textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion

KEY MESSAGES

- A Flood Warning is in effect through at least early next week along the Gila River between Painted Rock Dam and Dateland, Arizona due to water released from the dam.

- Dry and tranquil weather with slightly above normal temperatures will continue through Thursday.

- A more unsettled pattern is expected starting Friday and lasting well into next week with occasional rain chances and cooler temperatures.

SHORT TERM /TODAY THROUGH THURSDAY/

High pressure remains in full control across the Southwestern U.S. with the dry air mass keeping skies clear. Forecast H5 heights across the Desert Southwest will stay between 582-585dm today before beginning to drop on Thursday as Pacific trough approaches the region from the west. Temperatures both days will barely budge from what has occurred the past several days with lower desert highs mostly between 82-85 degrees, or around five degrees above normal for mid November.

LONG TERM /FRIDAY THROUGH TUESDAY/

Model guidance continues to show a significant pattern change starting Thursday and eventually affecting our region by Friday, but a decent amount of spread and uncertainty remains with any rain potential for the first two shortwaves that will brush by our area. The leading shortwave is still slated to approach southern California by Friday morning, but the track should keep the best energy across northern Baja and Sonora Mexico. The system will at least advect a decent amount of moisture into the region later Thursday into Friday pushing PWATs to around 200% of normal by Friday afternoon. Lower level moisture will noticeably improve during this time, but mixing ratios will only top out at 6-7 g/kg.

There is at least some improved optimism for rain chances as models have mostly kept the track of the system not too far away on Friday with the weakening circulation moving along or just south of the Arizona/Mexico border. This track along with the modest moisture should at least allow for around a 12 hour period of rain chances from later Friday morning through mid to late evening Friday. The best focus for the expected shower activity (and maybe a weak thunderstorm or two) should be south of Phoenix earlier Friday before shifting east of Phoenix by the evening. Forecast PoPs have increased to include 25-40% chances in the Phoenix area to 50-70% over the high terrain northeast and east of Phoenix. Rainfall amounts with this first round of rain chances should only amount to a few hundredths for any the lower deserts to at maybe 0.10" in higher terrain areas.

A second follow-on shortwave trough is then shown to quickly move in from the northwest as early as sunrise Saturday morning, lasting through at least Saturday afternoon. The track of this next disturbance will at least bring rain chances to the northern half of Arizona with more doubt for the Arizona lower deserts. The latest NBM PoPs of 40-70% for Phoenix and 60-90% for the high terrain seem too optimistic, but have held off on making any adjustments at this time. Rainfall amounts for Saturday should at least be higher than the first round with forecast soundings pointing at a near saturated mid-level layer, but with a less favorable upslope west southwest wind component we'll have to mostly rely on system dynamics for forcing.

By Saturday evening, the shortwave is expected to push to our east quickly decreasing rain chances and likely ending them all together by around midnight. Sunday will bring brief shortwave ridging and some slight dry air advection from the northwest and this should lead to considerably less clouds and virtually no rain chances. Temperatures this weekend will easily fall into the 70s for highs with most lower deserts likely not surpassing 75 degrees both days.

The high amplitude unsettled weather pattern will continue into next week, but model uncertainty increases even more. Guidance suggests one after another northern Pacific waves will get ejected southeastward toward the U.S. West Coast with the next potential system reaching the California coast early Monday before reaching our region Monday night into Tuesday. This may even be followed by another system during the second half of next week. It is too early to have any good sense on the track of these systems as they could move directly through the Desert Southwest or mostly miss us to the north. NBM/WPC PoPs of 20-60% are still in the forecast for the Tuesday disturbance, but that could easily change depending on the eventual track. So far, any system that may move through is not expected to carry anything more than average moisture, so any rainfall amounts are likely to be on the lighter side. However, the expected northwestward trajectory of the weather systems next week should usher in even cooler temperatures with highs trending more toward the upper 60s to lower 70s during the middle part of the week.

AVIATION

Updated at 0540Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather concerns are expected through the TAF period. Current easterly winds will struggle to shift westerly this afternoon, likely becoming variable before settling back out of the east by tonight. However KIWA may be able to push a NW'rly flow this afternoon before also returning out of the east for the overnight period. Wind speeds will yet again be light, with speeds aob 6kts. The FEW passing high clouds will slowly move out of the region leaving clear skies in the later half of the period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather concerns are expected through the TAF period. Winds will favor a westerly component at KIPL, while KBLH will favor a more NW to NE direction. Wind speeds are expected to be aob 5 kts so periods of VRB can be expected at both terminals. Other wise clear skies will persist through the TAF period.

FIRE WEATHER

The dry conditions and above normal temperatures will persist through Thursday before chances for mostly light rain begin Friday. Minimum humidity values through Thursday will range between 20-30% for the lower deserts to 30-40% for higher terrain areas, while overnight recoveries stay good to excellent at 40-70%. Expect overall light winds, but also some marginally breezy conditions across ridge tops and terrain gaps of eastern districts during the morning hours. Winds will increase starting Friday, but gusts should mostly stay under 25 mph. Several passing weak weather disturbances will bring occasional showers and maybe an isolated thunderstorm Friday and Saturday and potentially again early next week.

HYDROLOGY

Lower Salt: Water releases above 1000 cfs continue from the Bartlett to Granite Reef Dams. Therefore, a Flood Warning remains in effect this morning between Granite Reef Dam and Tempe Town Lake with low-water crossings impacted.

Gila: A Flood Warning is in effect from Painted Rock Dam through the Dateland area through at least early next week due to water released from the dam. Water release levels are expected to increase during the next couple of days, peaking at 3000 cfs. These increased releases will have the potential to flood farm fields and low-water crossings along the river downstream from the dam.

PSR WATCHES/WARNINGS/ADVISORIES

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