textproduct: NWS Phoenix

UPDATE

Updated 12Z Aviation Discussion.

KEY MESSAGES

- Residual tropical moisture will continue to stream into southeastern AZ on Friday, promoting scattered showers and storms across the foothills and higher terrain areas east of Phoenix

- The moisture axis and corresponding rain chances will shift west into SE California and SW Arizona on Saturday and Sunday.

- Temperatures will remain in a near to slightly below normal category through this weekend with highs warming back above normal early next week, resulting in HeatRisk increasing from widespread minor to moderate.

SHORT TERM /TODAY THROUGH SUNDAY/

Latest wv imagery and 500 mb streamline analysis reveals an elongated area of high pressure extending from the Southern Plains into the southeastern U.S. while a broad trough encompasses the Pacific Northwest and much of the West Coast. Our forecast area remains centered between both of these features, resulting in continued dry southwest flow aloft. Meanwhile, Hurricane Marie is churning over the E Pacific, well southwest of the tip of the Baja Peninsula. A plume of moisture from this storm continues to advect through N Mexico and into southeastern AZ overnight. Isolated showers with a few embedded lightning strikes have been forming over the foothills and high terrain NE of Phoenix, and this will likely continue overnight and into early this morning where PoPs range from 30-50%. By this afternoon, a sharp moisture gradient will again be present across the lower deserts as drier air associated with the Pacific trough overspreads SE California and SW Arizona. Although PWATs in southcentral AZ will remain meager around 1.4- 1.5", there will be just enough late afternoon instability (MUCAPE ~500 J/kg) for a few pop up showers and storms in Central Maricopa and N Pinal Counties. Any shower activity will likely be short-lived and wane quickly after sunset due to loss of sfc heating.

Hurricane Marie will continue to track slowly northwestward into open waters through this weekend which will allow additional moisture to be transported nwd into SoCal and southern AZ as PWATs rise to around 1.6-1.8" areawide. On Saturday, ridging aloft will also begin to strengthen over the southern Plains and retrograde wwd, causing the subtropical jet axis to shift over SE California and western AZ. Therefore, we will see an abrupt shift in PoPs from E to W with shower activity becoming focused over SE California and SW Arizona by Saturday afternoon. Due to increasing moisture and extensive cloud cover, instability and lapse rates will be poor and thus the threat for any heavy rainfall will remain low. Rainfall accumulations across the western half of the forecast area look to remain light, around 0.10" or less through Sunday. The latest WPC QPF totals still indicated void in precipitation across southcentral AZ including the Phoenix Metro Saturday and Sunday.

Due to the presence of troughing to our west helping to maintain 500 mb hghts within a 588-590 dam range, temperatures will remain near to slightly below normal through this weekend. Lower desert highs will range from the upper 90s to lower 100s each afternoon with Saturday being the "coolest" day overall. Morning lows will also remain near normal mainly in the upper 70s to middle 80s. The associated height falls from the West Coast trough will also result in afternoon/early evening breeziness across portions of southeast CA and southwest AZ with peak gusts around 20-30 mph, potentially reaching up to 40 mph in the typical wind prone areas of far southwest Imperial County.

LONG TERM /MONDAY THROUGH THURSDAY/

Deterministic and ensemble guidance continue to differ on the magnitude and positioning of the subtropical ridge early next week which will dictate how hot temperatures get and how soon rain chances will return to our area. Both the EPS and GEFS show the ridge strengthening over the Southern Plains through the middle of the week which will allow hghts aloft to increase across much of the Desert Southwest. In turn, temperatures will also increase from near normal Monday to slightly above normal on Tuesday. The temperature forecast becomes much more unclear heading into the middle of next week with large spreads in the NBM interquartile range. This is likely due to differences in the magnitude of the ridge with many EPS members showing a stronger ridge with 500 mb hghts approaching 596-598 dam while the GEFS shows slightly lower overall hghts. For now NBM temperatures show a cooling trend after Tuesday which is likely due to an increase in moisture as southeasterly flow aloft returns to the lower deserts.

PWATs are expected to increase back to around 1.5-1.8" by the middle of next week which will bring rain chances back into the picture by the Wednesday-Thursday timeframe when PoPs increase to around 20-40% areawide. The GFS is even showing an easterly wave/inverted trough arriving into southern AZ along with additional tropical Pacific moisture on Wednesday which could boost rain chances significantly, but we will likely have to wait for more run to run consistency as these features are always difficult to resolve at longer time scales. Either way, most of the GEFS and EPS members are showing measurable precipitation across portions of the area by the middle of next week.

AVIATION

Updated at 1125Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The likelihood of another slow transition to westerly winds with a period of gusty south cross runway winds and then the slight (10-20%) possibility of TSRA/SHRA this afternoon and early evening will be the main weather issues this TAF period. Current SE'rly winds are expected to slowly transition to W'rly/SW'rly winds this afternoon. The slow transition will cause a period of S'rly crosswinds (150v230), and some occasional gusts in the upper teens during this time will also be possible. Once W'rly winds develop this afternoon, occasional gusts into the upper teens will continue to be possible through the early evening. Chances for TSRA/SHRA late this afternoon and evening are too low (10-20%) to include in this TAF package. Winds are then expected to be W'rly into the overnight hours before developing their usual E'rly component during the overnight hours. SCT mid and high clouds will become BKN at times this afternoon before gradually clearing out this evening and overnight.

Southeast California/Southwest Arizona including KIPL and KBLH: Occasional late afternoon/early evening gusty winds will be the main weather issue through the TAF period under mostly clear skies, with FEW high clouds starting to move in at the end of the TAF period. SW gusts 20-25kt will be common at KBLH late afternoon while KIPL should experience the most pronounced gusts during the evening. Speeds will relax overnight and early morning where brief periods of nearly calm conditions will exist.

FIRE WEATHER

Isolated showers and storms will be possible in southcentral AZ this morning and again late this afternoon. Rain chances will expand westward through this weekend, becoming focused over the western districts Saturday and Sunday. The best chance for any wetting rainfall will remain over the higher terrain of eastern and southeastern AZ. Afternoon minimum humidities will range from 7-15% across southeast CA and between 20-35% for the the AZ deserts today and will likely increase above 25% areawide this weekend. Overnight recoveries will range from poor across the western deserts to good across the eastern districts tonight and increase to good areawide this weekend. Winds will remain elevated out of the south to southwest, with the strongest gusts in Southeast CA and along the Lower Colorado River Valley peaking between 20-30 mph this afternoon/early evening. Lighter winds, generally around 15 mph or less will transpire this weekend.

PSR WATCHES/WARNINGS/ADVISORIES

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