textproduct: NWS Phoenix

KEY MESSAGES

- Abundant moisture will remain situated across the eastern half of Arizona well into next week providing at least daily chances for isolated showers and thunderstorms.

- Shower and thunderstorm chances will be focused more over the high terrain of Northern and Eastern Arizona, but chances will also extend into the south-central Arizona lower deserts.

- Near to slightly above normal temperatures are expected this weekend and likely through all of next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Moisture advection yesterday was stronger than predicted and thus has left the area under PWATs of 1.7-1.8" and low level mixing ratios of 12-13 g/kg. This higher than anticipated moisture allowed for greater instability and lower CIN, which in turn resulted in more widespread storm coverage during the afternoon and evening hours over the Arizona high terrain. Eventually that translated into scattered showers and storms developing southward toward the Phoenix area late in the evening before gradually winding down over northern and western Phoenix since midnight.

The weather pattern that is shaping up now and likely to last through much of next week is a bit complicated and could result in multiple days of fairly active weather. The subtropical ridge that brought the hot temperatures during the workweek has weakened and become more stretched out, while a large scale Pacific trough is taking shape across the Northwestern U.S. As the subtropical ridge develops a new center over New Mexico today and gradually drifts into the Southeastern U.S. by Monday, the Pacific trough will become more predominant over the Western U.S., while keeping a consistent flow of moisture northward into the eastern half of Arizona.

Hi-res CAMs yesterday under estimated the storm coverage for last evening, although it did have the general areas depicted well. Today and even Sunday will carry additional chances for showers and storms, but coverage is expected to be much less as there will not likely be a trigger like the weak shortwave that moved through last evening. The latest CAM runs show isolated to at most scattered high terrain showers and storms today and Sunday with no clear signs of any activity developing over the lower deserts. Temperatures today will drop off from the 5-7 degree above normal readings yesterday and settle in right around seasonal normals through the rest of the weekend.

LONG TERM /MONDAY THROUGH FRIDAY/

The first half of next week will continue to bring rain chances across the eastern half of Arizona as the Pacific trough lingers just to our north and northwest and the ridge stays centered over the Southeastern U.S. This will continue place Arizona in a south southwesterly flow area providing periods of moisture advection out of moisture rich northern/western Mexico. The biggest question that remains is what day or days will represent the best chances for more than just scattered showers and isolated storms. Models do agree plentiful moisture will remain over eastern and central Arizona through at least the middle of next week with PWATs running 150-180% of normal and low level mixing ratios anywhere from 11-14 g/kg. However, there are uncertainties with the amount of instability due to a good deal of forecast cloud cover and lack of any obvious trigger mechanisms. Last night's model runs were more optimistic with upper level support and this will likely be a piece of the puzzle needed for an active weather day given the questionable instability and inhibition.

The NBM is still honing in on late Monday through Tuesday as the best potential for showers and thunderstorms across eastern and central Arizona, but confidence in this is still fairly low. It would not be surprising to have any day from Monday through Thursday to be a good storm day, but it is still too early to pinpoint which day or days. With the upper level support leaning toward being less of an influence, we may just have to rely on differential heating and/or wherever the western edge of the moisture axis sets up. Forecast instability does look to be enough to support some strong storms and with the moisture levels expected, heavy rainfall leading to localized flooding could also become an issue. Overall, rain chances for next week look quite conditional and PoPs are likely to change. Forecast temperatures for next week have also been trending upward over the past few days with decreasing chances of having lower desert highs dipping below 100 degrees on any day. The latest NBM shows highs hovering right around normal to a few degrees above.

AVIATION

Updated at 1000Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

The only weather issue will be low confidence on wind directions this morning and timing of a later than usual SW/W wind shift this afternoon, under FEW-SCT mid and high cloud decks. In the wake of an outflow that moved through last night, winds have settled out of primarily easterly directions, however, as speeds relax AOB 6 kts early this morning, anticipate some periods of variability. A later than usual shift to west winds is anticipated this afternoon, with some guidance even suggesting a prolonged period of southerly variability midday into the afternoon. Overall, the wind pattern today and tonight should return to familiar diurnal tendencies.

Southeast California/Southwest Arizona including KIPL and KBLH:

Winds will continue to favor SE at KIPL and SSE to SW at KBLH. Speeds will remain generally between 6-14 kts with gusts at KBLH this afternoon and this evening in a 20-25 kt range. Mostly clear skies will prevail other than periods of FEW high cirrus.

FIRE WEATHER

Slight chances for showers and thunderstorms can be expected through the weekend, with the best chances over the Arizona high terrain. Chances are expected to increase across the eastern districts early next week. MinRHs through early next week will generally be hover close to 15-25% for the far western districts, while higher values closer to 25-35% will be seen elsewhere. Winds will somewhat follow typical diurnal patterns, but with more of a south southwesterly predominant wind across the western districts. Daily afternoon gusts of 20-25 mph will be common across the Lower CO River Valley this weekend before becoming more widespread early next week.

PSR WATCHES/WARNINGS/ADVISORIES

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