Montgomery
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Montgomery clear sky chart from 2005-11-06 to 2024-10-24.

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	12% 9% 3 8% 5% 4 5% 4 6% 7% 38%	101459
	Night	12% 9% 3 8% 5% 4 4 4 5% 6% 40%	97411
Transparency	Day	46% 3 13% 26% 11% 1	101254
	Night	46% 3 12% 26% 13% 2	97287
Seeing	Day	16% 10% 31% 27% 13% 3	15964
	Night	16% 9% 33% 31% 11% 1	25804

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	10% 17% 6% 18% 6% 5% 5% 3 5% 6% 18%	2527
	11th to 20th	Day	5% 13% 5% 12% 9% 8% 8% 6% 9% 5% 19%	2626
	21st to end	Day	8% 19% 7% 16% 7% 6% 5% 3 5% 5% 19%	3135
February	1st to 10th	Day	8% 11% 5% 11% 7% 7% 5% 5% 5% 6% 28%	1710
	11th to 20th	Day	9% 11% 4 11% 8% 6% 6% 4 5% 5% 31%	1664
	21st to end	Day	12% 12% 4 8% 6% 4 6% 3 6% 8% 31%	1463
March	1st to 10th	Day	13% 9% 4 7% 4 4 4 3 5% 6% 40%	3401
	11th to 20th	Day	10% 10% 3 8% 4 4 4 4 5% 8% 39%	3480
	21st to end	Day	25% 13% 6% 10% 7% 4 4 2 4 5% 22%	3832
April	1st to 10th	Day	16% 12% 3 7% 5% 5% 4 4 6% 7% 33%	2280
	11th to 20th	Day	20% 13% 4 6% 4 4 4 3 5% 5% 33%	2270
	21st to end	Day	20% 13% 4 7% 4 5% 4 3 5% 5% 31%	2470
May	1st to 10th	Day	17% 7% 2 5% 4 4 5% 4 6% 7% 37%	4200
	11th to 20th	Day	12% 7% 2 6% 4 4 4 4 5% 7% 44%	4399
	21st to end	Day	17% 7% 3 7% 5% 4 4 4 6% 7% 36%	4824
June	1st to 10th	Day	11% 6% 2 6% 4 4 4 4 7% 7% 47%	2660
	11th to 20th	Day	14% 7% 3 5% 5% 4 4 4 6% 9% 39%	2660
	21st to end	Day	10% 5% 3 6% 5% 5% 6% 4 7% 9% 41%	2660
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 5% 8% 10% 37%	4440
	11th to 20th	Day	6% 3 1 4 3 3 4 3 6% 9% 58%	4440
	21st to end	Day	6% 4 1 5% 5% 5% 5% 5% 8% 8% 48%	4671
August	1st to 10th	Day	12% 6% 2 6% 5% 4 5% 4 6% 7% 43%	4104
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 7% 8% 42%	4041
	21st to end	Day	8% 6% 2 7% 4 4 4 3 5% 7% 49%	4343
September	1st to 10th	Day	12% 6% 2 5% 3 4 4 3 6% 7% 48%	2280
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 3 5% 7% 49%	2230
	21st to end	Day	14% 6% 3 5% 4 4 4 4 5% 7% 44%	2011
October	1st to 10th	Day	14% 8% 2 6% 4 4 3 3 5% 6% 44%	1900
	11th to 20th	Day	14% 9% 3 5% 4 4 4 3 5% 6% 43%	1900
	21st to end	Day	18% 10% 4 7% 3 3 3 4 5% 5% 37%	2010
November	1st to 10th	Day	11% 10% 3 8% 5% 4 4 3 4 7% 39%	1567
	11th to 20th	Day	10% 13% 6% 11% 5% 4 4 4 5% 6% 30%	1520
	21st to end	Day	13% 10% 5% 8% 5% 3 3 3 6% 7% 36%	1520
December	1st to 10th	Day	11% 13% 5% 10% 10% 7% 4 4 4 6% 27%	1520
	11th to 20th	Day	10% 14% 5% 11% 6% 5% 5% 4 5% 7% 28%	1918
	21st to end	Day	19% 14% 7% 18% 5% 4 3 3 4 5% 18%	2783
January	1st to 10th	Night	8% 15% 7% 18% 7% 4 4 3 5% 4 25%	4428
	11th to 20th	Night	7% 11% 5% 15% 8% 7% 8% 6% 8% 5% 20%	4344
	21st to end	Night	10% 18% 8% 13% 5% 5% 4 3 5% 5% 24%	4532
February	1st to 10th	Night	7% 13% 5% 11% 7% 6% 5% 3 5% 5% 34%	2470
