textproduct: NWS Phoenix

KEY MESSAGES

- Near normal temperatures with a decent amount of clouds are expected through tonight, with low chances for sprinkles or a brief shower. Temperatures warm a few degrees into Sunday and Monday. - Very hot temperatures will return early next week creating Moderate to Major Heat Risk by Tuesday and lasting through at least Thursday.

- An Extreme Heat Watch 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.

- Isolated afternoon storm chances increase over the Arizona high terrain during the coming week, with low chances to expand into the lower deserts late in the week.

SHORT TERM /TODAY THROUGH MONDAY/

Radar at midday showed scattered echoes across southern AZ and CA. Most of the echoes were just virga or light sprinkles, but there have been several slightly stronger showers that have developed and produced brief rain showers. These showers have mainly developed along a narrow band of mid-level convergence across South-Central AZ. Parts of the greater Phoenix area have even seen a few hundredths of an inch of measurable rain out of these. There were also a few lightning flashes this morning. Chances for sprinkles and a brief shower will likely continue through this evening for areas west of Maricopa County and through tonight and early Sunday morning for Maricopa County eastward as mid and upper level moisture advection continues. Odds of measurable rain (>0.01") will remain very low (<5%) due to very dry air below 700mb (sfc T-Td spreads up around 60F). Dry air eventually moving in above 400mb Sunday, as shown in RH x-sections, will confine the moisture mainly to the 600-400mb layer and should cut down the shower chances by late- morning/midday in South-Central AZ. The drying aloft will also help to gradually disperse the high clouds from west to east.

Afternoon high temperatures for today will likely be hindered by the clouds, especially across South-Central AZ where there was broken to overcast coverage heading into the afternoon. The forecast highs of 102-106F across South-Central AZ may actually come up 2-5F shy of the forecast should the greater cloud coverage persist through the 4-5 PM hour. Greater insolation heading into Sunday should result in daytime highs reaching near 110 degrees for some locations, including Phoenix. Another couple degrees of warming is expected Monday, with the sub-tropical high persisting over the region while the center also repositions near the AZ-NM border. The temperatures Sunday-Monday will lead to widespread Moderate HeatRisk. Gradual increases in boundary layer moisture are expected over the next few days, from southerly gulf surges and storm driven pushes from the E/SE during the evening and overnight hours, but through Monday the lower level moisture will still fall well short of ideal for any monsoon convection to develop over lower desert locations. Parts of far eastern AZ will at least see an increase in afternoon monsoonal storm chances beginning Monday.

LONG TERM /TUESDAY THROUGH FRIDAY/

Forecast confidence has increased in a more pronounced period of very hot conditions for next week. The subtropical ridge is expected to gradually shift right over the region heading into Tuesday with guidance now favoring some strengthening of the high going into mid week. Forecast H5 heights are shown rising to between 594-596dam by Tuesday before peaking between 595-597dam, which is around the 95th percentile of climatology.

NBM guidance over the past 24 hours has trended noticeably warmer for the middle part of next week, mostly due to the higher heights but also somewhat due to less than previously expected moisture moving into the area. NBM forecast highs for Tuesday- Thursday are well into a 112-116 degree range for much of the lower deserts. This heat episode is very likely to bring our hottest temperatures so far this summer. The uptick in forecast temperatures has led us to issue an Extreme Heat Watch for Tuesday-Thursday for all of the lower deserts across southeast California and southern and central Arizona.

There is still some uncertainty with the evolution of the subtropical high during the second half of the week, with model guidance having it shift more to the west later next week, potentially re-centering to off the southern California coast. If this occurs, it should lower temperatures a couple of degrees by next Friday, but just as important is the potential for additional boundary layer moisture advecting northwestward into the area. There is still a good amount of uncertainty with this potential moisture increase as it will largely depend on the position of the high center. If the high center does end up moving far enough to the west, this scenario should allow for at least enough of a moisture increase and weakening subsidence to bring some high terrain showers and storms. Any chances for the lower deserts is more likely than not to hold off until next weekend when the high may again recenter toward the classic Four Corners positioning.

AVIATION

Updated at 1715Z.

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

No significant weather concerns will exist through the TAF period under periods of thicker mid and high cigs. With these cigs, expansive areas of virga and potentially an isolated SHRA/some areas of sprinkles will be likely at any point from the late morning through the evening, but with limited impact to operations. Winds will follow familiar diurnal trends, with perhaps some occasional afternoon gusts in the mid to upper teens.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major weather concerns will exist through the TAF period under periods of thicker mid/high cigs, occasional virga, and potentially an isolated SHRA/a few areas of sprinkles. Chances for operational impacts from cigs/SHRA remain too low to include in this TAF package. Winds will follow familiar diurnal trends, with extended periods of VRB conditions expected at each terminal.

FIRE WEATHER

High pressure will prevail through the coming week with near normal temperatures today warming to above normal by Monday. Surface conditions will be driest today with afternoon humidities around 5-10% and will improve only slightly to 10-15% Sunday through the first half of the week. Overnight recoveries will improve to 25-40% by Monday. There is potential for a further increase in moisture late in the the week. Winds will continue to follow diurnal upslope/downvalley patterns with modest upslope afternoon breeziness through the first half of the week before a slight increase is forecast for the second half (gusts up to 20-25 mph). Despite winds below Red Flag conditions, seasonably elevated fire danger will likely persist into next week due to dry conditions and dry fuels. There is a low chance (5-10%) for sprinkles of a brief very light shower through tonight. Otherwise, with the gradual increase in moisture through the coming week, there will likely be an increase in monsoon thunderstorm development across eastern AZ high terrain, but any chances for wetting rains in South-Central AZ is more likely to hold off until late in the week at the earliest.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Watch from Tuesday morning through Thursday evening for AZZ530>534-536>551-553>555-559-560-562.

CA...Extreme Heat Watch from Tuesday morning through Thursday evening for CAZ562-564>570.