textproduct: NWS Phoenix

UPDATE...Updated 06z Aviation Discussion

KEY MESSAGES

- Elevated fire danger across the Arizona high terrain will persist for another day or two with daytime breezy and very dry conditions.

- Temperatures will gradually warm through the rest of the week, but will at least stay below normal through Thursday.

- As the heat builds into the weekend and early next week it will lead to increasing coverage of Moderate Heat Risk and highs eventually reaching 110 degrees by next Monday or Tuesday.

SHORT TERM /TODAY THROUGH FRIDAY/

High temperatures today will once again be below normal, as a broad trough remains in place across much of the West. Under clear skies, with very dry conditions (minimum RHs around 5-15%), this afternoon's highs will reach the 98-102F range across most lower desert locations to low to mid 90s in many higher elevation communities. With an embedded shortwave trough currently exiting through the Four Corners region, winds will not be nearly as strong as they were yesterday. Most areas will see peak wind gusts up to 15- 25 mph. The one exception will be the potential for 25-30 mph peak sundowner wind gusts across portions of Imperial County CA this evening.

Heading through the end of the week, H5 heights are expected to gradually rise, up to around 592dam (~90th climatological percentile) by the end of the day Friday, as the broad western trough weakens and high pressure strengthens over the region. This will result in steady warming, +1-4 degrees each day on the highs. While highs are forecast to warm back to seasonal levels by Friday, morning lows will remain several degree below normal, thanks largely to the very dry air. Winds Thursday and Friday will be slightly lighter than today, with the weakening of the trough, but seasonal afternoon breezes are still expected with peak gusts up to 15-20 mph. The atmosphere will continue to be very dry through the rest of the workweek with PWATs running 25-50% of normals and surface dew points mostly staying in the 20s and 30s.

LONG TERM /SATURDAY THROUGH TUESDAY/

By the weekend, the weather pattern will begin to shift with the broad troughing shifting northward over the Pacific Northwest and Southwest Canada. The subtropical ridge currently over the Eastern U.S. into Mexico will then begin to shift west northwestward, quickly raising H5 heights over our region into the weekend and then further heading into next week.

A developing tropical system (TD Four-E) is currently around 1000 miles west southwest of southern Baja. This system will not have any direct impact on our weather, but guidance favors some of its higher level moisture and clouds working into our region from late Friday through late Saturday/early Sunday. The timing and the positioning of the clouds could still change somewhat, but as of now we are likely to see a good deal of higher clouds centered on Saturday. These clouds may help to stem the building heat over the region, keeping temperatures close to normal through at least Saturday and potentially even Sunday. The current NBM forecast highs show readings between 103-108 degrees on Saturday and 106-110 degrees Sunday, both of which are down a degree or so from previous forecast runs. There is also a low chance for some virga or very light showers developing Saturday with the thicker clouds, should deep enough moisture be drawn into the area, which GEFS guidance is more supportive of than the EC Ens.

By Sunday, guidance shows the subtropical ridge consolidating and forming a new center somewhere to our east northeast. This developing ridge is expected to take a little while to really strengthen as H5 heights are not likely to reach above the 90th percentile until next Tuesday or Wednesday. Temperatures are expected to climb a bit further early next week as the ridge strengthens with 110-113 degree highs becoming very likely by Tuesday.

Moisture should also begin to improve starting around Sunday, potentially becoming meaningful for some isolated convection to begin showing up over the eastern Arizona high terrain as early as Monday. If the high becomes more established close to the Four Corners area by the middle of next week, deeper moisture may move into our area from the southeast providing more widespread convection chances. Models still differ on the timing and the extent of this deeper moisture potential, so it may take another few days to gain more forecast confidence on shower and thunderstorm potential later next week.

AVIATION

Updated at 0510Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns under generally clear skies can be expected through Thursday evening. The overall wind pattern will follow the typical diurnal tendencies with a period of southerly winds late morning/early afternoon before the westerly shift. Overall wind speeds will remain aob 10 kts with some limited afternoon/early evening gusts into the mid to upper teens.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns under generally clear skies can be expected through Thursday evening. At KIPL, westerly winds through the overnight will shift out of the south to southeast during the morning hours and continue into the afternoon hours before shifting back out of the west during the early evening hours. At KBLH, winds will generally fluctuate out of the south to southwest. Overall wind speeds will remain under 12 kts with some limited afternoon and early evening gusts in the mid to upper teens.

FIRE WEATHER

A diminishing threat of breezy to windy conditions will help to gradually lower the fire danger over the next couple of days, but very low humidities (<10%) will persist through at least the weekend. Despite the diminishing wind threat, there will still be the typical afternoon upslope/upvalley breeziness with gusts reaching 20-25 mph today and 15-20 mph each day Thursday through the weekend. Afternoon minimum humidities will mostly range between 5-10% through Saturday with mostly poor overnight recoveries of 15-30%. Despite the decrease in winds later this week, seasonably elevated fire danger will persist through the weekend due to very dry conditions, seasonably warm temperatures, very dry and receptive fuels, and the typical upslope/upvalley breeziness each afternoon into the early evening.

PSR WATCHES/WARNINGS/ADVISORIES

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