textproduct: NWS Phoenix

KEY MESSAGES

- Dry and tranquil weather under mostly clear skies can be expected mid-week before potentially another period of wet weather materializes by the end of the week into the weekend.

- Near to slightly below normal temperatures are expected throughout much of the week.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Latest GOES IR imagery shows a batch of high clouds associated with showers and storms from yesterday is now progressing into NM as much drier air is advecting into AZ under W-SW flow aloft. Although upper- lvl moisture has been scoured out, there is still plenty of residual moisture in the lower levels with dew points still hovering in the low to mid 60s across much of the region with the exception of SE California where dew points are in the 50s. We will continue to hold onto this moisture through the afternoon which could lead to an isolated storm or two developing over the typical terrain features including the Harquahala Mountains in La Paz County and the Table Top wilderness in western Maricopa County. High-res models are indicating this scenario unfolding for a few hours this afternoon, but activity should wane early this evening with the loss of daytime heating. Further drying of the boundary layer can be anticipated on Wednesday with mixing ratios falling to around 8 g/kg. This will lead to another quiet day across our forecast area with any isolated convection relegated to the higher terrain of northern and southeastern AZ.

A large trough of low pressure will remain situated over the West Coast through the middle of this week with the subtropical ridge displaced well east of the region. This pattern will result in 500 mb hghts remaining in a seasonable 587-590 dam range. In response, temperatures are not expected to fluctuate much at all with lower desert highs topping out in the upper 90s to lower 100s and lows in the upper 70s to mid 80s. Due to a slight enhancement of the mid-lvl jet, winds will become gustier each afternoon, especially across SE California and the Lower Colorado River valley.

LONG TERM /THURSDAY THROUGH SUNDAY/

The forecast becomes a bit more muddy heading into the end of this week and through the weekend. Currently the NHC shows a TC likely forming over the E Pacific, south of the tip of the Baja Del Norte within the next 24-48 hrs. Most forecast models show the storm itself curving out into open waters, however there is good evidence that at least some tropical moisture will get pulled up into Mexico and making it as far north as southern AZ as early as Thursday. Roughly 90% of the GEFS and EPS members show PWATs increasing from 1.5" on Thursday to around 1.8-2.0" over portions of southcentral and southwest AZ by Friday or Saturday. Given this likely increase in moisture, NBM PoPs have increased to around 40-50% with the initial moisture push late Thursday into Friday. Thereafter, PoPs remain quite low in a 20-30% range through the weekend which is most likely due to uncertainty in timing and coverage of rainfall within the deterministic model output.

Although there will be adequate moisture return, the positioning of the ridge/trough features over the west will play a key role in how much rainfall may actually materialize. If the ridge strengthens too much and retrogrades wwd, then the focus for heavier rainfall may be much further west into SoCal and north into UT and CO as indicated by the latest ECMWF and GFS runs. It will likely be at least 2 or 3 more days until we have a good idea on what will happen late this week, and any forecast that does not show a range of possible outcomes should be disregarded at this time.

Uncertainty in the temperature forecast by this weekend is also apparent as indicated by large (8-10 degree) spreads within the NBM interquartile range. Once our region does begin to draw in the Pacific moisture, temperatures will likely dip down to around 3-5 degrees below normal by the end of this week. However, as ridging aloft attempts to build over the area this weekend, temperatures may warm closer to normal by Sunday or Monday.

AVIATION

Updated at 0515Z.

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

No major aviation concerns are expected during the TAF period. Winds will return to following light and diurnal trends with variability during directional shifts. There are hints of an isolated afternoon VCTS and later evening outflow, but current chances for either of these events is around 10% or less and therefore have been excluded from the TAFs. Other than a FEW low- level bases around 7-10 kft, skies will be mostly clear.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns are expected during the TAF period. Winds will follow familiar diurnal trends with perhaps some variability occurring during directional switches. Other than a FEW bases around 10 kft, skies will be mostly clear.

FIRE WEATHER

After abundant wetting rainfall occurred across south-central AZ yesterday, drier conditions will settle into the region today with rain chances falling to around 10% or less through the middle of this week. Better area-wide rain chances will return by late week and into this weekend. Expect MinRHs of 15-25% across the western districts to 30- 50% over the next few afternoons. Overnight recovery will range from poor across SE California to good across south-central AZ. Temperatures will range from near to slightly below normal over the next several days with lower desert highs in the upper 90s to low 100s.

PSR WATCHES/WARNINGS/ADVISORIES

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