textproduct: NWS Phoenix

KEY MESSAGES

- Temperatures around five degrees above normal will result in localized major Heat Risk again today with Extreme Heat warnings remaining in place.

- Critical fire weather conditions are then expected over much of the region Friday through Sunday due to dry and windy conditions developing.

- Cooling temperatures this weekend will eventually push readings to slightly below normal starting Sunday.

SHORT TERM /Today through Friday/

Above normal temperatures will continue over the next couple of days while the subtropical high centered to our southeast slowly weakens and eventually shifts farther away from the region. Very warm early morning temperatures with most locations well into the 80s will quickly rise to above 100 degrees mid morning before topping out between 108-112 degrees across the majority of the lower deserts. Extreme Heat Warnings remain in effect for portions of the area through early evening largely due to the very warm overnight temperatures combining with highs around five degrees above normal.

The modest mid-level moisture that has been present over the past day or two is still resulting in some isolated light shower activity from time to time, but very dry air in the lower levels has kept much of the activity from reaching the ground. The lingering moisture may have more of an impact today as the high weakens and subsidence decreases. Hi-res guidance largely agrees convection will be more expansive today, but only across the eastern Arizona high terrain. Any convection is still expected to be high-based and should not amount to much precipitation. Drier air is already beginning to work its way across southern California and will continue to make eastward progress through much of Arizona tonight into Friday. As H5 heights continue to lower into Friday, forecast highs dip a bit further with readings more in a 106-110 degree range.

The main forecast concern will shift away from the heat to increasing fire danger starting Friday. A large Pacific trough will spread over the Northwestern U.S. today and then over the entire Western U.S. Friday into Saturday. The incoming trough will bring gradual height falls across the Desert Southwest starting Friday as well as a tight pressure gradient which will last for several days. Winds will become breezy to locally windy on Friday and as the atmosphere dries out, humidities will drop to critical levels Friday afternoon. Red Flag Warnings have been posted for the Lower CO River Valley and over the Arizona high terrain where critical fire weather conditions are expected starting late Friday morning. Near critical fire weather conditions are anticipated across the rest of the area.

LONG TERM /Saturday through Wednesday/

The large Pacific trough will be the dominant weather feature across the Western U.S. over the weekend and likely even through the first half of next week. The deep low with H5 heights briefly reaching near climatological record lows over the Great Basin late Saturday into Sunday will keep the pressure gradient abnormally tight for late June. Strong gradient winds over the entire region on Saturday and then more focused across the eastern half of Arizona on Sunday will pose a major fire weather threat. Gusts of 25-40 mph are expected to impact a good portion of the area this weekend as humidities lower into a 5-15% range. Red Flag conditions will impact much of the region on Saturday and then over eastern Arizona on Sunday. Expect rapid spread and growth of any new or existing fires. Guidance eventually shows the deep low gradually filling early next week, but remaining in place at least through the middle of next week. Winds will also diminish somewhat early next week, but breezy conditions are likely to persist.

The presence of the large trough will bring some relief from the heat starting this weekend with NBM forecast highs dropping to below normal first across the western deserts on Saturday and then areawide by Sunday. Daytime highs anywhere from the upper 90s to just over 100 degrees are expected on Sunday and Monday before temperatures begin to slowly rise back closer to normal at some point during the latter half of next week. Overnight lows will also become quite pleasant with readings as low as the mid 60s across the western deserts to the low to mid 70s over the rest of the lower deserts.

AVIATION

Updated at 1000Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through Thursday night. Winds will follow diurnal trends with gusts this afternoon upwards of around 20 kt. Can't rule out some very high based isolated light showers through this afternoon, but no impacts are expected for the area terminals. SCT to sometimes BKN mid-level clouds will last through the first part of today with clearing expected by this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: The main aviation concern will be breezy to windy conditions at each terminal this afternoon and evening. Until then W'rly and S'rly winds should be favored at KIPL and KBLH respectively. Gusts 25-30 kt will then become common later in the period, with stronger gusts upwards 35 kt possible at KIPL. FEW mid-level clouds are likely to clear by this afternoon.

FIRE WEATHER

Elevated fire danger will continue today due to low humidity, very warm temperatures, and afternoon upslope/upvalley breezy conditions with critical conditions developing Friday. Red Flag Warnings have been issued for Friday through Sunday for much of the area. Expect MinRHs today into the single digits across the western districts, but closer to 20% in the east. These values will fall closer to 5-15% starting Friday and stay in this range for several days. Winds will generally remain terrain driven today with upslope gusts during the latter half of the afternoon peaking around 25 mph. Winds will increase starting Friday with gusts into a 20-35 mph range and locally higher over higher terrain areas. Winds are likely to peak on Saturday with gusts commonly reaching 25-40 mph. These windy and dry conditions will combine with the very dry fuels to create a risk of extreme fire behavior. Temperatures will cool off this weekend reaching to slightly below normal starting Sunday. Winds are expected to gradually diminish next Monday into Tuesday.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST this evening for AZZ530-532- 533-537-540-542>544-546-548-550-551.

Red Flag Warning from 11 AM Friday to 8 PM MST Saturday for AZZ131.

Red Flag Warning from 11 AM Friday to 8 PM MST Sunday for AZZ133.

CA...Extreme Heat Warning until 8 PM PDT this evening for CAZ562-566- 567-569.

Red Flag Warning from 11 AM Friday to 8 PM PDT Saturday for CAZ231.