textproduct: NWS Phoenix

UPDATE

06Z Aviation Discussion.

KEY MESSAGES

- A slow moving weather system through early next week will bring much cooler temperatures, breezy to locally windy conditions, and late Monday and early Tuesday rain chances.

- Weak high pressure will eventually settle back into the region during the middle of next week leading to warmer and drier conditions.

SHORT TERM /TODAY THROUGH SUNDAY/

shows another large troughing feature in the Eastern Pacific with the core just off the coast of northern California. This trough is expected to move inland late this evening and into Sunday morning. However, before this system moves inland dry air will filter back into our region behind a separate, weaker system that impacted the region early this morning, which brought virga and areas of sprinkles across portions of Maricopa County. With drier air entering the region, today will be clear skies with afternoon highs in the mid to upper 80s in the lower desert areas.

As mentioned previously a second upper level trough is currently off the northern California coast. As this system moves inland over the weekend, tightening in the pressure gradient will help develop widespread breezy to windy conditions, especially Sunday afternoon/evening. Winds will be under wind advisory levels with wind gusts between 20-30 mph for most of the region, while across southeast California gusts between 30-40 mph will be common. Otherwise, moisture will begin to be reintroduced into the region from the SW on Sunday as the system progresses. This will lead to steadily increasing cloud coverage throughout the day, and cooling temperatures. Sunday's afternoon temperatures will be mostly in the lower 80s across western Arizona and into the upper 70s across much of eastern California.

LONG TERM /MONDAY THROUGH FRIDAY/

Guidance continues to show the late weekend disturbance over the Great Basin merging with a third shortwave quickly diving down the back side of the large scale trough on Monday. The exact track and timing of this last shortwave feature is still a bit uncertain, but for now it is favored to move through central and northern Arizona Monday evening with lingering troughing lasting through the first part of Tuesday. As with the other disturbances, the lack of good moisture will be an inhibiting factor for rain chances. Models do show an increase in moisture in the mid- levels on Monday, but it is likely to be quite marginal with forecast mixing ratios only in a 4-6 g/kg range. Considerable dry air is forecast above and below this 750-650mb moisture layer, so any showers that do develop are not expected to produce much if any rainfall. The latest NBM PoPs are largely unchanged from yesterday's runs with evening/early overnight 10-15% chances for the south-central Arizona lower deserts to 20-30% over the high terrain northeast of Phoenix.

Monday will also be another breezy to windy day with widespread gusts of 20-30 mph to as high as 30-40 mph across portions of southeast California and over the Arizona high terrain. Temperatures should bottom on Monday with lower desert highs mostly in the upper 70s, or 5-8 degrees below normal. Overnight lows Monday night may also dip into the 40s for some locations, but lingering elevated winds and cloud cover may keep most spots from dipping below the low to mid 50s.

Once the shortwave trough exits to the east Tuesday morning, drier air will surge into the area starting Tuesday afternoon. Other than a lingering 10-15% chance of a light shower across far eastern Arizona Tuesday morning, sunny skies and pleasant weather conditions are expected across the area. Quiet weather with near normal temperatures are then favored for the latter half of next week under a zonal to broad troughing upper level pattern.

AVIATION

Updated at 0540Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns over the next 24 hrs will be another period of gusty winds Sunday afternoon and evening. Until then, winds will tend to follow their typical diurnal tendencies with an E-SE shift anticipated overnight followed by a switch back to westerly around 17Z-18Z Sunday. Speeds will diminish to aob 8 kts overnight, but will increase to around 10-12 kts with gusts up to 20-25 kts by Sunday afternoon. High clouds will increase in coverage through the forecast period.

Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation concerns at both TAF sites will be gusty winds, especially Sunday afternoon and evening. Winds will remain westerly at KIPL and south to southwesterly at KBLH through the TAF period, although periods of calm and vrb will be possible at KBLH early Sunday morning. Increasing winds with gusts up to 20-30 kts will become common at both terminals by Sunday afternoon and persist well into the evening. FEW-SCT high clouds will continue to be common through the period.

FIRE WEATHER

A more unsettled weather pattern throughout this weekend through early next week will result in near to below normal temperatures and slightly improved humidities. MinRHs this weekend will mostly average 15-25%, while overnight recoveries improve into a fair to good range (40-70%). Winds will somewhat follow diurnal patterns, but with more of a predominant southwesterly direction as winds increase areawide. Expect late afternoon/early evening enhanced gusts of 25-35 mph over much of the area today through Monday, with peak winds expected on Sunday. A disturbance is then expected to move through the region late Monday into Tuesday bringing the potential for light showers focused mostly over the Arizona high terrain. Weak high pressure will then settle back over the region during the latter half of next week leading to drier conditions and temperatures at or just above normal.

PSR WATCHES/WARNINGS/ADVISORIES

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