textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- Near record warmth expected once again today as high temperatures top out at or just above 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/

A transition in the overall weather pattern is beginning to take shape across the Desert Southwest as the ridge of high pressure, responsible for bringing the record warmth the last couple of days, is shifting eastward as a compact upper-level shortwave trough is traversing the Great Basin. Even though upper-level heights are lowering across the region, low-level thermal profiles continue to remain quite warm with 850 mb temperatures ranging between 17-20C. Therefore, another day of near record warmth is expected as afternoon high temperatures across most of the lower desert communities top out around to just above 90 degrees. With the upper-level shortwave trough traversing the Great Basin, the regional pressure gradient will tighten somewhat leading to widespread breezy conditions this afternoon/early this evening with peak gusts upwards of 20-30 mph, strongest across the western deserts and the AZ higher terrain.

The upper-level trough will move into the central Rockies on Tuesday with the overall trough axis hanging back across the region. A cooler air mass in the wake of the trough will lead to a 4-5 degree drop in 850 mb temperatures and thus cause afternoon high temperatures to retreat into the mid 80s across the lower deserts. Heading into Wednesday, weak ridging will move in out ahead of the next troughing feature moving into the Pacific Northwest and will influence the weather pattern heading towards the latter half of the week. Afternoon high temperatures on Wednesday will remain nearly similar to Tuesday with readings in the mid 80s.

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 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 2352Z.

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

Winds will continue to follow typical diurnal directions through Tuesday, with westerly breezes to around 20 kts expected to subside this evening. Winds will be lighter Tuesday, with speeds mostly staying below 10 kts. There will likely be a period of light variability late Tuesday morning through noon, during the diurnal westerly wind shift. High cirrus will continue to pass over the area through tonight and clear by sunrise Tuesday. Southeast California/Southwest Arizona including KIPL and KBLH: Westerly winds will prevail at both terminals through Tuesday morning. Wind gusts to around 20-25 kts will continue through sunset before subsiding tonight. Winds will shift northerly at both terminals during the late-morning hours Tuesday, with lighter speeds, mostly aob 10 kts, at KIPL, while KBLH sees speeds up to 10-15 kts with gusts to around 20 kts. The high cirrus over the area will clear 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.