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FXUS65 KPSR 071738 AFDPSR

Area Forecast Discussion National Weather Service Phoenix AZ 1038 AM MST Thu Dec 7 2023

UPDATE
Updated Aviation Discussion.

SYNOPSIS
A cooling trend will begin today as a couple weak weather systems pass by just to the north of the region through early Saturday. This will push daytime highs back to normal starting Friday while also bringing periods of breezy to locally windy conditions later Friday into Saturday. Slightly warmer temperatures are likely to return by early next week as high pressure sets up just to our west while dry conditions persist across the region.

DISCUSSION
The unseasonably warm temperatures for early December are basically over as the ridge that brought the warmth has pushed to the east of the region. Current water vapor imagery shows a weak and fairly moisture starved shortwave trough tracking east northeastward across Utah early this morning and this has helped to tamper down heights aloft across the Desert Southwest. As a result, temperatures today will fall well short of what we saw the last couple days with highs mostly in the mid 70s across the lower deserts.

Farther upstream, a second shortwave trough is seen just off the coast of the Pacific Northwest and this is forecast to track across the Great Basin tonight before more slowly tracking through the Four Corners area Friday into early Saturday. Considering the overall dry nature of this system and the fact any energy is forecast to stay well to our north, precipitation chances will remain outside of Arizona. The system will at least bring some minor impacts to our area later Friday into Saturday as winds increase over much of the area starting in the afternoon and much cooler air will push southward throughout the day Friday. The strongest winds with gusts actually not expected until Saturday with gusts of 25-35 mph possible across the western desert and over the Arizona high terrain.

The cooler temperatures will drop daytime highs down to around 70 degrees on Friday and even into the mid to upper 60s on Saturday, but even those temperatures are right around normal. Overnight lows will also drop considerably over the weekend with some areas seeing upper 30s Saturday morning, but the coolest night should be Sunday morning when lows of mid 30s to lower 40s are expected. A few areas like central La Paz County and the Globe area may also see their first freeze of the season Sunday morning.

Yet another ridge is forecast to build over the Pacific just to our west over the weekend before partially moving into the Desert Southwest early next week. This should moderate temperatures a bit pushing highs back into the lower 70s by around next Tuesday, but there remains a good deal of model spread as there will also be several shortwave troughs dropping out of Canada into the North- central U.S. which may hinder any substantial warming across our region. In fact the latest 00Z is now showing a trough developing across the Pacific Northwest on Monday before potentially diving southeastward into or around or region by next Wednesday. It is still too early to know if and exactly how much this potential trough could impact our region during the middle of next week, but for now only around 10% of members support a closed low with any precipitation chances across our region. It will be something to watch over the next several days.

AVIATION
Updated at 1738Z.

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

No aviation weather concerns are expected through the TAF period as dry, tranquil conditions persist. Winds will overall favor light, diurnal trends mostly less than 8 kts with periods of variability.
Across SE California, light winds (aob 8 kts) will continue with directions favoring the west at KIPL and NNW at KBLH through much of the period. Otherwise, SCT-BKN high clouds will push across the Phoenix metro this morning before clearing out later this afternoon with mostly clear skies prevailing thereafter.

FIRE WEATHER
A couple weak weather systems will pass across the northern portion of the region through Friday bringing a decent cooling trend and temperatures back to normal as early as Friday. Afternoon MinRHs through Friday will mostly be between 20-25% across the lower deserts before falling to 10-15% on Saturday. Overall light winds will persist across the area today before winds become breezy to locally windy on Friday and Saturday. Conditions Saturday could pose an elevated fire danger across the Lower CO River Valley and over the Arizona high terrain.

PSR WATCHES/WARNINGS/ADVISORIES
AZ...None.
CA...None.

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