Bridgman
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Bridgman clear sky chart from 2005-11-06 to 2024-11-28.

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 8% 5% 4 4 3 5% 7% 36%	101415
	Night	15% 12% 5% 9% 5% 4 4 3 5% 6% 32%	98187
Transparency	Day	48% 3 11% 23% 13% 1	104999
	Night	53% 3 10% 20% 13% 1	102744
Seeing	Day	18% 14% 29% 23% 12% 4	15848
	Night	21% 11% 27% 27% 12% 1	25706

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	13% 24% 10% 13% 6% 4 4 3 3 5% 14%	2527
	11th to 20th	Day	13% 19% 9% 17% 9% 8% 10% 2 2 2 8%	2530
	21st to end	Day	23% 25% 7% 12% 5% 3 3 2 3 4 13%	2783
February	1st to 10th	Day	14% 17% 6% 13% 9% 5% 5% 3 5% 5% 19%	1803
	11th to 20th	Day	14% 12% 5% 15% 8% 5% 5% 3 4 5% 23%	1848
	21st to end	Day	15% 15% 7% 11% 6% 4 4 3 5% 5% 24%	1570
March	1st to 10th	Day	18% 13% 6% 7% 5% 4 4 3 4 6% 29%	3120
	11th to 20th	Day	10% 8% 9% 10% 4 4 4 4 5% 8% 33%	3316
	21st to end	Day	18% 12% 6% 10% 5% 4 5% 3 5% 5% 26%	4055
April	1st to 10th	Day	16% 13% 4 7% 5% 3 4 3 5% 7% 33%	2280
	11th to 20th	Day	15% 10% 3 6% 3 4 4 3 5% 7% 39%	2254
	21st to end	Day	18% 10% 3 7% 4 3 4 3 6% 7% 35%	2463
May	1st to 10th	Day	18% 8% 2 6% 4 4 4 4 6% 9% 36%	4082
	11th to 20th	Day	14% 8% 2 6% 4 3 3 3 6% 8% 42%	4108
	21st to end	Day	11% 6% 3 6% 4 4 4 3 5% 9% 47%	4824
June	1st to 10th	Day	10% 6% 2 6% 5% 3 4 4 6% 8% 46%	2660
	11th to 20th	Day	9% 4 2 5% 5% 4 4 4 6% 7% 48%	2660
	21st to end	Day	11% 5% 2 6% 3 5% 4 4 6% 8% 45%	2660
July	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 6% 8% 39%	4440
	11th to 20th	Day	7% 4 1 4 4 3 4 4 7% 9% 52%	4440
	21st to end	Day	7% 6% 2 6% 4 5% 5% 4 6% 8% 46%	4813
August	1st to 10th	Day	10% 6% 2 6% 4 4 4 3 5% 8% 49%	4176
	11th to 20th	Day	10% 5% 2 5% 3 4 4 4 6% 7% 49%	3930
	21st to end	Day	7% 4 2 6% 4 4 5% 4 6% 8% 50%	4180
September	1st to 10th	Day	10% 5% 2 6% 4 3 5% 3 6% 8% 47%	2280
	11th to 20th	Day	12% 4 1 5% 4 4 4 4 6% 7% 48%	2092
	21st to end	Day	14% 7% 2 6% 4 4 4 4 6% 8% 40%	2090
October	1st to 10th	Day	15% 6% 2 6% 4 4 4 4 3 6% 45%	2090
	11th to 20th	Day	22% 8% 3 6% 4 4 4 3 6% 7% 32%	1863
	21st to end	Day	24% 12% 3 8% 4 4 5% 4 5% 7% 25%	1881
November	1st to 10th	Day	15% 13% 3 7% 4 3 3 4 5% 6% 36%	1762
	11th to 20th	Day	17% 21% 6% 9% 4 4 4 3 4 5% 24%	1800
	21st to end	Day	21% 18% 6% 9% 5% 4 4 3 3 5% 23%	1773
December	1st to 10th	Day	15% 22% 10% 11% 5% 3 2 2 3 5% 19%	1561
	11th to 20th	Day	14% 23% 10% 12% 5% 4 3 3 5% 5% 17%	1918
	21st to end	Day	20% 24% 8% 14% 6% 4 4 2 3 5% 10%	2783
January	1st to 10th	Night	17% 23% 10% 13% 6% 4 4 3 3 5% 11%	4428
	11th to 20th	Night	15% 22% 9% 17% 6% 7% 7% 2 2 3 9%	4440
	21st to end	Night	24% 21% 10% 13% 5% 4 3 3 3 3 11%	4884
February	1st to 10th	Night	17% 16% 5% 11% 9% 4 4 3 4 5% 21%	2375
	11th to 20th	Night	14% 15% 4 14% 6% 5% 5% 3 4 5% 24%	2218
