textproduct: NWS Phoenix

KEY MESSAGES

- Temperatures will remain near seasonal levels through Monday under clear to mostly clear skies.

- Strong high pressure will build back into the region by the middle of the upcoming work week, pushing daytime highs to around or just above 110 degrees across the lower deserts.

- Minor to Moderate Heat Risk through early next week will become widespread Moderate to localized Major Heat Risk during the latter half of the week.

SHORT TERM /TODAY THROUGH SUNDAY/

Very dry and seasonably hot conditions will be the main story through the rest of the weekend. Moisture has effectively been scoured out of the column over the last couple days thanks to enhanced, deep southwesterly flow, with the 12Z KPSR sounding this morning estimating PWAT just under 0.5" and a notable inversion between 700-500 mb, indicative of synoptic scale subsidence. Across the forecast area, dewpoint temperatures in the 20s and 30s F have become commonplace and will persist into early next week. The upper level pattern is characterized by a somewhat progressive northern stream, with troughing over the Northwest US. To the south, midlevel water vapor imagery and 500 mb RAP analysis indicate a subtropical high/anticyclonic flow, stretching from off the Northern Baja all the way through Western TX and the TX Panhandle. Ensembles remain in excellent agreement that the subtropical high and associated heights aloft will remain suppressed as the northern stream troughing progresses into the Northern Plains this weekend. As a result, rather stable H5 heights in a 588-591 dam range will prevail through Sunday, representing values between the 70th-90th percentile of climatology. Despite the positive midlevel height anomalies, very dry conditions and clear to mostly clear skies will provide for effective radiative cooling overnight, leading to widespread early morning lows in the 70s (near to slightly below normals). Afternoon highs are expected to reach a near normal range, around 105F for the typically hotter lower desert locales.

LONG TERM /MONDAY THROUGH FRIDAY/

By Monday, the broad trough situated to our north is forecast to eject into the Central Plains followed by the subtropical high over northern Mexico starting to shift northward into our region. Monday will be somewhat of a transition day with heights rising to 592-594dm as the high center nears southwest New Mexico and our flow also shifts out of the south. Forecast highs rise more into a 105-109 degree range Monday while the first Gulf moisture surge pushes surface dew points out of the 20s.

Guidance then shows the center of the ridge shifting along the southern border of Arizona/New Mexico Tuesday into Wednesday with heights rising more into a 594-596dm range by Wednesday. The position of the high will help to bring additional Gulf moisture surges into midweek, likely raising surface dew points into the low 40s to low 50s Tuesday and upper 40s to mid 50s Wednesday. This is a slight improvement from what models showed 24 hours ago and now may be enough for an introduction of low-end PoP chances only within higher terrain areas. The NBM does not really depict these chances, but if the moisture forecast holds we may introduce some isolated 10-15% PoPs for higher terrain locations in southwest and south-central Arizona on Tuesday and/or Wednesday. The moisture may end up being enough for convection, but with the ridge basically being right overhead the subsidence will likely inhibit convection a good amount. As of right now, the moisture only looks to last through around Wednesday or at the latest Thursday as drier westerly flow is suggested again late next week.

Temperatures will continue to heat up through the middle part of next week as the ridge strengthens and shifts into our region. NBM forecast highs reach near 110 degrees Tuesday leading to a widespread Moderate HeatRisk before likely peaking closer to 115 degrees on Thursday. Localized areas of Major HeatRisk begin to show up on Wednesday as highs reach 110-113 degrees, but more so on Thursday with forecast highs between 112-115 degrees. Fortunately, guidance shows another trough moving into the Northwestern U.S. Wednesday into Thursday before shifting more into California and the Great Basin Friday into next weekend. As a result, temperatures are expected to begin to lower starting Friday, but the 110 degree days may still hold on into Saturday.

AVIATION

Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns under clear skies can be expected throughout the TAF period. The overall wind pattern will favor the typical diurnal tendencies with occasional afternoon/early evening gusts in the mid to upper teens, otherwise wind speeds will be aob 7 kt.

Southeast California/Southwest Arizona including KIPL and KBLH: Gusty winds, especially at KIPL, will continue to be the main weather issue under clear skies throughout the TAF period. A westerly wind component will prevail at KIPL while winds will fluctuate between the south to southwest at KBLH. At KIPL, wind gusts of 20-25 kts are expected this evening, with some occasional gusts of 25-30 kts possible. Gusts will taper off during the overnight hours becoming light and variable. At KBLH, some occasional gusts into the mid to upper teens are possible during this afternoon and early Saturday evening hours.

FIRE WEATHER

Near normal temperatures and very dry conditions will continue through Monday with fairly light winds. MinRHs will be in the single digits each day, while overnight recoveries will be poor, ranging between 15-35%. Some afternoon and early evening upslope breeziness will be common, but gusts will mostly stay below 20 mph. The very low RHs and light breezes should lead to elevated fire weather conditions during the latter half of the afternoon/early evening hours. Going into the middle part of next week, moisture will improve raising MinRHs to between 10-15% by Wednesday, but temperatures will also warm to above normal. Daytime breeziness should also increase with more gusts reaching the 20-25 mph range.

PSR WATCHES/WARNINGS/ADVISORIES

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