textproduct: NWS Phoenix

UPDATE

Updated 00Z Aviation Discussion.

KEY MESSAGES

- Major waterways such as the Salt and Gila Rivers will continue to experience high volumes flows through at least the weekend due to dam releases.

- With the exception of a slight chance for mountain showers on Friday, dry weather will be common through at least the middle of next week.

- Temperatures a few degrees below normal will warm near to just above seasonal readings by this weekend.

SHORT TERM /Today through Saturday/

Afternoon upper-air analysis reveals phasing shortwaves stretching from the Great Lakes down through the Southern Plains, while another weak disturbance transitions from the Pacific Northwest toward the Northern Rockies. Even though it is located well off to our north, the latter of these features will actually have some influence on conditions for parts our forecast area as we finish out the work week. Before we get there though, prevailing quasi-zonal flow, which has promoted multiple days of dry and tranquil conditions, will have to break down. The dissolving of the west-east flow will come in the form of the western vorticity lobe becoming heavily stretched out thanks to a developing anti-cyclone in its wake, forcing some of this energy down across the Great Basin. Falling heights aloft associated with this southern dive will eventually find their way over Arizona early Friday, deepening enough to become a cut-off low, before continuing on into northern Mexico. However, the expectation continues to be that this disturbance will be rather weak, resulting in minimal impacts. Synoptic and orographic ascent squeezing out a few mountain showers and some breezy northerly winds over the lower Colorado River Valley thanks to a tight regional pressure gradient would likely be the most we see. Breezy conditions will linger in Saturday morning, but areawide dry and tranquil conditions return soon thereafter as strong ridging takes over across the Intermountain West.

Even with the presence of the Friday cold-core, temperatures the next few afternoons will be relatively steady, running the mid 70s to lower 80s for desert locations, with low 60s to low 70s being common for high terrain areas. Low and mid-level thermal profiles will not see much fluctuation during this timeframe, owing to how shallow the upcoming system will be and how lower-troposheric heating will make up for any cooling. By Saturday, temperatures will rise to near and slightly above seasonal levels as the aforementioned ridging migrates over the region.

LONG TERM /Sunday through Wednesday/

Some variation of a Rex or omega block will define the southern stream flow pattern early next week as broad ridging dominates the northern Conus and northern stream jet energy retreats into southern Canada. While there are certainly differences among ensemble members regarding the exact placement and intensity of quasi-cutoff features in the southern stream, this synoptic pattern will promote surface pressure rises over the intermountain West and dry N/NE boundary layer flow. As a result, periods of breezy east winds are likely at times over the eastern CWA (very common occurrence this time of year), though speeds should not be particularly strong or unusual. At some point early next week, most ensemble members suggest the aforementioned cutoff feature opening and residual energy moving through the region, though it remains to be seen whether an introduction of mid/upper level moisture can overcome the dry boundary layer airmass. The greatest odds and large preponderance of ensemble membership indicate dry weather persisting through the middle of the week. Forecast confidence is very good that H5 heights will remain nearly constant in a 580-584dm range resulting in a near persistence temperature forecast with readings very near climatology.

AVIATION

Updated at 2355Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds will tend to follow their typical diurnal tendencies with speeds aob 7 kt through the period. Extended periods of light and variable winds are expected. Confidence is low in a westerly shift this evening. Winds will likely just be light and variable, but may tend to have a W/NW component, before reestablishing an easterly component overnight. FEW-SCT and at times BKN high clouds will be common through the period. Some FEW clouds with decks aoa 6-7 kt are expected to develop tomorrow afternoon/evening, mainly north and east of Phoenix.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns are expected through the next 24 hours under passing high clouds. Winds will be light through mid morning tomorrow with speeds aob 7 kt, periods of light and variable to calm winds are also possible. By late tomorrow morning wind speeds will pick up and be around 10-15 kt, with some gusts (mainly at KBLH) up around 20 kt expected. Wind directions will be out of the west at KIPL prior to going NW late tomorrow morning. Winds will continue to exhibit a northerly component at KBLH.

FIRE WEATHER

An isolated shower may affect mountains of eastern districts Friday, albeit with little chance of wetting rainfall while the remainder of the region remains dry through at least the middle of next week. Minimum afternoon humidity levels will largely fall into a 20-30% range in western districts and 30-50% in eastern districts. This will follow fair to good overnight recovery in western districts and good to excellent levels in eastern districts. 20-30 mph northerly gusts will be common in western districts Friday night through Saturday, while a period of enhances easterly winds will develop over eastern districts early next week. Outside of these time frames, winds will be very light with little to no gustiness.

PSR WATCHES/WARNINGS/ADVISORIES

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