textproduct: NWS Phoenix

UPDATE

06Z Aviation Discussion

KEY MESSAGES

- Wind advisories in effect tonight through Saturday morning across southern Arizona and southeast California, with breezy to windy conditions expected as forecast peak wind gusts reach up to 40-55 mph.

- Strong winds on Friday will likely lead to widespread lofted dust, leading to hazy conditions, and localized dust channels occasionally reducing visibility below one mile.

- Dry weather with near normal temperatures the next couple days, then slightly cooler with a slight chances for rain showers this weekend. - A Pacific low pressure system moving down the coast early next week is currently forecast to bring regional rain chances, breezy conditions, and cooler temperatures by the middle to latter portions of next week.

SHORT TERM /TODAY THROUGH SATURDAY/

Dry conditions under clear skies continue across the area today. Synoptically a blocking pattern is developing with high pressure ridging spreading into the Northwest CONUS and a developing weak cutoff low south of it over the local area. Despite the developing cutoff low, H5 heights have risen over the last 24 hours and temperatures have warmed 5-10 degrees across southern AZ and southeast CA. High temperatures this afternoon are forecast to reach the mid to upper 80s and there is around a 60-70% chance of reaching 90 degrees in Phoenix. High temperatures tomorrow will be similar to today, except for the western deserts where it will be a few degrees warmer, reaching the low 90s. Temperatures then cool down again for Saturday with an increase in clouds, possibly some light showers/virga, and cold air advection from the east.

The main sensible weather impact the next few days will be the wind and perhaps a lot of lofted dust as a result. This may be one of the the strongest easterly gradient wind events of the last decade. Surface analysis at midday today showed a strong 1040-1042mb high centered over Montana, which is near record strength for this time of year. The pressure gradient between the strong high to the north and the lower pressure over the local area is leading to breezy to locally windy conditions across northern AZ and across parts of southeast CA this afternoon. Wind gusts were consistently reaching 35-40 mph across these areas early this afternoon. As the strong surface high spreads further into the Plains and south along the southern Rockies, the pressure gradient will continue to increase across the local area and as a result so will the winds. A strong cold front moving south through the Plains will backdoor into southern AZ tonight/tomorrow morning. Models continue to show 850mb LLJ winds reaching 40-50 kts over south-central AZ early tomorrow morning, and even upwards of 60 kts across southeast AZ. While these winds are not expected to fully mix to the surface, the strong gradient will still lead to widespread 20-25 mph sustained and 30-40 mph wind gusts. Higher peak wind gusts up to 45-50 mph are expected, with locally up to 55 mph over mountain peaks, but the window for these stronger gusts will mostly be in the morning tomorrow and again Saturday morning. Winds this strong will surely kick up a lot of dust and create 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.

Wind advisories will be in effect for this wind event, starting initially this evening across southeast CA and along the Lower Colorado River Valley with 35-45 mph northerly winds. Southwest and south-central AZ are then added to the advisory tomorrow morning. The decision was made to add the greater Phoenix area to the advisory for a period from 8 AM - 3 PM MST. During this period, model soundings show potential for 30-35 kt (35-40 mph) to mix down to the surface. The advisory for Pinal and southern Gila counties will continue through Saturday morning, as the easterly LLJ restrengthens overnight, and portions of southwest AZ will likely be re-added the advisory for Saturday morning as well.

As mentioned there will be an increase in clouds Saturday, as moisture is drawn north into the area by the weak cutoff low to the southwest. Vertical cross-sections and model soundings show this moisture will mostly be focused aloft between 700-300mb with a dry sub-cloud layer. Still, soundings suggest thick clouds with potential for light showers and virga beginning around midday and heading into the afternoon Saturday. Model guidance also shows a wing of vorticity or shortwave trough moving up from the south Saturday, with an enhancement to the upper level jet. This should provide decent ascent over southern AZ and further support at least light shower/virga activity. NBM PoPs Saturday are only around 10-20% across south-central AZ (30% east of Phoenix) and QPF is very light with NBM 75th percentile only showing 0.01" for Phoenix to 0.10" for southern Gila County.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

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. There will still be some easterly breeziness, but nowhere near the magnitude of Friday through Saturday. The synoptic pattern will also shift, with the ridge over the Northwest CONUS sliding east through the Plains and the cutoff low will also weaken into an open wave and lift through the area Sunday-Monday, downstream of the next Fall trough digging down the West Coast.

Lingering light showers are possible across portions of AZ, mainly east and southeast AZ, Sunday into the start of next week downstream of the lingering shortwave trough, but drier air is shown to move in aloft prior to the arrival of the next coastal trough. Temperatures should warm Sunday into the start of next week with the latest NBM showing highs returning back close to normal by Monday.

Tuesday through the middle of next week forecast confidence decreases as model spread increases considerably. Most notably there is a lot of model disagreement on timing out when the coastal trough will move inland, how quickly, and how deep the trough will be. Typically models will trend toward the slower solutions with these coastal lows. So, something moving through late week is the current thinking. This next coastal trough will bring chances for rain, breezy winds, and cooler temperatures, but to what magnitude is still uncertain.

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. North and northeasterly breezes up to 25-35 mph are expected through this evening in portions of southeast CA and along the lower CO River Valley, as well as in the mountains north and northeast of of Phoenix. Winds turn easterly and become 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 tomorrow, 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 Friday to 11 AM MST Saturday for AZZ547- 552-553-555-557-558-560>562.

Wind Advisory until 2 PM MST Friday for AZZ530.

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

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

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