	21st to end	Night	19% 15% 6% 12% 5% 3 3 2 5% 4 26%	1884
March	1st to 10th	Night	17% 12% 5% 9% 4 4 3 4 4 6% 33%	3733
	11th to 20th	Night	10% 8% 5% 8% 5% 4 5% 4 5% 6% 41%	3642
	21st to end	Night	19% 12% 6% 9% 5% 4 5% 3 4 5% 27%	3604
April	1st to 10th	Night	15% 11% 3 7% 5% 5% 4 4 5% 7% 35%	1900
	11th to 20th	Night	19% 10% 2 6% 4 4 4 4 5% 5% 36%	1875
	21st to end	Night	18% 8% 3 7% 5% 5% 3 3 6% 6% 35%	1715
May	1st to 10th	Night	17% 8% 3 7% 5% 4 4 4 5% 8% 35%	2813
	11th to 20th	Night	18% 7% 3 6% 4 3 3 4 5% 8% 40%	2783
	21st to end	Night	15% 6% 2 7% 4 4 4 3 6% 7% 42%	2743
June	1st to 10th	Night	9% 5% 2 5% 4 4 3 5% 6% 10% 47%	1520
	11th to 20th	Night	8% 7% 2 6% 5% 4 4 5% 6% 8% 44%	1520
	21st to end	Night	9% 5% 2 7% 6% 4 5% 5% 7% 9% 41%	1520
July	1st to 10th	Night	10% 4 2 6% 6% 5% 5% 4 7% 9% 40%	2530
	11th to 20th	Night	8% 4 2 4 3 3 4 3 5% 8% 55%	2530
	21st to end	Night	6% 6% 2 6% 4 5% 5% 4 8% 8% 46%	2750
August	1st to 10th	Night	8% 5% 2 6% 4 5% 5% 4 7% 9% 45%	2754
	11th to 20th	Night	9% 4 2 5% 5% 4 4 4 6% 7% 50%	2896
	21st to end	Night	9% 5% 2 6% 4 4 4 4 6% 7% 49%	3476
September	1st to 10th	Night	11% 6% 2 6% 4 4 3 3 4 8% 48%	1900
	11th to 20th	Night	11% 5% 2 4 3 3 3 3 5% 8% 53%	2068
	21st to end	Night	13% 6% 2 7% 4 5% 4 3 5% 8% 42%	2090
October	1st to 10th	Night	16% 6% 2 6% 4 4 3 3 5% 6% 46%	2090
	11th to 20th	Night	22% 9% 3 8% 4 3 4 3 4 5% 35%	2311
	21st to end	Night	25% 10% 3 8% 4 3 4 3 4 5% 31%	2717
November	1st to 10th	Night	17% 14% 3 6% 4 3 4 3 4 5% 37%	2536
	11th to 20th	Night	15% 20% 5% 11% 5% 4 3 3 5% 5% 25%	2600
	21st to end	Night	20% 20% 6% 8% 4 3 3 3 3 6% 24%	2562
December	1st to 10th	Night	17% 26% 7% 11% 5% 3 3 2 3 4 17%	2617
	11th to 20th	Night	15% 22% 10% 14% 6% 4 3 3 4 4 15%	3279
	21st to end	Night	24% 22% 7% 12% 5% 4 4 3 4 4 11%	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	75% 1 11% 10% 3	2528
	11th to 20th	Day	85% 2 6% 7% 1	2530
	21st to end	Day	78% 1 7% 12% 2	2783
February	1st to 10th	Day	68% 3 10% 13% 6% 1	1803
	11th to 20th	Day	63% 3 9% 16% 7%	1858
	21st to end	Day	63% 3 11% 14% 8% 1	1570
March	1st to 10th	Day	58% 2 10% 21% 9%	3120
	11th to 20th	Day	50% 2 11% 28% 7% 1	3316
	21st to end	Day	63% 2 11% 19% 4	4055
April	1st to 10th	Day	52% 4 9% 22% 13%	2280
	11th to 20th	Day	47% 3 9% 23% 14% 3	2254
	21st to end	Day	49% 3 11% 21% 13% 3	2463
May	1st to 10th	Day	47% 2 10% 28% 11% 1	4120
	11th to 20th	Day	43% 2 13% 30% 12% 1	4112
	21st to end	Day	37% 3 10% 25% 24% 2	4837
June	1st to 10th	Day	37% 4 10% 27% 19% 2	2660
	11th to 20th	Day	35% 4 11% 26% 20% 3	2660
	21st to end	Day	37% 5% 15% 24% 16% 3	2660
July	1st to 10th	Day	43% 5% 12% 21% 17% 3	4371
	11th to 20th	Day	27% 5% 15% 34% 17% 2	4365
	21st to end	Day	35% 6% 15% 20% 21% 3	4662
August	1st to 10th	Day	34% 4 14% 31% 15% 1	4161
	11th to 20th	Day	33% 6% 12% 33% 16% 1	3969
