textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Moisture arriving into the region through Friday morning will increase rain chances across the foothills and higher terrain areas east of Phoenix.

- Rainfall chances shift west into southwest Arizona and southeast California this weekend.

- Temperatures will remain in a near to slightly below normal category through this weekend resulting in widespread minor Heat Risk and localized areas of moderate HeatRisk.

SHORT TERM /TODAY THROUGH FRIDAY/

Latest objective analysis reveals a broad subtropical ridge extending from the southern Plains into the southeastern U.S. while a broad trough is encompassing the Pacific Northwest. This overall pattern configuration is resulting in southwesterly flow across the region, especially in the mid to upper-levels, which has advected considerably drier air aloft. Meanwhile, moisture advection from Hurricane Marie, located southwest of the tip of the Baja Peninsula will result in a surge of low-level moisture heading into this afternoon and tonight with PWATs likely to exceed 1.5 inches across much of south-central and southeast AZ while much drier air with PWATs of less than one inch is expected to be confined across southwest AZ and southeast CA. The latest Hi-Res guidance for later this afternoon and this evening does show some isolated showers and storms popping up near some of the terrain features such as the Table Top and Estrella Mountains in south-central AZ, however, the very dry air above 600 mb will likely limit the residence time of any activity. Some gusty winds and locally heavy rainfall will be the main threats with any of these storms. Heading into tonight and early Friday morning, guidance is showing another round of showers and storms to develop across portions of southeast AZ and move northward, affecting the foothills and higher terrain areas east of Phoenix where the best moisture axis is likely to set up. With the activity overnight into early Friday morning, some locally heavy rainfall that could lead to localized flooding will be the main threat. Quieter conditions are anticipated starting late Friday morning as drier air filtering in from the west moves in, dropping PWATs under 1.3" with little to no instability and thus eliminating any rain/storm chances through the rest of the day.

Due to the presence of the troughing across the Pacific Northwest, afternoon high temperatures this afternoon and Friday will be within a few degrees of the daily normals as readings top out in the upper 90s to low 100s across much of the lower desert communities. The associated height falls from the trough will also cause some afternoon/early evening breeziness across portions of southeast CA and southwest AZ with peak gusts upwards of 20-30 mph, potentially upwards of 40 mph in the typical wind prone areas of far southwest Imperial County.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Global models are coming into somewhat better agreement with the pattern evolution this weekend. Both the ECMWF and GFS show high pressure strengthening over the southern Plains with the western periphery of the ridge extending over E AZ and NM. This will cause the subtropical jet to shift wwd beginning Saturday, setting up better moisture advection over southeast CA and southwest AZ. NBM PoPs are still not overly impressive, mainly in the 20-30% range on Saturday, however the GEFS/GFS indicates a final slug of moisture from Marie being pulled into southeast CA on Sunday with PWATs rising above 2.0". Therefore we will have to monitor for heavier rainfall potential in portions of SE California including Joshua Tree NP on Sunday. Elsewhere, across southcentral AZ, rain chances look to be meager due to more extensive cloud cover and very low instability. The latest WPC QPF field shows a local minimum in rainfall totals (<0.10") in southcentral AZ including the Phoenix Metro through this weekend. By early next week, there are large discrepancies in the ridge/trough positioning which will complicate the precipitation forecast, but there will still be adequate moisture across our region which will keep low end PoPs in place across eastern and southeastern AZ Monday and Tuesday with potentially better precipitation chances arriving Wednesday.

The temperature forecast this weekend into early next week remains largely unchanged, although there will likely be a gradual increase from near normal temperatures on Saturday to slightly above normal temperatures Sunday into early next week as ridging strengthens over the region. Depending on how strong the ridge gets, NBM temps could climb a few more degrees in subsequent runs and it is not out of the question that we could see lower desert highs approaching 110 degrees as indicated by the NBM 75th percentile on Monday and Tuesday.

AVIATION

Updated at 0505Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The threat for SHRA impacting eastern gates early Friday morning, then the possibility of a slow transition to westerly winds with a period of gusty south cross runway winds will be the main weather issues this TAF period. While an isold SHRA could directly affect any given terminal overnight, the best odds suggest SHRA staying east of the metro acting to reinforce an easterly wind component through Friday morning with only occasional midlevel cloud decks. As a result, winds may be slower to transition to W/SW Friday afternoon with a prolonged period of 150v230 possible while incurring gusts 15- 20kt. Chances for TSRA/SHRA Friday afternoon are too low to include in this TAF package, though not zero. The highest odds are for little to no SHRA activity and winds finally obtaining a W/SW component by later afternoon, then keep that heading well into the overnight.

Southeast California/Southwest Arizona including KIPL and KBLH: Occasional late afternoon/early evening gusty winds will be the main weather issue through Friday night under clear skies. SW gusts 20- 25kt will be common at KBLH late afternoon while KIPL should experience the most pronounced gusts during the evening. Speeds will relax overnight and early morning where brief periods of nearly calm conditions will exist.

FIRE WEATHER

Isolated to widely scattered showers and storms will be possible in southcentral AZ later today through Friday. Rain chances will expand westward through this weekend, becoming focused over the western districts Saturday and Sunday. The best chances for wetting rainfall will be over the higher terrain areas of eastern and southeastern AZ. Afternoon minimum humidities will range from 7-15% across southeast CA and between 20-35% for the remainder of the region through Friday and will likely increase above 25% areawide this weekend. Overnight recoveries will range from poor across the western deserts and good to excellent across the eastern districts. Daytime winds will remain elevated out of the south to southwest, with the strongest gusts in Southeast CA and along the Lower Colorado River Valley peaking between 20-30 mph during the afternoon/early evening.

PSR WATCHES/WARNINGS/ADVISORIES

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