Area Forecast Discussion

UPDATE

Updated Aviation

KEY MESSAGES

- Fairly stable temperatures around 4 to 8 degrees above daily normals will result in widespread Moderate Heat Risk, with isolated pockets of Major Heat Risk through the middle of next week.

- An increase in moisture by the end of the week into the weekend will lead to slight chances for showers and storms, with better chances currently focused during morning and overnight periods.

- Overnight low temperatures will be noticeably warmer as a result of increased humidity, with the typically warmer lower desert locales struggling to cool below 80 degrees by the weekend.

SHORT TERM /TODAY THROUGH SATURDAY/

Current RAP analysis and satellite imagery shows broad ridging over the Eastern Pacific and an upper level low off the western coastline of the Baja Peninsula. With this upper level low a swath of moisture can already be seen pushing into the Desert SW from the Gulf of California. Models remain in good agreement that this upper level low will continue to track northeastwards along the Baja Peninsula causing PWATs to climb to 1.0-1.5" or near 200-250% of normal, throughout the weekend.

The first chance of activity will be Friday morning in southeastern CA and southwestern AZ. During this time, in addition to the plentiful moisture, deterministic runs signal for decent pocket of cyclonic vorticity riding up along the Colorado River Valley Friday, with the HREF showing MUCAPEs between 250-500 J/Kg. These conditions will be favorable for the development in isolated showers starting early Friday morning before dissipating heading into the afternoon hours. By Saturday much of the lifting mechanisms in place from Friday will have dwindled, however mixing ratios over southcentral AZ and the Phoenix Metro will begin to increase from 7-8 g/Kg to between 8-10 g/Kg by Saturday afternoon/evening, and minimal MUCAPE (~100-250 J/Kg) will remain over the region. This can be enough to facilitate the development of isolated showers in the lower deserts, however models hint at the bulk of the activity remaining east of the Phoenix Metro in the eastern higher terrain areas where PoPs are currently only around 10-15%.

Temperatures through the remainder of the workweek and into the beginning of the weekend will remain fairly stable between 104F-110F across the lower deserts. This is a result in H5 heights remaining fairly stable as well, with heights between 588-591 dam persisting over the Desert SW. One notable difference will be warmer overnight lows, thanks to the increase in moisture and some influence from cloud cover Friday-Saturday leading to lows in the upper 70s to mid 80s. All that being said, widespread Moderate to localized areas of Major HeatRisk will in place through the weekend and into next week. So ensure to stay hydrated and follow proper heat safety protocol.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

A few changes are noted in the latest ensembles and global model runs: measures of moisture over the forecast area (e.g., PWATs, mixing ratios) are peaking at slightly lower values, however, moisture is not effectively scoured out and will likely linger into early next week, providing further chances for afternoon AZ high terrain thunderstorms. The limited instability with large T/Td spreads and dry sub-cloud layer will favor dry lightning and gusty outflow winds versus heavy rainfall, as is typical with convective activity in June. These changes come as ensembles now show the cyclonically curved polar jet, and any attendant shortwave troughs rotating through the base of the mean trough over the North-Central CONUS, remaining further east of the region. While flow aloft will turn out of a drier westerly or northwesterly direction Sunday, the more distant influence of polar jet will mean that the flow stays fairly weak over region, much less effective at scouring out lingering moisture. Positive midlevel height anomalies remaining fairly stagnant through the middle of the week will allow for steady temperatures in a 4 to 8 degree above normal range. Temperatures will be slightly higher in the western deserts, but regardless, lower desert highs will peak near or just above 110F for the typically hotter spots.

AVIATION

Updated at 2325Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Wind forecasts will be the primary weather issue through Friday evening under thickening mid/high cloud decks. Confidence is good that W/SW winds will persist longer into the overnight than previous days. Modeling suggests periods of stronger gusts ~20kt will be possible through the evening, though confidence on coverage and duration is low. Some areas may never truly obtain an easterly fetch Friday morning, but rather becoming variable before rapidly switching back to a westerly component. More widespread and pronounced gustiness is likely Friday afternoon/evening.

Southeast California/Southwest Arizona including KIPL and KBLH: The prospect for a few SHRA Friday morning will be the main weather issue under mid/high cigs. Confidence is good that S/SE winds will swing W/SW briefly mid/late evening before reverting to S/SE overnight. Have not included a VCSH mention in this TAF package, however a few SHRA will be possible around and just after sunrise with periods of virga likely throughout the day.

FIRE WEATHER

Temperatures 3-6 degrees above normal will prevail with lower desert highs near 110F in some of the hotter spots, especially by the weekend. Dry conditions will continue today with relative humidity bottoming out around 8-15%. Low level moisture will continue to improve improve through this weekend with minimum humidity largely above 15% and overnight recoveries generally improving from poor to fair. With the increasing moisture will also come increasing chances for isolated shower/T-storm activity starting Friday morning along the Colorado River Valley and then again across the AZ high terrain over the weekend, with gusty outflow winds and dry lightning potentially leading to natural fire starts being the main hazards. The overall wind pattern will remain diurnal with speeds at or below 15 mph and limited afternoon upslope gustiness.

PSR WATCHES / WARNINGS / ADVISORIES

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