Joshua Tree, CA is resolved to the town (about 34.1°N, 116.3°W), Bortle 4 / SQM 21.17 per Clear Outside; I assumed your 8-inch Dobsonian from a pullout near town. Forecast is solid for Oct 6–8 and rough beyond; recheck the evening before.
01Clear Outside / NWS · Oct 11Sunday Oct 11 is the weekend pick: clear, moonless, windy
Clear Outside (run Oct 5, 5:39 pm PDT) shows total cloud near 1% at 7–8 pm and 0% from 9 pm through the following morning, with no precipitation probability. Astronomical dark runs 7:38 pm to 5:25 am. The Moon is a 5% crescent that sets about 6:37 pm, so your whole 8 pm–1 am window is moonless.
The catch is wind: Clear Outside shows about 9–10 mph from 8 pm, and NWS Las Vegas (issued 3:37 pm Oct 5) calls Sunday night breezy with a slight chance of showers, mostly clear, low near 61°F. That is five days out, so confidence is low; recheck Saturday night.
For your 8-inch Dobsonian: arrive by 7:15 pm to cool the mirror, shield the tube from wind, and recheck cloud and wind Saturday evening.
02Clear Outside · Oct 6 – 12Week outlook: clear Tue–Fri, cloudy Saturday, clear but breezy Sunday
Cloud is Clear Outside's total cover; moon times are local. Tue Oct 6: 0% all night, moonrise 3:40 am, dark 7:44 pm–5:22 am, confidence high. Wed Oct 7: 0–1%, moonrise 4:44 am, high. Thu Oct 8: about 0–6%, moon sets 5:13 pm, medium-high; Draconid peak is near 6 pm PDT, before dark. Fri Oct 9: 31–46% medium cloud until about 8 pm, then 2–3% from 9 pm; wind 3–5 mph; medium.
Sat Oct 10 (new moon 8:50 am): 34–61% medium and high cloud from 8 pm to 1 am, clearing toward 4 am; low confidence. Sun Oct 11: clear, 9–10 mph wind; low. Mon Oct 12: NWS says sunny that day; no night forecast found. Computed moon sets about 7:08 pm, Mercury at greatest elongation east. SWPC Kp peaks at 4.00 through Oct 8, so no aurora at 34°N.
For your 8-inch Dobsonian: Fri Oct 9 after 9 pm and Wed–Thu are the best skies outside your weekend limit; Saturday is the weak night.
03timeanddate / computed · Oct 11Saturn, days past opposition, is your best planet all night
Saturn reached opposition Oct 4 and is at its brightest, per timeanddate. My ephemeris calculation (pyephem, computed) for Joshua Tree puts Saturn rising about 6:00 pm on Oct 11, then at 24° (ESE, az 105°) at 8 pm, 46° (SE) at 10 pm, 58° (south) at midnight and 55° (SSW) at 1 am, magnitude about 0.4.
Midnight is best for steadier air: it is highest then. At 8 inches, expect the ring gap (Cassini Division) and Titan on good seeing; seeing is not forecast, so judge on site. Neptune (mag 7.8, computed) sits at about 53° high in the south after 11 pm if you want a faint blue dot. Jupiter and Mars rise after 1 am (computed), outside your window.
For your 8-inch Dobsonian: view Saturn around 11:30 pm–12:30 am at 150–200x, and keep eyepieces in the cold with the scope.
04Computed for Joshua Tree · Oct 10 – 11Six galaxies stand high in the east before midnight
Computed altitudes (pyephem, about 9 pm PDT, Oct 10; within a degree on Oct 11): M31 Andromeda 52° ENE rising to 74° by 11 pm; M33 40° E, 64° at 11 pm; NGC 891 34° NE, 56° at 11 pm; NGC 7331 and Stephan's Quintet both 77° E, past the meridian by 11 pm and descending in the west.
NGC 253 (Sculptor) is low: 15° SE at 9 pm, 28° at 11 pm, about 31° due south at 12:30 am. Bortle 4 suits M31 and NGC 7331; M33 and the faint NGC 891 need averted vision and patience. Also well placed: Double Cluster at 54° N at 11 pm and globular M15 at 68° S at 9 pm.
For your 8-inch Dobsonian: hunt M33 and NGC 891 first, 9–11 pm; leave NGC 253 until midnight when highest; finish on M15.
05Computed for Joshua Tree · Oct 10 – 11Milky Way core is nearly gone: a 70-minute low window
The galactic center (Sagittarius) is computed at 22° altitude (SSW, az 205°) at 7:00 pm, but astronomical dark only begins 7:39 pm (Clear Outside). It is then 18° at 7:40 pm, 16° at 8:00 pm, 12° at 8:30 pm and sets about 9:45 pm. That is roughly 70 minutes under 20° over the southern horizon, where I expect glow from the Coachella Valley (estimate; I did not measure it).
Sat Oct 10 is cloudy in that window; Sun Oct 11 is clear. The NPS notes the Milky Way is best on moonless summer nights. Realistic plan: a wide-field of the band through Cygnus and Cassiopeia as it climbs overhead after 8:30 pm, and save core imaging for next spring-to-summer.
For your camera or tracker: skip the core this week; shoot the northern Milky Way after 8:30 pm on Sunday, or wait for spring.
06NPS Joshua Tree · Oct 11Use the park's stargazing lots and stay within 20 feet of the car
NPS lists four designated stargazing areas: the parking lots at Quail Springs, Hidden Valley, Cap Rock and Ryan Mountain. Stay awake and within 20 feet (6 m) of your vehicle. Day-use-only areas close dusk to dawn, overnight camping is not allowed in lots or roadsides, and paint-with-light photography is not permitted. NPS says Cottonwood Campground has the darkest skies, and Pinto Basin Road has the least traffic and darkest skies.
Use red light only; NPS says full dark adaptation takes 20–30 minutes. Bring layers; Sunday's NWS low is near 61°F. Because you finish near 1 am, check entrance-station status and park alerts beforehand. The Draconids (IMO ZHR about 5, per timeanddate; peak about 6 pm PDT Oct 8, before dark) are weak; my estimate is a few per hour at most.
For your 8-inch Dobsonian: set up in a designated lot at least 45 minutes before dark, keep gear within 20 feet, and use red light only.
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