textproduct: NWS Phoenix

KEY MESSAGES

- Temperatures around 3 to 8 degrees above daily normals will result in widespread Moderate Heat Risk, with isolated pockets of Major Heat Risk at times, through the middle of next week.

- Chances for showers and thunderstorms will exist through the remainder of the weekend and into the start of the upcoming week, with the best chances focused over high terrain areas and portions of Southeast Arizona.

- Brief gusty winds from distant outflows and low probabilities for a thunderstorm or two over the foothills of Maricopa County cannot be ruled out today and again Monday during the afternoon and evening hours.

SHORT TERM /Today through Monday/

Early morning objective analysis reveals a bit of a mess of a pattern over the Desert Southwest as a number of different weather regimes hover around the region. Clashing areas of low and high pressure continue to funnel enhanced moisture flux into Arizona and Southern California (the main reason for some convective activity on Saturday), while a separate weak trough floats over Central/Northern California. With presence of the former two features, moisture levels will remain elevated through today and even into Monday, which will keep shower and thunderstorm potential in the forecast, mainly for high terrain areas and portions of SE Arizona, over the next few days. Mesoscale analysis shows PWATs ranging from 0.9-1.3" which is still not quite enough to pop widespread convective activity for our forecast area given how dry and hot we are throughout a good portion of the atmospheric column. However, there are still some minimal PoPs (10-15%) across the foothills of Maricopa County, portions of Southern Gila County, and even areas around the Table Top Wilderness this afternoon and evening. Where the "best" PoPs are, and how limited they are, is a good indicator of how reliant convection will on orographic influences given the unfavorable synoptic setup and barely sufficient moisture. Main impacts with any potential shower and thunderstorms will be occasional lightning and gusty winds in excess of 35 mph. Some localized areas of blowing dust cannot be ruled out if storms do pop along the border of southern Maricopa and Pinal Counties.

Transitioning from the weekend into the start of the upcoming week, some hi-res guidance is picking up on early morning precipitation activity across La Paz, Yuma, and western portions of Maricopa Counties. Taking a closer look at the synoptic pattern, nothing really stands out as to what might trigger these morning showers. One possible explanation could be a subtle gravity wave that gets kicked out from distant convection. However, there are some models that show virtually nothing over these same areas, so confidence regarding this episode of potential rain is quite low. This uncertainty is reflected in current PoPs as they currently max out around 10-15%. This activity looks to be highly conditional on how things evolve this afternoon and evening, but even if the "rainier" solutions come to fruition, very little impacts can be expected.

Rain potential Monday will not be limited to just the morning hours as lingering moisture will keep precip chances over parts of the region as we advance into the afternoon and evening hours. In fact, chances, at least for our forecast area, during this timeframe appear slightly better (15-30%) compared to today, though coverage is not that much better as those chances remain focused over similar areas mentioned above. Again, nothing really sticks out as a triggering mechanism for convection, other than orographic lift, so it is a bit puzzling as to why chances increase, but a deeper dive indicates that upper-level mass speed divergence over eastern portions of Arizona might be the key. We will also see flow switch more out of the W/NW, which may actually allow for the Phoenix metro to get in on some rainfall action as well. This setup should create a more favorable pattern for potential outflows over high terrain areas to descend toward the lower deserts, triggering more convection, which is why chances for Phoenix are better for Monday as well, but still remain low (10-15%) due the highly dependent nature of where storms may pop.

Even with all this talk of rain we can't give a forecast for the Desert Southwest during the late spring without mentioning temperatures. After we witnessed the first 110 degree day at Phoenix, which occurred right around when it typically does as the average first date it 6/11, it looks like readings will be much of the same as readings hover between 106-110 for the metro. Similar readings can be expected for the remainder of the lower deserts not only for today, but for Monday as well as day-to-day readings will not fluctuate much over during the next few days.

LONG TERM /Tuesday through Saturday/

Models indicate that moisture will not completely scour out through the middle of the week, allowing for at least some diurnally driven shower and thunderstorm activity during this window across the southeastern portion of Arizona and some high terrain areas. However, guidance continues to show eastern Pacific ridging stretching into our forecast area, generating a broad area of subsidence aloft and therefore limiting near-future rainfall for at least most of our forecast area. This area of near to slightly above normal height anomalies will help to keep temperatures around 3-8 degrees above normal through at least Wednesday. Beyond that, we begin to flip the script as an eastern Pacific trough develops in conjunction with the northward migration of a sub- tropical jet streak. This feature will increase winds regionally as the subtropical jet imparts deep southwesterly flow, decrease heights aloft, and substantially scour out the low level moisture across the region. As a result, anticipate elevated fire weather concerns, especially for Southeast CA and Southwest AZ, temperatures moderating closer to daily normals, and the diurnally driven shower/storm chances over AZ high terrain to end.

AVIATION

Updated at 1225Z.

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

Gusty west winds this afternoon followed by the potential for strong, abrupt northerly outflow winds this evening and low confidence on VCSH/VCTS conditions will be the main aviation concerns under FEW-SCT mid to high decks. After a period of lighter E/SE or VRB winds this morning, west winds will establish between 14- 17Z across the terminals and likely become gusty by the latter half of the afternoon with gusts around 20 kts. Convection will again affect higher terrain areas Sunday afternoon with a few showers or isolated storms potentially reaching the northern fringes of the Phoenix Metro by early evening. Confidence is moderate that most if not all terminals will see an abrupt wind switch out of the north as an outflow overspreads the Metro area between 01-04Z, with gusts potentially exceeding 25 kts briefly.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major weather concerns will exist through Monday morning under mostly clear skies. Confidence is good that a southerly wind component with occasional gustiness will be maintained at KBLH while directions oscillate between SE and SW/W at KIPL.

FIRE WEATHER

ELevated moisture levels will result in isolated convection the next few afternoons, mainly for higher terrain areas, that will be capable of producing gusty and erratic winds and dry lightning. Outside of any thunderstorm outflows, winds will be diurnally driven with the typical afternoon and evening upslope/upvalley breeziness between 15-25 mph. Enhanced moisture will bring some benefit as MinRHs range between 15-20% for the majority of the region, with the exception being SE California where readings will be closer to 10%. For those areas with better moisture, MaxRHs will offer at least some modest relief as readings rise to 30-50% each night. Those drier spots further west however will only see values increase to around 25%. Moisture scours out during the back half off the week, which will decrease dry thunderstorm potential, but drop RHs closer to 10% during the afternoons.

PSR WATCHES/WARNINGS/ADVISORIES

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