textproduct: NWS Phoenix

KEY MESSAGES

- Dry and tranquil conditions, along with near to slightly above normal temperatures, will continue for most of the region through at least the middle portion of the week.

- Low pressure and associated moisture will reintroduce rain chances for portions of Arizona over the next few days, but any rainfall activity for our forecast area will be focused primarily over foothill and high terrain areas through Wednesday.

- Isolated lower desert rainfall chances get introduced to the forecast during the latter portion of the week.

SHORT TERM /Today through Wednesday/

Current objective analysis reveals shortwave troughing over the Northern Plains, while a more potent upper-level low spins over California. The latter of these systems will be the main weather regime over the Desert Southwest during the front half of this week as it pushed intermediate low-amplitude ridging further eastward. However, the expectation is that the Pacific wave will weaken as it moves further inland, so no significant day-to-day conditions changes are in the forecast as dry and tranquil conditions will continue for the vast majority of the region. Even with modest height falls, temperatures will continue to run near to slightly above normal for this time of year, which translates to lower elevation highs hovering between 93-102 degrees.

The one exception to the dry and tranquil statement above during the front half of the week will be portions of Northern and Eastern Arizona thanks to increased moisture advection from the previously- mentioned Pacific low. Not only will decent moisture be in place over these areas with PWATs approaching 150-200% of normal, upper- level ascent from anti-cyclonic flow and an upper-level jet streak will provide and added layer of support for the development of shower and thunderstorm activity. With that being said, coverage over our forecast area will be minimal at best as atmospheric thermodynamic profiles will not be quite enough to provide lower desert rainfall. Rather, most, if not all, potential rainfall within our forecast boundaries will be confined to higher terrain areas.

LONG TERM /Thursday through Sunday/

By the latter half of the work week, the influence of the weakening southwestern low will all but disappear. The focus will then shift toward the interplay between large scale troughing over the eastern Pacific/West Coast, and the sub-tropical high over the Southern Plains and Northern Mexico. Global ensembles favor the retrograding back toward the Desert Southwest as we approach the weekend, likely staving off any advance, at least temporarily, of more anti-cyclonic waves. This progression 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, thankfully, 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 0530Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through the TAF period. Dry and tranquil conditions will persist with mid-high level cloud decks. Winds will predominately follow typical diurnal tendencies with speeds AOB 5-8 kts. However, expect periods of light and variable winds overnight into early Monday morning. Heading into late Monday morning and afternoon, a southerly (cross-runway for KPHX and KDVT) wind component is anticipated. Westerly wind shift is forecast to happen later than normal around 22-00Z late tomorrow afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather impacts are anticipated through the next 24 hrs under SCT to BKN high clouds. Winds will generally remain light (AOB 10 kts), favoring a south to southeasterly direction at KBLH for most of the period, shifting westerly tomorrow evening. A westerly direction at KIPL is forecast for the TAF period. However, confidence remains moderate to high for extended periods of light and variable wind conditions overnight into Monday morning.

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.