textproduct: NWS Phoenix

KEY MESSAGES

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

- Dry conditions will prevail through the weekend with typical afternoon breeziness.

- There is a slight chance for a few storms and lightning strikes over eastern Arizona high terrain early next week, however rainfall should be minimal, at best.

SHORT TERM /Today through Thursday/

Latest objective analysis depicts elongated, positively tilted troughing covering the western Conus helping depress midtropospheric heights over the forecast area, and resulting in the recent period of below normal temperatures. Ensemble model output over the next 60 hours strongly argues for the northern portion of the negative height anomalies to propagate into the Upper Midwest, yet with the trough base and marginally lower heights lingering over the forecast area. While H5 heights will be maintained in a near persistence level not far from 576dm, boundary layer thermal profiles will moderate in response to the seasonally increased sfc insolation such that H8 temperatures warm from 18C to 22C through Thursday. As such, forecast confidence is excellent that afternoon highs will rebound very close to the daily normals with extremely narrow ensemble numerical spread. Otherwise, widespread dry weather will continue along the the typical afternoon May breeziness.

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 1100Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns are anticipated through the forecast period. East winds this morning will slowly transition back to W-SW during the part of the afternoon with a few hours of southerly/VRB winds expected during the shift. Expect clearing skies this morning.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather issues will exist through the forecast period under clear skies. At KIPL, westerly winds will shift to the north mid morning lasting until the evening when winds will again turn westerly. At KBLH, northerly winds will continue through the afternoon before going southerly in the evening. Wind speeds will be aob 10 kt at both terminals through the TAF period.

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.