textproduct: NWS Phoenix

UPDATE...Updated 12z Aviation Discussion

KEY MESSAGES

- Wind advisories continue across portions of the region through this morning with gusts occasionally over 35 mph resulting in areas of blowing dust and difficult travel for high profile vehicles.

- A slight chance of light rain will arrive into parts of south- central Arizona over the weekend with the better chances focused over higher terrain locations. - A Pacific low pressure system moving into the Southwest during the middle of next week will lead to much better rainfall chances with the possibility of a few embedded thunderstorms, as well as cooler temperatures

SHORT TERM /Today through Sunday/

A defined Rex block can be seen on both GOES WV imagery and RAP-40 500mb analysis. The core of the high is currently over Rockies and the core of the cut off low remains positioned over the northern coast line of the Baja Peninsula. The high pressure will continue to push eastwards into the northern Plains throughout the afternoon today and the pressure gradient that brought wide spread windy conditions across the region will begin to weaken. Until then lingering strong gusts will linger throughout the morning hours today, with potential for areas of lofted dust. Thats said a Wind Advisory remains in effect until 11 AM MST for most of Pinal County and the higher terrain east of Phoenix of southern Gila County, where gusts between 40-55 mph will be possible, especially along the mountain peaks. Afterwards the combined effect of a weakening pressure gradient with an increase in thicker cloud coverage as the cut off low opens open through the region will lead to less mixing and therefore cutting winds down below advisory level leading into the afternoon.

As mentioned previously the Rex block is expected to open by tonight and drift through the region over the weekend. This is expected to advect a decent amount of mid to high level moisture into the region with PWATs forecasted to rise near to slightly above 1" over the weekend. While this amount of moisture is between 150-200% of normal, the lower levels are expected to remain quite dry restricting much rainfall from reaching the surface in most areas. However, PoPs between 20-35% remains in the forecast for today- Sunday across south-central and the higher terrain areas east of Phoenix. By late Sunday afternoon PoPs reduce to below 10% CWA wide as the open wave trough lifts into Northern Arizona.

LONG TERM /Monday through Thursday/

By early next week next week the high pressure will be well over NE CONUS and the open wave trough will begin to be absorbed into the mean SW flow head of the next incoming low pressure system diving down the western coastline. Another low chance (20-30%) of showers manifest Monday morning across the higher terrain, however yet again, if anything does develop total accumulations are expected to be near zero. By Tuesday, deep troughing and strong negative height anomalies will amplify and intensify along the west coast, however confidence in the timing and depth of this feature remains low to moderate. The ECMWF deterministic is forecasting a slower and more robust rainfall scenario, while the GFS deterministic provides a faster and more mild rainfall potential. Regardless, the timing of any rainfall potential is highlighting Wednesday and Thursday. Additionally, with the uncertainty of this next system a wide spread in NBM temperatures have presented themselves throughout the week, though below normal highs are likely.

AVIATION

Updated at 1105Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Main aviation weather concerns in this TAF package will be the gusty easterly winds and slantwise visibility reductions due to lofted dust. Elevated winds of 10-15 kts, with locally higher gusts in excess of 20 kts, especially at KSDL, will continue through the early morning hours before boundary layer mixing allows stronger gusts in excess of 20-25 kts to materialize after 15z. The gusty winds will continue to keep slantwise visibilities reduced. Gusts are expected to subside by the mid to late afternoon hours with sustained speeds reducing to under 12 kts across much of the area with slantwise visibilities expected to improve in conjuction. Thereafter, guidance continues to show an increase in shower chances heading into the evening through the overnight hours with VCSH across all terminals. Uncertainty of overall SHRA coverage still precludes a mention of -SHRA in the TAFs, however, any operational impacts should remain minimal. Considerable cloud cover with bases as low as 9-12 kft will be common starting this afternoon, potentially lowering to as low as 7 kft this evening into the overnight period in any more persistent SHRA activity.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected during the next 24 hours. Overall winds will generally be out of the northeast with periods of light variability likely at KIPL. An expansive area of light showers near the international border will continue to result in VCSH at KIPL through the early morning hours. Considerable cloud cover with bases as low as 8-12 kft will continue through this evening before overall coverage gradually decreases during the overnight period.

FIRE WEATHER

Strong east winds will continue through this morning across southern Arizona with the most pronounced gusts over mountain tops of eastern districts. Gusts 40-45 mph may be common over these locations with a portion of these winds building into lower elevations by late morning, before weakening heading into the afternoon hours, with even weaker winds Sunday through the middle of next week. Light showers are possible this weekend, and particularly over eastern districts, but the chance for wetting rain is low (~10%). The strong east winds will result in minimum humidity levels 15-30% today, but increasing closer to a 30-50% range thereafter. Overnight recovery should be good to excellent. A Pacific weather disturbance will bring increased chances of wetting rainfall, breezy winds, and cooler temperatures during the latter half of next week.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Wind Advisory until 11 AM MST this morning for AZZ547-552-553- 555-557-558-560>562.

CA...None.