textproduct: NWS Phoenix

UPDATE

18Z 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 1750Z.

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

No aviation weather impacts are expected through Tuesday. Winds will follow typical diurnal tendencies, with a period of light southerly cross winds through early afternoon at KPHX and KDVT, before shifting westerly later this afternoon. Wind speeds will mostly stay aob 10kts with occasional gusts into the teens. FEW to SCT passing high clouds will be common this afternoon and tonight.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather impacts expected through Tuesday morning under mostly clear skies. Winds at KIPL will favor a SE component through this afternoon and shift W-SW this evening, with speeds mostly aob 10 kts and a few gusts up to 15-20 kts this evening. At KBLH winds will favor a SSW-SSE component through the period. Wind speeds will also mostly be aob 10 kts, with the exception of some breeziness this afternoon with gusts up to 15-20 kts.

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.