Westfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Westfield clear sky chart from 2005-11-06 to 2026-02-16.

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	19% 10% 3 7% 4 4 4 4 5% 7% 33%	130680
	Night	19% 10% 3 7% 4 4 4 3 5% 6% 34%	130298
Transparency	Day	49% 7% 12% 20% 11% 1	134199
	Night	51% 6% 10% 20% 11% 1	134854
Seeing	Day	26% 20% 32% 16% 5% 1	18066
	Night	26% 17% 31% 20% 5%	26063

By Month

Percentage Cloud Cover NE (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	12% 14% 4 9% 5% 4 4 3 5% 6% 33%	4093
	11th to 20th	Day	16% 14% 4 10% 6% 4 4 2 4 5% 32%	4591
	21st to end	Day	11% 9% 3 6% 5% 4 5% 5% 6% 8% 39%	5718
February	1st to 10th	Day	15% 12% 4 7% 5% 5% 4 4 5% 7% 32%	1890
	11th to 20th	Day	15% 12% 3 9% 5% 5% 4 4 6% 7% 32%	1798
	21st to end	Day	11% 12% 3 9% 5% 4 5% 4 5% 7% 36%	1599
March	1st to 10th	Day	23% 13% 3 12% 5% 3 3 2 4 4 28%	4751
	11th to 20th	Day	18% 15% 3 8% 5% 5% 4 3 5% 6% 27%	4980
	21st to end	Day	27% 11% 5% 7% 4 4 4 4 5% 5% 24%	5466
April	1st to 10th	Day	21% 14% 3 8% 5% 4 3 3 5% 6% 28%	2324
	11th to 20th	Day	19% 11% 3 7% 4 4 4 3 4 6% 35%	2572
	21st to end	Day	24% 9% 2 7% 4 4 3 3 5% 6% 33%	2600
May	1st to 10th	Day	27% 12% 3 8% 5% 5% 5% 4 4 6% 22%	5886
	11th to 20th	Day	22% 9% 2 7% 5% 4 4 4 5% 7% 31%	6175
	21st to end	Day	20% 9% 3 7% 5% 5% 4 4 6% 8% 29%	7032
June	1st to 10th	Day	23% 10% 3 7% 5% 5% 4 3 5% 7% 28%	3000
	11th to 20th	Day	21% 8% 3 7% 4 4 4 3 5% 6% 35%	3000
	21st to end	Day	28% 8% 2 7% 5% 3 4 4 5% 6% 28%	3000
July	1st to 10th	Day	16% 8% 3 8% 5% 5% 6% 4 7% 8% 30%	6820
	11th to 20th	Day	19% 8% 3 6% 4 4 4 4 6% 7% 36%	6783
	21st to end	Day	16% 7% 2 6% 5% 4 5% 4 6% 8% 37%	6480
August	1st to 10th	Day	22% 8% 3 7% 4 4 5% 4 6% 8% 30%	4235
	11th to 20th	Day	17% 7% 2 6% 5% 4 5% 4 6% 8% 37%	4175
	21st to end	Day	12% 5% 2 6% 4 4 5% 4 6% 8% 44%	4661
September	1st to 10th	Day	14% 6% 2 6% 3 4 4 4 6% 7% 45%	2376
	11th to 20th	Day	17% 5% 2 5% 3 3 3 3 5% 5% 49%	2200
	21st to end	Day	19% 6% 1 5% 3 3 4 3 4 6% 45%	2200
October	1st to 10th	Day	17% 7% 2 6% 4 4 4 4 4 6% 42%	2030
	11th to 20th	Day	19% 7% 3 6% 5% 3 4 4 5% 5% 39%	2000
	21st to end	Day	20% 9% 3 7% 4 5% 5% 4 4 6% 34%	2098
November	1st to 10th	Day	21% 8% 2 7% 4 5% 4 3 4 6% 36%	1783
	11th to 20th	Day	19% 7% 3 6% 4 4 3 4 5% 6% 39%	1680
