textproduct: NWS Phoenix

UPDATE...Updated 12z Aviation Discussion

KEY MESSAGES

- Temperatures will continue to warm through the rest of the week and into the first part of next week, reaching above normal levels by around Monday. - As the heat builds, it will lead to increasing coverage of Moderate Heat Risk and highs eventually reaching 110 degrees next week.

- Dry conditions will prevail through at least the weekend before isolated storm chances return over the Arizona high terrain during the first part of next week.

SHORT TERM /TODAY THROUGH FRIDAY/

Broad upper level troughing remains positioned over the Western U.S., but it continues to weaken while also beginning to shift northward away from the Desert Southwest. A very strong upper level ridge is also centered over the Southeastern U.S. and this is expected to expand westward into Friday, quickly raising heights over our region. H5 heights are forecast to rise from the current 582-586dm to 589-593dm by Friday afternoon, but temperatures will lag the rising heights by roughly a day. Highs today will top 100 degrees across the bulk of the lower deserts with the warmest locations reaching 102-104 degrees. Hotter temperatures will be realized on Friday with forecast highs more in a 104-107 degree range, but some higher clouds are expected to begin moving in from the southwest. The low and mid levels will however remain very dry going into the weekend with surface dew points averaging 25-35 degrees and afternoon humidities still dipping below 10%.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

The not so bad temperatures to start off July will unfortunately not last any longer as the subtropical high is expected to gradually become more of a dominant feature starting this weekend. Models have been struggling a bit with the incoming cloud cover from a decaying tropical system well to our southwest and how much it could impact temperatures this weekend. Forecast temperatures for this weekend have been trending lower over the past couple of days, likely somewhat due to the expected higher clouds but also due to the ridge not strengthening any further. A decent amount of semi-thick higher cloud cover on Saturday will easily keep daytime highs within the normal range, but that may change going into Sunday as the clouds should be decreasing. Forecast highs Sunday still fall short of 110 degrees in most spots, but readings are likely to reach between 107-109 degrees overall.

We will also have to begin to contend with increasing boundary layer moisture and higher dew points making it feel more uncomfortable as early as Sunday, but the higher humidities will be more noticeable going into the middle of next week. Ensembles have begun to shift where the center of the subtropical high is most likely to set up early next week with it more likely shifting directly over southern and central Arizona instead of to our northeast. This should not last long however, as the high is then favored to shift farther westward, potentially even settling off the coast of California by next Wednesday. The exact positioning of the high will not stop it from getting hotter as H5 heights are heavily favored to rise more into a 592-595dm range starting Monday and likely staying there through at least Tuesday and possibly Wednesday before lowering slightly again. Temperatures and humidities are expected to rise at the same time early next week with daytime highs peaking on Tuesday and/or Wednesday between 110-114 degrees across the lower deserts. This will lead to a widespread Moderate HeatRisk with potentially even some localized Major HeatRisk. Overnight temperatures will react to the increasing moisture and higher daytime temperatures with lows rising into the 80s nearly everywhere and potentially to near 90 degrees for portions of the Phoenix area by Tuesday.

Even with the increase in moisture during the first part of next week, we are not expecting much convective potential. Lower level moisture will still be very marginal with afternoon surface dew points still mostly in the mid to upper 40s. The marginal moisture will also have to contend with a high center directly over or close to our area creating a decent amount of subsidence. We may get some isolated Arizona high terrain showers or storms starting Monday or Tuesday, but PoPs are barely reaching 10-15%. For the latter half of next week, guidance is hinting at a further increase in moisture, but nothing too drastic. It may be enough to increase shower and storm coverage somewhat over higher terrain areas, but for now storm chances for the lower deserts still look to mostly remain below 10%.

AVIATION

Updated at 0510Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through the TAF period. Winds will follow typical diurnal tendencies with a brief period of southerly winds late this morning before the afternoon westerly shift. Winds will mostly be aob 10 kts, however, the possibility of gusts in the mid teens may be possible this afternoon. Otherwise, skies will remain mostly clear, with FEW high clouds moving into the area near the end of the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected through the TAF period. At KIPL, westerly winds shift out of the south to southeast by 14Z and continue into the afternoon hours before shifting back out of the west during the early evening hours. At KBLH, winds will generally fluctuate out of the south to southwest. Overall wind speeds will remain under 12 kts with some limited afternoon and early evening gusts in the mid to upper teens. Skies will remain mostly clear, with FEW high clouds moving into the area near the end of the TAF period.

FIRE WEATHER

High pressure will gradually move into the region over the next few days allowing winds to return to normal patterns with only the typical afternoon upslope/upvalley 15-20 mph gusts. Temperatures will warm up further, rising into the normal range starting Friday. Afternoon minimum humidities will continue to range between 5-10% through at least Saturday with overnight recoveries only reaching 15-30%. Despite the decrease in winds, seasonably elevated fire danger will persist through the weekend due to very dry conditions and very dry and receptive fuels. Moisture is likely to begin to increase over the region during the first half of next week allowing minimum humidities to improve to 10-15%, but temperatures will also heat up further with lower desert highs likely reaching 110 degrees.

PSR WATCHES/WARNINGS/ADVISORIES

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