textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion.

KEY MESSAGES

- A weather system will swing through the region today and tonight bringing more breezy to locally windy conditions as well as chances for light showers focused over the Arizona high terrain.

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

SHORT TERM /TODAY THROUGH TUESDAY/

Current objective analysis shows a large scale trough encompassing the majority of the Western U.S., while two pieces of PV energy are in the process of combining over California. Water vapor imagery continues to show abundant upper level moisture over the Desert Southwest, but also a swath of dry air moving into our region from the west. As we dry out in the upper levels today, the consolidate shortwave trough will finally move into our region from the west beginning this afternoon. Guidance does indicate some modest mid-level moisture advecting in just ahead of the shortwave focusing just ahead and along a weak cold front forecast to move through this evening.

Winds will again become quite breezy by this afternoon, but gusts should mostly reach between 20-30 mph. As the cold front and main PV center sweeps eastward across the region this evening through early tonight, Hi-Res CAMs suggest some isolated showers are likely to develop. These showers will be fighting against a dry boundary layer, so the bulk of lower desert locations will at most see a trace while the Arizona higher terrain may see a few hundredths to up to a tenth of an inch in a few spots. As the disturbance continues to weaken and lifts to the northeast on Tuesday, a few light showers may still be possible during the morning hours over far eastern Arizona.

Temperatures today are expected to be quite mild with highs only reaching into the mid to upper 70s across southeast California to the upper 70s to around 80 degrees in the Phoenix area. After the cold front moves through this evening, overnight temperatures should dip well into the 50s for the Phoenix metro to as cool as the mid 40s across the western deserts where skies are likely to become clear by late evening. Tuesday's weather should be the pick of the week as the cool air mass remains in place keeping highs mostly in the upper 70s under sunny skies and fairly light winds.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Shortwave ridging will briefly move through the region on Wednesday leading to another quiet day while temperatures warm back into the mid 80s for most lower desert locations. A robust Pacific low pressure system will also move through the Pacific Northwest on Wednesday on its way to the Great Basin by Thursday. Ensembles continue to favor a more northern track with this low across the Great Basin and into the Central Rockies while also weakening. The base of the trough may clip Arizona, but all indications so far keep any system energy and moisture well to our north. However, the fairly close proximity of the system should be enough to bring more breezy to locally windy conditions on Thursday and/or Friday while also leading to a slight dip in temperatures likely for Friday.

Looking ahead for next weekend a more significant ridge is expected to move over the Western U.S. with the NBM suggesting a return of highs back into the 90s by Sunday. Fortunately, this warm up may be fairly brief as guidance mostly favors another trough moving in from the west northwest at some point during the first half of next week.

AVIATION

Updated at 1120Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concern for the next 24 hrs will be a prolonged periods of gusty winds this afternoon and evening. Until then, light easterly flow this morning is expected to quickly transition back out of the W-SW by 15Z-17Z. Speeds will gradually increase throughout the early afternoon with gusts reaching 20-25 kts. A period of higher gusts up to 25-30 kts will also be possible after sunset this evening as a frontal boundary passes through the area. Mid-lvl cloud cover will be abundant through the period with bases as low as 8-10 kft. Virga and a few sprinkles will be possible early this morning, with another round of very light showers possible this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation concerns at both TAF sites will be gusty winds, this afternoon and evening. Winds will remain westerly at KIPL and south to southwesterly at KBLH through the TAF period. Gusts up to 20 kts will continue this morning at KIPL, and remain generally aob 12 kts at KBLH. By mid-afternoon, gusts up to 20-30 kts will become common at both terminals. SCT-BKN high clouds will diminish by sunrise, however a cu field is expected to develop this afternoon with bases around 7-8 kft.

FIRE WEATHER

A weather system will pass through the region later today through tonight with chances for mostly high terrain showers, but CWR will be less than 10%. Today will again be quite breezy with afternoon and evening wind gusts between 20-30 mph over much of the area. MinRHs today will rise to 25-30% before lowering to 15-25% Tuesday and 10-15% starting Wednesday as dry air fully encompasses the region. Overall light winds are forecast for Tuesday and Wednesday while temperatures warm back into the normal range by Wednesday. Dry conditions will prevail through the rest of the week, but a passing weather system on Thursday and Friday should bring another round of breezy to windy conditions. The low humidities and the increased winds late week may bring a period of elevated fire weather conditions.

PSR WATCHES/WARNINGS/ADVISORIES

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