	21st to end	Day	21% 10% 3 6% 4 4 4 4 5% 6% 32%	1680
December	1st to 10th	Day	21% 10% 2 5% 3 4 3 4 5% 6% 36%	2690
	11th to 20th	Day	25% 11% 2 7% 4 3 3 2 3 4 37%	2761
	21st to end	Day	20% 11% 3 5% 3 3 4 4 5% 6% 36%	3553
January	1st to 10th	Night	12% 12% 4 8% 5% 5% 5% 3 5% 6% 34%	8831
	11th to 20th	Night	20% 12% 3 8% 5% 4 4 3 5% 6% 30%	8295
	21st to end	Night	9% 13% 3 6% 3 4 4 3 6% 7% 42%	8460
February	1st to 10th	Night	16% 12% 4 7% 5% 4 4 4 6% 7% 33%	2730
	11th to 20th	Night	15% 12% 3 8% 5% 5% 5% 4 5% 5% 32%	2599
	21st to end	Night	15% 11% 3 8% 5% 4 4 4 5% 6% 34%	2029
March	1st to 10th	Night	26% 13% 4 7% 4 5% 4 2 3 4 27%	5089
	11th to 20th	Night	19% 14% 4 7% 5% 5% 5% 4 5% 5% 28%	4979
	21st to end	Night	30% 10% 3 6% 3 4 4 3 4 5% 29%	5466
April	1st to 10th	Night	23% 12% 4 7% 5% 4 4 3 4 4 31%	2072
	11th to 20th	Night	23% 9% 3 6% 4 4 4 3 4 6% 33%	1778
	21st to end	Night	24% 10% 3 6% 5% 4 4 4 5% 6% 30%	1800
May	1st to 10th	Night	27% 11% 2 7% 6% 5% 5% 3 5% 5% 24%	4054
	11th to 20th	Night	21% 9% 3 7% 4 4 4 4 5% 7% 32%	3731
	21st to end	Night	17% 12% 4 8% 5% 4 5% 3 5% 6% 31%	3906
June	1st to 10th	Night	24% 10% 3 8% 5% 3 5% 3 5% 8% 26%	1400
	11th to 20th	Night	21% 8% 3 6% 6% 3 4 3 5% 6% 34%	1400
	21st to end	Night	29% 9% 2 7% 5% 5% 3 3 4 5% 28%	1400
July	1st to 10th	Night	19% 10% 3 10% 6% 5% 6% 4 6% 7% 24%	3160
	11th to 20th	Night	20% 9% 3 8% 5% 5% 5% 4 6% 7% 29%	3192
	21st to end	Night	16% 8% 2 6% 5% 4 4 4 6% 8% 37%	4325
August	1st to 10th	Night	22% 11% 3 7% 4 5% 5% 3 5% 7% 28%	2915
	11th to 20th	Night	16% 9% 3 8% 4 5% 4 4 6% 7% 35%	2872
	21st to end	Night	12% 6% 2 6% 3 4 4 4 6% 7% 45%	3223
September	1st to 10th	Night	18% 6% 2 5% 4 4 5% 3 5% 8% 41%	2020
	11th to 20th	Night	17% 7% 2 5% 3 3 4 3 4 6% 46%	2200
	21st to end	Night	20% 5% 2 5% 3 4 3 3 6% 6% 43%	2200
October	1st to 10th	Night	19% 6% 2 6% 4 4 3 3 5% 6% 42%	2370
	11th to 20th	Night	18% 9% 2 6% 4 3 4 3 5% 6% 40%	2400
	21st to end	Night	22% 10% 3 7% 4 4 4 3 4 5% 34%	2740
November	1st to 10th	Night	21% 6% 2 6% 4 4 4 3 5% 6% 38%	2732
	11th to 20th	Night	19% 8% 2 7% 4 4 4 4 5% 7% 36%	2940
	21st to end	Night	20% 9% 3 7% 4 3 4 4 5% 6% 34%	2940
December	1st to 10th	Night	18% 10% 3 6% 3 4 4 3 5% 6% 38%	4720
	11th to 20th	Night	24% 11% 2 5% 4 3 3 3 4 4 38%	5663
	21st to end	Night	20% 12% 3 7% 4 3 4 3 4 5% 34%	7667

