Tomahawk
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tomahawk clear sky chart from 2005-11-06 to 2024-11-05.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	13% 10% 4 9% 5% 5% 5% 4 5% 7% 34%	101573
	Night	13% 11% 4 9% 5% 5% 4 4 5% 6% 34%	97562
Transparency	Day	48% 6% 12% 22% 10% 1	105067
	Night	48% 6% 12% 22% 11% 1	102208
Seeing	Day	17% 13% 31% 23% 12% 3	16041
	Night	17% 10% 32% 29% 10% 1	25906

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	11% 16% 7% 19% 6% 5% 4 2 4 5% 19%	2527
	11th to 20th	Day	7% 16% 6% 16% 9% 8% 8% 4 4 5% 16%	2530
	21st to end	Day	11% 20% 9% 16% 5% 5% 5% 3 4 6% 17%	2797
February	1st to 10th	Day	8% 14% 5% 10% 7% 5% 7% 4 5% 7% 28%	1710
	11th to 20th	Day	9% 11% 5% 12% 7% 5% 5% 4 7% 7% 29%	1718
	21st to end	Day	12% 14% 6% 10% 7% 6% 4 3 5% 8% 26%	1570
March	1st to 10th	Day	12% 12% 3 7% 5% 4 3 3 4 6% 41%	3120
	11th to 20th	Day	7% 10% 4 13% 6% 5% 6% 4 6% 7% 30%	3376
	21st to end	Day	19% 13% 4 13% 5% 4 4 3 4 5% 26%	4096
April	1st to 10th	Day	16% 13% 4 9% 6% 5% 5% 3 6% 5% 29%	2280
	11th to 20th	Day	19% 12% 5% 8% 5% 5% 4 3 5% 5% 29%	2254
	21st to end	Day	19% 10% 3 8% 6% 5% 5% 3 5% 7% 30%	2386
May	1st to 10th	Day	18% 8% 2 7% 5% 5% 4 3 5% 6% 38%	4399
	11th to 20th	Day	14% 8% 3 6% 4 4 5% 4 5% 7% 40%	4399
	21st to end	Day	15% 9% 3 8% 5% 4 4 3 6% 7% 35%	4824
June	1st to 10th	Day	13% 6% 2 7% 4 5% 5% 4 6% 8% 40%	2660
	11th to 20th	Day	15% 7% 2 7% 5% 5% 5% 5% 5% 7% 37%	2660
	21st to end	Day	11% 7% 3 6% 5% 4 5% 5% 7% 9% 37%	2660
July	1st to 10th	Day	14% 4 2 6% 4 5% 6% 5% 8% 9% 37%	4440
	11th to 20th	Day	6% 5% 2 4 4 4 5% 5% 7% 9% 49%	4440
	21st to end	Day	9% 6% 2 7% 5% 5% 5% 4 6% 8% 44%	4813
August	1st to 10th	Day	13% 7% 3 8% 5% 4 5% 4 6% 8% 39%	4423
	11th to 20th	Day	14% 5% 2 5% 3 3 4 3 5% 8% 47%	3988
	21st to end	Day	12% 9% 3 7% 5% 5% 5% 4 5% 8% 38%	4180
September	1st to 10th	Day	13% 7% 2 6% 4 3 4 3 5% 8% 44%	2280
	11th to 20th	Day	12% 7% 3 6% 4 4 4 4 6% 8% 41%	2237
	21st to end	Day	16% 9% 2 7% 4 5% 5% 3 6% 7% 37%	2090
October	1st to 10th	Day	16% 9% 3 6% 4 5% 5% 4 5% 7% 37%	1900
	11th to 20th	Day	19% 13% 4 9% 5% 4 5% 4 5% 7% 26%	1900
	21st to end	Day	21% 13% 4 9% 4 4 3 3 5% 6% 28%	1885
November	1st to 10th	Day	15% 11% 3 7% 5% 4 4 3 6% 7% 34%	1708
	11th to 20th	Day	14% 16% 4 13% 6% 5% 4 4 5% 5% 23%	1582
	21st to end	Day	13% 14% 4 12% 7% 4 5% 4 6% 6% 25%	1520
December	1st to 10th	Day	11% 14% 6% 15% 9% 7% 5% 3 5% 5% 20%	1520
	11th to 20th	Day	12% 17% 6% 14% 8% 6% 5% 4 4 6% 17%	1918
	21st to end	Day	20% 24% 6% 11% 6% 5% 4 3 2 3 15%	2783
January	1st to 10th	Night	11% 15% 7% 16% 7% 5% 5% 3 4 5% 21%	4428
	11th to 20th	Night	7% 15% 5% 17% 8% 8% 7% 5% 6% 6% 16%	4440
	21st to end	Night	10% 19% 8% 17% 6% 5% 4 3 5% 5% 19%	4856
February	1st to 10th	Night	7% 12% 6% 12% 7% 6% 5% 5% 5% 6% 30%	2470
	11th to 20th	Night	8% 12% 3 11% 6% 6% 5% 5% 6% 7% 32%	2348
