textproduct: NWS Phoenix

UPDATE

Updated 18Z Aviation Discussion.

KEY MESSAGES

- High pressure aloft will result in dry conditions and above normal temperatures through the end of this week

- An approaching weather system will result in increased cloud cover, breezy conditions, and cooling temperatures by this weekend

- Scattered light shower activity will also be possible late Saturday into early Sunday, mainly over the AZ high terrain

SHORT TERM /Today through Friday/

Latest GOES-18 mid-lvl water vapor imagery depicts an amplified ridge of high pressure currently centered over the Great Basin. The ridge axis is projected to slide ewd over the 4-Corners region by this afternoon. In turn, 500 mb hghts are expected to climb to around 576-578 over the forecast area. Hghts of this magnitude are not particularly unusual for this time of year, however thermal profiles in the lower atmosphere are still rather warm with 850 mb temperatures approaching 20-22C. This will equate to sfc highs reaching the mid to upper 90s across the lower deserts which is a good 10+ degrees above normal for early April. A few locations along and near the Lower Colorado River Valley may even approach 100 degrees this afternoon. Dry and tranquil conditions will continue into tonight with low temperatures settling into the low to mid 60s across the lower deserts and mid 50s in the foothills and mountains.

On Thursday and Friday, the ridge axis is expected to shift ewd into the Southern Plains while a trough of low pressure approaches the West Coast. As this occurs, our region will remain between both features which will result in increasing southwesterly flow over the forecast area. Deterministic guidance shows 500mb hghts falling from 576-578 dm on Thursday to 573-576 dm on Friday which will result in lower desert temperatures cooling slightly from the mid to upper 90s on Thursday to the upper 80s and lower 90s on Friday. Due to the increasing 500 mb hght gradient, there will be increased breeziness both days, especially across SE California and SW Arizona where gusts could reach 20-30 mph at times.

LONG TERM /Saturday through Tuesday/

There still remains a decent amount of uncertainty amongst ensemble members regarding the track and strength of the weather system this weekend once it moves onshore. A majority of the GEFS and ENS clusters are now showing a much weaker and faster moving trough that will lift into the Great Basin region after it moves onshore. The result of this northern shift in the models is now being reflected in the NBM PoP and QPF fields which have both been significantly reduced in the latest run. Although PoPs remain around 40-50% across the AZ high terrain late Saturday into Sunday, chances across the lower deserts are now only around 20-25% at most. The main impacts with this system will likely be gusty winds due to an increased 500- 700 mb hght gradient setting up over the region. Winds will gust around 20-30 mph both Saturday and Sunday afternoon, with locally higher gusts around 30-35 mph in SE California. The arrival of negative 500 mb hght anomalies and thicker cloud cover will allow temperatures to decrease to around seasonal norms this weekend. Highs will fall back into the 80s (upper 60s to mid 70s) across the lower deserts (higher terrain) on Saturday and cooling to near to even slightly below normal region-wide on Sunday.

Ensemble members and deterministic guidance continues to show a follow-on system arriving early next week with a deeper trough progressing through the Intermountain West. This trough will reinforce negative hght anomalies over the entire forecast area and promote near to below normal temperatures Monday and Tuesday, with afternoon highs in the upper 70s to mid 80s (lower 70s) across the lower deserts (higher terrain). At this time, the best moisture and lift associated with this system will be focused well north of our region, and thus any rain chances will remain relegated to the higher terrain of N AZ.

AVIATION

Updated at 1655Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns under mostly clear skies can be expected throughout the TAF period. The overall wind pattern will continue to exhibit the typical diurnal tendencies with speeds aob 10 kts with periods of light variability expected, especially during the overnight and early morning hours and before the diurnal switchover. KIPL could see some occasional gusty sundowner winds approaching 20 kts later this evening.

FIRE WEATHER

Dry conditions and well above normal temperatures will persist through the end of this week. MinRHs will range from 10-15% today and Thursday before increasing above 15% starting on Friday. Overnight recovery will generally range from poor to fair across the region through the rest of this week. Winds will be around 10 mph or less today, but are expected to increase across the western districts Thursday and Friday. A weather system will move into the region this weekend, resulting in breezy to locally windy conditions, cooler temperatures, and much improved moisture. Scattered showers will be possible mainly over the higher terrain of southcentral AZ, but CWR will remain low <30%.

PSR WATCHES/WARNINGS/ADVISORIES

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