textproduct: NWS Phoenix

KEY MESSAGES

- Scattered light showers will continue across the area today with the most widespread coverage across higher terrain locations north and east of the Phoenix area.

- Drier weather will return for much of the weekend before more unsettled weather is expected during the first half of next week.

- Temperatures are expected to remain at least slightly above normal through the first half of next week.

SHORT TERM /TODAY THROUGH SATURDAY/

The cut-off low centered off the coast of southern California is continuing to weaken while it is getting absorbed back into the larger scale troughing regime over the eastern Pacific. Broad upper level divergence ahead of the cut-off low has been in place over much of the Desert Southwest since yesterday afternoon, while moisture continues to saturate the atmospheric column from the top down. We have seen a couple rounds of very light rain showers move through the area since yesterday afternoon with the only appreciable rainfall amounts of around 0.25" occurring across western portions of Imperial and central Riverside Counties.

The dry boundary layer has yielded only trace to maybe a few hundredths of an inch over much of southwest and south-central Arizona, but as moisture continues to saturate the lower levels through the rest of the overnight hours more of the rain shower activity will reach the surface. The best coverage of shower activity through the rest of the morning hours should be across south-central Arizona, but rainfall amounts are expected to be light. Hi-res models do show another round of showers potentially affecting portions of southeast California during the afternoon hours, while higher terrain areas in Arizona should continue to see periods of scattered showers through at least this afternoon.

Drier air aloft will quickly spread through the area from the west during the evening hours with the shower activity ending for all areas except across the Arizona high terrain. Shortwave ridging will quickly move into the region late tonight and last through at least the first part of Saturday bringing a bit more sunshine but little drying within the boundary layer. Depending on the amount of clearing that occurs tonight and early Friday morning, we may see some patchy fog develop with the most favored areas across the Imperial Valley into the Lower CO River Valley. Clouds are likely to linger enough across south-central Arizona tonight to prevent or at the very least hinder fog development. Saturday is expected to remain dry, but we will see increasing clouds by Saturday afternoon ahead of the next approaching disturbance for early next week.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

An unsettled weather pattern is expected for the first half of next week as the large scale eastern Pacific trough is likely to send at least two different disturbances into or even through our region. The first piece of energy is likely to be fairly weak in the form an upper level jet streak moving through our region late Sunday and Monday. However, since we are likely to maintain good moisture in the boundary layer through the weekend this next disturbance may be enough to bring some light rain shower activity to portions of the region. NBM PoPs are not very high at around 20-30%, but for now that seems reasonable given the overall weak forcing and with the likelihood there will still be dry air within the mid-levels.

Ensemble guidance then slightly favors a more significant shortwave trough with better moisture and a bit colder of an airmass to move through our region next Tuesday into Wednesday. However, there are still around 30% of the members showing a very weak system. If we do manage to see a decent system move through, much of the area should see some rainfall, but there is still too much uncertainty to have a good idea on rainfall amounts. As usual, the NBM PoPs are probably too optimistic so they have been dialed back some, especially during the beginning and ending of the potential time range.

Temperatures early next week are forecast to continue to run 5-8 degrees above normals, but then cool off starting Wednesday due to the potential weather system. If we do see a fairly strong weather system or even a second system behind it later next week, we have a good shot at seeing temperatures dip to around or even to below normal at some point.

AVIATION

Updated at 0540Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns will be the low CIGs through the much of today, possibly becoming MVFR (low to moderate confidence), as well as lower than usual confidence in wind directions due to virga/light showers in the vicinity. Winds will generally remain light (AOB 10 kts) through the period and favor an easterly component. Guidance has shifted the timing with best chances (30-55%) for TEMPO MVFR CIGs to late morning/early afternoon, though CIGS will most likely prevail in a 4-6 kft AGL range through the period. Expect a temporary improvement in CIGS and some scattering out late in the afternoon into the evening before CIGs fill back in Thursday night into Friday morning.

Southeast California/Southwest Arizona including KIPL and KBLH: The only weather issues through the evening will be lower than usual confidence on winds, extended periods with VFR CIGs, and the potential for FEW-SCT low cloud decks or reduced visibilities in BR/FG at KIPL this morning. Winds will somewhat favor NW, but will be quite variable for extended periods today. Anticipate wind speeds to remain AOB 10 kts. One more round of VCSH/-SHRA may materialize during the afternoon, more likely at KBLH, but confidence in this remains low.

FIRE WEATHER

Periods of scattered showers today will bring decent chances of wetting rains for higher elevation of eastern districts before we see a break in the rain chances starting Friday. Moisture levels will remain elevated through the weekend with MinRHs above 60% today and between 40-60% for the weekend. Wind speeds will remain light with limited gusts. The weather pattern is likely to bring additional weather disturbances near or through the region during the first half of next week supporting chances for light rain at times. Elevated moisture with humidities above 40-50% are likely to persist through the first half of next week with temperatures at or just above seasonal normals.

PSR WATCHES/WARNINGS/ADVISORIES

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