textproduct: NWS Phoenix

KEY MESSAGES

- Aside from some light shower chances across Joshua Tree National Park today mostly dry and quiet weather conditions are expected through the first half of this week.

- Thunderstorm chances will start to increase, mainly across south-central and eastern Arizona, by the latter half of the upcoming workweek.

- Temperatures will be near to around 5 degrees above normal through the upcoming week.

SHORT TERM /TODAY THROUGH TUESDAY/

Early this morning reveals that the overall synoptic pattern remains largely unchanged with the omega block in tact. The ridge of high pressure remains in place across the central US with troughing along both coasts, with the low pressure centers over the Pacific NW and New England. Hurricane Marie also continues to spin well off the coast of the Baja Peninsula. This pattern continues to support mid and upper level moisture advection into the region, with the highest moisture content across SE CA and SW AZ. This can be seen on the SPC Mesoscale Analysis, where PWATs are around 1.5-1.7" across SE CA and SW AZ. This forcing, in combination with the increased moisture, is resulting in some light shower activity, for our CWA, mainly across eastern Riverside County. The SPC Mesoscale Analysis also shows little to no CAPE, so no thunderstorm activity is expected. Throughout the day today, the high will begin to retrograde westward with the trough across western CONUS beginning to lift northeastward. Additionally, Hurricane Marie will continue to move northwestward. The combination of these three things will result in the better moisture plume moving northwestward. So, the best shower chances, for our CWA, today will be confined to Joshua Tree National Park. There will be little to no instability so no thunderstorms are expected. Little to no rainfall accumulations are also expected. The best rainfall today will be north of our CWA into San Bernardino County in CA, into the Las Vegas area, and NW AZ. With the shower activity across this region, outflow winds from the northwest are expected to impact much of the lower deserts during the afternoon and early evening, with peak gusts of 20-30 mph likely.

Heading into the beginning of the workweek, the subtropical high will continue to retrograde westward. H5 heights over our area will go from 588-591 dm today to 591-594 dm for the beginning of the workweek. This will result in a return of southwesterly flow which will bring in drier air. PWATs will decrease to 1.3-1.6" area wide. In addition to the decrease in moisture, with high pressure moving back in dry and quiet conditions are on tap to start the workweek. Temperature wise, with high pressure building back in temperatures will increase slightly through Tuesday. For areas across SE CA they should see temperatures a couple degrees below normal today due to the increased cloud cover from the increased mid and high level moisture. Otherwise, lower desert afternoon high temperatures are forecasted to be in the 100-108 degree range and for the higher terrain, in the 92-102 degree range. Temperatures of this magnitude are around 2-4 degrees above normal, which results in Minor to Moderate HeatRisk area wide.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

Heading into the later half of the workweek, ensemble model guidance has come into slightly better agreement on the overall synoptic pattern. The models have come into better agreement on the placement of the features, but still differ on the overall strength of the features. Both the GEFS and the EPS show a shortwave trough across norther CONUS and southern Canada, a broad subtropical ridge stretching across much of the lower 2/3 of CONUS, along with a closed low off the coast of northern California. The EPS continues to be the stronger solution, with a stronger closed low in the Pacific and a stronger subtropical high. These changes can be seen in the now slightly smaller temperature spread in the NBM interquartile range, however, the spread remains large enough (5-7 degrees) that you can tell the models are still in some disagreement. The GEFS show the high at peak strength (H5 heights of 594-597 dm) during the middle of the week before weakening (H5 heights of 591-594 dm) and moving overhead on Thursday. The high looks to continue to weaken (h5 heights of 588-592 dm) heading into the weekend. So temperatures are forecasted to remain slightly above normal during the middle of the week before beginning a slight cooling trend to slightly below normal for the end of the workweek and into the weekend.

As for shower and storm chances, the ensemble members continue to show those chances starting to increase, for at least portions of the CWA, beginning on Wednesday. PWATs look to increase to around 1.5-1.9" for the latter half of the week, so moisture should not be a limiting factor. With the high forecasted to move overhead on Thursday, rain chances will likely be limited to the higher terrain areas across eastern Arizona on Wednesday and Thursday. Rain chances may extend into the lower deserts of south-central Arizona heading into the weekend. However, the current WPC PoPs of 30-50%, for Friday into Saturday, seem rather aggressive, especially this far out. WPC's Saturday PoPs of 10-30% seem more reasonable.

AVIATION

Updated at 1000Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Minor uncertainty in wind direction will be the only weather concern through Monday morning under periods of thick mid/high cigs and areas of virga. Instead of winds fully shifting east this morning at KPHX, they may instead just become variable for several hours. A return to a pronounced west direction should occur by late morning with some modest gusts (20-25 kts at most) late this afternoon into early evening.

Southeast California/Southwest Arizona including KIPL and KBLH: Thick mid/high cigs with virga/sprinkles will persist through this evening, albeit with little to no operational impact. Confidence is good that light W/SW winds will gradually veer to the NW by late morning with gusts 20-25kt developing mid/late afternoon.

FIRE WEATHER

Temperatures will be slightly below normal across SE CA today. Otherwise, temperatures will be near to slightly above normal through the workweek. Rain chances today will be confined to Joshua Tree National Park, with chances for wetting rainfall very low. MinRH's will be around 20-30% area wide through much of this upcoming week with good overnight recovery. Some elevated afternoon/early evening breeziness out of the northwest is expected today with peak gusts of 20-30 mph. A more typical diurnal wind pattern with some occasional afternoon upslope breeziness can be expected through much of this coming week.

PSR WATCHES/WARNINGS/ADVISORIES

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