textproduct: NWS Phoenix

KEY MESSAGES

- Scattered showers and thunderstorms will develop over the high terrain of southcentral AZ this afternoon with much higher chances for storms surviving into the lower deserts. There is also a slight risk for severe thunderstorms in Maricopa and Pinal Counties today.

- With high pressure shifting into the Great Plains, daily shower and thunderstorm chances will continue over the Desert Southwest through much of this week.

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

SHORT TERM /Today through Monday/

Latest IR satellite imagery shows a decaying complex of thunderstorms progressing through Sonora MX. Gusty outflow winds from this complex may reach the Lower Colorado Valley early this morning causing winds to increase and generating patchy blowing dust in Yuma and Imperial Counties. It is possible a few showers and even some embedded lightning strikes could occur early this morning over southcentral AZ where a pocket of higher mid-lvl instability is present. As we progress into this afternoon, high pressure currently located over the Rockies will continue migrate into the Northern Plains. This pattern shift will allow 500 mb steering flow over AZ to transition from E to SE allowing for much better moisture to advect into central portions of the state.

Most of the CAMs indicate storms initiating along the Mogollon Rim and S Gila County this afternoon and generating a strong SW moving outflow boundary which will encroach on the lower deserts late this afternoon into early this evening which will likely generate additional showers/storms and areas of blowing dust. The environment across the lower deserts will consist of modest instability with ML CAPE values ranging between 500-800 J/kg and a narrow axis of higher values up to 1000-1200 J/kg mainly over the foothills E of Phoenix. Forecast soundings also indicate ML CIN values around 50-70 J/kg which may inhibit greater storm coverage across the lower deserts. Overall this setup poses a much more conditional severe threat depending on the strength of the initial outflow. Nevertheless, any storm that does develop could produce strong wind gusts up to 50-60 mph due to high DCAPE up to 1200-1500 J/kg. The Storm Prediction Center has still maintained a slight chance (15%) for severe level wind gusts (>58 mph) which includes the Phoenix Metro and the I-10 corridor south to Tucson this afternoon/evening. By late this evening into the overnight, colliding outflows from storms in Pima county and western Maricopa County will likely generate additional showers/storms across the lower deserts east of the Colorado River, where NBM PoPs are 30-40% after 00Z.

The upper-lvl pattern is not expected to change heading into Monday which will result in a very similar evolution as storms first develop over the high terrain E and SE of Phoenix and attempt to survive into the lower deserts by the later afternoon/early evening. The environment will be similar to today with maybe slightly less overall wind shear. Thus, a few strong to marginally severe storms will be possible Monday afternoon. NBM PoPs are indicating 30-40% coverage across southcentral AZ and up to 20% for the lower deserts E of the Colorado River.

Due to the increase of boundary layer moisture and 500 mb hghts ranging from 593-595 dam, high temperatures will run near to slightly above normal with lower desert locations hovering between 102-109 degrees each afternoon. The added humidity will unfortunately make it feel worse with apparent temperatures (heat index) reaching 110-115 degrees across the lower deserts. 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/

There is still excellent agreement within the EPS and GEFS members regarding the placement of the upper high over the northern Plains and Upper Midwest through midweek before retrograding over the central Rockies by the latter half of the week. The overall position of the 500 mb high will maintain deep easterly flow across the Desert Southwest, helping enhance moisture transport. Latest EPS and GEFS continue to show PWATs hovering around 1.5"-1.8" through the entire week with low-level mixing ratios remaining between 10-12 g/kg. Therefore, conditions will continue to remain conducive for daily thunderstorm activity with variations in the overall coverage. Both the mean of the EPS and GEFS show an uptick in QPF across the region by the end of this week due to an easterly wave/inverted trough approaching the area by Thursday-Friday. If this occurs, this troughing feature will likely enhance convective activity potentially introduce a risk for heavy rainfall across portions of AZ. This will have to be monitored closely in the coming days.

Temperatures through the first half of the workweek will generally remain steady state at near to slightly above normal with highs generally between 102-110 degrees, resulting in the continuation of widespread Moderate HeatRisk. The NBM continues to indicate temperatures cooling to well below normal by the end of the week with highs falling into the 90s to around 100 degrees across the lower deserts by Friday. This is likely due to the increased signal for thicker cloud cover and the potential for more widespread rainfall.

AVIATION

Updated at 0600Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Lingering haze and reduced vsby, and a strong NE'rly outflow tomorrow night will be the main aviation concerns this TAF package. The S/SW outflow is continuing to move northward through the Metro with pockets of reduced VIS (down to 3-4SM), BLDU, and HZ. Outflow is weakening as it moves northward and VIS is only expected to drop to around 6SM with HZ at KSDL respectively. Some wind gusts up around 20kt are expected with the outflow. VIS is improving at KPHX and KIWA and should be back to above 6SM during 06Z hour. By 08-09Z winds are expected to go SE'rly with wind speeds up around 7-10 kt. A period of light and variable winds is then expected tomorrow morning at most terminals prior to the westerly shift by the late morning hours, with winds generally aob 10 kt. SCT-BKN mid and high level cloud bases will remain through out the period.

Sunday night: Confidence remains high that tomorrow night a complex of showers and storms will be moving off the Mogollon Rim towards the Phoenix Metro. However, confidence remains low on how much of this activity will survive into the lower deserts. But, we are expecting some isolated to scattered shower and storm activity across the Phoenix Metro. These storms are expected to arrive around 00-01Z tomorrow night and have been introduced into all the TAFs. 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. A strong complex of storms is 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 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. Some occasional gusts in the upper teens to around 20 kt are possible again tomorrow afternoon. 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 are expected to remain out of the SE through the whole period. 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. Scattered showers and thunderstorms will be possible this afternoon and evening bringing a threat of strong winds. Daily thunderstorm activity will be possible through this week with the potential for wetting rainfall increasing across the high terrain later in the week. Due to increasing boundary layer moisture, afternoon humidity levels will remain in a 20-30% range which will keep any fire weather concerns at a minimum. Overnight recoveries will be fair to good, or between 40-70%. Outside of any thunderstorm driven outflow, winds should favor diurnal trends with the typical afternoon breeziness around 20-25 mph.

PSR WATCHES/WARNINGS/ADVISORIES

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