textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion

KEY MESSAGES

- Temperatures between 5 and 10 degrees above normal will result in widespread Moderate Heat Risk with localized Major Heat Risk through Thursday.

- Extreme Heat Warnings will remain in effect for portions of the area through Thursday.

- Marginally better moisture levels through the middle of the week could lead to isolated showers and virga, with better chances for showers and storms over Northern Arizona high terrain.

- Drying conditions and a regional increase in winds late this week will result in areas of critical fire weather, and so Fire Weather Watches have been issued for the Lower Colorado River Valley and Tonto National Forest on Friday and Saturday.

SHORT TERM /TODAY THROUGH THURSDAY/

Local conditions through Thursday will be heavily influenced by the subtropical high currently centered near El Paso according to early afternoon water vapor satellite imagery and 500 mb RAP analysis. Heights aloft have increased over the forecast area as this high amplifies/strengthens, with analyzed H5 heights up around 595-597 dam, between the 97th-99th percentile of climatology. Meanwhile, a period of southerly flow imposed by the high has imported marginal levels of midlevel moisture into the area. The 12Z KPSR sounding indicated PWATs around 0.95", up from 0.41" only 24 hours ago. In Yuma, a sounding taken at 12Z this morning showed PWAT around 1" and increased to around 1.2" by 18Z in a followup sounding. However, the bulk of this moisture is in a relatively shallow layer above 600 mb, and low level mixing ratios below 8 g/kg coupled with poor lapse rates/instability measures preclude chances for deep moist convection over the forecast area. A few disturbance may rotate through the area along the periphery of the subtropical high, increasing midlevel moisture and providing a transient lifting mechanism for isolated showers/virga and maybe even releasing some elevated instability at times, resulting in some localized rumbles of thunder. One of these disturbances can be seen in the midlevel water vapor imagery moving north northwestward over the Gulf of California and will be overhead late this afternoon into the evening.

The levels of moisture forecast in the short term with this period of southerly flow will be supportive of Northern Arizona high terrain thunderstorms, especially by Wednesday. From experience, storms will not form or survive over lower elevations, away from prominent terrain features. The greatest coverage of high terrain showers and thunderstorms will likely occur Wednesday, coincident with the best available moisture, then flow turns southwesterly aloft and increases as northern stream cyclonic curvature enters the Northwest US. This will begin a drying trend from west to east across the area through the latter half of the week.

Temperatures will likely peak Wednesday, as lower level thermal profiles will have had time to respond to the increased heights aloft. However, some amount of cloud cover associated with the increased midlevel moisture complicates the forecast, and lower desert highs have trended down a degree or two in some places. Regardless, much warmer overnight lows (80s across the typically warmer spots) and afternoon highs near or in excess of 110F to as much as 113F-114F will result in areas of Major HeatRisk, particularly for urban areas like the Phoenix Metro. Drying conditions and less cloud cover Thursday should result in similarly hot conditions to that of Wednesday, but decreasing heights aloft will preclude the possibility of temperatures warming any further. Thus, Extreme Heat Warnings will be in effect Wednesday and Thursday for portions of the area.

LONG TERM /FRIDAY THROUGH MONDAY/

Global ensemble members remain in pretty good agreement on the overall synoptic patter for the end of the week and into the beginning of next week. The aforementioned upper level trough will push further into our region by the end of the workweek and this weekend. This trough will linger over our area into the beginning of next week. This trough feature will lead to lower heights aloft and as a result cooling temperatures. Temperatures will cool heading into the weekend before leveling out by the end of the weekend and beginning of next week. Temperatures on Friday and Saturday are still forecast to be around 2-5 degrees above normal for this time of year. Then by the end of the weekend and beginning of next week temperatures are forecast to fall slightly (2-4 degrees) below normal. Afternoon high temperatures are currently forecast to be in upper 90s to around 105 degrees across the lower deserts and in the 90s across the higher terrain areas for the end of the weekend and beginning of next week. Morning low temperatures will also be decreasing and are forecast to fall into the 70s to upper 60s across the lower deserts and in the 60s across the higher terrain areas. As a result of these decreasing temperatures, HeatRisk will also be decreasing across the region. In fact, with temperatures forecast to fall below normal, HeatRisk will fall into the Minor category across the entire region.

In addition to the cooler temperatures this trough will also bring in much drier conditions along with increasing winds. These drier conditions in combination with increasing winds will result in increasing fire danger. Thus, a Fire Weather Watch has been issued for the Lower Colorado River Valley and Tonto National Forest Foothills/Southern Gila County on Friday and Saturday.

AVIATION

Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected during the TAF period under increasing mid-level cloud cover. Winds will continue to favor diurnal trends with occasional gusts during the afternoon and evening hours. Much like the previous night, confidence regarding a full E'rly shift at KPHX is low, with a few hours of VRB conditions looking more likely at this time. Regardless of what comes to fruition, W'rly flow should become established a bit earlier than normal on Wednesday. Some virga around the terminal cannot be ruled out this evening, but chances of SHRA at the terminals is too low to include in the TAFs.

Southeast California/Southwest Arizona including KIPL and KBLH: The potential for some virga and erratic winds this evening and tonight will be the main aviation concern. However, chances for SHRA in the vicinity of the terminals is less than 10% so any mention of rain has been excluded from the TAFs. Outside of any erratic winds, typical diurnal trends will be favored at each site, with flow fluctuating between SE and W at KIPL, and generally S'rly flow at KBLH. Windows of VRB to calm conditions can be expected during the overnight hours.

FIRE WEATHER

Locally elevated fire weather conditions due to low humidity and afternoon breeziness will continue through the middle of the week. Afternoon minimum humidities will increase to around 15% areawide Wednesday before drying out again through the rest of the week and into the weekend. Poor to fair overnight recoveries between 20-40% tonight and Wednesday night will also deteriorate through the rest of the week and this weekend. Temperatures will remain in an above normal category much of the week with lower desert highs topping 110 degrees at least through Thursday, and overnight lows will offer little relief, mostly in the 80s for the lower deserts. Winds will remain generally terrain driven through the middle of the week with upslope/upvalley gusts between 20-25 mph during the latter half of the afternoon into the early evening. Areas of critical fire weather conditions look likely by Friday and into this weekend as southwesterly winds increase across the region. A Fire Weather Watch has been issued for the Lower Colorado River Valley and Tonto NF/Southern Gila County zones Friday-Saturday.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Thursday for AZZ530-532-533-537-540-542>544-546-548-550-551.

Fire Weather Watch from Friday morning through Saturday evening for AZZ131-133.

Extreme Heat Warning until 8 PM MST Wednesday for AZZ560.

CA...Extreme Heat Warning from 10 AM Wednesday to 8 PM PDT Thursday for CAZ562-566-567-569.

Fire Weather Watch from Friday morning through Saturday evening for CAZ231.