textproduct: NWS Phoenix

UPDATE

Updated Short Term Discussion.

KEY MESSAGES

- A few isolated showers or weak storms may form over prominent terrain features this afternoon, such as in Western Joshua Tree National Park, La Paz County, and Tabletop Mesa south of Phoenix.

- Chances for showers and thunderstorms mostly confined to the eastern Arizona high terrain and southeastern portion of the state this weekend through the middle of the upcoming work week.

- Temperatures hover near to slightly below daily normals through the middle of next week, with lower desert highs generally between 100 and 108 degrees, resulting in Minor to Moderate HeatRisk.

SHORT TERM /TODAY THROUGH SATURDAY/

Convective cumulus developed rapidly across the region today, but so far the cumulus have mostly struggled to see much vertical growth. Even the showers that have developed so far over the AZ high terrain north of Phoenix have been fairly weak and short- lived. There are a few factors contributing to this today, including an active drying trend. Despite mesoanalysis showing very limited inhibition, CAPE values are relatively low, sub- optimal for strong updrafts, and forcing is very limited. Surface to 6 km shear of 25-35 kts is also shearing off some of the early afternoon updrafts. Still spotty convection is expected this afternoon, mainly favoring terrain areas like Joshua Tree NP, the Kofas and Harcuvar Mtns in La Paz County, Tabletop Mesa south of Phoenix, and southern Gila County. Strong storms are not expected in this environment. HREF neighborhood probabilities for 40 dBZ radar echoes is quite low for most of the area at 5-10%. So, expect very minimal impacts from any convective showers today. Similar conditions are expected tomorrow, but with continued drying, most notably out in western AZ and SoCal, afternoon convection will mostly be limited to the high terrain east of Phoenix. There is potential as well for some overnight and early morning high-based convection in South-Central AZ through Sunday morning, with any mid-level gravity waves emanating from stronger monsoon activity well to the east and southeast, as supported by a few hi-res models, including the HRRR. If any of this activity materializes it could provide some rumbles of thunder, a brief light rain, and localized gusty winds, but that is about it.

Aside from the meager storm chances the next couple of days, temperatures will continue to hover right around seasonal norms, with high pressure centered over the Southern Plains and a weakening low pressure centered over Northern Baja, keeping H5 heights around seasonal levels (589-592 dam). Lower desert highs the next couple of days will be around 104-109 degrees, with tomorrow being the warmer of the two days. Morning lows will mostly be in the 80s. Despite being seasonal, these temperatures will result in Moderate HeatRisk for all lower desert communities.

LONG TERM /SUNDAY THROUGH THURSDAY/

Overall quiet and not so hot weather conditions are expected to continue through the middle of the upcoming workweek. As a result of the upper level flow pattern (dry S-SW flow over much of the CWA with S-SE flow encroaching on eastern AZ), which should be maintained through Monday, ensemble mean PWATS should continue to remain around 100-120% of normal over the eastern half of the state, allowing daily chances (20-35%) for isolated showers and thunderstorms over the high terrain (Rim, White Mountains) and southeastern portion of the state. Chances for showers/storms over the South-Central AZ lower deserts remain generally below 15%, though chances may improve slightly Monday PM with some models indicating additional moisture drifting northwestward from Mexico. Early next week, the very weak upper low over SoCal is likely to join with a trough over the Pacific Northwest that is then advertised to split off of the northern stream and retrograde offshore, settling off the CA Coast midweek. During this time, the proximity of this trough will act to suppress heights aloft and strengthen deep SW flow over the region, resulting in ensemble mean PWATS dropping to around 50% of normal by the latter half of the upcoming workweek and further suppressing rain chances. The latest NBM continues to show afternoon highs near or even a few degrees below normal through midweek. This should keep the HeatRisk over our area anywhere from high-end Minor to low-end Moderate.

AVIATION

Updated at 1730Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT: No major aviation concerns are expected during the TAF period. Winds will generally remain out of the W through tonight, with occasional gusts this afternoon in the mid-teens to around 20 kts. Higher gusts near 25 kts, mainly at KPHX, should be anticipated tonight for a brief period, most likely between 05-07Z. The other terminals may experience a few gusts during this timeframe as well, but speeds should quickly relax thereafter. Any rainfall activity should occur well outside the vicinity of the terminals, but there are hints of some shower activity developing early Saturday morning. However, chances for any VCSH remain too low (<10%) to warrant inclusion in the TAFs at this time.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected over the next 24 hours. Winds will continue to favor diurnal trends, with some periods of variability, especially during the overnight and early morning hours. Besides a FEW afternoon CU and some mid to high clouds Saturday morning, skies should be mostly clear.

FIRE WEATHER

A few isolated showers or weak thunderstorms may form over prominent terrain features across the area this afternoon, but most places will stay completely dry and areas that do see a shower or storm will see very little rainfall. Shower and storm chances will remain limited to the South-Central Arizona high terrain east of Phoenix this weekend, with perhaps a slight increase in chances (15-20%) for the lower deserts Monday evening. Afternoon MinRHs will be around 12-20% for most areas and nearly every day. Winds should mostly follow diurnal patterns with only light periodic breezes in the afternoons and early evenings, with peak gusts mostly between 15-25 mph.

PSR WATCHES/WARNINGS/ADVISORIES

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