textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion.

KEY MESSAGES

- Seasonably hot temperatures will persist through the next several days with widespread Moderate HeatRisk.

- Chances for showers and thunderstorms will remain confined to southeastern Arizona today, with the potential for distant outflows to move through south-central Arizona this evening with gusty winds and areas of blowing dust.

- Deeper moisture will increase the chances for more widespread shower and thunderstorm activity on Sunday with elevated thunderstorm chances continuing through all of next week.

SHORT TERM /Today through Sunday/

Latest objective analysis reveals that the subtropical high is currently centered near southern Nevada with the mid-level flow now in the process of shifting out of the east. The subtropical high is expected to quickly migrate northeastward, reaching the central Rockies by this evening and then the northern Plains by Sunday evening while strengthening in the process. As this whole pattern evolution takes place, the mid-level easterly flow will gradually cause moisture levels to increase during the next several days and thus transitioning the Desert Southwest into a more active monsoonal pattern.

A strong storm complex that developed over northern Sonora last evening will send an northwestward propagating outflow towards the Lower Colorado River Valley area, creating gusty winds, potentially in excess of 30 mph and areas of blowing dust through early this morning. Heading into this afternoon and early evening, thunderstorms are expected to develop mainly across southeastern AZ with more isolated activity over Gila County. The thunderstorm activity that develops is likely to sending a strong outflow northwestward into south-central AZ as depicted by most of the hi-res guidance. Potential gusts in excess of 30-40 mph will be possible as the outflow plows through along with areas of blowing dust, potentially dense in some areas, especially across Pinal and southern Maricopa Counties. Given this strong signal for a strong outflow and thus the potential for significant blowing dust, in coordination with WFO Tucson, a Blowing Dust Advisory has been issued for Pinal and southern Maricopa Counties for this evening for visibilities potentially dropping below one mile. Even though most of south-central AZ should be storm-free this evening due to a good deal of convective inhibition in place, it is not out of the question that the outflow may spark a few isolated storms in some spots.

Heading into Sunday, environmental conditions will be far more conducive for thunderstorm activity to affect the south-central AZ lower deserts as the increasing moisture, with low-level mixing ratios exceeding 10 g/kg, will result in less convective inhibition. Thus, thunderstorms that develop over the higher terrain to north and east of Phoenix will have an easier time surviving into the lower deserts. The latest hi-res guidance have storms developing near the Mogollon Rim by the mid-afternoon hours before moving through and affecting the lower elevations by the late afternoon/early evening hours. Latest forecast sounding profiles for Phoenix during this time period indicate CAPE values near 1000 J/KG along with DCAPE values in excess near 1500 J/KG. Therefore, conditions will be favorable for strong downburst wind gusts and strong outflows and as a result of this potential, the Storm Prediction Center has highlighted most of south-central AZ under a marginal risk for severe winds.

Temperatures throughout the weekend will generally be near to slightly above normal with afternoon highs generally between 105-110 degrees along with overnight lows generally in the 80s across the lower deserts with widespread Moderate HeatRisk in place. Therefore, if planning outdoor activities, make sure to take the necessary heat precautions.

LONG TERM /Monday through Friday/

Very good agreement continues amongst the guidance in the overall pattern setup as the upper high will position itself over the northern Plains and Upper Midwest area through midweek before repositioning itself across the central Rockies by the latter half of the week. This overall pattern setup will maintain easterly flow in place across the Desert Southwest, helping with moisture transport. Latest EPS and GEFS continue to show PWATs staying above 1.5" through all of next week along with low-level mixing ratios remaining above 10-12 g/kg. Therefore, conditions will continue to remain conducive for daily thunderstorm activity with daily variations in the overall coverage. Heading towards the latter half of the week, forecast uncertainty increases as there continues to be some indication from the guidance of an easterly wave/inverted trough potentially approaching the area. However, models are all over the place in terms of the timing and track of this feature. However, if the easterly wave/inverted trough scenario comes to fruition, it will likely enhance convective activity and thus this will be something that will have to be monitored during the next several days.

Temperatures through the first half of the week will generally remain steady state at near to slightly above normal with highs generally between 106-110 degrees, resulting in the continuation of widespread Moderate HeatRisk. The latest NBM shows temperatures cooling to below normal levels, potentially into the low 100s for afternoon highs across the lower deserts, by the end of the week most likely due to increasing cloud cover and the potential for more widespread rainfall, especially if the easterly wave/inverted trough scenario pans out.

AVIATION

Updated at 1150Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Blowing dust, reduced vsby, and a strong southerly cross-runway wind will be the main aviation concerns this evening. Winds this morning will start off out of a NW direction before shifting back out of W-SW at by the late morning hours with speeds increasing to around 10 kt. Afternoon gusts up to 15-20 kts can be expected at all terminals. Confidence remains high that storms in eastern and southern Arizona will send a strong outflow boundary towards Phoenix by this evening. While thunderstorms are not anticipated to directly affect the terminals, the main concern will be an abrupt southerly wind shift with blowing dust between 03Z-06Z which may cause vsby to briefly deteriorate to MVFR or IFR. Winds will then gradually shift out of the SE overnight with speeds falling below 10 kts. Cloud bases today should remain aoa 15 kft with periods of SCT to at times BKN cigs.

Southeast California/Southwest Arizona including KIPL and KBLH: Aviation concerns will remain low at both SE CA terminals for this forecast period. Winds will be predominately SE at KIPL and S-SW at KBLH through this evening with gusts reaching 20 kts at times. Any convection should remain well east of the TAF sites with only SCT-BKN high clouds anticipated over the region.

FIRE WEATHER

Seasonably hot temperatures will prevail through the next several days as readings will be near to slightly above normal. Isolated thunderstorm activity is expected today, mainly across the far eastern districts. More widespread monsoonal activity is likely starting Sunday and continuing through all of next week along with elevated probabilities of wetting rains. Afternoon humidity levels today will bottom out between 15-25%. Starting on Sunday and persisting through much of next week, afternoon humidity levels will increase even further and bottom out above 20-30% as moisture levels increase, and thus alleviating much of the fire weather concerns. Outside of any potential outflows/thunderstorm winds, winds should favor diurnal trends with the typical afternoon breeziness around 20-25 mph.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Blowing Dust Advisory from 6 PM to 10 PM MST this evening for AZZ539-551-553-554-559.

CA...None.