textproduct: NWS Phoenix

KEY MESSAGES

- This morning will feature the coldest temperatures of the month, but will be followed by rapid warming through the rest of this weekend, with highs pushing 5 to 10 degrees above normal tomorrow.

- Dry conditions and strong high pressure will persist through the coming week, with lower desert high temperatures pushing into the upper 80s to lower 90s, and near daily records, during the second half of the week.

SHORT TERM /TODAY THROUGH SUNDAY/

Quasi-zonal westerly flow is currently in place across the Desert Southwest early this morning and skies are clear as dry air has moved in. Winds are also much lighter across the region. This combo of dry air, clear skies, and light winds will lead to this morning being the coldest morning of February, with most of the region expected to experience a low below 40 degrees, including parts of Phoenix. Several higher elevation and rural valley locations are also forecast to dip to to just below freezing. With just a little bit of lingering surface moisture, some light frost may develop this morning. After the cold morning, temperatures should warm to around seasonal levels, with lower desert highs in the upper 60s to lower 70s, under mostly clear skies and continued light winds.

Ridging will develop and H5 heights will rise very quickly through today and Sunday. H5 heights shortly after midnight this morning were around 564-567dam and guidance shows heights will rise to around 580dam by the end of today and 583-585dam by the end of the day tomorrow. Climatologically H5 heights are typically in the 565-575dam range, with anything above 580dam being above the 90th percentile. This rapid high pressure development will lead to rapid warming as well. Latest NBM forecast adds roughly 10 degrees of warming to both the high and low forecast for tomorrow. There will be an influx of high clouds late this evening and tonight and there will be an increase in easterly gradient winds across south-central AZ tonight/tomorrow morning, in response to strong surface high pressure to the northeast. The clouds and wind tomorrow morning may keep low temperatures a few degrees warmer than what is currently forecast, but should not have any influence on the afternoon highs as the winds weaken and clouds thin out and move east through the afternoon.

LONG TERM /MONDAY THROUGH FRIDAY/

The warming trend will not stop with this weekend. The synoptic and large-scale pattern favors ridging persisting over the Desert Southwest, with H5 heights staying around 582-585dam through the end of the month. Under this riding pattern, persistent southwesterly flow will lead to continued warming through the coming week, with 850mb temperatures forecast to reach up to 17-19C by mid to late week. Temperatures of 17-19C at 850mb is more common for late April and early May. High temperatures in the upper 80s to around 90 degrees is normal for late April and early May and that is precisely what is in the forecast for this coming week. Latest NBM has forecast highs in the low to mid 80s for Monday and Tuesday across the lower deserts and then upper 80s to lower 90s Wednesday through the end of the week. Both high and low temperatures will be pushing daily records late this coming week. Daily record highs in Phoenix for the end of February are around 89-92F (see CLIMATE section below) and 92F is also the record highest February temperature. So there is even a decent chance of setting a new monthly record in Phoenix. The 07Z run of the NBM has a forecast high of 92F in Phoenix on the final day of February with around a 75% chance of 92F or higher. Lower desert high temperatures in the 80s to around 90F will lead to Minor HeatRisk and the heat will pose a health risk if you spend extended time outdoors in the afternoon without breaks from the sun and/or proper hydration. Besides the coming heat, the atmosphere in the Desert Southwest will remain dry through the next week and winds will generally be light with occasional late morning and afternoon breezes.

AVIATION

Updated at 0530Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No aviation weather concerns under initial clear skies before some high level clouds move in later in the TAF period. Light winds will eventually settle out of the east tonight, likely persisting well into the afternoon hours Saturday. A brief westerly shift should occur by around sunset Saturday before turning back out of the east between 05-08Z Sunday. Overall speeds will generally be aob 10 kts.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns under some passing mid to high level clouds can be expected throughout the TAF period. The overall winds will generally be out of the west to northwest aob 10 kts with periods of light variability developing later tonight.

FIRE WEATHER

Dry conditions will persist through the next week, with temperatures warming rapidly this weekend through the first half of next week. Besides a brief and small uptick in moisture during the middle of the coming week, MinRH values will be around 10-20% and overnight recoveries will be around 35-50% each day. Afternoon high temperatures will go from low to mid 80s Sunday through Tuesday to upper 80s to low 90s Wednesday through the end of the week, up around 15-18 degrees above normal. Winds will be light with an occasional afternoon breeze and follow typical diurnal directional patterns most days over the next week. There will be an uptick in easterly winds tomorrow morning across south- central AZ, with general winds up to 10-15 mph and gusts up to 20-25 mph across lower elevations (below 3000') and a bit higher over higher elevations, up to 15-25 mph sustained with gusts up to 30-35 mph. There may be another uptick in easterly winds at the end of next week, but forecast confidence is currently low. There is no precipitation in the forecast for the next week.

CLIMATE

Daily High Temperature Records.

Phoenix --------- 2/25 92 (1921) 2/26 91 (1986) 2/27 92 (1986) 2/28 89 (1986) 3/1 89 (2016)

PSR WATCHES/WARNINGS/ADVISORIES

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