textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion.

KEY MESSAGES

- Temperatures will warm toward seasonal normals starting Tuesday, likely staying there for the rest of the workweek. Hotter temperatures with lower desert highs into the nineties look possible by the weekend.

- A weather system is likely to bring rain chances to portions of the region on or around Thursday, but the timing and potential rainfall amounts are still quite uncertain.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Tranquil conditions will be the norm through the front half of the week under dry quasi-zonal westerly flow. Sub-tropical high pressure will begin to nudge its way northward over the next few days, but before it becomes the more dominant feature, there is still some lingering troughing around the Great Basin to be dealt with. As this transition evolves, the regional thermal profile will take some time to catch up, so high temperatures today will actually continue the brief trend of running below normal for this time of year. Readings for the lower deserts will range from the upper 70s to lower 80s, while higher terrain locations can expect lower to middle 70s.

Heights aloft will trend upwards heading into Tuesday as the previously mentioned ridge amplifies slightly. However, even though there will be a good 4-7 degree jump in day-to-day temperatures, afternoon highs should remain right around, to even slightly below, normal. This is in part to the scuffle between the cooler air that will remain to our north and that building high pressure. Not much change is expected in the height field for Wednesday, but temperatures aloft should be caught up by then to bump regional surface readings more toward the upper 80s to around 90 degrees for lower desert communities. The only other notable change during the next three days or so will be an increase in high clouds for the middle of the week as a closed low meanders over the Eastern Pacific. That disturbance will have a greater influence on our forecast area during the back half of the week.

LONG TERM /THURSDAY THROUGH SUNDAY/

Thursday may be shaping up to be an interesting weather day across portions of Arizona if the Pacific weather system passes close enough or even across southern Arizona. Model uncertainty is still somewhat high with the GEFS indicating a slightly stronger system with more moisture getting pulled northward into our area compared to the EPS. Timing differences are also there with the EPS being around 12 hours behind the GEFS and CMCE, but for now sometime Thursday looks to be the best chance for any rain chances. The track of the low will also come into play as guidance shows the low center moving along the Arizona/Mexico border. Any shift toward the south would be detrimental for rain chances, while a shift more into Arizona would be more ideal.

Upper level moisture will advect into the region from the south southwest on Wednesday, with moisture gradually lowering with time as the disturbance nears our area on Thursday. Ensembles do mostly agree on PWATs increasing on Thursday to around 0.60-0.75", or 150-175% of normal with some members exceeding 1.00". Initially, some very high-based showers should become possible by Thursday morning from Phoenix and areas the east and southeast, but very dry air in the low levels is likely to prohibit any measurable rainfall. It should not be until the afternoon/evening hours when moisture improves enough within the low and mid levels and forcing reaches its peak for showers and potentially some thunderstorms to affect the area. So far moisture within the lower levels looks quite meager, but it would not be surprising to have enough moisture and instability in the mid-levels for some convective activity to occur. Some ensemble members are picking up on the convective potential indicating a potential of localized QPF amounts of a half an inch or more. Additionally, any thunderstorms that may develop could bring strong gusty winds with the potential for blowing dust. PoPs remain somewhat low due to the uncertainty with 10-20% across the western lower deserts, 25-40% over the south-central Arizona lower deserts to as high as 44-55% over the eastern Arizona high terrain.

Temperatures should dip again into or just below the normal range on Thursday due to the weather system skirting by to our south, but the slight cool down is likely to be short-lived. Once the system moves east southeast of the region by around Friday, upper level ridging should begin to filter in from the west. Whether the warmer temperatures move in already on Friday or wait until Saturday is still uncertain, but at the very least the lower deserts should reach into the low to mid 90s by Saturday. The 90s for highs are forecast to persist into Sunday and possibly into next Monday, but NBM guidance shows another slight cool down may occur early next week bringing temperatures back into the normal range.

AVIATION

Updated at 2330Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation concerns are anticipated through the next 24 hours. Winds will follow typical diurnal tendencies, with some light variability during diurnal wind shifts. Any lingering gusts out of the W-SW will diminish by sunset, with speeds falling below 10 kts overnight. Skies will remain generally clear aside from a few passing high clouds.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are anticipated through the forecast period. W-NW winds will prevail at KIPL, while S-SW winds continue at KBLH through this evening. Directions will become more N-NW at both terminals early Tuesday morning. Any lingering gusts should subside late tonight at KIPL with speeds falling to 8 kts or less at both terminals overnight. Mostly clear skies will prevail.

FIRE WEATHER

Drying conditions along with a slight warm up are expected through Tuesday. Look for MinRHs to fall to 15-20% this afternoon and 10-15% on Tuesday, while overnight recoveries transition from good to poor to fair (25-40%) by Tuesday night. Winds will be on the light side following diurnal patterns with only some occasional upslope breeziness during the afternoon hours. Another weather system is then forecast to move through the region during the later half of the workweek leading to increased RH and chances for rain and possibly some isolated thunderstorms.

PSR WATCHES/WARNINGS/ADVISORIES

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