	11th to 20th	Night	7% 10% 4 7% 6% 6% 5% 4 5% 7% 39%	2403
	21st to end	Night	11% 10% 3 9% 6% 5% 5% 3 5% 6% 37%	1990
March	1st to 10th	Night	9% 7% 3 7% 5% 4 4 3 5% 6% 48%	3480
	11th to 20th	Night	9% 7% 2 8% 5% 5% 5% 4 5% 8% 42%	3480
	21st to end	Night	26% 12% 3 10% 4 4 3 2 3 4 29%	3798
April	1st to 10th	Night	14% 12% 4 7% 4 4 4 3 5% 7% 37%	1900
	11th to 20th	Night	19% 10% 4 8% 5% 3 4 3 4 6% 34%	1857
	21st to end	Night	19% 9% 3 7% 5% 3 4 3 5% 6% 36%	1710
May	1st to 10th	Night	14% 8% 2 7% 4 4 4 3 5% 6% 42%	2705
	11th to 20th	Night	13% 5% 2 5% 3 3 3 3 6% 8% 50%	2506
	21st to end	Night	14% 7% 3 6% 4 4 4 3 5% 7% 43%	2743
June	1st to 10th	Night	11% 4 2 4 3 3 4 4 6% 8% 50%	1520
	11th to 20th	Night	9% 6% 2 6% 5% 5% 5% 5% 6% 8% 45%	1520
	21st to end	Night	8% 3 1 5% 4 3 4 4 5% 8% 54%	1520
July	1st to 10th	Night	11% 4 2 4 4 4 4 5% 8% 10% 45%	2530
	11th to 20th	Night	3 2 1 4 3 3 4 4 5% 8% 62%	2530
	21st to end	Night	5% 4 1 4 3 4 4 4 6% 9% 57%	2875
August	1st to 10th	Night	11% 7% 2 5% 4 4 4 4 5% 6% 48%	2836
	11th to 20th	Night	13% 4 2 4 3 3 3 3 5% 8% 51%	2798
	21st to end	Night	9% 6% 2 6% 4 4 4 3 5% 7% 50%	3317
September	1st to 10th	Night	10% 4 1 4 3 3 3 2 6% 7% 57%	1900
	11th to 20th	Night	11% 4 1 4 3 3 4 4 5% 8% 53%	1947
	21st to end	Night	11% 6% 2 5% 4 3 3 3 4 6% 53%	2148
October	1st to 10th	Night	14% 6% 2 5% 4 3 3 3 4 6% 51%	2280
	11th to 20th	Night	13% 9% 3 6% 3 3 5% 3 4 7% 42%	2280
	21st to end	Night	17% 11% 3 6% 3 3 3 3 4 6% 39%	2413
November	1st to 10th	Night	13% 9% 3 5% 4 4 4 4 5% 6% 44%	2508
	11th to 20th	Night	11% 13% 4 10% 5% 5% 4 3 4 5% 36%	2660
	21st to end	Night	13% 10% 3 7% 6% 4 3 4 4 7% 39%	2660
December	1st to 10th	Night	9% 11% 4 11% 8% 5% 4 4 6% 7% 31%	2660
	11th to 20th	Night	11% 12% 5% 10% 8% 6% 4 4 5% 6% 28%	3279
	21st to end	Night	21% 14% 6% 14% 6% 5% 4 3 4 5% 20%	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	69% 2 10% 15% 4	2528
	11th to 20th	Day	63% 2 10% 18% 7%	2626
	21st to end	Day	69% 2 11% 13% 4	3135
February	1st to 10th	Day	57% 3 11% 19% 9% 1	1710
	11th to 20th	Day	53% 4 11% 23% 7% 1	1673
	21st to end	Day	52% 3 13% 19% 12%	1463
March	1st to 10th	Day	46% 2 12% 28% 11% 1	3401
	11th to 20th	Day	44% 3 9% 32% 11% 2	3480
	21st to end	Day	67% 3 9% 17% 5%	3832
April	1st to 10th	Day	51% 3 11% 23% 11% 1	2280
	11th to 20th	Day	55% 2 10% 20% 12% 1	2270
	21st to end	Day	56% 3 12% 20% 8% 1	2470
May	1st to 10th	Day	46% 3 11% 28% 12% 1	4238
	11th to 20th	Day	40% 3 8% 32% 14% 2	4403
	21st to end	Day	48% 3 10% 28% 10% 1	4837
June	1st to 10th	Day	35% 3 14% 31% 15% 1	2660
	11th to 20th	Day	42% 4 14% 23% 15% 2	2660
	21st to end	Day	38% 4 17% 27% 12% 2	2660
July	1st to 10th	Day	39% 6% 20% 24% 10% 1	4371
	11th to 20th	Day	23% 4 15% 37% 19% 2	4365
	21st to end	Day	30% 6% 14% 32% 16% 1	4524
August	1st to 10th	Day	39% 4 11% 31% 13% 2	4090
	11th to 20th	Day	39% 5% 14% 33% 10%	4080
