textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion.

KEY MESSAGES

- Dry conditions and well above normal temperatures will prevail through the first week of February.

- A period of breezy northeasterly to easterly winds will return during the middle of the work week.

SHORT TERM /TODAY THROUGH MONDAY/

Midlevel water vapor imagery shows the center of an unseasonably strong area of high pressure just southwest of the Four Corners early this afternoon. H5 heights over the forecast area are still advertised in excess of the 90th percentile of CFSR climatology, however, NAEFS mean 850 mb temperatures are perhaps more impressive at around 15-16C today, which is in excess of the 99th percentile over portions of the Colorado River Valley and Central AZ. The notably high heights and warm temperatures aloft, coupled with easterly downslope winds, will provide an excellent setup for lower desert highs reaching the 80s in many places. In fact, Phoenix Sky Harbor Airport had already hit 80F as of 12:15 PM MST, and is likely (70% chance) to at least tie the record high of 83F for today's date.

A weak upper low west of Baja California, and to its north/west, a meridionally elongated SW-NE oriented deformation zone are apparent in midlevel water vapor imagery early this afternoon, which will influence the region as high pressure continues to weaken and shift eastward Monday. As these features approach the region, the main sensible weather impacts will be an increase high clouds later today into Monday, and weakening surface pressure gradients resulting in a return to light and mostly terrain-driven winds early in the work week. Under increased high clouds and lower heights aloft, temperatures will also drop off a bit Monday, but still generally reach the upper 70s to near 80F for the typically warmer lower desert locales.

LONG TERM /TUESDAY THROUGH SATURDAY/

The rest of the coming week should remain quiet as another Rex block develops across the Western U.S. midweek. Even though this blocking setup will not last all that long (2-3 days), the ridge is forecast to strengthen quickly and reach near climatological record strength across western Montana, Idaho, and eastern Oregon. H5 heights for our region are likely to reach 582dm again by Wednesday, adding to the unseasonably warm temperatures already in place. Highs are expected to reach into the lower 80s for many lower desert locations on Tuesday before peaking on Wednesday between 81-85 degrees. Easterly downsloping winds should also start to kick in by Wednesday potentially pushing temperatures well into the 80s.

An upstream Pacific trough is then seen moving toward the Pacific Northwest on Thursday and this will help to break down the Rex block. A weak cut-off low that forms on Tuesday west of Baja should also slowly move northeastward into at least western portions of our region Thursday into Friday, but guidance continues to show little if any weather impacts. Moisture advection is expected to be quite low and any forcing is likely to be limited, so PoPs remain well under 10% for Thursday and Friday. The only real impact is likely to be an increase in easterly winds with some areas across eastern and south-central Arizona potentially seeing gusts up to 30-35 mph Thursday morning. The decaying cut-off low may end up eventually getting mostly absorbed into the incoming Pacific trough, but there is still a good amount of uncertainty with the eventual evolution of the two systems. For now, due to the lack of expected moisture, rain chances remain quite low through next weekend. The breakdown of the ridge should at least allow for some cooling late in the week with the NBM showing lower desert highs mostly falling back into the upper 70s.

AVIATION

Updated at 2345Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns expected throughout the TAF period. Easterly winds will prevail through the rest of tonight with speeds falling below 6 kts after sunset. Winds are expected to return to normal diurnal patterns tomorrow, with a westerly shift anticipated during the late afternoon hours. Periods of SCT high cirrus will overspread the Phoenix Metro late this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns expected throughout the TAF period. Winds will transition from westerly to southeasterly at KIPL and remain generally northerly at KBLH with speeds aob 7 kts at both sites. SCT to at times BKN high cirrus will stream across the region through Monday afternoon.

FIRE WEATHER

Well above normal temperatures and dry conditions will persist over the next several days. Humidities will remain quite low with with afternoon minRHs commonly between 12-20% range areawide. Overnight recoveries will remain fair to poor with humidities generally topping out in a 35-55% range. Light and mostly terrain-driven winds will prevail early in the work week. The weather pattern will again support breezy northeasterly to easterly winds mid to late week, which could result in locally elevated fire weather conditions over prominent/exposed higher terrain areas and ridgetops of Southern AZ.

CLIMATE

Phoenix, AZ Daily Record High Temperatures.

2/1 83 (2003) 2/2 82 (2025) 2/3 86 (2025) 2/4 86 (2025) 2/5 87 (1963)

PSR WATCHES/WARNINGS/ADVISORIES

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