Grande Prairie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grande Prairie clear sky chart from 2005-11-06 to 2026-07-01.

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	9% 9% 4 9% 6% 5% 6% 5% 7% 8% 33%	142055
	Night	8% 11% 4 10% 6% 6% 6% 5% 7% 8% 30%	138991
Transparency	Day	45% 8% 16% 21% 9% 1	141733
	Night	48% 8% 15% 20% 8% 1	138896
Seeing	Day	14% 9% 24% 29% 19% 6%	18750
	Night	14% 8% 27% 33% 16% 2	26762

By Month

Percentage Cloud Cover NW (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	6% 17% 6% 12% 7% 5% 6% 5% 9% 9% 19%	3527
	11th to 20th	Day	5% 12% 3 9% 6% 6% 7% 5% 8% 9% 30%	3621
	21st to end	Day	7% 12% 5% 9% 5% 5% 6% 5% 7% 9% 29%	4805
February	1st to 10th	Day	8% 13% 5% 12% 7% 7% 5% 5% 7% 8% 23%	1680
	11th to 20th	Day	4 16% 5% 13% 8% 6% 6% 4 6% 7% 26%	1703
	21st to end	Day	5% 16% 6% 12% 8% 7% 6% 5% 6% 6% 25%	1643
March	1st to 10th	Day	3 9% 4 13% 10% 9% 6% 5% 6% 8% 26%	4618
	11th to 20th	Day	6% 15% 5% 11% 5% 5% 5% 4 6% 8% 29%	4778
	21st to end	Day	6% 11% 5% 11% 7% 5% 6% 5% 7% 8% 28%	6101
April	1st to 10th	Day	5% 11% 4 10% 7% 6% 7% 5% 8% 7% 30%	2520
	11th to 20th	Day	7% 11% 3 11% 7% 5% 5% 5% 7% 7% 32%	2696
	21st to end	Day	9% 11% 3 9% 6% 5% 6% 5% 7% 8% 31%	2940
May	1st to 10th	Day	6% 7% 3 8% 6% 5% 6% 6% 8% 10% 36%	8227
	11th to 20th	Day	7% 9% 4 11% 7% 8% 7% 6% 8% 9% 25%	8773
	21st to end	Day	12% 8% 3 8% 6% 6% 6% 5% 7% 9% 29%	10305
June	1st to 10th	Day	13% 9% 3 8% 6% 6% 5% 4 6% 8% 32%	3360
	11th to 20th	Day	17% 9% 4 9% 6% 5% 5% 5% 6% 7% 27%	3360
	21st to end	Day	11% 8% 3 8% 6% 5% 5% 4 6% 8% 36%	3360
July	1st to 10th	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 43%	7241
	11th to 20th	Day	7% 6% 2 8% 5% 5% 5% 4 6% 7% 44%	7240
	21st to end	Day	12% 5% 2 5% 4 4 4 4 6% 9% 44%	7553
August	1st to 10th	Day	10% 6% 2 5% 4 4 5% 3 6% 7% 48%	4541
	11th to 20th	Day	11% 5% 2 8% 4 5% 4 5% 7% 10% 39%	4470
	21st to end	Day	13% 6% 3 8% 5% 5% 4 4 6% 7% 40%	4748
September	1st to 10th	Day	14% 6% 3 6% 4 3 4 4 5% 7% 44%	2400
	11th to 20th	Day	13% 7% 3 7% 5% 4 4 4 7% 8% 40%	2367
	21st to end	Day	12% 7% 3 7% 5% 5% 5% 4 7% 8% 37%	2186
October	1st to 10th	Day	10% 9% 3 10% 5% 5% 5% 4 7% 8% 33%	3280
	11th to 20th	Day	11% 9% 4 9% 6% 5% 6% 5% 8% 7% 30%	2982
	21st to end	Day	10% 12% 6% 8% 4 4 5% 4 7% 7% 32%	3142
November	1st to 10th	Day	12% 16% 5% 10% 7% 6% 5% 3 6% 7% 24%	1574
	11th to 20th	Day	10% 16% 5% 11% 5% 4 4 4 5% 7% 29%	1470
	21st to end	Day	7% 16% 5% 12% 8% 5% 5% 3 6% 7% 26%	1444
December	1st to 10th	Day	12% 19% 5% 12% 7% 7% 6% 4 5% 5% 20%	2020
	11th to 20th	Day	10% 15% 6% 13% 7% 7% 7% 4 4 6% 21%	2322
	21st to end	Day	4 10% 4 10% 5% 5% 7% 4 7% 8% 36%	3058
