textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- An Extreme Heat Watch has been issued for Phoenix and portions of southeast California on Sunday and Monday.

- Widespread moderate HeatRisk will develop today into Saturday with isolated major HeatRisk early next week.

- Monday should be the warmest day next week with lower desert high temperatures peaking between 105 and 110 degrees.

SHORT TERM /Today through Saturday/

Upper level ridging will fully spread across the region today as the weak cut-off low ejects eastward into west Texas. H5 heights will rise to 581-583dm later today, or near the 90th percentile of climatology for early May. Temperatures are expected to easily top 100 degrees across the western deserts with just more than a 50% probability of reaching 100 degrees in Phoenix. Very dry air in place will keep skies completely clear while also allowing for overnight temperatures to cool to within a few degrees of normals. Some flattening of the ridge will occur on Saturday as a weak disturbance tracks southeastward across the Northern and Central Rockies, but it will not allow for any cooling. In fact, lower level warming will still be occurring into Saturday with H8 temperatures rising another degree C. As a result, Saturday's forecast highs bump up a degree or so across the western deserts to 102-105 degrees and by 2-3 degrees in Phoenix to 102-104 degrees. The hot temperatures for both days will cause Moderate HeatRisk across the majority of the area.

LONG TERM /Sunday through Thursday/

A stronger subtropical ridge will also build across the eastern Pacific through Saturday, eventually shifting eastward into our region Sunday into Monday. This will give a quick boost to upper level heights raising H5 heights to 585-588dm Sunday before peaking between 588-591dm Monday, which is near the 99th percentile of climatological records. Even hotter temperatures will occur across the area Sunday into Monday with some Major HeatRisk developing across the lower deserts. Highs Sunday are expected to reach 104-106 degrees in Phoenix to 105-108 degrees across the lower deserts of southeast California and southwest Arizona. With peak heights on Monday, highs are likely to be between 106-108 degrees in Phoenix to 107-110 degrees across the western deserts. Monday's highs should be the closest to records with the forecast only 2-4 degrees shy.

An Extreme Heat Watch has been issued for the Phoenix metro for Sunday and Monday, while the Watch remains in effect for the same time period across western Imperial County. This heat event will bring our hottest temperatures so far this spring, but again the dry conditions will allow for a decent reprieve during the overnight hours with most locations dipping into the upper 60s to the lower 70s.

By Monday night into Tuesday, a weak cut-off low that forms over the weekend just off the coast of southern Baja, is expected to track toward southern California as an open wave. This disturbance is not anticipated to bring much of anything other than some higher level clouds on Tuesday and Wednesday, but it should help to lower heights and temperatures slightly. Although the forecast temperature spread increases starting Tuesday, models still heavily favor a cooling trend into the latter half of next week as the ridge weakens and ejects eastward. High temperatures are shown to drop back closer to 100 degrees by next Wednesday or Thursday.

AVIATION

Updated at 1124Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather impacts are expected through Saturday morning under mostly clear skies. Winds will follow typical diurnal tendencies with a W'rly shift expected by early afternoon today. W'rly winds this afternoon and evening will increase to around 8-12 kts with gusts up to around 20 kts. An increase in W'rly winds above the surface this evening is expected to delay the diurnal E shift until close to sunrise Saturday at KPHX. No slantwise visibility impacts are expected today.

Southeast California/Southwest Arizona including KIPL and KBLH: No significant aviation weather impacts are expected over the next 24 hours under clear skies. Winds will tend to follow typical seasonal and terrain trends. At KIPL a light E is expected to develop by midday and shift back W this evening with speeds increasing up to 8-12 kts and gusting up to 20 kts for a few hours. At KBLH winds will predominantly favor a S/SW component. Both terminals will see periods of light variability, especially this morning.

FIRE WEATHER

High pressure will remain in place leading to hot and dry conditions lasting through at least the first half of next week. Highs are forecast to top 100 degrees across the lower deserts by Saturday with the peak of the heat occurring on Monday. Expect MinRHs from 7-12% each day with poor overnight recoveries mostly between 20-35%. Winds will remain relatively light for much of the period, but some afternoon breeziness with gusts around 20 mph likely. The combination of the hot temperatures, very low RHs, dry fuels, and breezy conditions focused during the late afternoon hours should result in elevated fire weather conditions for portions of the area.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Watch from Sunday morning through Monday evening for AZZ537-540-542>544-546-548-550-551.

CA...Extreme Heat Watch from Sunday morning through Monday evening for CAZ562-563-566.