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San Francisco Tlalcilalcalpan

19.295° N   99.768° W  ·  2769 M
77 /100
PEAK
A genuinely good night — 8 hours of clear, dark sky from 22:00.
BEST WINDOW 22:00–06:00 · ASTRO DARK 21:00–06:00 · MOON 1%
Transparency
0.43
Seeing
1.00
Cloud
1%
Moon
1%

Excellent tonight

Hour by hour, local to San Francisco Tlalcilalcalpan. Colour encodes the score and nothing else; every other measurement is luminance.

Sky state
Lighter = daylight and twilight  ·  unshaded = astronomical dark
Score
19
20
21
22
23
00
01
02
03
04
05
06
0
20
26
49
62
63
67
77
73
77
75
0
BEST WINDOW
Low cloud
1%
4%
15%
14%
3%
9%
2%
0%
5%
0%
0%
2%
Mid cloud
12%
21%
51%
16%
7%
6%
1%
0%
0%
0%
0%
1%
High cloud
64%
54%
28%
11%
6%
4%
20%
1%
1%
1%
0%
0%
Transparency
0.37
0.30
0.30
0.30
0.28
0.36
0.42
0.42
0.42
0.43
0.40
0.38
Seeing
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
Moon clear
0%
down
down
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down
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down
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Inspect

Cloud tracks show clear sky — a longer bar is better. The figure inside each track is the raw measurement.

Why this hour scored what it did
19 Clouded out · 0/100
Starting from
100
Cloud
−43
Transparency
−15
Seeing
−0
Moonlight
−0
Darkness
−43
Score
0
CLOUD 68% LOW 1% MID 12% HIGH 64% SUN 1.3° MOON 6.1° / 0% WIND 1 TEMP 14°
Excellent 75+ Good 55+ Fair 35+ Poor 15+ Not worth it Seeing is estimated from surface wind — see how we score.

What are you doing tonight?

The same forecast, weighted for the target. Planetary work barely cares about moonlight; long exposures die on high cloud a visual observer would never notice.

SET UP 21:30 · OBSERVE 22:00–06:00 · 8H · MEAN 68

Darkness and moonlight dominate. Faint fuzzies need a genuinely dark sky more than they need steady air.

192123010305
HIGH CLOUD CLEARS 22:00TWILIGHT BEGINS 06:00
SET UP 21:30 · OBSERVE 22:00–06:00 · 8H · MEAN 80

Seeing is everything and moonlight is irrelevant. Bright targets punch through twilight, so darkness barely counts.

192123010305
HIGH CLOUD CLEARS 22:00TWILIGHT BEGINS 06:00MOONLIGHT IGNORED FOR THIS TARGET
SET UP 21:30 · OBSERVE 22:00–06:00 · 8H · MEAN 63

Tolerates soft seeing, but high cloud wrecks a wide frame and moonlight raises the background everywhere.

192123010305
HIGH CLOUD CLEARS 22:00TWILIGHT BEGINS 06:00
SET UP 22:30 · OBSERVE 23:00–06:00 · 7H · MEAN 57

Needs conditions to hold still for hours. Sustained transparency matters more than any single good hour.

192123010305
CLOUD BREAKS 23:00TWILIGHT BEGINS 06:00
SET UP 21:30 · OBSERVE 22:00–06:00 · 8H · MEAN 70

Naked eye, whole sky. Total cloud and moonlight are the only things that count.

192123010305
HIGH CLOUD CLEARS 22:00TWILIGHT BEGINS 06:00
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The next week of nights

Tonight · 12 Aug
77
Excellent
MOON 0%
22:00–06:00
Tomorrow · 13 Aug
73
Good
MOON 3%
00:00–06:00
Friday · 14 Aug
64
Good
MOON 7%
23:00–01:00
Saturday · 15 Aug
47
Fair
MOON 15%
00:00–01:00
Sunday · 16 Aug
69
Good
MOON 23%
00:00–01:00
Monday · 17 Aug
41
Fair
MOON 32%
00:00–01:00
Tuesday · 18 Aug
35
Fair
MOON 42%
00:00–01:00
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Nearby locations

About this forecast

Conditions for San Francisco Tlalcilalcalpan, Mexico are computed from the MET Norway forecast model for these exact coordinates, combined with sun and moon positions we calculate directly. The score weighs cloud cover by layer, atmospheric transparency, estimated seeing, moonlight and how dark the sky actually gets. Read the full method →