textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Temperatures will continue to warm through the weekend and into 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 for most of next week.

- Dry conditions will prevail through the weekend, although a sprinkle cannot be ruled out Saturday into Sunday, before isolated storm chances return over the Arizona high terrain by the middle part of next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Subtropical high pressure has nudged into the region, with 594dam heights centered over southern NM and 590-592dam heights over the local area. This increase in heights over the area has yielded a warming of temperatures. Midday temperatures were running around 2-5 degrees warmer than the same time yesterday and with this warming, afternoon high temperatures are forecast to be around seasonal averages, with lower desert highs in the 104-107F range.

Some high-level clouds have begun spreading into the region. Much of this is moisture shedding off of former tropical system Douglas. Clouds will continue to stream into the region from the southwest and thicken, through this weekend as remnant midlevel vorticity is also shown to move north toward L.A. later on Saturday with a weak shortwave progressing across AZ. PWATs will go from abnormal dry at around 0.3" today to seasonal levels, 0.9-1.1", by the end of the day Saturday. This moisture flux will be confined to the mid and upper levels, with dry air persisting below 700mb. Dew point temperatures will hardly budge from today to tomorrow. The moisture aloft will be deep enough to support spotty light showers Saturday, but with the dry sub-cloud layer most precipitation over the lower deserts will evaporate before reaching the ground. There will be better chances for showers and even light rainfall accumulation over higher elevations of northern AZ. Sprinkles have at least been added to the forecast for portions of South-Central AZ. The chances of getting a lightning strike out of this activity is very low (<5%), due to very low instability. Heading into Sunday cloud cover will gradually scatter out as the weak shortwave and lift progresses off to the north.

The thicker clouds Saturday will likely moderate the surface temperatures to a degree, limiting the solar radiation. Latest NBM forecast highs have trended a degree cooler on Saturday than previous forecasts, but it would not be surprising to see highs fail to reach 105F, especially across South-Central AZ. The added cloud- cover will also help insulate morning temperatures Saturday morning, with lows likely staying in the 80s in a few spots. With more sun mixing in on Sunday, and the gradual warming atmosphere, surface temperatures will likely run a few degrees warmer than Saturday. A few lower desert spots will even near 110F, including in Phoenix where there is around 30-50% odds of reaching the mark. Besides the heat, and potential wet stuff falling from the sky, winds will remain seasonally breezy in the afternoons through the weekend, with gusts mostly up to 15-20 mph.

LONG TERM /MONDAY THROUGH THURSDAY/

The weather pattern is expected to gradually shift more into a monsoonal pattern starting next week. However, a good deal of uncertainty remains with the positioning of the subtropical ridge and thus the amount of subsidence, and whether or not much moisture will advect into the area. The ridge is expected to strengthen early next week and briefly form a center somewhere along the Arizona/New Mexico border, but guidance is now leaning toward the center of the high eventually shifting westward to off the southern California coast by around Thursday. At least for a brief period before potentially repositioning again back toward the Four Corners toward next weekend.

H5 heights are still expected to fall within seasonal normals on Monday, but some strengthening Tuesday into Wednesday is likely to push heights above the 90th percentile. The more favorable positioning of the high by Monday should also allow for some modest Gulf of California moisture surges, potentially leading to surface dew points nearing 50 degrees and low level mixing ratios of 6-7 g/kg. Although this moisture will be an improvement, it will not be enough to counteract the subsidence from the ridge, at least on Monday. Some further improvement in moisture over the eastern Arizona high terrain into the middle of next week should finally allow for some isolated convection, but as of now it does not look to be much more than 10-20% chances.

The bigger forecast concern next week will be the widespread Moderate HeatRisk developing by Tuesday and potentially some areas of Major HeatRisk. Ensemble peak H5 heights of 594-596dm look to occur on Tuesday into early Wednesday and this should lead to daytime highs rising into a 110-115 degree range both days, with odds of exceeding 115F at 30-50% in some locations, including Phoenix. Overnight lows will also trend upward with many locations staying in the 80s and potentially near 90 degrees in central Phoenix. Guidance then indicates lowering heights over at least Arizona later next week as the ridge center shifts west southwestward to off the coast of California. If this occurs, it should shave off 2-3 degrees from our highs by next Friday.

AVIATION

Updated at 2300Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather issues will exist through Saturday evening under periods of thicker mid/high cigs. In fact, expansive virga and very isolated SHRA will be likely during daylight hours Saturday. Trends in wind shifts and speeds should be similar to the past 24 hour with limited gustiness.

Southeast California/Southwest Arizona including KIPL and KBLH: No weather issues will exist through Saturday evening under period of thicker mid/high cigs, occasional virga, and a few isolated SHRA. Chances for operational impacts are far too low to include in this TAF package. Confidence is good that winds will oscillate between SE and SW with modest afternoon/early evening gustiness. Periods of near calm conditions may be common after sunrise.

FIRE WEATHER

Building high pressure over the next several days will lead to warming temperatures, eventually leading to above normal temperatures by early next week. Winds will remain fairly light into next week with only the typical afternoon upslope/upvalley 15-20 mph gusts and mainly starting Sunday. Afternoon minimum humidities will continue to range between 5-10% through at least Saturday, with overnight recoveries only reaching 15-30% through Saturday night, before improving to 10-15% starting Sunday. Despite the diminished winds, seasonably elevated fire danger will persist through the weekend due to very dry conditions and very dry and receptive fuels. Moisture is still expected to gradually increase over the region during the first half of next week, but overall dry conditions should persist.

PSR WATCHES/WARNINGS/ADVISORIES

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