	21st to end	Day	33% 5% 12% 27% 21% 3	4179
September	1st to 10th	Day	36% 5% 14% 25% 17% 4	2280
	11th to 20th	Day	34% 4 11% 30% 19% 2	2092
	21st to end	Day	41% 5% 9% 27% 17% 1	2090
October	1st to 10th	Day	30% 3 8% 36% 22% 1	3480
	11th to 20th	Day	40% 4 11% 22% 23%	3066
	21st to end	Day	52% 2 9% 25% 10% 2	3081
November	1st to 10th	Day	49% 3 13% 21% 13% 1	1762
	11th to 20th	Day	64% 2 9% 17% 7% 1	1800
	21st to end	Day	67% 2 9% 17% 5%	1773
December	1st to 10th	Day	70% 2 11% 13% 4	1561
	11th to 20th	Day	70% 2 12% 13% 2	1915
	21st to end	Day	81% 1 7% 9% 2	2783
January	1st to 10th	Night	76% 2 8% 12% 2	4428
	11th to 20th	Night	82% 2 8% 7% 2	4440
	21st to end	Night	79% 1 9% 9% 2	4884
February	1st to 10th	Night	66% 3 9% 14% 7% 1	2375
	11th to 20th	Night	63% 2 10% 17% 7% 1	2219
	21st to end	Night	64% 2 8% 17% 7% 2	1884
March	1st to 10th	Night	55% 2 12% 23% 7%	3733
	11th to 20th	Night	46% 2 11% 26% 14% 2	3642
	21st to end	Night	61% 2 11% 19% 7% 1	3604
April	1st to 10th	Night	50% 4 11% 21% 13% 1	1900
	11th to 20th	Night	49% 3 7% 22% 17% 3	1875
	21st to end	Night	50% 4 10% 19% 15% 2	1715
May	1st to 10th	Night	49% 2 11% 24% 12% 1	2840
	11th to 20th	Night	45% 2 12% 25% 15% 1	2784
	21st to end	Night	42% 3 10% 20% 24% 2	2751
June	1st to 10th	Night	33% 4 11% 30% 19% 3	1520
	11th to 20th	Night	37% 4 12% 24% 20% 2	1520
	21st to end	Night	38% 4 18% 24% 14% 2	1520
July	1st to 10th	Night	38% 5% 14% 24% 13% 6%	2490
	11th to 20th	Night	28% 5% 13% 24% 28% 3	2482
	21st to end	Night	34% 5% 17% 18% 23% 3	2662
August	1st to 10th	Night	35% 5% 13% 30% 16% 1	2745
	11th to 20th	Night	33% 5% 11% 29% 21% 1	2923
	21st to end	Night	35% 4 8% 30% 20% 3	3476
September	1st to 10th	Night	37% 4 11% 24% 19% 5%	1900
	11th to 20th	Night	31% 3 8% 31% 25% 2	2068
	21st to end	Night	41% 3 10% 27% 18% 2	2090
October	1st to 10th	Night	28% 3 9% 33% 26% 2	3480
	11th to 20th	Night	45% 2 7% 21% 23% 1	3847
	21st to end	Night	45% 2 8% 27% 16% 1	4467
November	1st to 10th	Night	51% 3 8% 22% 14% 2	2536
	11th to 20th	Night	62% 3 10% 16% 8% 1	2600
	21st to end	Night	65% 2 11% 17% 5%	2562
December	1st to 10th	Night	73% 2 8% 12% 5%	2617
	11th to 20th	Night	73% 2 10% 12% 3	3281
	21st to end	Night	79% 2 10% 8% 2	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	21% 21% 36% 16% 5% 1	270
	11th to 20th	Day	24% 22% 36% 13% 4 1	270
	21st to end	Day	26% 23% 29% 18% 3	297
February	1st to 10th	Day	30% 21% 31% 13% 4 1	270
	11th to 20th	Day	24% 30% 32% 12% 1	270
	21st to end	Day	28% 32% 31% 7% 3	225
March	1st to 10th	Day	23% 28% 35% 11% 2	270
	11th to 20th	Day	24% 20% 31% 17% 6% 1	361
	21st to end	Day	31% 18% 29% 16% 6% 1	506
April	1st to 10th	Day	26% 21% 29% 21% 3 1	460
	11th to 20th	Day	24% 23% 28% 15% 8% 2	452
	21st to end	Day	25% 18% 31% 17% 6% 3	460
May	1st to 10th	Day	25% 16% 30% 19% 8% 2	463
