textproduct: NWS Phoenix

UPDATE...Updated 00z Aviation Discussion

KEY MESSAGES

- Isolated to widely scattered thunderstorms will return this afternoon, mainly over the foothills of Maricopa County, but a few storms could form in the lower deserts with the main threats being gusty outflow winds and blowing dust.

- Temperatures up to 8 degrees above normal will cool closer to the seasonal average by the end of the week allowing moderate HeatRisk to be reduced towards a minor category.

- An approaching east Pacific weather disturbance late this week will dry out the region, while bringing increasingly breezy conditions and cooling temperatures.

SHORT TERM /Today through Thursday/

Latest mid-lvl wv imagery and 500 mb streamline analysis reveals an area of low pressure situated over the AZ/CA border allowing much drier air to advect into the western half of the forecast area. Out ahead of this features in south-central and southeastern AZ, sfc moisture remains relatively high with dewpoints hovering in the mid 50s. PWAT values are also around 1.2"-1.5" or around 175% of normal for mid-June. The moisture in place coupled with diffluence aloft ahead of the approaching low will provide a focus for widely scattered shower and thunderstorm activity by this afternoon. Latest high-res guidance, especially the HRRR does suggest higher coverage than previous runs with the main focus areas for initiation in southern Yavapai and central Pinal Counties. Latest visible satellite imagery does confirm initiation underway in these areas. Cape values in excess of 1500 J/kg across the lower deserts may support well defined outflow boundaries which could generate additional showers and storms by this evening, however coverage still looks to remain limited. The main threats with any storm will be strong, gusty winds with around a 30-50% chance of gusts exceeding 35 mph in Maricopa and N Pinal Counties this afternoon/evening. By Thursday, activity should become relegated to the White Mountains of eastern Arizona, only potentially clipping far eastern Gila County as dry air continues to filter into the state from W to E.

Overall 500 mb hghts will continue a downward trend over the next 24 hours as the ridge axis shifts ewd into NM and the weak area of low pressure moves over central AZ. This reduction in heights/thickness will result in temperatures across the lower deserts decreasing from 105-111F today to around 102-107F on Thursday. With drier air overspreading the forecast area, overnight lows will not be as warm as previous nights, mainly in the upper 70s to mid 80s on Thursday morning with further cooling anticipated by the end of this week.

LONG TERM /Friday through Tuesday/

There is excellent agreement among ensemble membership that more pronounced East Pacific troughing will eject into the Great Basin resulting in strong zonal flow across the forecast area. This flow pattern will completely scour away moisture such that mixing ratios fall closer to 2-3 g/kg eliminating all chances for precipitation. While H5 heights will not drop markedly, subtle cooling along with the introduction of this much drier airmass will result in temperatures falling to near normal levels over the weekend. The initial round of modest height falls combined with seasonably deep mixing depths will promote repeated chances of gusty afternoon winds late in the week. Juxtaposed with the incoming dry airmass and receptive, dessicated fuels, fire danger will become quite elevated. Ensemble spreads grows somewhat towards the middle of next week, however the majority of members indicate building subtropical ridging over the CWA after the trough passage. H5 heights should rebound over 594dm with the anti-cyclone center becoming positioned directly over Arizona. Some of the more aggressive modeling in the upper quartile of the model distribution even suggests heights breaching 597dm by the middle of the week which would equate to lower elevation temperatures reaching 115F yielding expansive major HeatRisk.

AVIATION

Updated at 2345Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Near the short term, an northward surging outflow boundary carrying blowing dust will affect KPHX and KIWA through 01z before conditions improve afterwards. Otherwise, gusty winds upwards of 20-25 kts out of the west will continue through the evening hours. Gusts will subside during the overnight period with winds backing out of the east through Thursday morning before shifting out of the west by the late morning hours. Some afternoon gusts near 20 kts will once again materialize. No threat of TS/outflows expected for Thursday. FEW mid to high clouds will be common throughout the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation concern will be gusty winds that will continue through this evening and once again materialize Thursday afternoon/early evening. At KIPL, winds will generally prevail out of the west while at KBLH, winds will fluctuate out of the south to southwest. Afternoon/early evening gusts upwards of 25 kts will be common at KBLH and upwards of 25-30 kts at KIPL. Heading into Thursday, another round of afternoon gusts upwards of 20-25 kts can be expected at KBLH while gusts at KIPL may exceed 25 kts late afternoon/early evening. Skies will remain clear throughout the TAF period.

FIRE WEATHER

A pronounced drying trend will transpire across the region through the remainder of this week with terrain induced showers/storms becoming completely eliminated from the forecast by Friday. Isolated to widely scattered showers and thunderstorms will be possible over higher terrain features this afternoon, however chances of wetting rainfall will be remote. The main impacts with any storm will be gusty and erratic winds and dry lightning. Despite temperatures cooling closer to normal later this week, a much drier airmass will allow minimum humidity levels primarily in a 10-20% range to deteriorate into widespread single digits over the weekend and early next week. Correspondingly, overnight recovery will deteriorate into a poor to fair 15-40% range. Winds will frequently become gusty the remainder of the week yielding a widespread elevated fire danger, however at this time, speeds appear to remain below critical thresholds.

PSR WATCHES/WARNINGS/ADVISORIES

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