textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion.

KEY MESSAGES

- Temperatures today will again be around records, especially for Phoenix as highs top out at or just over 90 degrees.

- A series of dry weather systems will influence the region during the remainder of the week leading to periods of breezy conditions and cooler but still above normal temperatures.

SHORT TERM /TODAY THROUGH WEDNESDAY/

The unseasonably strong high pressure ridge that brought record temperatures the last few days is starting to push eastward out of the region as a Pacific trough moves through northern California into the Great Basin. Despite the fairly rapid height falls occurring today, the lingering warm air mass will allow for highs to again reach 90 degrees for much of the lower deserts. The NBM is showing a 90% probability of Phoenix tying today's record high of 90 degrees. Higher level clouds will again be around the region today, most likely mainly affecting the western deserts through this afternoon before moving through south-central and eastern Arizona this evening and tonight. The passage of the Pacific trough across the Great Basin will help to bring a return of breezy conditions today with much of the area seeing periodic gusts up to around 25 mph.

The center of the trough is forecast to move into Colorado early on Tuesday with a trailing trough axis moving across our area by the afternoon. Modestly cooler air aloft will usher into the area with H8 temperatures showing around a 3-4C drop. This will help to lower daytime highs on Tuesday into the mid 80s across the lower deserts. The passage of the trough will also help to usher in even drier air behind it with clear skies expected on Tuesday. A quick moving shortwave ridge will be set to move through on Wednesday as temperatures remain stable. Model guidance is in good agreement a larger trough will then dive southward through the Pacific Northwest into our region Wednesday night into Thursday, but the system will contain very little moisture.

LONG TERM /THURSDAY THROUGH SUNDAY/

The main forecast concern late week into early next week is the uncertainty with a potential cut-off low that could develop near our region and linger for several days. The initial development of the system begins on Wednesday across Oregon and California before likely moving through Nevada into our region by Thursday. Models have been in good agreement with the initial development of the system, but high uncertainty remains with the eventual track and how long it may impact our region. Increase winds will be the first aspect that will affect our region with breezy to locally windy conditions over much of the area starting Thursday. A cooler air mass should also move in for Thursday, lowering daytime highs down to around 80 degrees for the lower deserts.

By Friday into Saturday, guidance indicates the low may become cut off from the main flow. If this occurs, it would likely retrograde to the southwest, possibly stalling out somewhere to our southwest for a day or more into early next week. Given the system is expected to contain very little system moisture as it initially moves through our region late this week, no realistic precipitation chances are forecast. For our region to receive any chances for precipitation, the low would have to become cut-off and stall out to our southwest for at least a day or two allowing moisture to get entrained into the system and eventually making its way northward. The EPS is more bullish on this potential solution as its ensemble mean QPF shows an average of 0.10-0.20" across southern and central Arizona later Sunday into next Monday. The GEFS also attempts to show some precipitation chances around the same time, but to a much lesser degree. Forecast temperatures for next weekend into early next week are also quite uncertain as they will depend on the evolution of the low, but we are still expected to keep above normal temperatures in place.

AVIATION

Updated at 0950Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Winds will start off this morning out of the E-SE with speeds mainly aob 8 kts. By 19Z-21Z this afternoon, winds will shift out of the W-SW and become elevated with speeds reaching 8-13 kts and gusts up to 15-20 kts at all terminals. Gustiness will subside by sunset this evening. SCT to at times BKN cirrus clouds will continue to progress through the region into tonight. Southeast California/Southwest Arizona including KIPL and KBLH: Westerly winds will prevail at both terminals through the forecast period. Speeds will remain generally aob 8 kts this morning before increasing out of the W-SW heading into the afternoon. Gusts up to 20-25 kts are expected to materialize at both terminals by mid- afternoon. Gustiness will subside around sunset this evening. SCT to BKN cirrus will continue to pass overhead through much of the day before clearing out late tonight.

FIRE WEATHER

Above normal temperatures and dry conditions will persist this week, however the overall weather pattern become more active with a few dry systems influencing the region. Afternoon minRHs each day will range between 10-15% areawide, followed by fair overnight recoveries commonly between 30-50%. A passing dry system today will act to increase afternoon and evening breeziness, with widespread gusts 15-25 mph and locally higher over the AZ high terrain and portions of Southeast CA. Expect lingering breeziness Tuesday for the typical wind prone areas of the western districts. Another dry weather system later this week should again bring widespread breezy conditions by Thursday.

CLIMATE

Daily High Temperature Records:

Phoenix Yuma El Centro --------- --------- --------- 3/2 90 (2016) 94 (1910) 92 (2016)

PSR WATCHES/WARNINGS/ADVISORIES

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