textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion.

KEY MESSAGES

- Above normal temperatures with widespread moderate HeatRisk will prevail through the remainder of the week before readings retreat closer to normal by the end of the weekend.

- Other than a slight chance of a shower or thunderstorm this afternoon over eastern Arizona, dry conditions under mostly sunny skies will prevail through at least the middle part of next week.

- Locally breezy conditions will develop for the end of the week and into the weekend, particularly across the lower Colorado River Valley and higher terrain communities of Arizona.

SHORT TERM /Today through Saturday/

The weak low pressure system to the south in Northern Mexico continues to slowly meander eastward this afternoon. The position has shifted far enough eastward to the point where anticyclonic flow has become more dominant over SoCal to central AZ with more subsidence over the area. This increased subsidence and lower instability than yesterday across southeastern AZ should make terrain convection more limited and less robust than yesterday through the rest of this afternoon and evening. This is already evident based on the more limited convective cumulus coverage so far this afternoon. For the local CWA, maybe a shower or storm clips through southeast Gila County this afternoon with some gusty winds and a lightning risk.

Temperatures at 1300MST this afternoon were running around 1-2 degrees warmer than the same time yesterday and should top out a touch warmer than yesterday as well. High temperatures are forecast to reach 106-109F across the lower deserts this afternoon. The latest NBM does have low odds (10-20%) of reaching 110F this afternoon in a few lower desert communities, including the Phoenix area and the Imperial Valley. The highs today, while 6-8 degrees above normal, will still be well shy of daily records which are around 112-116F. Through Friday and Saturday high temperatures will cool, but only by a degree or two each day as the pattern across the western CONUS slowly transitions to negative height anomalies with longwave troughing across the region. This pattern shift will lower H5 heights slightly over the Desert Southwest and induce a deeper southwest flow across the region.

The pattern shift heading into the weekend will also support drier more stable conditions across the area, clearing out the moisture that crept into the southeastern AZ. The pressure gradient will also increase across the area, leading to an increase in winds across the region. Strongest southwesterly wind gusts will approach 25-30 mph, and locally up to 35 mph, along the lower Colorado River and the high terrain east of Phoenix both Friday and Saturday, but will be strongest on Saturday. With afternoon humidity values only hovering around 5-10% the next several afternoons, any enhanced gusts will result in widespread elevated fire weather conditions and areas of critical conditions, especially in the areas with the strongest winds.

LONG TERM /Sunday through Wednesday/

It appears that ensembles have come into better agreement in terms of the evolution of the previously mentioned Gulf of Alaska low. Some friction remains, but trends point towards a weaker solution that was being favored by the GEFS at this time yesterday. Both the GEFS and ECMWF Ens show this closed low becoming an open wave and extending from the British Columbia down the length of the Pacific Coast, so there will likely be at least some influence from this disturbance on the Desert Southwest. This influence will more than certainly come in the form of continued breezy to locally windy conditions through the end of the weekend and into the weekend. The associated negative height anomalies will promote some slight cooling, but the vast majority of lower desert highs will remain in triple digit regardless. This trough will not provide anything in terms of moisture flux, so with continued breeziness forecasted, daily elevated fire weather risk is expected to extend at least into next Monday for parts of the forecast area.

There appears to be better agreement, compared to 24 hours ago, regarding the pattern toward the middle of next week. Clusters have honed in on the continued presence of troughing across the Great Basin, but where they differ is how strong this feature might be. Some clusters even suggest cyclonic curvature collocated with positive height anomalies over the Desert Southwest, perhaps keeping breezy conditions in the forecast as well as triple digit temperatures. There is still some wiggle room so things are likely to change over the next few days. One thing that does appear certain is continued dry conditions through at least the middle of next week.

AVIATION

Updated at 2324Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns are expected through the TAF period. Winds in the Phoenix Metro will exhibit typical diurnal tendencies with periods of elevated speeds and gusts up to 20kts possible through sunset and again tomorrow afternoon. Out west, KIPL will maintain a SE'rly component throughout the period, with wind speeds around 8-12 kts overnight, then relaxing during the morning hours, before increasing again tomorrow afternoon. KBLH will maintain a S/SSW component with speeds generally around 10 kts, increasing tomorrow afternoon to 10-15 kts with gusts 20-25 kts possible. Skies will be clear for most of the period with FEW mid level clouds passing tomorrow afternoon.

FIRE WEATHER

The threat for an isolated dry thunderstorm over southern Gila County this afternoon is the main fire weather hazard in the short term. Winds through this afternoon will follow typical diurnal tendencies with typical afternoon upslope breeziness. Gusts pick up Friday and into the weekend, mainly across the Lower Colorado River Valley and high terrain areas of the eastern districts with readings reach upwards of 25-30 mph. With daily MinRHs hovering close to 5- 10% for the majority of the region, even marginal breezes will result in periods of elevated fire weather conditions. Isolated instances of near critical to critical conditions can be expected with localized higher gusts. Overnight recovery will offer very little in terms of relief as MaxRHs run only between 15-45% for most locations. Breezy conditions are likely to continue into the weekend, perhaps even lingering into next week, potentially resulting in a prolonged period of daily occurrences of elevated to near critical fire weather conditions starting Friday.

PSR WATCHES/WARNINGS/ADVISORIES

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