Phoenix forecast discussion

Short Term /Today Through Saturday/

Mid-level WV imagery and RAP40 500mb analysis show the cut off low now developed over southern California and northern Baja, while high pressure continues to strengthen over NW CONUS. The high pressure will be be the driving force for temperatures remaining near normal today. Though the core of the ridge is to the north of the state, H5 heights will still reach between 585-588 dam over the desert SW. As mentioned, near normal afternoon highs can be expected today with temperatures in the upper 80s to low 90s in the western lower deserts and along the Colorado River Valley, while south-central AZ will maintain highs in the mid to upper 80s. The upper level ridge will quickly pass and move into the Plains by Saturday, allowing heights aloft to dampen and be influenced by the lingering cut off low. This will result in Saturday cooling into the upper 70s to low 80s. This will also be in conjunction with increasing cloud coverage and about a 10-20% chances of light showers/virga across south- central AZ and the eastern high terrain as early as Saturday afternoon.

Otherwise, the main weather concern will be winds due to a strong pressure gradient. This may be one of the the strongest easterly gradient wind events of the last decade. With strong winds lofted and blowing dust also poses a threat, especially across dust prone areas. Northerly winds gusts have already developed in the SE CA and along the Colorado River Valley and are under a Wind Advisory through Friday afternoon, where peak gusts between 40-45 mph can be expected. Over the next several hours this morning the surface high will migrate from southern Montana into the southern Plains/southern Rockies region and the pressure gradient will continue to strengthen and shifting the winds from the north to out of the east. Near sunrise this morning the Wind Advisory will expand eastwards into SW and SC Arizona, where gusts between 45-50 mph will be possible, while the Phoenix Metro will be slightly lower with gusts between 35- 45 mph. Winds this strong are likely to pick up a good amount of dust, creating hazy conditions, and will likely lead to some dust channels developing, with reduction in visibilities to under 1 mile at times, depending on land use. Most of the region will be under advisory level by mid afternoon today, while Pinal County and southern Gila County will continue with strong gusts through the overnight periods into late Saturday morning, with locally up to 55 mph over mountain peaks.

Long Term /Sunday Through Thursday/

The strong pressure gradient and resultant strong easterly winds across southern AZ will weaken heading into Sunday as the strong surface high in the Plains weakens and shifts to the Mid-Atlantic. Winds early Sunday morning will remain elevated over south- central Arizona and the higher terrain with gusts between 20-25 in SC AZ, and 30-35 mph in the higher terrain. Past sunrise these winds will quickly weaken as the upper level pattern continues to quickly shift. The ridge will continue to push eastwards, and the cutoff low will begin to weaken and become an open wave, lifting through the region Sunday- Monday. As the open wave moves drifts through, lingering light showers/virga remain in the forecast, 20-35% Sunday, then 10-20% Monday. This will be confined to the higher terrain areas, where with enough extra lift may be possible for showers to develop. However, if any activity does develop total accumulations are expected to be only a few hundredths, or near zero. For the lower deserts temperatures are expected to rebound back into the mid to upper 80s Sunday and into early next week.

By late Monday into Tuesday a troughing feature will begin to dive down the western coastline, however confidence is low in the timing and strength of the feature. This has resulted in a decent amount of spread in for temperatures by mid next week. As it stands now temperatures will remain near to slightly below normal Monday-Tuesday then start to fall 6-9 degrees below normal for the later half of the week.

Aviation

Updated at 0530Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns during the TAF period will be breezy to windy conditions along with lofted dust late Friday morning into the afternoon. In the meantime, NE flow will continue through tonight with sporadic gusts, though exact timing of these gusts remains low. Regardless, sustained speeds will remain relatively elevated compared to what is typical, and much stronger winds just above the surface may result in some localized LLWS. The strongest gusts during the forecast window look likely to occur Friday morning, sometime between 16-20Z, with observations nearing 30-35 kt. These strong winds will be capable of producing areas of BLDU which could result in instances of sub-VFR surface VIS. Whether or not dust impacts are seen at the surface, confidence is much greater in lofted dust resulting in slantwise VIS issues through much of the daylight hours. Clear skies will prevail through Friday afternoon before mid and high level cloud decks spread over the region after sunset.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy conditions late Friday morning and afternoon will be the main aviation concern during the next 24 hours. However, some sporadic gusts around 25 kt cannot be ruled out overnight, especially at KBLH. NW-NE flow will be common at each terminal through the morning hours before tilting toward the NE/E beyond that. FEW to sometimes SCT mid-level clouds decks may be seen tonight, but more noticeable cloud cover will migrate over the region by the end of the forecast period.

Fire Weather

Drier air will persist over the region over the next couple of days with mostly clear skies and seasonally low humidities. MinRHs will be between 15-30% across the region through Saturday. Winds will turn easterly over the morning, becoming stronger tonight through Saturday across southern AZ. Winds will be strongest over mountain tops during the overnight and early morning hours tomorrow and Saturday, with gusts up to 50-55 mph. Strong gusty winds will spread more to the lower deserts during the daylight hours and be strongest in the morning through early afternoon today, with gusts up to 40-45 mph. These strong easterlies and 20-25% RHs may still create locally elevated fire weather conditions midday through the afternoon tomorrow, but fuels are not the most receptive after recent rains. The easterly breezes will not be nearly as strong during the day Saturday and will trend down further into Sunday. Light showers are possible this weekend, but the chance for wetting rain is low (<10%). A Pacific trough is expected to bring regional rain chances, breezy winds, and cooler temperatures next week.

Psr Watches/Warnings/Advisories

AZ... Wind Advisory from 5 AM early this morning to 11 AM MST Saturday for AZZ547-552-553-555-557-558-560>562.

Wind Advisory until 2 PM MST this afternoon for AZZ530.

Wind Advisory from 5 AM early this morning to 3 PM MST this afternoon for AZZ531>534-536-538-539-554-559.

Wind Advisory from 8 AM this morning to 3 PM MST this afternoon for AZZ537-540>546-548>551.

CA...Wind Advisory until 2 PM PDT this afternoon for CAZ564-565- 568>570.

SHORT TERM...Ryan LONG TERM...Ryan AVIATION...RW FIRE WEATHER...Benedict/Ryan