textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion.

KEY MESSAGES

- Temperatures will hover in a slightly above normal range much of the week before retreating closer to normal over the weekend.

- Other than a slight chance of a thunderstorm in eastern Arizona during the middle of the week, dry conditions under mostly sunny skies will be the main weather theme this week.

SHORT TERM /Today through Wednesday/

Early morning objective analysis depicts a well defined northern stream omega block defined by pronounced ridging across central Canada and bounded by negative height anomalies on either side. Meanwhile, an enhanced southern stream subtropical jet continues to be reinforced across the eastern Pacific allowing weak troughing and predominant westerly flow to be maintained over the SW Conus. There is excellent ensemble agreement that the northern stream block will be undercut through the middle of the week with northern stream energy helping pull a weak vorticity center in the southern stream into northern Mexico.

Despite mean troughing entering the region, there will be an overall weakening phase with H5 heights currently in a 582-585dm range actually increasing close to 586dm by the middle of the week. As a result, temperatures will steadily warm with afternoon highs reaching around 5F above normal by Wednesday, and narrow ensemble numerical spread yielding excellent forecast confidence. Given the dry airmass in place, overnight lows will remain fairly comfortable and not far from the seasonal average resulting in only patchy areas of moderate HeatRisk. This troughing pattern will allow a more meridional flow pattern by the middle of the week with wave structure favorable for weak ascent. While the majority of the CWA will remain too dry for precipitation, moisture backed into New Mexico will support diurnal mountain thunderstorms with moist outflow leaking into far eastern Arizona. Thus, it would not be out of the question for a few thunderstorms/lightning strikes skirting far eastern Gila County Wednesday afternoon.

LONG TERM /Thursday through Sunday/

During the latter half of the week, NAEFS members are in fair agreement showing weak southern stream troughing slowly translating into the southern plains as deep negative height anomalies approach the western Conus. The primary uncertainty is the forward speed at which this occurs, and how quickly the forecast area falls under anti-cyclonic subsidence. The preponderance of ensemble output suggests the trough axis not passing into the southern Rockies until Friday, thus keeping modest ascent mechanisms into eastern Arizona Thursday with a continued slight chance of storms over mountainous areas. Regardless, the pattern evolution late in the week will promote height falls and dry westerly flow with H5 readings retreating closer to 580-582dm by the weekend (and possibly much lower early next week). While numerical guidance spread widens during the evolution, an increasing number of ensemble members indicate deeper troughing and more robust cooling arriving over the weekend such that temperatures should return to near normal, or even into a slightly below normal category.

AVIATION

Updated at 1119Z.

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

No major aviation concerns are expected throughout the TAF period. Winds will generally exhibit typical diurnal tendencies, with a brief period of light southerly cross winds this morning at KSDL and KDVT around 16-18Z, before shifting westerly for the afternoon. Speeds will be mostly aob 10kts with KPHX potentially seeing a few hours of speeds between 10-15kts near 05Z. Otherwise, FEW passing high clouds will be common throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns throughout the TAF period. Winds at KIPL will follow typical diurnal tendencies with speeds mostly aob 10kts. At KBLH winds will shift from the NW to a more S/SE component by ~16Z this morning with wind speeds increasing to aoa 10kts by 21Z. During this time gusts between 15-20 kts may be possible through the afternoon hours. FEW passing high clouds will be common throughout the period.

FIRE WEATHER

The threat for a few lightning strikes with little rainfall in far eastern Gila County Wednesday and Thursday is the main fire weather hazard this week. With temperatures hovering slightly above normal, winds will maintain a diurnal upslope/nocturnal drainage pattern. Gusts will be limited the first half of the week, then increase later in the week, particularly across the lower Colorado River valley and over mountainous locations. Minimum afternoon humidity levels will generally fall in a 5-15% range following a widely ranging poor to fair overnight recovery of 15-45%.

PSR WATCHES/WARNINGS/ADVISORIES

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