textproduct: NWS Phoenix

UPDATE

Updated 00Z Aviation Discussion.

KEY MESSAGES

- An Extreme Heat Warning is in effect for the Phoenix Metro area through Tuesday and for portions of the western deserts today and Monday. - Widespread moderate HeatRisk will impact the majority of the region through the first half of the week with isolated pockets of major HeatRisk lasting through Tuesday.

- Monday will be the hottest day of the week with lower desert highs reaching 105-112, followed by a gradual cooling through the remainder of the week.

SHORT TERM /TODAY THROUGH TUESDAY/

Latest mid-lvl wv imagery and 500 mb streamline analysis reveals a shortwave trough passing through the 4-Corners region while a ridge of high pressure strengthens over SE California and the Great Basin. This ridge will become the predominant feature over our region for the next few days as it slowly migrates ewd. Due to increasing mid-lvl hghts/thickness, temperatures are expected to top out well above normal this afternoon. As of 2:00 PM, Phoenix Sky Harbor has already reached 106 degrees. High across the lower deserts will generally range from 102-108 today which is a solid 12-15 degrees above normal. An Extreme Heat Warning is now in effect or the Phoenix Metro area and far W Imperial County in SE California, so heat precautions should be taken, especially if spending any amount of time outdoors. The one silver lining is overnight lows will still remain comfortable in the upper 60s to low 70s thanks to very dry air in place which will lead to ample radiational cooling.

On Monday, the center of the ridge will migrate directly over N AZ which will lead to 500 mb hghts approaching 590 dam or the 99th percentile of climatology for mid-May. This increase in hghts aloft along with clear skies and very low RH will result in the hottest temperatures of the year so far. Highs across the lower deserts are expected to reach upwards of 103-109 degrees and even a few locations in SW AZ and the Lower Colorado River valley hitting the 110 degree mark. Monday's readings should fall just shy of daily records by about a degree or two, however there is still a low (20-30%) chance of at least tying the record high of 110F at Sky Harbor. The Extreme Heat Warning will also expand on Monday to encompass all of the major populations centers including Phoenix, Yuma, Blythe, and El Centro.

Short-range Model guidance continues to indicate a weak shortwave trough developing west of Baja and being pulled nwd around the western periphery of the ridge on Tuesday. This disturbance will nudge the ridge axis further ewd, however positive hght anomalies will remain in place across the eastern half of Arizona. Highs on Tuesday will be slightly cooler, but still reach 103 to 107 degrees in Phoenix. Therefore, the Extreme Heat Warning will remain in place for the greater Phoenix Metro through early Tuesday evening. Areas farther west including Southeast California will be noticeably cooler due to the proximity of the passing disturbance with highs dropping to 102-105 degrees. Winds are also expected to increase Tuesday afternoon across the Lower Colorado River valley where gusts could reach up to 25-30 mph. The elevated winds coupled with low RHs during the afternoon hours will promote elevated to near critical fire weather conditions.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

The latter half of the coming week will involve a larger Pacific system moving into northern California on Wednesday displacing the ridge over our region well to the east by Thursday. Wednesday should be a bit of a transition day as heights really start to lower, but daytime highs may react more to the influx of upper level moisture and clouds. Forecast highs are still shown to top 100 degrees, but on average should be between 100-103 degrees across the lower deserts. As the flow turns from the south on Wednesday to more out of the west on Thursday, any moisture and clouds will get pushed to the east out of the region. The Pacific system is then favored to move east northeastward through northern Nevada into Wyoming on Thursday, but it will also help to further depress heights over our region lasting through Friday. Models are now trending slightly cooler late this week with highs potentially dipping into the mid to upper 90s on Friday. The outlook for next weekend favors temperatures warming back up to 100 or just over 100 degrees as a brief ridge moves through the region, while dry conditions and generally clear skies prevail.

AVIATION

Updated at 2315Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation concerns are expected throughout the TAF period. Winds will tend to follow typical diurnal tendencies, with a later than usual (22-00Z) westerly shift late tomorrow afternoon. Some occasional gusts into the mid teens are possible early this evening and then again late tomorrow morning, otherwise wind speeds will be aob 10 kt. Skies will remain mostly clear for the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected through the TAF period. At KIPL, winds will be SE'rly through the afternoon turning W'rly by this evening for the over night hours and then back SE'rly by tomorrow morning. At KBLH, winds will fluctuate between S'rly and SW'rly. Overall wind speeds, at both terminals, will be aob 10 kts. Skies will remain clear throughout the period.

FIRE WEATHER

Hot and dry conditions will prevail through the first half of this week with lower desert highs in a well above average category. Relative humidity will bottom out in the single digits each afternoon with only very minimal improvement across the eastern districts late in the week. Overnight recoveries will remain poor to fair, averaging 20-35%. Winds will remain light and diurnal today, before elevated easterly winds with gusts to around 25 mph impact the eastern districts Monday morning. Tuesday will bring more of a predominant southerly wind, particularly across the western districts where afternoon gusts of 25-30 mph will be possible. The combination of the hot temperatures, very low RHs, dry fuels, and breezy conditions focused during the late afternoon hours should result in elevated to near critical fire weather conditions for portions of the area.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 11 AM to 8 PM MST Monday for AZZ530- 532.

Extreme Heat Warning until 8 PM MST Tuesday for AZZ537-540- 542>544-546-548-550-551.

CA...Extreme Heat Warning from 11 AM to 8 PM PDT Monday for CAZ567- 569-570.

Extreme Heat Warning until 8 PM PDT Monday for CAZ562-563-566.