textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- Temperatures will gradually cool through the middle of the week, but only from record breaking levels to a more typical above normal threshold.

- Isolated showers and potentially a few thunderstorms will be possible through Wednesday, primarily focused over higher terrain of south-central Arizona.

- Temperatures will warm again by early next week potentially approaching record highs.

SHORT TERM /Today through Wednesday/

A complex flow pattern exists over the SW Conus early this afternoon with a broad trough/quasi-zonal jet emanating from the East Pacific containing several low amplitude shortwaves aimed towards the forecast area. One such wave was lifting through northern Arizona today while the southern Arizona pattern becomes even more complicated by the presence of nearly stationary MCV's over northeast Sonora. Shallow 7-8 g/kg mixing ratios continue to hover over much of the CWA with 12Z PWATs likely nearing 1.00", or near a late March climatological maximum. While deep layer westerly flow will thin boundary moisture closer to 6 g/kg this afternoon, forecast BUFR soundings suggest MLCape ~500 J/kg with minimal CinH. However with ascent mechanisms becoming absent across the CWA this afternoon, there appears to be little impetus towards deep convection, and recent HREF output depicts very limited activity in and around the forecast area. While some gusty winds could be generated by any convective elements given DCape nearing 1500 J/kg, strengthening deep westerly winds through the lower troposphere should disrupt any organized outflow boundaries fairly rapidly.

Jet energy with additional embedded shortwaves will enter the region Tuesday and Wednesday providing the next modest chances of accumulating rainfall. Copious amounts of mid/upper level moisture will stream into the Southwest starting tomorrow with extended periods of thick cloud cover. While periods of ample synoptic scale lift will be present across the area during this time frame, paltry low level moisture with mixing ratios falling below 5 g/kg will limit the ability for saturated midlevel ascent to materialize into rain reaching the surface. Instead, widespread virga should be common with only a few isolated showers surviving, and better chances for accumulation focused over higher terrain areas given a smaller sub-cloud dry layer. The best chance for accumulating showers still appears to arrive late Tuesday night through Wednesday morning. NBM POP output seems to be exhibiting an overzealousness in both raw magnitude and expanse, and have trimmed back values in both respects. Otherwise, prolonged periods of thick clouds could easily narrow the diurnal temperature spread and retard afternoon highs below the mandated NBM forecast such that readings Tuesday may struggle to reach 90F, and middle 80s on Wednesday.

LONG TERM /THURSDAY THROUGH SUNDAY/

The weather pattern will shift once again later this week with upper level troughing setting up across the central U.S. and a ridging building off the West Coast before eventually sliding into our region by the weekend. Dry west northwesterly flow takes over across the Desert Southwest starting Thursday with moisture levels lowering and temperatures initially staying fairly stable as a weather system passes by to our north. NBM forecast highs remain in the mid to upper 80s for Thursday and Friday, but this will not last long as the ridge will be entering our region by Saturday. Fortunately, guidance favors the ridge already weakening as it moves into our region, but it will be enough to push daytime highs back into the low to mid 90s over the weekend.

AVIATION

Updated at 0550Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Easterly winds overnight and through the morning will stay somewhat elevated at KPHX and KIWA at speeds of 5-10 kt. But winds at KSDL and KDVT will remain light and variable. By late this morning/early this afternoon winds will go south/southwesterly with speed sup around 10 kt. Then winds will pick up out of the west by 21Z with gusts upwards of 20-25 kt continuing into the overnight hours. Shower and storm chances Tuesday afternoon will be low (<10%), and thus excluded from TAFs, but development near the metro area cannot be ruled out. A cold front will move through during the overnight/morning hours on Wednesday. A broken line of light showers is possible (<10%), but most activity may fall as virga. Due to the low chances this has also been excluded from the TAFs. Mid and high clouds will continue to pass over the area, with convective cloud bases as low as 9-10K ft AGL in the afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: Westerly winds at KIPL and southwesterly winds at KBLH aob 10 kt will become light and variable around 09Z. Winds will then redevelop a westerly component (southwesterly at KBLH) by the mid- to-late morning hours. Wind gusts upwards of 20-25 kts are once again expected during the afternoon and evening hours. SCT to BKN mid and high clouds will persist.

FIRE WEATHER

Moisture levels have improved helping to boost humidities and MinRHs to around 20%. The better moisture has also helped to bring back low- end rain chances with a few isolated thunderstorms still possible today across the eastern districts. Isolated rain chances should continue for the eastern districts through Wednesday, but thunderstorm chances will mostly end after today. Outside of any convective induced winds, expect typical spring afternoon upslope gusts 20-25 mph. The near record breaking temperatures will cool slightly by Tuesday and more so starting Wednesday. Rain chances will completely come to an by Thursday as gradual drying and warming occurs. Daytime breeziness will also continue through Friday with fire weather conditions worsening as MinRHs drop to below 15%.

PSR WATCHES/WARNINGS/ADVISORIES

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