textproduct: NWS Phoenix

UPDATE

Updated 00Z Aviation Discussion.

KEY MESSAGES

- A broad scale troughing pattern will persist over the western U.S. through the end of the workweek keeping temperatures overall near normal.

- Weak shortwave ridging will build over the Desert Southwest this weekend,allowing temperatures to rise a few degrees above normal, with lower desert highs reaching the upper 90s to around 100 degrees.

- Dry conditions, with no threat of rain, and seasonal afternoon breezes are expected through the next several days.

SHORT TERM /TODAY THROUGH THURSDAY/

Latest GOES infrared wv imagery and 500 mb streamline analysis reveals a broad trough of low pressure extending from the Pacific NW into the Central Plains. Our forecast area still remains at the base of this positively tilted trough with a broad fetch of southwesterly flow currently in place over the forecast area. A plume of Pacific moisture is currently being pulled NE into the Desert Southwest this afternoon which is resulting in abundant high cloud cover. Despite the increased cloudiness, temperatures have warmed into the upper 80s to lower 90s across the lower deserts, slightly warmer than yesterday, but still around 3 to 5 degrees below normal. Very dry air at the sfc (Td ranging from the single digits to the 20s) will again result in another relatively cool night across the region with lows ranging from the mid 50s to upper 60s.

On Wednesday and Thursday, the troughing pattern will remain intact over the Intermountain West, which will keep 500 mb hghts near to slightly below seasonal levels in a 575-576 dam range. Despite the below normal 500 mb hght field, there will be a slight warming trend in the low-level thermal profile which will promote at least a degree or two increase in temperatures mid-week. This will result in highs reaching back into the mid to upper 90s in most lower desert communities both Wednesday and Thursday afternoon. Winds each day will mostly follow seasonal trends; light winds during the overnight and morning hours and modest upslope breezes in the afternoons with gusts up to 15-25 mph.

LONG TERM /FRIDAY THROUGH MONDAY/

The slow warming trend is forecast to continue through Friday and this coming weekend. Global ensemble guidance supports the large- scale synoptic pattern across the west finally evolving out of the current state, with the strong blocking ridge near B.C. Canada giving way/weakening as a strong low traverses across Alaska. This change will result in at least a temporary de-amplification of the pattern across the western CONUS for the weekend and a trend toward positive 500mb height anomalies with brief anticyclonic flow developing over the Desert Southwest. This trend will lead to high temperatures reaching into the upper 90s by Friday and pushing 100 degrees by Sunday - Monday (30-60% odds of >=100).

This pattern shift will also allow for some moisture to seep into AZ, from the southeast and with evening gulf surges, as global guidance shows a slow uptrend in PWATs Friday through the weekend. This may end up leading to some AZ high terrain afternoon convection, which is supported by some low-end NBM PoPs this weekend (<25% over eastern AZ mountains). The odds are a little higher Monday with the potential for a weak Pacific low to move inland from the west, but this is about all that can be anticipated this far out. This is climatologically the driest time of year for the AZ and SoCal lower deserts, so it is hard to put much optimism into a long-range precip forecast for the lower deserts.

AVIATION

Updated at 2345Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns are anticipated through the forecast period. W-SW winds will continue into the overnight hours, with speeds mainly aob 10 kt. = The diurnal easterly shift should occur late tonight at KIWA and KPHX. A slow transition back to W-SW is anticipated again tomorrow with a few hours of southerly/VRB winds expected prior to the shift. Winds should go W-SW by 21Z. BKN high cirrus clouds will continue through the overnight hours and slowly clear out tomorrow afternoon and evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather issues will exist through the forecast period under decreasing high cirrus decks. Current NW winds will go W later tonight and continue through the morning. Winds will then go back NW after sunrise tomorrow. Wind gusts up around 20 kt will continue at KBLH for the next couple of hours. Otherwise winds, at both terminals, will be aob 10 kt.

FIRE WEATHER

There will be a slow day-to-day warming of temperatures, but overall high temperatures will remain near seasonal normals throughout the rest of this week. Very dry conditions will also persist through the end of the week with relative humidity bottoming out around 5-15% each day. There will be a slight bump up in moisture late this weekend/early next week that may lead to isolated dry thunderstorms in the mountains of eastern AZ, but minimum RHs will still be low around 10-15%. Overnight recoveries will be also remain poor to fair, mostly around 25-45%. Seasonal wind patterns are expected through the rest of the week, with afternoon upslope breezes up to 15-25 mph. There will also be a slight uptick in southerly up-river winds along the Colorado River Valley Friday through this weekend, but afternoon and evening gusts are currently forecast to top out in the 20-30 mph range along the river. There will also likely be a return of evening and early-overnight gulf surge boundaries moving up from the Gulf of California through the AZ deserts. These boundaries will mostly lead to a brief uptick in winds and sudden southwesterly wind shifts.

PSR WATCHES/WARNINGS/ADVISORIES

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