textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- A weather system arriving later today will bring rain chances tonight, breezy to windy conditions, and noticeably cooler temperatures.

- Another weather system clipping the area Wednesday will bring more windy conditions and precipitation chances over the Arizona high terrain.

- Yet another system Thursday into Friday will at least help keep temperatures cooler than normal through the end of the week.

SHORT TERM /TODAY THROUGH WEDNESDAY/

The main forecast concern over the next few days will be the strong gradient winds likely to impact much of the area. A deep occluding upper level low is currently centered off the coast of central California with a strengthening upper level jet within the base of the trough extending northeastward into the Great Basin. As the system nears the region, increasing southwesterly flow will help drive breezy to windy conditions starting this afternoon and last through much of tonight. The strongest winds today should be across southeast California this afternoon/early evening and then across south-central and eastern Arizona tonight out ahead of an advancing cold front. Advisory level winds with gusts to around 45 mph are expected across portions of southeast California into western Arizona this afternoon/early evening and then over the Arizona higher terrain tonight. Winds across south-central Arizona should stay below advisory level, but it would not be surprising to see a brief window of gusts at or just above 40 mph with the passage of the cold front tonight.

Dry air remains fairly entrenched across much of our region, but that will quickly change later today as moisture begins to advect in from the southwest as the system moves to the east. We can expect a period of strong moisture advection within the low and mid levels starting this afternoon out ahead of the advancing cold front. Forecast PWATs are shown to rise to around 200% of normal this evening into tonight before quickly decreasing on Tuesday after FROPA. CAMs show a band of precip moving onshore across southern California this afternoon, but the interior mountains are likely to break up most of the band as it attempts to move into southeast California this evening. Low and mid level moisture is expected to advect through the gaps in the mountains across Baja making its way into southern and central Arizona this evening.

As the cold front advances eastward into western Arizona by late evening, rain shower activity should again gradually fill in as the front advances eastward during the overnight hours. CAMs show the best coverage over the Arizona high terrain tonight, but they also suggest a somewhat broken line of showers should move across the south-central Arizona lower deserts. Forecast soundings for Phoenix show around a 6 hour window of near saturated conditions from around 3-12K feet along with some very minimal elevated CAPE. Rainfall amounts are still somewhat uncertain, but the lower deserts are not likely to see much more than a trace across southeast California and southwest Arizona to maybe 0.10-0.15" across the south-central Arizona lower deserts. Locations across north Phoenix into the foothills areas could see up to around 0.25" by sunrise Tuesday to as much as 0.30-0.75" over the higher terrain northeast and east of Phoenix. Dry air will quickly move in behind the cold front early Tuesday morning, ending the shower activity from west to east.

Tuesday should be an overall dry day with a good amount of sunshine, but the post-frontal air mass will be a bit chilly as highs will struggle to reach 70 degrees for most of the lower deserts. Another strong upper level wave is forecast to quickly dive southward just off the Pacific Northwest coast on Tuesday reaching northern California Tuesday night. This will help to keep a strong pressure gradient in place leading to another breezy to locally windy day on Tuesday, but below advisory level.

Models are in good agreement the next disturbance will weaken quickly as it approaches our region from the northwest Tuesday night before mostly moving across northern Arizona and southern Utah on Wednesday. A slug of moisture is expected to accompany the shortwave trough, but it will be considerably drier than tonight's system. The best precip chances on Wednesday will be over the Arizona high country where lowering snow levels will lead to more widespread accumulating snows. Portions of our area may see some shower activity on Wednesday with PoPs as high as 50-60% just to the north of Phoenix. Little additional rainfall is expected across the south- central Arizona lower deserts, including the Phoenix area.

Strong gradient winds Wednesday will also be a problem for much of the region with widespread near advisory or advisory level winds possible during the daytime hours. Additional Wind Advisories are expected to be issued for Wednesday. Temperatures will also become quite chilly with morning temperatures starting out in the 40s to the lower 50s as winds start gusting over 25 mph. I suggest wearing some warm clothing if going out and about Wednesday morning.

LONG TERM /THURSDAY THROUGH SUNDAY/

Late week will bring even colder temperatures into the region as the air mass behind the exiting Wednesday system will be fairly cold and it should persist with yet another shortwave trough potentially moving through or near our region late Thursday into Friday. NBM forecast highs Thursday have now dropped into the lower 60s for much of the lower deserts with morning lows Thursday and Friday morning well into the 40s to even some 30s for rural desert areas. Model uncertainty is still quite high for the potential Thursday night/Friday disturbance as the GEFS is much more bullish on any precip chances compared to the EPS. NBM guidance is still mostly on the drier side with PoPs only around 20% across the Phoenix area to upwards of 30-40% for the Arizona higher terrain. We are likely to have to wait another couple of days to have a better idea on what may happen with this late week system. Temperatures are expected to stay below normal through at least Friday before quickly warming late weekend into early next week.

AVIATION

Updated at 1725Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Gusty winds, lowered cigs, and potentially MVFR cigs/vsby with SHRA will all be weather issues through Tuesday morning. Winds should veer to south by early/mid afternoon with increasing gusts and a prolonged cross runway component, though uncertainty exist regarding how quickly gusts begin with the cloud cover as well as magnitude. Confidence is good that mid/high cigs rapidly lower this evening with decks falling below 060 AGL mid evening. Fropa with SHRA and further decaying flight conditions arrive after midnight with moderate confidence of brief periods of MVFR cigs/vsby in bands of SHRA. Winds gusts 30-40kt may also accompany fropa with direction veering to W/SW. Prior to sunrise, winds should weaken and cigs rise and scatter, however lingering moisture and prevailing SW flow may allow cigs to fall back below 060 again Tuesday late morning.

Southeast California/Southwest Arizona including KIPL and KBLH: Strong gusty winds late afternoon/evening will be the primary weather issue along and behind a passing cold front. Confidence is good that south winds will veer to SW late afternoon with gusts in excess of 30kt at times this evening. At the same time, cigs should lower closer to 5-7K ft AGL with a few SHRA passing through the area. Forecast uncertainty grows overnight as some gusts may persist under clearing skies, particularly at KIPL, though the tendency will be for wind speeds to gradually weaken Tuesday morning.

FIRE WEATHER

A series of weather systems will impact the region this week with the best rain chances tonight into early Tuesday across the eastern districts. Breezy to windy conditions are also expected through Wednesday with gusts across portions of southeast California and the Arizona high terrain exceeding 40 mph at times later today and again on Wednesday. A cold front tonight may also lead to sudden strong westerly wind gusts and there is a low chance for lightning with showers along the front (10%). MinRH values through much of this week will range between 25-40% across the lower deserts to 30-55% over higher terrain areas.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Wind Advisory from 2 PM this afternoon to 2 AM MST Tuesday for AZZ530-533.

Wind Advisory from 8 PM this evening to 11 AM MST Tuesday for AZZ557-558-563.

CA...Wind Advisory from 1 PM this afternoon to 1 AM PST Tuesday for CAZ560-561-564-568>570.

Wind Advisory from 1 PM this afternoon to 10 PM PST Wednesday for CAZ562.