textproduct: NWS Phoenix

UPDATE

Updated 00Z Aviation Discussion.

KEY MESSAGES

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

- Chances for showers and thunderstorms will remain confined to southeast 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 rainfall chances continuing through all of next week.

SHORT TERM /Today through Sunday/

Current objective analysis reveals that the the sub-tropical high has continued to migrate its way northward and is now centered near the Four Corners region. This progression has flipped the flow across the region from northerly/northwesterly to the east/southeast, allowing for much better moisture flux across the Desert Southwest. Though parts of Arizona have occasionally seen rain since June, with frequency increasing over the past week or so, the pattern that is setting up is the first time this summer we have seen a more traditional monsoon setup.

For today, even though moisture will be better compared to the past few days, shower and thunderstorm coverage will remain primarily where is has been since the front half of this past work week, along parts of the Rim, over the White Mountains, and across southeast Arizona. However, given the easterly wind component, better thermodynamics, and sufficient shear to support convective lifespans, storms are expected to move off higher terrain areas toward the lower deserts. However, the vast majority of desert activity will remain mostly in the confines of the Tucson CWA. A low end chance (~20%) does exist to see a quick shower or storm over our portion of Pinal County, so it would not be surprising for locations such as Florence, Coolidge, and even Casa Grande to experience some convective activity. The greater and more far reaching impact will be from a potential outflow pushed out by the activity over southeastern AZ and moving up through Pinal and Maricopa Counties. Main impacts with this feature would be gusty winds near or in excess of 35 mph, and areas of dense blowing dust that could drop visibility to 1 mile and below at times. If you plan to travel along the I-8 and I-10 corridors this evening, be prepared for potentially hazardous driving conditions. Due to the strong signal of a robust outflow and its associated dust impacts, a Blowing Dusty Advisory has been posted for Pinal and southern Maricopa Counties. Even though most of the Phoenix metro is not included in this advisory, reduced visibility still may observed depending on how strong the boundary becomes.

This evenings activity will help set the stage for further, and more widespread convection for Sunday, thanks to the introduction of better boundary layer moisture. This, combined with ample moisture getting pumped in thanks to the southeasterly flow of the high will result in very favorable environment to see greater coverage of showers thunderstorms over the typical mountainous areas, but also the lower deserts. Given the nature of the monsoon, not everywhere in the lower elevations will see rainfall, but current PoPs indicate some of the best chances (30-40% for the deserts east of the Colorado River, 50-70% for foothill and higher terrain locations of eastern AZ) we have seen so far this summer. Convective initiation for western Maricopa, La Paz, and Yuma Counties will be heavily dependent on colliding outflows, but hi-res data points toward this outcome, this is likely why rain chances continue for these areas, even after the sun goes down and instability starts to decrease. Main impacts will be heavy downpours, strong winds greater than 35 mph, and another round of blowing dust for some locations. It isn't out of the realm of possibility that some storms even become strong to severe. HREF neighborhood probabilities indicate 10- 30% chance of winds exceeding 58 mph, and the Storm Prediction Center concurs as they have highlighted the I-10 corridor with a slight chance (15%) of storms generating severe level winds. Small hail can't be ruled either out with the strongest cells as model soundings indicate the presence of CAPE within the hail growth zone.

Even though atmospheric heights this weekend will not dramatically different from what see saw this past week when temperatures will consistently hitting between 110-115 degrees, afternoon highs today and Sunday will be a few degrees lower, likely a result of the increasing moisture. Readings will run near to slightly above normal with lower desert locations hovering between 104-111 degrees. However, the humidity giveth, humidity taketh away as that extra moisture will counteract any temperature decreases by making it feel hotter than was is observed. Moderate HeatRisk will remain widespread across the region, so heat precautions should continue to be exercised if plans take you outside.

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 0005Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Blowing dust/haze, reduced vsby, and a strong southerly cross- runway winds will be the main aviation concerns this evening. Current westerly winds will prevail into the evening hours tonight, with gusts in the upper teens to around 20kt. Confidence remains high that storms in SE Arizona will send a strong outflow towards Phoenix this evening with an abrupt shift to S'rly winds between 02-04Z (~03Z for KPHX). This outflow boundary will bring wind gusts in the 20-25kt range with some occasional gusts up around 30-35kt within the first hour or two of the outflow moving through. Additionally, S'rly winds of this magnitude will likely bring areas of BLDU and HZ to the region causing vsby to deteriorate to MVFR or IFR conditions. Winds will then gradually shift out of the SE during the overnight period with speeds falling below 10 kts. A period of light and variable winds is expected tomorrow morning before winds go back westerly by the late morning hours. Cloud bases today should remain aoa 15 kft with periods of SCT to at times BKN cigs.

Sunday night: Confidence is high that tomorrow night a complex of showers and storms will be moving off the Mogollon Rim and towards the Phoenix Metro. Confidence is low on how much of this activity will survive into the lower deserts. However, we are expecting some isolated to scattered shower and storm activity across the Phoenix Metro. These storms are expected to arrive around 23-01Z tomorrow night and have been introduced into the KPHX TAF. As this complex of storms moves into the Metro, winds will abruptly shift out of the NE. With NE'rly winds, no reductions in VIS from BLDU/HZ are anticipated. However, wind gusts up around 30 kt are possible as the outflow initially moves through, then wind gusts are expected to drop into a 20-25 kt range. VCTS has also been introduced into the TAF with SHRA/TSRA being left out for now due to the confidence being lower with how much of the activity will survive into the lower deserts.

Southeast California/Southwest Arizona including KIPL and KBLH: Main aviation concern through this TAF period will be another period of reduced visibilities with HZ at KBLH tomorrow morning. Another strong complex of storms have developed over Sonora Mexico and is expected to push another strong outflow northwestward towards KBLH. Similar to the past couple of nights winds will remain out of the south with speeds in the 12-17 kt range expected initially as the boundary moves through. Visibility is expected to drop to around 5SM with HZ during the 11-13Z timeframe. Outside this outflow winds will be southerly the whole period. Current wind gusts of 20-25kt will taper off around sunset. Wind speeds will then pickup again tomorrow afternoon with some occasional gusts in the upper teens to around 20 kt. At KIPL, similar to the past couple of nights, no reduction in VIS is expected tomorrow morning. While the outflow may reach the terminal, it would likely only increase wind speeds to around 10-15kt for a couple hours. Otherwise, winds will remain out of the SE through the whole period. Current gusts into the upper teens will taper off around sunset. SCT-BKN high level cloud bases will remain through out the period.

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 until 10 PM MST this evening for AZZ539- 551-553-554-559.

CA...None.