Area Forecast Discussion

UPDATE

Updated Aviation.

KEY MESSAGES

- High pressure encompassing the Desert Southwest will allow temperatures to hover around 5 to 10 degrees above daily normals through Tuesday.

- A Wind Advisory has been issued for SW Imperial Valley starting Tuesday 3 PM through Wednesday 8 AM.

- A weather system passing north of the region will result in periods of breezy to locally windy conditions and cooler temperatures during the latter half of the week.

SHORT TERM /TODAY THROUGH TUESDAY/

Latest mid-lvl wv imagery and 500 mb streamline analysis shows the the upper level ridge shifting eastwards into the Four Corners region, while a deep cut-off low continues to approach northern California. The Desert SW will continue to be influenced by positive height anomalies today with H5 heights between 577-580 dam, driving temperatures to above normal for this time of year. Expect afternoon highs today in the mid to upper 90s across the lower deserts while the higher terrain areas will generally be in the mid 80s. However, within this upper level ridge, a weak shortwave looks to pass through the region this afternoon/evening providing enough moisture and lift for the development of isolated showers and storms over northern Arizona. While most of the activity is expected to be along the Mogollon Rim, there is a non-zero (~5%) chance of storms developing over southern Gila County late this afternoon.

Tuesday's temperatures will be much of the same, with highs across SC and eastern Arizona relatively unchanged under the departing ridge, while out west temperatures will be 1-2 degrees cooler as the cut-off low begins to move onshore of northern California. Ahead of this feature, southwesterly flow will continue to strengthen over the western half of our CWA causing widespread breezy to locally windy conditions starting Tuesday afternoon. Due to this a wind advisory has been issued for the SW portion of Imperial Valley starting Tuesday 3 PM through Wednesday 8 AM. During this time the affected area can expect winds between 25-35 MPH and wind gusts up to 55 mph are possible. Meanwhile the remaining portions of Imperial and Riverside Counties can expect gusts between 20-30 MPH and in south-central and eastern Arizona gusts between 10-15 MPH will be common throughout Tuesday afternoon.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Deterministic and ensemble guidance are in good agreement that the cutoff low over the West Coast will transition to an open wave and progress through the Intermountain West from Wednesday into Thursday. Negative height anomalies from the passing system will result in cooler temperatures (likely closer to seasonal levels, in the mid 80s across the lower deserts) beginning on Wednesday. Periods of breezy to locally windy conditions can also be anticipated across the entire forecast area due to H7-H5 gradient remaining compact. The most widespread breezy conditions look to be on Wednesday and then stronger winds will transition to the high terrain of eastern AZ on Thursday as the trough axis passes through the region. Quasi-zonal flow aloft will return by Friday and into next weekend ahead of another potential shortwave trough. This will allow for a temporary boost in temperatures Friday and Saturday before the next weather system and subsequent cooler temperatures arrive on Sunday.

AVIATION

Updated at 2310Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Locally gusty winds and an extended period of a southerly cross runway wind early Tuesday afternoon will be the main weather issues under occasional thick high cirrus decks. Confidence is good that W/SW winds will prevail somewhat longer into the evening/overnight versus usual timing with a chance of mid evening gusts nearing 20kt. After the typical morning east winds, an extended period of south cross runway winds with speeds in excess of 10kt will be likely before veering SW mid/late afternoon. Another round of gusts near 20kt will be possible around sunset Tuesday.

Southeast California/Southwest Arizona including KIPL and KBLH: Strengthening wind gusts Tuesday afternoon/evening will be the primary weather issue under brief periods of thicker high cirrus decks. Confidence is good that winds will switch to a westerly component at KIPL and remain in place through Tuesday while southerly winds will be preferred at KBLH. Gusts 20-25kt will materialize Tuesday afternoon with speeds likely strengthening further at KIPL Tuesday evening.

FIRE WEATHER

A very progressive pattern with multiple dry weather systems passing north of the region will result in breezy conditions and periods of elevated fire weather throughout this week. The beginning of the week will see above normal temperatures and breezy conditions combined with min RH values of 8-15% which will result in widespread elevated fire weather conditions. This will especially be seen across the western districts on Tuesday afternoon where a Wind Advisory has been issued for SW Imperial Valley where gusts up to 55 mph will be possible. Breezy and dry conditions will carry through the rest of this week and into this weekend with relative humidity remaining at or below 15% each afternoon. Overnight recoveries will also vary through the week, but remain mostly in the 30-50% range.

PSR WATCHES / WARNINGS / ADVISORIES

AZ...None. CA...Wind Advisory from 3 PM Tuesday to 8 AM PDT Wednesday for CAZ562.