	21st to end	Night	12% 13% 5% 9% 6% 5% 5% 4 5% 6% 30%	1884
March	1st to 10th	Night	9% 8% 2 6% 4 5% 4 4 6% 9% 42%	3733
	11th to 20th	Night	8% 10% 4 12% 5% 5% 4 4 6% 6% 35%	3613
	21st to end	Night	19% 14% 5% 10% 5% 4 4 3 4 5% 29%	3534
April	1st to 10th	Night	20% 11% 3 8% 4 4 4 4 6% 6% 31%	1900
	11th to 20th	Night	22% 10% 3 5% 4 3 3 4 4 6% 36%	1875
	21st to end	Night	18% 9% 4 7% 4 3 3 4 5% 7% 35%	1789
May	1st to 10th	Night	17% 10% 3 6% 4 4 5% 3 5% 7% 36%	2506
	11th to 20th	Night	11% 8% 3 6% 4 3 4 3 5% 6% 45%	2506
	21st to end	Night	15% 8% 2 7% 5% 5% 4 3 5% 7% 38%	2743
June	1st to 10th	Night	13% 6% 2 6% 3 4 5% 3 7% 8% 44%	1520
	11th to 20th	Night	11% 7% 3 7% 5% 5% 5% 5% 6% 8% 38%	1520
	21st to end	Night	9% 7% 3 5% 5% 4 4 4 6% 10% 43%	1520
July	1st to 10th	Night	15% 5% 2 5% 3 3 4 4 5% 8% 46%	2530
	11th to 20th	Night	5% 4 2 4 3 4 4 4 7% 10% 54%	2530
	21st to end	Night	8% 5% 2 6% 3 4 3 3 6% 7% 53%	2750
August	1st to 10th	Night	10% 6% 3 7% 5% 5% 5% 4 7% 8% 41%	2517
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 5% 7% 50%	2844
	21st to end	Night	14% 8% 3 6% 4 4 4 3 4 5% 44%	3476
September	1st to 10th	Night	11% 6% 2 5% 3 4 4 3 5% 7% 50%	1900
	11th to 20th	Night	11% 6% 2 5% 4 4 4 3 5% 7% 49%	1923
	21st to end	Night	14% 8% 2 6% 5% 3 4 3 5% 8% 42%	2090
October	1st to 10th	Night	14% 7% 3 6% 4 4 4 3 5% 6% 43%	2275
	11th to 20th	Night	16% 12% 4 7% 5% 3 4 4 4 7% 34%	2280
	21st to end	Night	18% 13% 3 7% 5% 5% 5% 3 6% 6% 28%	2712
November	1st to 10th	Night	15% 11% 4 8% 4 3 3 3 5% 7% 36%	2470
	11th to 20th	Night	14% 14% 4 11% 7% 5% 4 3 5% 6% 28%	2597
	21st to end	Night	13% 14% 5% 12% 6% 5% 4 3 5% 6% 26%	2660
December	1st to 10th	Night	10% 15% 5% 13% 6% 5% 5% 4 5% 6% 25%	2660
	11th to 20th	Night	11% 17% 7% 13% 8% 6% 4 4 6% 5% 21%	3279
	21st to end	Night	22% 21% 6% 11% 5% 4 4 3 4 5% 17%	4884

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	67% 5% 8% 16% 4	2528
	11th to 20th	Day	70% 6% 7% 11% 7%	2530
	21st to end	Day	68% 6% 11% 11% 4	2797
February	1st to 10th	Day	54% 6% 11% 17% 12% 1	1710
	11th to 20th	Day	51% 7% 11% 22% 7% 1	1727
	21st to end	Day	56% 6% 11% 18% 8% 1	1570
March	1st to 10th	Day	44% 4 15% 19% 17% 2	3120
	11th to 20th	Day	48% 6% 16% 19% 9% 1	3376
	21st to end	Day	60% 6% 8% 19% 7% 1	4096
April	1st to 10th	Day	55% 5% 11% 17% 11% 1	2280
	11th to 20th	Day	56% 5% 9% 19% 9% 1	2254
	21st to end	Day	54% 6% 9% 18% 12% 1	2386
May	1st to 10th	Day	44% 7% 11% 25% 12% 1	4440
	11th to 20th	Day	41% 6% 13% 27% 11% 1	4403
	21st to end	Day	48% 6% 11% 20% 14% 1	4837
June	1st to 10th	Day	40% 8% 14% 26% 11% 1	2660
	11th to 20th	Day	44% 8% 13% 21% 13% 1	2660
	21st to end	Day	40% 8% 17% 23% 10% 1	2660
July	1st to 10th	Day	39% 8% 16% 26% 10%	4371
	11th to 20th	Day	28% 7% 15% 34% 13% 2	4365
	21st to end	Day	36% 7% 13% 29% 15%	4662
August	1st to 10th	Day	43% 6% 14% 24% 12% 1	4408