	11th to 20th	Day	21% 15% 28% 24% 9% 4	501
	21st to end	Day	14% 12% 31% 25% 14% 4	734
June	1st to 10th	Day	11% 13% 31% 29% 12% 4	680
	11th to 20th	Day	13% 9% 30% 32% 13% 3	680
	21st to end	Day	14% 10% 33% 26% 12% 4	680
July	1st to 10th	Day	9% 7% 26% 27% 22% 9%	671
	11th to 20th	Day	11% 6% 31% 27% 18% 7%	668
	21st to end	Day	8% 5% 26% 36% 19% 6%	739
August	1st to 10th	Day	8% 4 22% 29% 24% 12%	533
	11th to 20th	Day	11% 6% 25% 25% 24% 9%	479
	21st to end	Day	9% 4 22% 34% 23% 9%	539
September	1st to 10th	Day	15% 5% 23% 30% 20% 6%	490
	11th to 20th	Day	10% 7% 19% 29% 26% 10%	490
	21st to end	Day	19% 12% 21% 25% 14% 8%	490
October	1st to 10th	Day	17% 10% 28% 26% 17% 3	490
	11th to 20th	Day	25% 18% 30% 20% 7%	352
	21st to end	Day	36% 14% 34% 15% 2 1	330
November	1st to 10th	Day	18% 18% 38% 18% 6% 2	300
	11th to 20th	Day	28% 27% 26% 14% 5%	300
	21st to end	Day	34% 19% 34% 12% 1	291
December	1st to 10th	Day	24% 31% 27% 13% 5% 1	270
	11th to 20th	Day	22% 30% 31% 13% 3 1	270
	21st to end	Day	23% 31% 34% 11% 1	297
January	1st to 10th	Night	25% 17% 35% 19% 4	950
	11th to 20th	Night	27% 15% 34% 19% 4 1	950
	21st to end	Night	24% 16% 34% 23% 4	1045
February	1st to 10th	Night	27% 16% 32% 22% 3	812
	11th to 20th	Night	22% 19% 33% 21% 4	743
	21st to end	Night	28% 19% 32% 17% 4	628
March	1st to 10th	Night	22% 18% 30% 22% 7% 1	760
	11th to 20th	Night	20% 13% 34% 26% 7%	760
	21st to end	Night	25% 13% 27% 29% 6%	713
April	1st to 10th	Night	20% 16% 33% 25% 6% 1	570
	11th to 20th	Night	25% 12% 30% 25% 7% 1	563
	21st to end	Night	22% 12% 30% 26% 9% 1	570
May	1st to 10th	Night	22% 7% 30% 30% 11% 1	570
	11th to 20th	Night	20% 7% 23% 36% 14% 1	561
	21st to end	Night	14% 4 23% 38% 20% 1	617
June	1st to 10th	Night	11% 5% 24% 41% 18% 2	570
	11th to 20th	Night	13% 3 29% 37% 16% 1	570
	21st to end	Night	11% 6% 23% 37% 22% 2	570
July	1st to 10th	Night	8% 3 16% 39% 30% 4	555
	11th to 20th	Night	10% 5% 19% 36% 27% 4	552
	21st to end	Night	8% 3 14% 44% 29% 2	624
August	1st to 10th	Night	9% 2 13% 43% 29% 3	567
	11th to 20th	Night	9% 3 14% 38% 30% 5%	564
	21st to end	Night	11% 3 13% 41% 29% 3	627
September	1st to 10th	Night	14% 4 17% 37% 24% 5%	570
	11th to 20th	Night	13% 4 15% 37% 27% 4	738
	21st to end	Night	16% 8% 23% 29% 21% 3	760
October	1st to 10th	Night	19% 7% 25% 29% 19% 1	760
	11th to 20th	Night	27% 15% 23% 27% 7% 1	760
	21st to end	Night	30% 15% 26% 23% 6%	836
November	1st to 10th	Night	26% 12% 30% 22% 10% 1	780
	11th to 20th	Night	27% 18% 30% 20% 4 1	800
	21st to end	Night	32% 13% 30% 21% 4	789
December	1st to 10th	Night	29% 20% 30% 17% 4	907
	11th to 20th	Night	27% 15% 36% 19% 4	950
	21st to end	Night	31% 17% 34% 17% 2	1045

Page generated at 2024-11-25 00:22:19. Version ac07

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