textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion.

KEY MESSAGES

- Very hot temperatures will return over the next few days creating Moderate to Major Heat Risk by Tuesday and lasting through at least Thursday.

- An Extreme Heat Warning has been issued for Tuesday through Thursday across the lower deserts, including Phoenix, Yuma, and El Centro. Forecast highs are currently 111 to 116 degrees.

- Dry conditions will prevail much of the coming week, although isolated storm chances are expected to return over the Arizona high terrain by Tuesday or Wednesday.

SHORT TERM /TODAY THROUGH MONDAY/

It looks a bit messy on early afternoon 500mb RAP analysis, but it appears that the center of the sub-tropical high has shifted westward toward Arizona after spending some time over Texas and New Mexico during the start of the weekend. As this shift occurs, drier air has been funneling in off the eastern Pacific toward the Desert Southwest, allowing for clearer skies after a very cloudy Saturday and first part of Sunday. The greater insolation this afternoon compared to yesterday will allow for a noticeable warm up for parts of the region after some areas (mainly in south- central Arizona) failed to reach the triple digits. In fact, highs for the Phoenix metro might be a good 5-10 degree warmer than the 4th of July, which translates to readings around 105-110 degrees. A similar temp range can be expected elsewhere across the lower deserts, but the day-to-day difference will not be as stark, running maybe 2-4 degrees hotter.

The high will more or less sit over the Desert Southwest as we transition into the start of the upcoming week, which will allow for further warming regionwide. Afternoon highs 110F and above will be common across lower elevation locations, pushing us to just below Major HeatRisk levels. Overnight lows will be the main reason why most areas avoid reaching this HeatRisk threshold, therefore preventing any Extreme Heat products from being issued for Monday. However, further strengthening of the high as we progress through the front half of the week means that we will not escape Extreme Heat completely, and that will be discussed more below.

LONG TERM /TUESDAY THROUGH SATURDAY/

Guidance remains very confident in the further amplification and repositioning of the subtropical high directly over Arizona for Tuesday and Wednesday before shifting more to the west late week. Forecast H5 heights are shown rising to above the 90th percentile later on Tuesday and lasting through Wednesday, while boundary layer moisture slowly improves. Daytime temperatures are expected to reach to 110-114 degrees on Tuesday before likely peaking at 112-116 degrees Wednesday. The slightly higher moisture will also help to keep overnight temperatures very warm with lows on average in the mid 80s to as warm as the low 90s in the urban core of Phoenix. Forecast confidence continues to increase for a period of 2-4 days of Extreme Heat later this week with the core days being Wednesday and Thursday. In response to the forecast certainty, the Extreme Heat Watch has been upgraded to a Warning, running between Tuesday and Thursday. Friday may also need to be included depending on how quickly and how far west the high center moves later in the week.

The gradual increase in moisture early this week should eventually bring some isolated shower and storm chances, but the strong subsidence under the ridge will definitely hold back the potential convection through midweek. Low end PoPs of 10-15% are mainly forecast for the higher terrain east of Globe through Thursday with little if any chance of anything nearing the lower deserts. Once the high shifts far enough to the west by Friday, guidance does show some additional moisture advection across southern and central Arizona, but how much and exactly when is still unknown. A good portion of the ensemble members then show the high center drifting back to the north northeast next weekend potentially setting up over Utah or western Colorado. If this occurs, it should be quite favorable for monsoon storm activity to increase across much of our area, either at some point next weekend or during the first part of the following week. The subtropical ridge is also expected to strengthen again as it shifts somewhere near the Four Corners area. This would keep higher than normal heights over the Desert Southwest and likely lead to a continuation of above normal temperatures through at least next weekend.

AVIATION

Updated at 2330Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No significant aviation weather concerns will exist through the forecast period. Winds will mostly follow typical diurnal trends, aside from extended periods of light and vrb prior to the onset of diurnal wind shifts. At KPHX, there will be a later than usual easterly shift on Monday morning, around to 10-12Z, due in part to an increase in west winds between 03-10Z, up to 20-25 kts, above the surface around 500-1000 ft AGL. Clouds have scattered out and will remain FEW to SCT through this afternoon and then will increase to SCT to BKN again this evening into early Monday morning with bases mostly staying aoa 15 kft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns will exist through the TAF period under mostly clear skies. At KIPL, current S-SW winds will shift out of the west by sunset tonight. Sundowner wind gusts of 20-25 kt will be likely later this evening for a few hours between 01-06Z. At KBLH, winds will favor a S-SW component with speeds to around 10 kts and gusts up to 20 kts.

FIRE WEATHER

Hotter conditions, but a slight improvement in moisture is expected for the first half of this week. Lower desert highs will warm to over 110 degrees as early as Monday before peaking at around 115 degrees midweek. Minimum afternoon humidities of 10-15% are anticipated each day with overnight recoveries of 25-40%. Winds will follow diurnal upslope/downvalley patterns with modest upslope afternoon breeziness mostly staying below 20 mph, which will continue to result in periods of elevated fire danger. A gradual increase in moisture this week should eventually lead to some isolated storm chances across the eastern Arizona high terrain, but any chances for wetting rains in South-Central AZ is more likely to hold off until next weekend.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Tuesday to 8 PM MST Thursday for AZZ530>534-536>551-553>555-559-560-562.

CA...Extreme Heat Warning from 10 AM Tuesday to 8 PM PDT Thursday for CAZ562-564>570.