textproduct: NWS Phoenix

UPDATE...Updated 12z Aviation Discussion

KEY MESSAGES

- Dry and tranquil weather conditions with well-above normal temperatures will continue to prevail across the region into early next week.

- An unsettled weather pattern is expected mid and late next week with increased rain chances and cooler temperatures.

SHORT TERM /TODAY THROUGH MONDAY/

An upper-level ridge currently situated just west of the Baja Peninsula will continue to influence the weather pattern across the Desert Southwest heading into early next week as it slowly migrates eastward. As it has been the case for the past several days, the ridge will continue to promote dry and tranquil weather with unseasonably warm temperatures of around 10-15 degrees above normal. Afternoon high temperatures today will be slightly cooler compared to yesterday, topping out in the mid to upper 70s across the lower deserts. For Sunday and Monday, temperatures will be slightly warmer, in the upper 70s to around 80 degrees across the lower deserts. Daily record highs are likely to be tied/broken both Sunday and Monday at Phoenix Sky Harbor, with the latest NBM showing a greater than 70% chance of occurrence.

LONG TERM /TUESDAY THROUGH FRIDAY/

Tuesday is likely to be a transition day of what is expected to become an unsettled weather pattern heading towards the Christmas Holiday period. The ridge of high pressure is expected to migrate into Texas while a deep trough develops off the west coast. Afternoon high temperatures on Tuesday will continue to remain unseasonably warm as afternoon high top out in the mid to upper 70s across the lower deserts.

Ensembles show moisture increasing quite rapidly between late Tuesday through Wednesday with both the EPS and GEFS showing PWATs reaching 200-300% of normal. Models show a weak subtropical shortwave moving Arizona Tuesday evening into early Wednesday and may spark some light isolated showers. A stronger shortwave out ahead of the main parent trough that will still be centered off the west coast will migrate from southwest to northeast towards the Great Basin. This shortwave in combination with the available moisture that will be in place will likely generate widespread shower activity later Wednesday into Thursday. There continues to be a good deal of uncertainty in the overall rain amounts as it will all be dependent on where this shortwave tracks with the upslope regions favored to receive the highest rainfall amounts at this time given that the forcing may be a bit too far to the northwest for the lower deserts to receive significant rainfall. However, if the shortwave does track a bit further east than currently projected, then the lower deserts will have a higher chance of receiving more significant rainfall.

After the aforementioned shortwave moves through, there may be a break in the rainfall activity before the main parent trough moves inland sometime late next week into next weekend and likely generates more shower activity. However, this part of the forecast is of high uncertainty given that both the deterministic and ensemble model guidance differ on the positioning, strength and timing of the trough as it migrates inland. Temperatures towards the latter half of next week will gradually cool down by about 5-10 degrees from the readings earlier in the week, but still remain above normal.

AVIATION

Updated at 1110Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns under periods of thicker cirrus cloud decks can be expected during the next 24 hours. Winds will remain light with only subtle diurnal directional shifts. Extended periods of variable to even calm conditions will be common.

FIRE WEATHER

High pressure across the region will continue to promote dry and tranquil weather as well as unseasonably warm temperatures, 10 to 15 degrees above normal, into early next week. Winds will generally be light under 15 mph. Afternoon MinRHs will range between 20-35% with good overnight recoveries of 40-70%. A transition to a more unsettled weather pattern with increasing rain chances and cooler temperatures is likely mid and late next week.

PSR WATCHES/WARNINGS/ADVISORIES

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