textproduct: NWS Phoenix

KEY MESSAGES

- Near normal temperatures will gradually warm through the weekend with lower desert highs reaching the upper 90s to near 100 degrees following comfortable morning readings.

- Dry conditions will prevail through the weekend with typical afternoon gusts up to 15-25 mph.

- Isolated thunderstorms with a few dry lightning strikes will be possible over eastern Arizona high terrain early next week, however little to no measurable rainfall is expected.

SHORT TERM /Today through Thursday/

Latest mid-lvl wv imagery and 500 mb streamline analysis reveals an elongated trough positioned over the western CONUS while an amplified ridge remains entrenched over the E Pacific well offshore from the Pacific NW coastline. This pattern will persist for the next several days, keeping mostly dry and tranquil weather in place over the Desert Southwest. 500 mb heights over the forecast area this afternoon remain between 575-576 dam which is near seasonal levels. Under mostly clear skies and very dry conditions, temperatures have risen into the upper 80s to low 90s across the lower deserts. We will likely see a third day in a row with highs below normal in the Phoenix Metro and most other desert communities across the region. With a very dry boundary layer in place, yet another round of comfortable overnight temperatures in the upper 50s to mid 60s can be expected.

On Thursday, mid-lvl heights will remain largely unchanged, however the overall boundary layer thermal profiles will moderate in response to increased insolation and dry subsidence aloft such that H8 temperatures warm from 20C to 22C. This atmospheric response will result in sfc highs rebounding by a degree or two from today's readings, but remaining right around the daily normal. Overall a dry and benign weather pattern, typical of late may will persist through the end of this week.

LONG TERM /Friday through Tuesday/

The weak troughing will gradually migrate into the southern plains late in the week as the Conus pattern becomes more progressive allowing low amplitude shortwave ridging to temporarily build into the SW Conus. While notable ensemble uncertainty exists in the northern jet stream structure, particularly over the northeast Pacific, only minimal model spread is evident across the forecast area and confidence is very good that H5 heights in a 582-585dm range will envelop the Southwest. As such, temperatures will warm several more degrees into a slightly above normal range, but certainly nothing particularly unusual for this time of year. As the ridge axis shifts east into New Mexico later in the weekend, deeper southerly flow and intense heating of higher terrain may encourage shallow Gulf surges and import of marginally better moisture profiles heading into next week.

Model uncertainty grows markedly next week as deep troughing enters the NW Conus while a very strong subtropical jet punches into northern Mexico, allowing some form of cyclonic flow and shortwave troughing to develop over the forecast area. This type of pattern is not uncommon for mid/late May transitioning season, but fine details in timing, intensity, and moisture availability will determine the extent (if any) of impacts across the region. General pattern recognition suggests the increased jet ascent and cooling aloft will promote deep mountain convection, tapping the marginally increased moisture early next week with the preponderance of ensemble output indicating Monday the most favored day for isolated storms. Given the thermodynamic profiles and historical precedent with similar systems, very little rainfall would be expected with this convection, but rather numerous dry lightning strikes and gusty outflow winds. Should this evolution come to fruition, the greatest concern would be wildfire starts over the back country followed by increasing winds midweek with the passage of stronger troughing through the Great Basin.

AVIATION

Updated at 1700Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation concerns are expected during the TAF period. Winds will follow light and diurnal trends with periods of variability during directional shifts. Other than a some high cirrus over the eastern portion of the airspace, skies should be mostly clear over the terminals.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected during the next 24 hours. Winds will favor light and diurnal trends with some periods of VRB conditions during directional shifts. Clear skies will be common through the front half of the forecast before FEW-SCT high clouds move in Thursday morning.

FIRE WEATHER

Temperatures will gradually warm through early next week, albeit remaining in a slightly above normal category. Dry conditions will prevail with minimum afternoon humidity levels falling into a 5-15% range this week, though a modest increase in moisture will result in these levels increasing closer to 10-20% over the weekend. This moisture increase along with an incoming weather disturbance will lead to a slight chance for afternoon/evening storms and lightning strikes over eastern districts high terrain. Little to no rainfall would be expected with this activity resulting in a heightened threat for new wildfire starts, particularly Monday afternoon. Poor to fair overnight recovery of 20-40% will only improve slightly over the weekend. Typical afternoon spring upslope gustiness of 15-25 mph will be common through the period with the most pronounced gusts over eastern district high terrain and through the lower Colorado River valley.

PSR WATCHES/WARNINGS/ADVISORIES

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