textproduct: NWS Tucson Arizona

SYNOPSIS

Warm today with breezy conditions. A weather system will move into the region tonight, bringing chances for rain showers and afternoon thunderstorms through Tuesday. Temperatures will warm to above normal in the mid to second half of the week.

DISCUSSION

A low pressure system is currently sitting southwest towards Baja California. This will be the weather maker for the start of the week.

But first, today will be one of the warmest days in the weekend. Southeasterly breezes will form in the morning hours and slowly calming down by the afternoon. Dew points will start to creep into the region by the afternoon, this is signal for more moisture is inbound.

Next, the low pressure will slowly move east-northeast and hugging along the border on Monday and Tuesday. The diffluence area will be in prime location over Southeast Arizona. That will bring rain chances and thunderstorms. Chances for rain showers will be increasing early Monday morning from the west and south. Expanding north and east throughout Monday to Tuesday. Diffluence and afternoon heating will prime the atmosphere of thunderstorm development. Plus, there will be good shear aloft to support stronger lived thunderstorms. Hi- res models are showing the early signs of thunderstorms in the late afternoon on Monday. But, there is still some uncertainty on how fast the low will move downstream. In the last 48 hours, it has slow down a bit and drifted a little more westward. Therefore, there is potential it could slow down again; delaying rain and or inhibiting thunderstorm development on Monday afternoon. With this forecast package, the best chances for rain showers will be Monday afternoon to Tuesday and chances for thunderstorms on Monday afternoon. Rainfall amounts will generally be 0.15" to 0.4" with locally higher amounts in the higher terrain or from a thunderstorm. The mountain peaks can get a dusting of snow to 2 inches.

The ensembles show the low leaving the region by late Tuesday to early Wednesday, but again, there is disagreement on the timing. Part of the challenge with closed lows. There is no clear indication upstream to force the low pressure center out. Right now, there is a ridge pushing against the low which it ain't doing much. Once the low leaves, Southeast Arizona will warm and dry out for the rest of the week. Temperatures will be trending back above normal by the weekend.

AVIATION

Valid through 09/12Z. Mostly SKC through 08/16Z. Then SCT high level cirrus at or around 20K ft AGL follow by FEW to SCT clouds at or around 12-15k ft AGL after 07/22Z from the west. SFC winds less than 10 kts southeasterly this morning. By 08/16Z, winds increasing to 9-15 kts with a few gusts up to 25 kts. By 08/00Z, shifting to southerly and less than 10 kts through the rest of the period. There is a 10 percent chance for isolated -SHRA developing west of KRYN after 08/22Z. -SHRA coverage and probability will increase towards the end of the period. Aviation discussion not updated for TAF amendments.

FIRE WEATHER

Warm, dry, and breezy easterly to southeasterly winds today. Winds will be up to 15 mph with strong gusts. Tonight, a weather system will inject moisture into the region for the first half of the new week. The best chances for rain showers and high elevation mountain snow will be Monday through Tuesday. Temperatures will be around to slightly below normal with this weather system. Afternoon thunderstorms are possible on Monday and have the potential to bring strong gusty winds. Starting Wednesday, conditions will start to warm and dry out, leading to above normal temperatures by the weekend.

TWC WATCHES/WARNINGS/ADVISORIES

None.