textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion

KEY MESSAGES

- Unseasonably hot conditions will continue to challenge daily temperatures records through the rest of the week and into the weekend.

- These hot conditions may be dangerous, especially for any strenuous outdoor activities without proper hydration and frequent breaks in the shade, or air conditioning.

- Temperatures should finally begin to back away from record territory by the end of the weekend as the high shifts east and cloud cover and shower chances increase.

SHORT TERM /TODAY THROUGH FRIDAY/

Current upper-level water vapor satellite imagery shows a high pressure system centered over northern Mexico, western TX, and southern NM along with a weak shortwave straddling the Lower CO River Valley. This shortwave is leading to some elevated winds across SE CA earlier this morning. This shortwave will quickly move east/northeastward into NM by this afternoon and will weaken as it does. As the shortwaves moves eastward wind speeds will gradually lower across SE CA through the morning.

Despite slightly lower heights aloft today from the aforementioned shortwave trough, H5 heights remain in the NAEFS max climatological percentile. Therefor temperatures will remain largely unchanged from yesterday, with afternoon high temperatures in the upper 90s to around 100 degrees today across the lower deserts. Tomorrow, H5 heights will rise slightly, to 585-588 dm, resulting in slight warming. Friday is forecasted to be the warmest day of the week with highs in the low 100s (100-103 degrees) across the lower deserts and in the low to mid 90s across the higher terrain. Highs of this magnitude will continue to flirt with daily records. Despite the unusually warm afternoons, mornings will continue to be on the pleasant side with low temperatures in the 60s across the lower deserts and in the 50s across the higher terrain.

LONG TERM /SATURDAY THROUGH TUESDAY/

The long term forecast remains on track from previous forecasts. A strong cold front will move through the Plains with a strong surface high building behind it, resulting in a tightening pressure gradient over our region. As a result, there will be breezy to locally windy conditions develop AZ, particularly over eastern AZ. Gusts of 20-30 mph are forecasted across the lower deserts of south-central and southwestern AZ. Higher gusts, 30-40 mph, are likely across the higher terrain east of the Phoenix Metro. Some gusts in excess of 40 mph are possible along the ridgetops. This would advisory level winds, however due to the limited spatial and temporal scope of 40 mph+ winds a Wind Advisory will not be issued at this time. However, one may be needed in future forecast updates. Temperature wise, the high pressure will start to weaken and shift further eastward, which will result in temperatures cooling slightly. Afternoon high temperatures are forecasted to be in the upper 90s to around 100 degrees across SE CA and SW AZ. As for the lower deserts of south- central AZ, cloud cover will start to move in keeping temperatures in the upper 90s, which is still near record territory.

Heading into the end of the weekend and beginning of next week, we will see a pattern change with the aforementioned high pressure becoming centered over the Plains. With the high centered over the Plains that will result in southerly flow over our region, which in turn will allow for some sub-topical moisture to make it's way up into our region. Ensemble members continue to show PWATs increasing to around 200-250% of normal across AZ on Sunday. This increase in moisture will at least bring an abundance of cloud cover to our region. The cloud cover in combination with the high shifted further east will result in cooling temperatures. Afternoon high temperatures are forecasted to be in the mid to upper 90s across the lower deserts both on Sunday and Monday. The influx of moisture will also result in some low-end shower and thunderstorm chances across the higher terrain to the north and east of the Phoenix Metro. Despite the abundance of moisture, with temperatures so high there will likely be too much dry air for any shower activity across the lower deserts. Additionally, the only forcing will be from orographic lift from the mountains. Any showers or storms that form will likely fall apart quickly as they move away from any topography. Any hope of rainfall for lower elevation areas will have to follow any outflow boundaries moving off the high terrain, but with where potential storms may initiate, and the expected storm motion, that appears to be an unlikely outcome at this point. Currently rain chances are sitting around 20-30% with thunderstorm chances around 10-15% across the higher terrain east of Phoenix on both Sunday and Monday.

Ensembles continue to show an East Pacific trough moving through the region during the middle of next week. This feature currently looks to drop H5 heights into a 567-575 dm range on Tuesday and Wednesday. As a result afternoon high temperatures will cool back into the 80s by Wednesday, which is near to slightly above normal for this time of year. The last time our region saw afternoon high temperatures in the 80s was on March 11, which will be 3 weeks by next Wednesday. Additionally, this trough may bring additional shower and storm chances to the region. The NBM currently has the best rain chances (20-30%) across the higher terrain to the north and east of Phoenix. Depending on the progression of the trough (if it digs further south) the rain chances could increase for the beginning of April. Stay tuned for future updates.

AVIATION

Updated at 1120Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation concerns are expected during the TAF period. Winds will continue to follow diurnal trends with speeds generally aob 10 kt. Other than a FEW distant high cirrus, skies will be mostly clear through Friday morning.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation concerns are expected during the next 24 hours. Outside of extended periods of VRB to calm conditions during the forecast window, winds will favor a W'rly component at each terminal. FEW-SCT high cirrus will clear by late morning, giving way to clear skies trough through Friday morning.

FIRE WEATHER

Record heat along with very dry conditions will continue through at least the start of the weekend. MinRH values will run generally around 5-10% today and tomorrow before increasing closer to 10-20% starting Saturday. MaxRHs will follow a similar uptrend with readings close to 20-40% the next few mornings before rising through the weekend. By the end of the weekend and beginning of next week, overnight recoveries will be in the 40-60% range. Some marginal breeziness (gusts 15-25 mph) is expected again this afternoon. Stronger winds (gusts 25-35 mph) enter the picture late Friday into Saturday mainly, for areas east of the Colorado River. Higher gusts upwards of 40+ mph will be likely (~80% chance) for portions of the eastern Arizona high terrain, but should be confined to the highest ridgetops. With very dry air in place, marginal breezes will lead to periods of elevated fire weather conditions through Friday. Even with the enhanced winds for Saturday, RHs should come up enough to limit critical thresholds for being met, but continued elevated, to near critical, conditions can be expected.

CLIMATE

Daily record highs through this week:

Date Phoenix Yuma El Centro ---- ------- ---- --------- 3/26 100 in 1988 99 in 1988 98 in 1988 3/27 98 in 1986 100 in 1986 99 in 1988 3/28 95 in 2015 98 in 2015 98 in 2015 3/29 97 in 2015 100 in 1897 97 in 1969

PSR WATCHES/WARNINGS/ADVISORIES

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