textproduct: NWS Phoenix

UPDATE

06Z Aviation Discussion

KEY MESSAGES

- A quick moving system Thursday night into Friday will reinforce cooler temperatures with additional chances for light showers across central Arizona.

- Drier weather with much warmer temperatures will return to the region early next week.

SHORT TERM /Today through Friday/

Early afternoon objective analysis and WV imagery depicts a well defined shortwave and vorticity center propagating along the UT/AZ border with an intense zonal jet streak just north of the CWA. This is part of a larger longwave troughing pattern covering the western Conus with another strong shortwave along the Pacific NW coast poised to dive into the mean trough base Friday before the translation of stronger jet energy towards the eastern side of the trough shifts the entire negative height anomaly into the plains. The current orientation of the jet streak over central Arizona is creating a tremendous midtropospheric inversion across the CWA, but also enhancing wind speeds into the lower levels with 40-50kt H8-H7 winds along a cold front associated with an enhanced pressure gradient. Mechanical mixing will partially tap this higher momentum airmass through mid afternoon before the gradient quickly relaxes behind the cold front, but not before some areas of blowing dust are realized across parts of SE California and far SW Arizona.

The aforementioned inversion will act to cap saturated ascent across the vast majority of the CWA with only a shallow, narrow layer along the frontal boundary. As such, orographic lift may become the primary impetus available to support organized showers and measurable precipitation through this evening before drier air infiltrates lower levels. While snowfall will be common across the Mogollon Rim north of the jet core and snow levels falling close to 4500ft, lack of moisture within the dendrite growth layer over southern Gila County will largely preclude any accumulation with only spotty snow grains and column favored. Otherwise, northern AZ shortwave energy will rapidly progress into the central Rockies tonight leaving flat, zonal flow and weak subsidence over the SW Conus Thursday. With H5 height depressed into a 558-562dm range, confidence is very good that temperatures continue to hover 5F-10F below normal.

The final shortwave in the series associated with the western trough will propagate through northern Arizona Thursday night and Friday with an abrupt Conus pattern shift thereafter. The track of this vorticty center will nearly mirror the current system, albeit possibly slightly displaced south and not as thermodynamically hostile across lower elevations. Nevertheless, being somewhat mistimed during the overnight and early morning along with only a brief period of saturation along another frontal boundary, rainfall chances and potential amounts will be quite limited and likely focused over foothills and mountains of central Arizona. A deeper moisture profile and snow levels around 4000ft may support some light accumulations over southern Gila County, however forecast soundings still suggest dry air above the H7 layer and dendrite formation may become somewhat ineffective significantly limiting amounts. Otherwise, confidence is excellent that temperatures Friday will follow a near persistence forecast, however clearing skies, light winds, and a cool, dry post-fronal airmass should result in chilly conditions by Saturday morning with readings likely the coolest experienced in well over a month.

LONG TERM /Saturday through Wednesday/

Much quieter weather will move in starting Saturday as upper level ridging overtakes the region after the Friday system exits to the east. The cold air mass will mostly stay around for Saturday as highs only warm back to around 70 degrees, but the warming trend will pick up speed going into early next week. Guidance shows H5 heights rising enough to breach the 90th percentile of climatology Monday into Tuesday before gradually lowering through the middle of next week. The latest NBM forecast highs show lower desert readings easily topping 80 degrees starting Monday with some potential for the warmest locations to reach 85 degrees during the first half of next week. However, there will likely also be a decent amount of higher level clouds next week as an atmospheric river is expected to just miss our region to the northwest. Higher clouds spilling into the ridge may at times limit daytime highs depending on the thickness of the clouds.

AVIATION

Updated at 0520Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concern tonight into Thursday morning will be low confidence surrounding prevailing wind directions at times. W'rly winds should prevail prior to sunrise before becoming more VRB and potential turning to the E/SE. However, it is not out of the question that W winds persist through the night. By the early afternoon hours, a SW'rly component will become established quickly, even gusting in the upper-teens to near 20 kts at times. Besides some passing high cirrus tonight, FEW lower bases around 6-8k ft will be observed throughout much of the forecast.

Toward the end of the forecast window, more persistent breeziness along with iso SHRA activity will accompany another frontal passage. CIGs starting around 04-06Z will begin to lower toward 4k ft, with even the slight potential (~30%) of seeing MVFR conditions being met.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to windy conditions will once again be the main aviation concern during the next 24 hours. Winds have relaxed this evening and should remain generally light through sunrise. Sustained speeds at KIPL might be relatively elevated at times between 8-12 kts. Gusts will quickly return by late morning, reaching upwards of 25-30 kts at each terminal. Periods of mostly clear skies will be joined by some windows of passing high cirrus and lower bases around 4-6k ft.

FIRE WEATHER

Wind speeds will increase again today, particularly across western districts with gusts 30-40 mph common. A few showers will be possible in foothill and mountain locations mainly this afternoon, however instances of wetting rainfall will be isolated before clearing Thursday with weaker winds. Minimum humidity values will range widely between 25-60% this afternoon, then tighten to 25-45% Thursday. This will follow good to excellent overnight recovery of 60-100%. Drying and warming conditions are expected for the weekend with MinRHs dropping into the teens for the lower deserts and temperatures rising to above normal.

PSR WATCHES/WARNINGS/ADVISORIES

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