	21st to end	Day	35% 5% 16% 30% 15% 1	4342
September	1st to 10th	Day	36% 3 13% 32% 16%	2280
	11th to 20th	Day	36% 3 16% 32% 12% 1	2230
	21st to end	Day	40% 3 12% 33% 13% 1	2011
October	1st to 10th	Day	41% 2 9% 32% 14% 1	1900
	11th to 20th	Day	43% 2 13% 25% 15% 2	1900
	21st to end	Day	49% 3 12% 24% 11% 1	2010
November	1st to 10th	Day	46% 3 12% 21% 15% 3	1567
	11th to 20th	Day	54% 4 11% 20% 10% 1	1520
	21st to end	Day	48% 2 19% 23% 7% 1	1520
December	1st to 10th	Day	59% 3 15% 15% 7% 1	1520
	11th to 20th	Day	56% 3 20% 15% 6%	1915
	21st to end	Day	71% 2 9% 14% 4	2783
January	1st to 10th	Night	64% 2 9% 19% 6%	4428
	11th to 20th	Night	63% 2 10% 19% 6%	4344
	21st to end	Night	64% 2 9% 18% 6%	4532
February	1st to 10th	Night	53% 2 11% 23% 10% 1	2470
	11th to 20th	Night	46% 3 13% 26% 10% 2	2404
	21st to end	Night	49% 2 11% 24% 13% 2	1990
March	1st to 10th	Night	38% 2 11% 30% 17% 1	3480
	11th to 20th	Night	41% 2 7% 32% 16% 1	3480
	21st to end	Night	61% 2 7% 21% 7% 2	3798
April	1st to 10th	Night	48% 2 10% 25% 14% 1	1900
	11th to 20th	Night	52% 3 8% 18% 17% 3	1857
	21st to end	Night	50% 3 7% 24% 15% 2	1710
May	1st to 10th	Night	44% 2 9% 22% 22% 1	2732
	11th to 20th	Night	35% 2 10% 28% 20% 5%	2507
	21st to end	Night	42% 3 10% 28% 16% 1	2751
June	1st to 10th	Night	33% 3 12% 34% 16% 2	1520
	11th to 20th	Night	37% 4 14% 24% 19% 3	1520
	21st to end	Night	30% 3 14% 33% 18% 3	1520
July	1st to 10th	Night	32% 6% 20% 28% 13% 2	2490
	11th to 20th	Night	20% 4 14% 40% 20% 2	2482
	21st to end	Night	24% 5% 16% 33% 20% 2	2783
August	1st to 10th	Night	37% 3 12% 30% 15% 4	2826
	11th to 20th	Night	32% 4 14% 33% 16% 1	2825
	21st to end	Night	33% 4 16% 28% 16% 2	3317
September	1st to 10th	Night	28% 2 13% 35% 21% 1	1900
	11th to 20th	Night	30% 3 15% 33% 17% 1	1947
	21st to end	Night	34% 2 11% 33% 19% 1	2148
October	1st to 10th	Night	36% 2 8% 32% 17% 4	2280
	11th to 20th	Night	42% 3 12% 24% 17% 2	2280
	21st to end	Night	46% 2 12% 25% 13% 1	2413
November	1st to 10th	Night	41% 3 13% 26% 16% 2	2508
	11th to 20th	Night	51% 3 11% 21% 13% 1	2660
	21st to end	Night	47% 3 15% 25% 9% 1	2660
December	1st to 10th	Night	52% 3 16% 21% 7% 1	2660
	11th to 20th	Night	57% 3 14% 19% 6% 1	3281
	21st to end	Night	69% 2 8% 17% 5%	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	13% 14% 39% 23% 9% 2	270
	11th to 20th	Day	13% 15% 41% 25% 5% 1	270
	21st to end	Day	15% 9% 41% 24% 9% 2	297
February	1st to 10th	Day	12% 16% 47% 22% 3	270
	11th to 20th	Day	15% 17% 39% 24% 5% 1	270
	21st to end	Day	20% 13% 42% 23% 3	225
March	1st to 10th	Day	19% 17% 39% 20% 6%	270
	11th to 20th	Day	23% 13% 33% 23% 7% 1	270
	21st to end	Day	29% 14% 28% 21% 6% 2	303
April	1st to 10th	Day	24% 14% 38% 19% 5%	460
	11th to 20th	Day	27% 16% 25% 22% 8% 1	468
	21st to end	Day	25% 13% 30% 22% 9% 2	650
