textproduct: NWS Phoenix

UPDATE

06Z Aviation Discussion

KEY MESSAGES

- A pattern change mid to late week will lead to cooler temperatures and increasing rain chances, particularly across the eastern half of Arizona on Friday.

- Weather conditions will briefly turn quieter over the weekend before becoming more unsettled once again early next week as another storm system impacts the region, resulting in better chances of more widespread precipitation.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Satellite imagery early this afternoon continues to show mid and high level clouds moving into the region. This is a result of an upper-level long wave trough that is sitting just off the west coast and is slowly moving eastward. This trough is the beginning of an overall pattern change leading to more unsettled weather and cooler temperatures. Initially today H5 heights aloft have lowered to around 571-575 dm. The combination of these lower heights and increasing cloud cover will allow for temperatures to cool from the previous few days, however they will still be well above normal. Temperatures, as of 1pm MST/12pm PST are around 3-7 degrees cooler than they were at the same time yesterday, and are forecasted to max out in the upper 70s to low 80s across the lower deserts and in the low to mid 70s across the higher terrain.

The aforementioned trough will move onshore overnight tonight and tomorrow, but will weaken as it does. Most of the PVA and associated forcing will be well north/northwest of our region, which will be where the best precipitation chances will be. However, we have seen an increase in moisture as a different low pressure system moved south of our region last night. This low is currently situated over northern Mexico/western TX. PWATS have increased to 0.5-0.8" over our area, which is up from 0.3-0.5" from yesterday. This increase in moisture is in the mid and upper levels, however, it may be enough to squeeze out some sprinkles over the higher terrain areas to the north and east of Phoenix. Models have backed off on this activity for tonight into tomorrow morning. However, some virga showers and a few sprinkles cannot be completely ruled out. If you do see any activity, little to no accumulations are expected.

H5 heights are expected to lower even further on Wednesday, falling into a 568-573 dm range across the area. Additionally, more mid and high level cloud cover will move into the region as the aforementioned trough continues to slowly progress eastward. The lowering heights aloft in combination with increased cloud cover will lead to temperatures cooling even more on Wednesday. Afternoon high temperatures are expected to cool an additional 3-7 degrees from today's temperatures, but remain above normal. Afternoon high temperatures will be in the mid to upper 70s across the lower deserts and in the upper 60s to mid 70s across the higher terrain.

LONG TERM /THURSDAY THROUGH EARLY NEXT WEEK/

Unsettled weather will remain in place through the end of the week as another troughing feature dives down through the west coast and swings through the Desert Southwest late Thursday into Friday. Model guidance in the last couple of iterations have trended a bit deeper with the trough as it swings through the region, however, the progressive nature will sort of limit any robust moisture advection and thus any precipitation that falls will be limited in coverage, with the greatest coverage expected mostly across the AZ high terrain where NBM PoPs range between 40-70% with considerably lower PoPs of 10-40% across the lower elevations of western and central AZ. With the trough passage, afternoon high temperatures on Friday will cool down to around 70 degrees across the south-central AZ lower deserts (which is right around seasonal norms) to middle 70s across the western deserts.

As the trough quickly exits to the east late Friday into early Saturday, a quieter weather pattern briefly settles in over the weekend as a transient ridge moves overhead with dry conditions and slightly warmer temperatures. Attention then turns to another, more potent longwave troughing feature that is expected to set up along the west coast heading into next week, with guidance showing multiple shortwaves moving onshore and if the overall trajectory is ideal, could lead to more widespread precipitation chances. Latest deterministic and ensemble model suite show the first shortwave moving through early next week, delivering the first widespread chance of precipitation with NBM PoPs ranging between 25-60% areawide. However, given that this potential system is still nearly a week out, lots of uncertainty still remains in the overall details and thus it will probably take until the end of the week to get a better grasp on how things will evolve. Even though the precipitation potential is uncertain, what is a bit more certain is that temperatures are likely to cool down several degrees early next week with the latest NBM deterministic showing highs in the low 70s across the lower deserts (values more typical for mid-February) with the 25th percentile in the upper 60s, which would be more likely if the cloudy/rainy scenario comes to fruition.

AVIATION

Updated at 0525Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation concerns are expected during the TAF period. Winds will follow familiar diurnal trends with speeds generally aob 10 kts. BKN-OVC skies will persist through much of the period before some clearing takes place late in the forecast. Cannot rule out a FEW bases around 7-9k ft.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected over the next 24 hours. Confidence is low in a prevailing wind direction at each terminal through the overnight hours. To reflect this uncertainty, an extended window of VRB conditions have been included in the TAFs at this time. W/NW'rly and S/SW'rly winds will eventually take over at KIPL and KBLH respectively. BKN-OVC high clouds will persist through most of the forecast before some clearing takes place late in the window. FEW bases around 7-9k ft cannot be ruled out.

FIRE WEATHER

Cooling temperatures (although remaining above normal) are expected through the remainder of the week. MinRH values will continue to be between 20-35% across most of the region through the remainder of the week with good to excellent overnight recoveries. Occasional breeziness, especially across the western districts, will be common during the next several days. A weather system late in the week will bring a 40-70% chance of wetting rains across the higher terrain areas of the eastern districts.

PSR WATCHES/WARNINGS/ADVISORIES

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