textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- A broad scale troughing pattern will persist over the western U.S. through the end of the week, with a slow warming trend, but overall near normal temperatures.

- Dry conditions, with no threat of rain, and seasonal afternoon breezes are expected through the next 7 days.

SHORT TERM /TODAY THROUGH THURSDAY/

A broad trough, with a few weak shortwaves swinging through, will persist across the Southwest through Thursday with rather benign Spring-like weather conditions expected. There will be a slow rise in temperatures as 500mb heights slowly rise despite the lingering trough. High temperatures this afternoon will be around 5 degrees warmer than yesterday, with lower deserts forecast to reach the lower 90s. Normal highs this time of year are in the middle-90s, which the lower deserts will return to tomorrow and Thursday as warming steadily continues. Mornings will remain pleasantly cool, mostly in the upper 50s and 60s. Scattered high clouds will be pulled northeastward across the Desert Southwest today through early tomorrow and another weak shortwave from the northwest will bring some high clouds for Thursday. The high clouds will not be too optically thick, so there will still be plenty of sun to go around. Otherwise, very dry conditions can be expected over the next three days, with afternoon humidity levels falling below 15% nearly everywhere, and there is no shot at any rain. Aside from some breezy northerly winds across southeast CA and the Lower Colorado River this morning (gusts up to 20-30 mph), driven by strong pressure rises over NV, winds each day will mostly follow seasonal trends; light winds during the overnight and morning hours and modest upslope breezes in the afternoons with gusts up to 15-25 mph.

LONG TERM /FRIDAY THROUGH MONDAY/

The slow warming trend is forecast to continue through Friday and this coming weekend. Global ensemble guidance supports the large- scale synoptic pattern across the west finally evolving out of the current state, with the strong blocking ridge near B.C. Canada giving way/weakening as a strong low traverses across Alaska. This change will result in at least a temporary de-amplification of the pattern across the western CONUS for the weekend and a trend toward positive 500mb height anomalies with brief anticyclonic flow developing over the Desert Southwest. This trend will lead to high temperatures reaching into the upper 90s by Friday and pushing 100 degrees by Sunday - Monday (30-60% odds of >=100).

This pattern shift will also allow for some moisture to seep into AZ, from the southeast and with evening gulf surges, as global guidance shows a slow uptrend in PWATs Friday through the weekend. This may end up leading to some AZ high terrain afternoon convection, which is supported by some low-end NBM PoPs this weekend (<25% over eastern AZ mountains). The odds are a little higher Monday with the potential for a weak Pacific low to move inland from the west, but this is about all that can be anticipated this far out. This is climatologically the driest time of year for the AZ and SoCal lower deserts, so it is hard to put much optimism into a long-range precip forecast for the lower deserts.

AVIATION

Updated at 1100Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No significant weather issues will exist through Wednesday morning under increasing high cirrus decks. Confidence is good that easterly winds will prevail through mid morning before starting to make the usual switch to W/SW. However, an extended period of variable (140v240) or southerly cross runway winds may exist before completing the switch early/mid afternoon. Wind gusts should be limited to around 15kt late afternoon/early evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through Wednesday morning under increasing high cirrus decks. Confidence is good that wind directions will oscillate between west and north at KIPL while a persistent northerly component affects KBLH. Wind gusts 20-25 kt may be common at KBLH late morning through late afternoon.

FIRE WEATHER

There will be a slow day-to-day warming of temperatures, but overall high temperatures will remain near seasonal normals as the normals also slowly rise. Very dry conditions will also persist through the end of the week with minimum RH values around 5-15% each day. There will be a slight bump up in moisture this weekend, that may lead to some dry thunderstorms in the mountains of eastern AZ, but minimum RHs will still be around 10-15%. Overnight recoveries will be poor to fair, mostly around 25-45%. Seasonal wind patterns are expected through the rest of the week, with afternoon upslope breezes up to 15-25 mph. There will likely be a slight uptick in southerly up-river winds along the Colorado River Valley Friday through this weekend, with a small pattern shift, but afternoon and evening gusts are currently forecast to top out in the 20-30 mph range along the river. There will also likely be a return of evening and early-overnight gulf surge boundaries moving up from the Gulf of California through the AZ deserts. These boundaries will mostly lead to a brief uptick in winds and sudden southwesterly wind shifts.

PSR WATCHES/WARNINGS/ADVISORIES

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