textproduct: NWS Phoenix

KEY MESSAGES

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

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

- Minor to Moderate Heat Risk is forecast through early next week before shifting to widespread Moderate to localized Major Heat Risk during the latter half of next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Latest mid-lvl wv imagery and 500 mb streamline analysis reveals broad troughing over the E Pacific while a low amplitude ridge is centered over the southern Rockies and New Mexico. The entire state of Arizona is now under W to SW flow aloft allowing notably drier air to overspread our forecast area. This dry air is also readily apparent in the 12Z KPHX RAOB with an observed PWAT value of 0.57". Sfc dew points have also decreased significantly into the upper 20s to lower 30s across the region. Coincidentally, chances of any convection developing this afternoon is essentially zero and even mountain cumulus development will be completely eliminated with clear skies expected over the entire state.

As large scale troughing begins to overspread the forecast area, heights aloft will decrease to a near normal range over the weekend, resulting in highs right around normal in a 100-106 degree range today through Sunday. Overnight lows will also be noticeably cooler due to the lower humidities and mostly clear skies which will lead to efficient radiational cooling. Most locations will see lows in the 70s through the weekend with more rural lower desert locations potentially dipping into the mid to upper 60s. The HeatRisk across the area will drop fully into the Minor category for this weekend.

LONG TERM /MONDAY THROUGH THURSDAY/

The upper level trough is forecast to break down and shift to our northeast starting early next week. As this occurs, the subtropical high centered just to our south will start to shift northward while also beginning to strengthen. Currently, model guidance favors the high center reaching southern Arizona by next Tuesday with H5 heights rising to around 595dm. This will allow for a warming trend to commence starting Monday with daytime highs as warm as 110 degrees by Tuesday.

Models also mostly suggest the high center setting up over or near southeast Arizona starting Tuesday and staying in that general vicinity through midweek. This positioning should allow for some modest Gulf of California moisture surges for a few days next week with forecast surface dew points gradually increasing back into the 40s to maybe the mid 50s. However, even with the modest increase in lower level moisture it will fall short of what would be needed for any convection to form. The close proximity of the high center and its strength will keep the subsidence quite strong next week, basically keeping a lid on any potential convection.

Guidance shows the ridge peaking at around 596-598dm next Wednesday and Thursday with daytime highs expected to break 110 degrees both days and some locations potentially reaching 115 degrees. Widespread Moderate HeatRisk will develop as early as Tuesday with a high probability of localized areas of Major HeatRisk for at least next Wednesday and Thursday. Guidance then favors another trough passing by to our north by next Friday or Saturday, likely dampening the ridge and starting a slight cooling trend.

AVIATION

Updated at 1730Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Gusty afternoon/early evening winds will be the only aviation weather issue through the TAF period under clear skies. Winds this morning have remained light (AOB 6 kts) with extended periods of VRB to calm conditions, which are likely to continue for the next hour or so. By the afternoon, south to southwest winds are likely to establish, with gusts to around 20 kts for several hours later this afternoon into the evening. Overnight, winds will relax and eventually shift out of their typical nocturnal E/SE directions.

Southeast California/Southwest Arizona including KIPL and KBLH: Gusty winds will continue to be the main weather issue through Saturday morning under clear skies. Confidence is good that a W/SW component will be maintained at KIPL. At KBLH, directions should oscillate between SSE and SW. Late afternoon/evening gusts above 20 kts are likely with good confidence of periodic gusts near 30 kts at KIPL this evening.

FIRE WEATHER

A pronounced drying trend will continue into the weekend, resulting in a complete elimination of rain chances across the entire region. Temperatures will fall to within a degree or two of normal today and seasonal temperatures will carry into this weekend. Minimum humidity levels will drop into the single digits by Saturday and remain there at least through next Monday. Correspondingly, overnight recovery will fall into a poor to fair 20-40% range. Upslope afternoon gusts up to around 20-25 mph will be common over the next several days resulting in periods of elevated fire danger. By the middle of next week, temperatures will warm markedly with minimum humidity levels hovering around 10-15% and continued gusty winds yielding dangerous conditions for any ongoing wildfires.

PSR WATCHES/WARNINGS/ADVISORIES

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