textproduct: NWS Phoenix

KEY MESSAGES

- A plume of moisture will yield minimal rain chances across portions of southeast California and southwest Arizona through the weekend.

- Mostly dry and quiet weather conditions can be expected early next week before thunderstorm chances increase by the latter half of the week.

- Temperatures will remain near to slightly below normal through this weekend before warming to slightly above normal by early next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Latest objective analysis reveals the subtropical ridge situated over the southern Plains while a broad upper trough encompasses much of the west coast with low pressure pressure centered across the Pacific Northwest. This overall pattern configuration is continuing to result in southwesterly flow aloft, which has helped advect a plume of mainly mid to upper-level moisture originating from Hurricane Marie, spinning well of the coast of the Baja Peninsula, into the region. The highest moisture content is expected to be confined across southwest AZ and southeast CA where PWATs are expected to climb in excess of 1.5" later today. This increase in moisture combined with some upper-level forcing from the aforementioned trough will cause isolated to scattered light showers to break out. However, since much of the moisture is mostly in the mid to upper-levels with the low-levels rather dry as surface dewpoints are in the 40s and 50s, any rain that falls will be mostly virga/sprinkles with little to no measurable accumulations. Some better low-level moisture will be in place on Sunday, however, most of the upper-level forcing will be shifting northward with the Mohave Desert Region expected to have the better rainfall potential as guidance shows an extensive area of light to locally moderate intensity rainfall materializing. Across south-central AZ, generally dry and quiet weather conditions are expected through the rest of the weekend as the combination of the lack of instability and forcing for ascent will hinder storm activity. With the rainfall activity over the Mohave Desert Region on Sunday, outflow winds from the northwest are expected to impact much of the lower deserts with afternoon/early evening peak gusts of 20-30 mph likely.

Temperatures today and Sunday will continue to run near to a few degrees below normal, with today being the cooler day given the presence of more abundant mid to high clouds. The cooler temperatures for this afternoon are expected across the western deserts where the thicker cloud cover will likely cause readings to fall shy of the triple digits, whereas further east into south-central AZ, slightly warmer readings into the low 100s under more sunshine can be expected. Temperatures will warm a few more degrees on Sunday under slightly less cloud cover.

LONG TERM /MONDAY THROUGH FRIDAY/

Ensemble model guidance has come into better agreement on the synoptic pattern for the beginning of the workweek. Ensemble members show the longwave trough over Western CONUS lifting northeastward and pushing into the Northern Rockies, TC Marie moving north/northwestward (staying well off the coast of California), and the subtropical ridge pushing back into the Desert Southwest. With the subtropical ridge building back overhead, H5 heights will rise to around 591-594 dm. This increase in heights aloft will result in a gradual warming trend. The NBM shows afternoon high temperatures increasing to 100-108 degrees across the lower deserts and 90-100 degrees across the higher terrain. Temperatures of this magnitude are slightly above normal, which will result in widespread Moderate HeatRisk across the lower deserts. The aforementioned synoptic pattern will also result in the continuation of dry southwesterly flow aloft. PWATs are expected to drop to around 1.3-1.6", resulting in mostly dry conditions across the CWA.

Heading into the later half of the workweek, ensemble model guidance continue to disagree on the synoptic pattern. Not only do the models differ on the strength and positioning of the subtropical ridge, they also differ on the strength and positioning of the low pressure system over the eastern Pacific. Overall the EPS has a stronger solution, it is showing a stronger subtropical ridge along with a stronger/deeper low pressure system in the Pacific (in fact it is showing a closed low). Additionally, the EPS has both of these features further west. The EPS shows the high maxing out around 597 dm during the middle of the week, with the center stretched across the Plains, and then the high weakening slightly, but moving overhead by the end of the workweek. Then the GEFS is showing a weaker ridge and a weaker, open wave trough, with both of these features further east. These difference can be seen in the large temperature spreads in the NBM interquartile range (with the EPS being a warmer solution and the GEFS being a cooler solution). The NBM continues to lean more towards the GEFS, with a gradual cooling trend beginning Wednesday. Both ensemble models do show a return of moisture by the middle of next week, with PWATs increasing to around 1.5-1.8" (EPS has slightly higher PWATs). This increase in moisture will result in rain chances returning to the region as early as Wednesday. The NBM shows PoPs of 20-40% area wide by the Wednesday- Thursday timeframe. The GFS also shows an inverted trough moving through the region during the middle of next week. If this were to occur it would significantly increase rain chances for the region. Despite this, both the GEFS and EPS do show measurable rainfall returning to at least some portions of the region during the latter half of the upcoming workweek. However, forecast confidence remains low and we'll have to wait to see how the models evolve over the coming days.

AVIATION

Updated at 1825Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather concerns will exist through through the forecast period under increasing mid/high level cloud decks. Mostly diurnal trends with a southerly crosswind before winds settle out of the west for the afternoon. Uncertainty exists if winds will go easterly for the overnight period into tomorrow morning, currently models suggest VRB conditions however favoring a westerly direction. Wind speeds will be aob 12kts throughout the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through the forecast period under thickening mid/high level clouds. Winds will follow general diurnal patterns, fluctuating between westerly to southeasterly at KIPL and southerly slowly shifting to the NW by tomorrow morning (~16Z) at KBLH. Confidence has lowered since the last package for VCSH at each terminal so they have been removed from the TAFs at this time, but the very slim chance they do materialize no operational impacts are expected.

FIRE WEATHER

Near to slightly below normal temperatures continue through the weekend. A gradual warming trend begins early next week before another cooling trend is expected for the end of the workweek. Rain chances today will be confined to the western districts, but chances for wetting rainfall remain very low. Afternoon minRH's today will be 15-30%, increasing slightly starting on Sunday with values above 20% area wide through much of next week along with good overnight recoveries. Winds will generally remain light today before some elevated afternoon/early evening breeziness out of the northwest return on Sunday with peak gusts of 20-30 mph. A more typical diurnal wind pattern with some occasional afternoon upslope breeziness can be expected through much of next week.

PSR WATCHES/WARNINGS/ADVISORIES

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