textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion

KEY MESSAGES

- Better moisture and more favorable conditions for showers and storms are expected by this evening, lasting into Thursday morning. - A Flood Watch has been issued for the high terrain across central and portions of eastern Arizona from late afternoon through tonight. Locally heavy rainfall will also be possible into the south-central Arizona lower deserts.

- Near to below normal temperatures are forecast through Friday before warming back up over the weekend into early next week.

SHORT TERM /TODAY THROUGH THURSDAY/

This afternoon and tonight continue to point towards being quite busy, with the main forecast concern being the potential for heavy rainfall stemming from a high likelihood of localized rainfall rates of 1-2"/hr and training of storms in the higher terrain areas, as depicted by CAMs. Due to this a Flood Watch has been issued for all of Gila County as well as over far northern Pinal and northeast Maricopa Counties from late this afternoon through tonight.

The upper level pattern shows the Desert SW sandwiched between the subtropical ridge, that has moved into Texas, and the upper level trough along the California coast line. This set up has promoted southerly flow aloft into our region and will be able to tap into plenty of moisture from a decaying MCV from earlier this morning over the Sonoran Desert. Current meso analysis along with this morning's 12Z sounding have PWATs near 1.7" and closer to 1.8-1.9" in the western lower deserts. The morning sounding also revealed a decent amount of MUCAPE, with most of the CIN near the surface. The 12Z convective temperature was only 95F, and with an afternoon high expected to to climb near to slightly above 100 degrees in the lower deserts, convection is likely to break through any lingering surface level CIN. Model soundings are forecasting MUCAPEs mainly between 750-1500 J/kg in the lower deserts and will steadily diminish through the late evening hours, into the overnight period, making late this afternoon and into the evening hours the expected peak time for storms, similar to earlier this week. However, CAMs still show storms likely continuing past midnight, mostly in the higher terrain, while the lower deserts, to include La Paz County, have the highest chance, 50-70%, of showers during the evening hours, as mentioned previously. Additional isolated showers and thunderstorms will again be possible Thursday afternoon, but with the atmosphere drying out and forcing waining there will be a significantly lower chance of localized heavy rainfall.

Temperatures will be quite pleasant compared to what is normally expected for mid August with afternoon highs mostly in the high 90s to low 100s, with many areas struggling to reach 100F. The only exception will be areas in the western lower deserts where temperatures will range in the low to mid 100s, keeping pockets of Moderate HeatRisk in place. Otherwise, widespread Minor HeatRisk is expected through the end of the week.

LONG TERM /FRIDAY THROUGH TUESDAY/

Dry air will continue to spread northeastward through Arizona on Friday with low level mixing ratios dropping to around 8 g/kg over the lower deserts to 9-10 g/kg over the eastern Arizona high terrain. These moisture levels during the summer monsoon season typically prohibit convection across the area with at most a 10-20% chance of isolated showers or weak storms across the far eastern Arizona high terrain. However, even with the drying conditions surface dew points well into the 50s will still keep that slight muggy feeling in the air. The trough will continue to influence the region through Friday keeping temperatures a few degrees below normal under partly cloudy skies.

Saturday looks to be quite similar to Friday with periods of higher clouds persisting, but temperatures will begin to tick upward again as the subtropical high begins to nudge back into our region. Guidance shows H5 heights gradually rising into a 592-595dm range by early next week, or back to around the 90th percentile of climatology. Moisture levels look to stay fairly steady for the rest of the weekend into early next week keeping at most low grade monsoon storm chances in place. The increased heights and somewhat dry conditions will help to push daytime highs to above normal by Monday with readings right around 110 degrees for next Monday and Tuesday.

AVIATION

Updated at 0000Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Main aviation concern during the TAF period will be convective activity around metro terminals this evening, and potentially once again overnight. First SHRA/TSRA will occur between now and around 05Z-06Z, with the second, but less certain window, being between 07Z-12Z. Main impacts will be sub-VFR VIS and gusty and erratic winds. How strong winds become remain uncertain, but there is currently not a strong signal indicating gusts will exceed 30 kt. Convective activity should begin to clear the area after 12Z at the latest, but lingering SHRA for a few hours beyond that cannot be completely ruled out. Outside of the variability and uncertainty of the convective timeframe, winds are expected to follow familiar diurnal trends.

Southeast California/Southwest Arizona including KIPL and KBLH: Main aviation concern will be SHRA/TSRA this evening into early tonight. Impacts associated with convective activity will be reduced VIS and winds exceeding 30 kt at times. Activity at KIPL will end within in the next few hours, but KBLH could see lingering activity until around 06Z tonight, potentially resulting in numerous strong outflows. Conditions through the remainder of the night into Thursday morning should be much calmer, with familiar diurnal wind trends and drier conditions returning.

FIRE WEATHER

Elevated humidity levels, cooler temperatures, and good chances for wetting rains are anticipated through Thursday morning over at least the eastern districts. The best rain chances will be during the evening and overnight hours tonight with lingering chances through Thursday afternoon. Afternoon MinRHs will range between 25-35% across the lower deserts and 40-50% for the eastern high terrain, while overnight recoveries will remain excellent. Winds will predominately be out of the south southwest much of the period with the exception of any modest outflows from thunderstorm activity. Drying conditions will move into the region Friday and through the weekend dropping MinRHs to between 15-25% while temperatures gradually rise back to above normal.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Flood Watch through late tonight for AZZ541-545-547-549-552- 555>558-560>563.

CA...None.