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	53% 5% 14% 19% 9% 1	4094
	11th to 20th	Day	56% 5% 8% 21% 9% 1	4621
	21st to end	Day	42% 6% 9% 20% 19% 3	5718
February	1st to 10th	Day	51% 7% 12% 18% 10% 2	1890
	11th to 20th	Day	51% 6% 12% 19% 11% 1	1806
	21st to end	Day	46% 6% 12% 23% 10% 3	1599
March	1st to 10th	Day	60% 4 8% 13% 12% 3	4755
	11th to 20th	Day	53% 9% 14% 16% 8% 1	4980
	21st to end	Day	60% 5% 6% 16% 11% 2	5466
April	1st to 10th	Day	56% 6% 8% 15% 12% 3	2324
	11th to 20th	Day	49% 5% 10% 21% 13% 2	2572
	21st to end	Day	51% 6% 10% 18% 12% 4	2600
May	1st to 10th	Day	60% 10% 9% 14% 7% 1	5897
	11th to 20th	Day	50% 9% 13% 19% 7% 2	6179
	21st to end	Day	50% 11% 12% 16% 10%	7032
June	1st to 10th	Day	54% 9% 11% 16% 9% 1	3000
	11th to 20th	Day	49% 6% 12% 20% 11% 2	3000
	21st to end	Day	55% 9% 10% 15% 9% 1	3000
July	1st to 10th	Day	53% 8% 13% 17% 9%	6745
	11th to 20th	Day	48% 8% 14% 22% 8% 1	6702
	21st to end	Day	43% 9% 15% 24% 10%	6295
August	1st to 10th	Day	53% 9% 11% 20% 7%	4222
	11th to 20th	Day	43% 10% 16% 22% 9%	4214
	21st to end	Day	35% 8% 14% 25% 16% 1	4661
September	1st to 10th	Day	37% 9% 14% 25% 14% 1	2376
	11th to 20th	Day	37% 6% 14% 24% 16% 3	2200
	21st to end	Day	41% 6% 9% 27% 17% 1	2200
October	1st to 10th	Day	44% 7% 10% 29% 10% 1	3303
	11th to 20th	Day	42% 5% 10% 33% 11%	3240
	21st to end	Day	42% 5% 17% 19% 17% 1	3361
November	1st to 10th	Day	49% 6% 12% 21% 11% 1	1783
	11th to 20th	Day	45% 7% 14% 18% 14% 2	1680
	21st to end	Day	54% 7% 12% 20% 7%	1680
December	1st to 10th	Day	49% 5% 14% 23% 8%	2690
	11th to 20th	Day	54% 3 11% 16% 12% 4	2761
	21st to end	Day	49% 5% 11% 20% 13% 2	3553
January	1st to 10th	Night	52% 5% 10% 24% 9% 1	8831
	11th to 20th	Night	56% 6% 9% 20% 8% 1	8340
	21st to end	Night	42% 5% 8% 24% 17% 4	8460
February	1st to 10th	Night	50% 7% 11% 18% 13% 1	2730
	11th to 20th	Night	52% 6% 10% 19% 10% 2	2602
	21st to end	Night	50% 7% 9% 20% 12% 3	2029
March	1st to 10th	Night	61% 4 5% 13% 13% 4	5098
	11th to 20th	Night	55% 9% 14% 14% 8% 1	4980
	21st to end	Night	59% 4 6% 18% 12% 1	5466
April	1st to 10th	Night	56% 6% 8% 14% 12% 4	2072
	11th to 20th	Night	51% 5% 11% 19% 13% 1	1778
	21st to end	Night	53% 6% 9% 17% 12% 2	1800
May	1st to 10th	Night	59% 9% 9% 14% 8% 1	4060
	11th to 20th	Night	51% 8% 12% 21% 6% 2	3732
	21st to end	Night	52% 9% 13% 18% 7% 2	3907
June	1st to 10th	Night	57% 7% 10% 18% 7% 1	1400
	11th to 20th	Night	51% 6% 12% 21% 9% 1	1400
	21st to end	Night	61% 5% 7% 16% 8% 2	1400
July	1st to 10th	Night	62% 7% 10% 13% 8%	3125
	11th to 20th	Night	59% 7% 8% 18% 8%	3150
	21st to end	Night	48% 7% 13% 20% 11% 1	4196
August	1st to 10th	Night	58% 7% 11% 18% 6%	2903
	11th to 20th	Night	50% 7% 15% 21% 7%	2899
	21st to end	Night	39% 7% 12% 24% 16% 1	3223
September	1st to 10th	Night	42% 6% 11% 25% 14% 1	2020
	11th to 20th	Night	41% 6% 12% 24% 17% 1	2200
	21st to end	Night	42% 6% 10% 27% 14% 2	2200
October	1st to 10th	Night	45% 4 12% 26% 13% 1	3877
	11th to 20th	Night	37% 5% 11% 29% 18%	3899
	21st to end	Night	47% 4 11% 23% 14% 1	4414
November	1st to 10th	Night	47% 7% 13% 20% 13% 1	2732
	11th to 20th	Night	49% 6% 11% 21% 12% 1	2940
	21st to end	Night	51% 7% 14% 18% 10% 1	2940
December	1st to 10th	Night	48% 5% 9% 28% 9%	4720
	11th to 20th	Night	51% 5% 9% 20% 13% 2	5664
	21st to end	Night	54% 5% 10% 18% 12% 3	7667