	11th to 20th	Day	36% 6% 13% 33% 12%	4028
	21st to end	Day	44% 6% 14% 24% 11% 1	4179
September	1st to 10th	Day	38% 6% 14% 29% 12% 1	2280
	11th to 20th	Day	39% 7% 18% 27% 7%	2237
	21st to end	Day	45% 7% 12% 27% 9%	2090
October	1st to 10th	Day	33% 4 14% 30% 19%	3160
	11th to 20th	Day	50% 5% 11% 20% 14% 1	3140
	21st to end	Day	50% 5% 17% 22% 6%	3085
November	1st to 10th	Day	48% 7% 12% 22% 10% 1	1708
	11th to 20th	Day	61% 6% 10% 15% 6% 1	1582
	21st to end	Day	58% 8% 14% 16% 3 1	1520
December	1st to 10th	Day	64% 6% 10% 16% 4	1520
	11th to 20th	Day	66% 6% 11% 12% 5%	1915
	21st to end	Day	74% 5% 6% 10% 5%	2783
January	1st to 10th	Night	61% 7% 10% 16% 5% 1	4428
	11th to 20th	Night	65% 7% 10% 13% 4	4440
	21st to end	Night	66% 6% 7% 16% 4	4856
February	1st to 10th	Night	53% 5% 8% 20% 12% 2	2470
	11th to 20th	Night	49% 6% 12% 21% 10% 2	2349
	21st to end	Night	53% 6% 13% 18% 8% 2	1884
March	1st to 10th	Night	37% 5% 16% 26% 13% 1	3733
	11th to 20th	Night	45% 7% 13% 24% 10% 1	3613
	21st to end	Night	58% 5% 8% 20% 9% 1	3534
April	1st to 10th	Night	52% 6% 9% 16% 16% 1	1900
	11th to 20th	Night	49% 5% 10% 20% 13% 3	1875
	21st to end	Night	47% 7% 10% 21% 14% 1	1789
May	1st to 10th	Night	45% 7% 15% 19% 13% 1	2530
	11th to 20th	Night	37% 7% 13% 27% 15% 2	2507
	21st to end	Night	44% 8% 14% 17% 15% 1	2751
June	1st to 10th	Night	37% 8% 13% 29% 12% 1	1520
	11th to 20th	Night	42% 7% 13% 21% 15% 2	1520
	21st to end	Night	35% 8% 16% 29% 10% 1	1520
July	1st to 10th	Night	36% 6% 20% 24% 12% 3	2490
	11th to 20th	Night	24% 7% 16% 38% 14% 2	2482
	21st to end	Night	30% 6% 12% 31% 19% 2	2662
August	1st to 10th	Night	38% 8% 15% 21% 16% 1	2508
	11th to 20th	Night	33% 6% 15% 31% 13% 2	2870
	21st to end	Night	41% 6% 13% 25% 13% 2	3476
September	1st to 10th	Night	33% 6% 13% 33% 15% 1	1900
	11th to 20th	Night	34% 7% 15% 34% 10%	1923
	21st to end	Night	40% 7% 13% 28% 12% 1	2090
October	1st to 10th	Night	31% 5% 8% 34% 20% 2	3795
	11th to 20th	Night	39% 5% 11% 31% 14% 1	3779
	21st to end	Night	54% 5% 9% 22% 10%	4462
November	1st to 10th	Night	48% 5% 13% 22% 12%	2470
	11th to 20th	Night	56% 7% 13% 14% 10% 1	2597
	21st to end	Night	57% 6% 13% 18% 5% 1	2660
December	1st to 10th	Night	58% 7% 13% 18% 4	2660
	11th to 20th	Night	63% 6% 11% 15% 5%	3281
	21st to end	Night	70% 5% 6% 14% 4	4884

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	16% 17% 33% 24% 9% 2	270
	11th to 20th	Day	20% 14% 36% 23% 6% 1	270
	21st to end	Day	18% 14% 37% 25% 6%	297
February	1st to 10th	Day	17% 14% 46% 15% 6% 2	270
	11th to 20th	Day	15% 23% 42% 13% 7%	270
	21st to end	Day	17% 21% 45% 15% 1	225
March	1st to 10th	Day	18% 20% 39% 16% 7%	270
	11th to 20th	Day	19% 19% 36% 15% 8% 3	270
	21st to end	Day	25% 14% 32% 21% 6% 2	463
April	1st to 10th	Day	25% 15% 32% 23% 5%	460
	11th to 20th	Day	31% 15% 25% 22% 7% 1	452
	21st to end	Day	23% 14% 30% 21% 9% 2	462
