least during this forecast period. Temperatures for the lower deserts Thursday through Sunday will range generally between 94-106 degrees, while overnight lows hover near 70-82 degrees.

AVIATION

Updated at 0551Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Primary aviation impact will be the potential for VCSH/VCTS Tuesday evening and gusty outflow winds. W'rly winds are expected to continue for the next few hours, then shift back E'rly or become VRB by 10-11Z. Winds will favor a S/SE direction through the entire day with perhaps a brief period of W/SW winds in the evening, but confidence in a W/SW shift is low. Wind speeds will mostly stay below 10 kts. SHRA/TSRA activity is expected to develop Tuesday afternoon and evening, but should mostly stay south and east of the metro with a low chance (10%) to spread into the metro. Outflow winds should move into the metro from the S/SE with gusts up to 20-25 kts most likely and a low chance (5-10%) for 30+ kts. FEW to SCT clouds will be common through the TAF period with lowest bases around 8-10K ft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation impacts are anticipated through the next 24 hours with mostly clear skies. Winds will favor W/NW at both KIPL and KBLH, with wind speeds mostly staying below 10 kts and periods of light VRB.

FIRE WEATHER

Near to slightly above normal temperatures will prevail over the next several days, with minimal day-to-day fluctuations. Dry conditions with no chances for rain continue through today ahead returning high terrain rain chances for foothill and high terrain areas starting Tuesday. MinRHs between 15-30% will be common across the region, with even higher readings (35-50%) for the far eastern districts. MaxRHs will range from fair to good over the western and central districts, to good and excellent for the eastern districts into the weekend. Outside of some marginal breeziness caused by an approaching weather system, winds will follow familiar diurnal trends with typical terrain induced afternoon gusts around 15-25 mph.

PSR WATCHES/WARNINGS/ADVISORIES

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