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	32% 26% 29% 11% 2	220
	11th to 20th	Day	37% 21% 31% 7% 3	220
	21st to end	Day	20% 28% 36% 14% 2	449
February	1st to 10th	Day	27% 24% 31% 13% 4 1	430
	11th to 20th	Day	27% 29% 31% 10% 2	411
	21st to end	Day	24% 26% 33% 15% 2	389
March	1st to 10th	Day	29% 26% 32% 10% 2	500
	11th to 20th	Day	25% 26% 31% 13% 4 1	500
	21st to end	Day	31% 25% 29% 10% 4 1	550
April	1st to 10th	Day	34% 29% 25% 9% 3	500
	11th to 20th	Day	30% 27% 28% 11% 4	492
	21st to end	Day	30% 24% 28% 13% 4 1	500
May	1st to 10th	Day	31% 21% 33% 12% 3	503
	11th to 20th	Day	27% 19% 31% 17% 5% 1	659
	21st to end	Day	25% 21% 31% 17% 5% 1	790
June	1st to 10th	Day	28% 19% 30% 18% 5%	730
	11th to 20th	Day	25% 17% 32% 19% 7% 1	730
	21st to end	Day	32% 14% 31% 17% 6% 1	730
July	1st to 10th	Day	22% 13% 41% 18% 6%	720
	11th to 20th	Day	24% 9% 34% 23% 9% 1	707
	21st to end	Day	19% 14% 39% 23% 4 1	576
August	1st to 10th	Day	18% 12% 34% 28% 6% 2	526
	11th to 20th	Day	22% 11% 32% 28% 6% 2	519
	21st to end	Day	17% 17% 31% 25% 8% 2	583
September	1st to 10th	Day	15% 14% 38% 23% 7% 2	530
	11th to 20th	Day	21% 15% 30% 21% 10% 3	530
	21st to end	Day	20% 18% 33% 18% 8% 2	530
October	1st to 10th	Day	20% 17% 27% 22% 10% 3	436
	11th to 20th	Day	23% 19% 30% 20% 7% 1	420
	21st to end	Day	27% 22% 33% 13% 5% 1	462
November	1st to 10th	Day	28% 21% 32% 13% 4 2	425
	11th to 20th	Day	28% 21% 33% 14% 3	430
	21st to end	Day	31% 25% 31% 10% 3	430
December	1st to 10th	Day	33% 20% 30% 14% 3	430
	11th to 20th	Day	36% 31% 23% 9% 1	267
	21st to end	Day	30% 26% 32% 9% 2	242
January	1st to 10th	Night	25% 24% 32% 16% 3	950
	11th to 20th	Night	29% 21% 29% 16% 4	851
	21st to end	Night	21% 25% 36% 15% 4	924
February	1st to 10th	Night	25% 24% 32% 16% 3	840
	11th to 20th	Night	26% 26% 31% 15% 2	804
	21st to end	Night	23% 21% 33% 19% 3	660
March	1st to 10th	Night	24% 23% 35% 16% 1	800
	11th to 20th	Night	25% 19% 33% 19% 4	800
	21st to end	Night	26% 18% 35% 17% 5%	880
April	1st to 10th	Night	31% 21% 32% 14% 2	702
	11th to 20th	Night	29% 17% 32% 18% 4	594
	21st to end	Night	29% 15% 30% 21% 5%	600
May	1st to 10th	Night	29% 12% 31% 24% 5%	600
	11th to 20th	Night	28% 14% 33% 21% 4	592
	21st to end	Night	23% 13% 41% 19% 4	633
June	1st to 10th	Night	31% 8% 32% 26% 4	400
	11th to 20th	Night	24% 10% 33% 27% 6%	400
	21st to end	Night	32% 8% 26% 30% 5% 1	400
July	1st to 10th	Night	22% 5% 36% 30% 7% 1	390
	11th to 20th	Night	26% 6% 27% 32% 8% 1	388
	21st to end	Night	24% 7% 32% 30% 7%	605
August	1st to 10th	Night	19% 5% 35% 32% 9%	598
	11th to 20th	Night	22% 8% 28% 31% 10%	592
	21st to end	Night	16% 7% 32% 32% 12% 1	660
September	1st to 10th	Night	22% 5% 38% 24% 10% 1	620
	11th to 20th	Night	20% 12% 25% 29% 13% 1	800
	21st to end	Night	23% 11% 31% 24% 11% 1	800
October	1st to 10th	Night	23% 10% 31% 26% 10% 1	800
	11th to 20th	Night	22% 16% 32% 21% 9% 1	800
	21st to end	Night	29% 20% 28% 20% 3	880
November	1st to 10th	Night	28% 17% 30% 18% 6% 1	855
	11th to 20th	Night	27% 20% 29% 18% 6%	950
	21st to end	Night	29% 22% 27% 18% 4 1	950
December	1st to 10th	Night	32% 19% 31% 16% 3	950
	11th to 20th	Night	32% 24% 30% 13% 2	950
	21st to end	Night	31% 24% 28% 14% 3	1045

Page generated at 2026-02-13 02:42:11. Version ac07

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