May	1st to 10th	Day	22% 16% 32% 21% 8% 1	653
	11th to 20th	Day	18% 15% 31% 23% 9% 3	675
	21st to end	Day	18% 14% 28% 23% 13% 4	734
June	1st to 10th	Day	13% 13% 31% 26% 12% 4	680
	11th to 20th	Day	16% 10% 33% 26% 10% 4	680
	21st to end	Day	14% 10% 31% 26% 15% 4	680
July	1st to 10th	Day	10% 5% 26% 30% 21% 9%	671
	11th to 20th	Day	11% 8% 28% 26% 18% 9%	668
	21st to end	Day	7% 6% 28% 33% 18% 9%	739
August	1st to 10th	Day	11% 6% 28% 27% 23% 6%	676
	11th to 20th	Day	16% 5% 21% 26% 25% 7%	608
	21st to end	Day	14% 11% 24% 26% 19% 6%	539
September	1st to 10th	Day	15% 11% 25% 25% 19% 5%	490
	11th to 20th	Day	12% 9% 28% 31% 16% 4	490
	21st to end	Day	19% 15% 23% 26% 15% 2	490
October	1st to 10th	Day	18% 17% 25% 28% 8% 3	300
	11th to 20th	Day	21% 24% 33% 16% 6%	300
	21st to end	Day	30% 17% 37% 14% 2	330
November	1st to 10th	Day	22% 13% 36% 22% 5% 2	282
	11th to 20th	Day	23% 21% 39% 12% 4	270
	21st to end	Day	21% 20% 41% 13% 4	270
December	1st to 10th	Day	18% 15% 40% 20% 6%	270
	11th to 20th	Day	23% 19% 40% 15% 2 1	270
	21st to end	Day	28% 22% 34% 14% 2	297
January	1st to 10th	Night	15% 11% 41% 27% 6%	950
	11th to 20th	Night	19% 11% 38% 25% 6% 1	950
	21st to end	Night	18% 9% 37% 31% 6%	1045
February	1st to 10th	Night	14% 12% 38% 29% 7%	950
	11th to 20th	Night	14% 15% 40% 26% 6%	874
	21st to end	Night	18% 14% 39% 23% 5%	628
March	1st to 10th	Night	15% 13% 35% 28% 8% 1	760
	11th to 20th	Night	17% 11% 38% 27% 6%	651
	21st to end	Night	21% 9% 31% 27% 10% 1	627
April	1st to 10th	Night	23% 10% 36% 24% 6% 1	570
	11th to 20th	Night	27% 10% 27% 29% 7%	563
	21st to end	Night	22% 9% 32% 28% 7% 1	570
May	1st to 10th	Night	22% 11% 32% 27% 6% 1	570
	11th to 20th	Night	20% 9% 33% 30% 8% 1	561
	21st to end	Night	16% 8% 25% 36% 14% 1	617
June	1st to 10th	Night	13% 8% 27% 39% 12%	570
	11th to 20th	Night	14% 8% 31% 38% 9%	570
	21st to end	Night	12% 7% 24% 41% 15% 1	570
July	1st to 10th	Night	9% 3 23% 40% 23% 2	555
	11th to 20th	Night	9% 6% 26% 35% 23% 1	552
	21st to end	Night	8% 2 21% 43% 22% 3	624
August	1st to 10th	Night	10% 3 22% 41% 24% 1	567
	11th to 20th	Night	14% 2 20% 35% 27% 2	564
	21st to end	Night	14% 7% 21% 34% 21% 2	627
September	1st to 10th	Night	14% 5% 22% 37% 18% 4	570
	11th to 20th	Night	12% 5% 28% 35% 18% 2	593
	21st to end	Night	19% 10% 26% 30% 14% 1	760
October	1st to 10th	Night	18% 9% 31% 28% 14% 1	760
	11th to 20th	Night	21% 12% 32% 27% 8%	760
	21st to end	Night	25% 8% 33% 25% 8%	836
November	1st to 10th	Night	19% 11% 37% 27% 5% 1	760
	11th to 20th	Night	19% 14% 39% 22% 6%	887
	21st to end	Night	20% 15% 35% 23% 5%	950
December	1st to 10th	Night	18% 13% 37% 25% 6% 1	950
	11th to 20th	Night	20% 12% 37% 23% 8% 1	950
	21st to end	Night	27% 12% 34% 23% 4	1045

Page generated at 2024-11-03 01:11:27. Version ac07

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