May	1st to 10th	Day	20% 13% 34% 24% 8% 1	653
	11th to 20th	Day	17% 15% 28% 26% 12% 3	675
	21st to end	Day	18% 9% 27% 28% 15% 2	734
June	1st to 10th	Day	11% 9% 25% 32% 18% 5%	680
	11th to 20th	Day	17% 7% 33% 29% 10% 3	680
	21st to end	Day	12% 8% 31% 29% 16% 3	680
July	1st to 10th	Day	8% 5% 24% 31% 24% 8%	671
	11th to 20th	Day	9% 6% 27% 30% 21% 7%	668
	21st to end	Day	6% 4 23% 40% 21% 6%	739
August	1st to 10th	Day	12% 3 21% 35% 24% 5%	676
	11th to 20th	Day	13% 4 21% 33% 23% 6%	665
	21st to end	Day	11% 4 28% 34% 18% 6%	637
September	1st to 10th	Day	16% 7% 27% 29% 18% 4	490
	11th to 20th	Day	15% 5% 29% 30% 17% 5%	440
	21st to end	Day	16% 11% 31% 22% 16% 4	300
October	1st to 10th	Day	16% 11% 26% 27% 15% 5%	300
	11th to 20th	Day	15% 17% 41% 18% 8% 1	300
	21st to end	Day	25% 16% 34% 16% 8%	306
November	1st to 10th	Day	19% 14% 36% 20% 11%	270
	11th to 20th	Day	16% 19% 41% 20% 4	270
	21st to end	Day	20% 13% 44% 19% 4	270
December	1st to 10th	Day	14% 13% 42% 24% 6% 1	270
	11th to 20th	Day	19% 15% 38% 23% 5%	270
	21st to end	Day	24% 16% 41% 15% 3	297
January	1st to 10th	Night	12% 13% 38% 28% 8% 1	950
	11th to 20th	Night	16% 10% 39% 28% 6% 1	950
	21st to end	Night	18% 11% 35% 29% 6%	1045
February	1st to 10th	Night	13% 12% 41% 28% 6% 1	950
	11th to 20th	Night	13% 13% 42% 25% 6% 1	929
	21st to end	Night	16% 11% 37% 28% 7% 1	734
March	1st to 10th	Night	17% 11% 37% 25% 9% 1	609
	11th to 20th	Night	17% 11% 37% 28% 6% 1	570
	21st to end	Night	22% 10% 31% 25% 11% 1	627
April	1st to 10th	Night	19% 13% 36% 26% 6%	570
	11th to 20th	Night	23% 11% 29% 29% 8%	563
	21st to end	Night	22% 10% 32% 27% 8% 1	570
May	1st to 10th	Night	18% 9% 32% 32% 8% 1	570
	11th to 20th	Night	18% 8% 30% 32% 11% 1	561
	21st to end	Night	16% 8% 28% 34% 14% 1	617
June	1st to 10th	Night	12% 3 30% 39% 15% 1	570
	11th to 20th	Night	12% 5% 31% 42% 10%	570
	21st to end	Night	9% 5% 23% 47% 15% 1	570
July	1st to 10th	Night	7% 1 21% 42% 27% 2	555
	11th to 20th	Night	4 4 23% 46% 21% 2	552
	21st to end	Night	6% 2 18% 53% 18% 2	624
August	1st to 10th	Night	8% 4 18% 47% 22% 2	567
	11th to 20th	Night	12% 3 18% 39% 25% 4	564
	21st to end	Night	9% 4 24% 39% 22% 2	627
September	1st to 10th	Night	12% 4 22% 42% 18% 3	570
	11th to 20th	Night	13% 6% 30% 33% 16% 2	570
	21st to end	Night	14% 8% 32% 32% 14% 1	628
October	1st to 10th	Night	17% 9% 28% 30% 15%	760
	11th to 20th	Night	18% 9% 37% 28% 7% 1	760
	21st to end	Night	24% 13% 28% 28% 7%	805
November	1st to 10th	Night	16% 12% 37% 26% 8% 1	852
	11th to 20th	Night	17% 13% 39% 25% 6%	950
	21st to end	Night	18% 13% 39% 24% 7%	950
December	1st to 10th	Night	17% 10% 38% 27% 8% 1	950
	11th to 20th	Night	20% 9% 39% 26% 6% 1	950
	21st to end	Night	24% 11% 35% 25% 5%	1045

Page generated at 2024-10-21 01:19:59. Version ac07

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