textproduct: NWS Phoenix

KEY MESSAGES

- Better moisture and more favorable conditions for monsoon storm development is expected through midweek with the most widespread activity across south-central and eastern Arizona. - Locally heavy rainfall and gusty thunderstorm winds will remain possible through Thursday before drying conditions ends rain chances as early as Friday.

- Cooling temperatures are expected through midweek, briefly falling to below normal Wednesday through Friday.

SHORT TERM /TODAY THROUGH THURSDAY/

GOES mid-level WV imagery and RAP40 500MB analysis continue to show the upper level pattern with southeasterly flow aloft and the core of the high pressure over the Four Corners region. By Wednesday the high will be pushed eastwards towards Texas while a trough deepens across the western coast, and is expected to remain in place through the end of the week, bringing southwesterly flow aloft. This will help gradually dry the region out especially towards the later half of the week and heading into the weekend. Otherwise for the rest of today, a mostly overturned atmosphere from the past active nights will likely to limit shower and thunderstorm activity compared to the last couple of days. HREF shows a 30-50% chance of storm development in the eastern high terrain with only a 10-20% chance of activity developing tonight and into the overnight period for the lower deserts. That being said the main impact/concern for the lower deserts will be breezy to windy conditions from outflows, thats if they can survive into the lower deserts.

Uncertainty remains high for Wednesday as the weak trough begins to enter western portions of the region turning the flow out of the south southwest. The incoming trough is expected to increase upper level forcing across much of the area for Wednesday into early Thursday, but as the flow shifts out of the south southwest some dry air will begin to filter into western and then south- central Arizona. However, plenty of moisture will remain from around Phoenix and areas to the east and northeast of Phoenix. The biggest question will be the areas of focus for shower and storms from Wednesday afternoon through Thursday morning. Guidance indicates the best chances from northern and eastern portions of Phoenix into the higher terrain with PoPs of 50-70% with decreasing chances to the south and west as that drier air enters the region. A faster than normal storm movement should help to limit the heavy rainfall threat, but the aforementioned factors could still lead to some instances of flash flooding, especially in NE AZ. The activity is likely to persist during the overnight hours/Thursday morning, but the threat for heavy rainfall is likely to gradually decrease.

The good news, outside of precipitation potential, will be that this activity will lead to ample cloud coverage over the next few days, helping temperatures to be near normal today, then 3F-6F degrees below normal starting Wednesday. This will lead to a large majority of the region dropping to Minor HeatRisk with the exception of a small corner of SE CA, where localized areas of Moderate will remain. Additionally the morning low temperatures will continue to be near to slightly below normal through out the rest of the work week.

LONG TERM /FRIDAY THROUGH MONDAY/

Drying is expected to pick up across the area during the latter half of Thursday with most of the shower and thunderstorm potential shifting to over the Arizona high terrain. By Friday, enough dry air is expected to filter into the area to completely end rain chances across the lower deserts while limited chances are forecast for the high terrain. The subtropical high is expected to stay centered across the Southeastern U.S. through at least the weekend with broad troughing over much of the Western U.S. This will keep dry air in place through at least the upcoming weekend with at most slight chances for afternoon convection over the far eastern Arizona high terrain. Ensembles do show the subtropical high becoming more elongated late this weekend with heights gradually increasing over our region. As a result, temperatures are likely to climb back to around or even a few degrees above normal by Sunday or Monday. The next potential for rain could come as early as next Monday or Tuesday, but uncertainty is quite high at a week away.

AVIATION

Updated at 1835Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: West winds will continue into the overnight hours. Gusts into the upper teens to around 20 kt is expected during the afternoon and early evening hours. A distant outflow from the NE may affect the Phoenix airspace during the evening (02-05Z timeframe), but confidence is too low for TAF inclusion at this time. Then, a second distant outflow may reach the terminals late evening into the overnight hours out of the SE, confidence for this outflow is also too low to include in the TAF at this time. Another period of VCSH/VCTS will need to be evaluated for the overnight period into Wednesday morning, with 20-30% chances for spotty coverage of SHRA/TS across the Phoenix airspace. Winds tomorrow morning are expected to be similar to this morning at KPHX with an earlier shift to westerly around 15Z at KPHX and KIWA.Lowest cloud bases will mostly stay at or above 10K ft AGL through the period.

Southeast California/Southwest Arizona including KIPL and KBLH: The potential for strong outflow winds to once again reach the terminals and VCSH/VCTS conditions this afternoon will be the primary aviation weather concerns. Winds will favor a southerly direction at KBLH with afternoon gusts to around 20 kts. VCSH/VCTS may develop at KBLH Tuesday afternoon beginning around 22Z. At KIPL, winds will primarily favor S-SE through the TAF period, with a period of W-SW later Tuesday afternoon and evening associated with storm outflow and VCSH/VCTS. VCSH/VCTS may develop at KIPL Tuesday afternoon beginning around 00Z. Strong gusty and erratic winds are also possible with any outflows. FEW to SCT clouds will be common over the area with lowest bases down to around 10K ft AGL.

FIRE WEATHER

Scattered showers and thunderstorms are anticipated each day through midweek across the higher terrain areas of the eastern districts, with slightly lower chances in the lower elevations. The best chances will fall during the latter half of Wednesday into Thursday morning. Afternoon MinRHs will range between 25-35% in the lower deserts and between 40-50% in the eastern high terrain through Wednesday with good to excellent overnight recoveries. Aside from gusty and erratic winds near thunderstorms, the overall wind pattern will follow the diurnal trends with modest afternoon upslope gusts. Near to below normal temperatures are expected through the rest of the week with drying conditions by Friday and lasting through next weekend.

PSR WATCHES/WARNINGS/ADVISORIES

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