January	1st to 10th	Night	6% 17% 7% 15% 7% 5% 5% 5% 6% 7% 20%	9366
	11th to 20th	Night	4 10% 4 10% 7% 6% 7% 6% 8% 8% 30%	9334
	21st to end	Night	7% 15% 4 9% 6% 6% 6% 4 7% 9% 28%	9375
February	1st to 10th	Night	8% 16% 6% 11% 7% 6% 5% 4 6% 8% 25%	2940
	11th to 20th	Night	6% 13% 6% 13% 7% 5% 5% 5% 5% 7% 27%	2799
	21st to end	Night	4 13% 6% 12% 8% 6% 6% 4 7% 7% 28%	2162
March	1st to 10th	Night	3 7% 4 14% 9% 7% 8% 5% 8% 8% 27%	5496
	11th to 20th	Night	6% 14% 5% 10% 6% 6% 6% 5% 9% 9% 25%	5437
	21st to end	Night	8% 11% 4 9% 5% 5% 5% 4 6% 8% 36%	5116
April	1st to 10th	Night	5% 10% 4 11% 7% 7% 6% 5% 8% 9% 28%	2100
	11th to 20th	Night	7% 10% 4 11% 6% 6% 5% 4 7% 7% 32%	1872
	21st to end	Night	9% 11% 3 8% 6% 5% 6% 4 7% 8% 33%	1680
May	1st to 10th	Night	7% 11% 3 9% 5% 5% 5% 4 6% 8% 37%	4691
	11th to 20th	Night	7% 9% 4 11% 7% 6% 7% 5% 8% 10% 26%	4070
	21st to end	Night	8% 7% 3 8% 5% 6% 6% 6% 10% 10% 32%	3866
June	1st to 10th	Night	11% 9% 4 9% 6% 6% 5% 5% 6% 7% 33%	1260
	11th to 20th	Night	17% 8% 3 8% 5% 6% 6% 6% 6% 9% 25%	1260
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 5% 8% 9% 34%	1260
July	1st to 10th	Night	11% 6% 2 6% 5% 5% 6% 5% 6% 7% 40%	2720
	11th to 20th	Night	9% 6% 2 7% 5% 5% 5% 4 8% 8% 39%	2720
	21st to end	Night	9% 5% 3 7% 5% 5% 5% 5% 7% 10% 40%	3284
August	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 6% 8% 49%	2609
	11th to 20th	Night	11% 6% 2 7% 5% 5% 5% 4 6% 7% 43%	2577
	21st to end	Night	8% 5% 3 9% 6% 5% 7% 4 6% 9% 38%	3156
September	1st to 10th	Night	12% 6% 3 8% 5% 5% 4 4 6% 8% 38%	2000
	11th to 20th	Night	11% 7% 2 6% 5% 4 5% 4 6% 9% 41%	2033
	21st to end	Night	12% 9% 3 9% 5% 5% 5% 3 6% 8% 36%	2210
October	1st to 10th	Night	10% 11% 3 9% 6% 7% 6% 4 5% 8% 32%	3920
	11th to 20th	Night	7% 6% 3 9% 6% 6% 5% 4 7% 9% 38%	4167
	21st to end	Night	9% 11% 4 9% 6% 6% 7% 5% 7% 8% 29%	4652
November	1st to 10th	Night	13% 15% 5% 10% 6% 5% 5% 4 5% 7% 26%	2923
	11th to 20th	Night	8% 18% 5% 11% 6% 5% 4 4 5% 6% 27%	3150
	21st to end	Night	9% 17% 4 11% 8% 5% 4 4 5% 7% 26%	3176
December	1st to 10th	Night	10% 15% 4 11% 8% 6% 5% 5% 6% 6% 24%	5380
	11th to 20th	Night	9% 18% 6% 14% 7% 5% 5% 4 5% 6% 20%	6090
	21st to end	Night	4 12% 5% 10% 7% 6% 6% 5% 6% 8% 31%	8140

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	57% 6% 11% 16% 10%	3527
	11th to 20th	Day	46% 6% 16% 19% 11% 2	3639
	21st to end	Day	47% 10% 22% 16% 5%	4806
February	1st to 10th	Day	55% 7% 13% 13% 11%	1680
	11th to 20th	Day	56% 8% 13% 15% 8% 1	1711
	21st to end	Day	57% 6% 13% 16% 7% 1	1643
March	1st to 10th	Day	52% 8% 13% 19% 9%	4618
	11th to 20th	Day	49% 8% 13% 19% 11%	4778
	21st to end	Day	47% 9% 14% 18% 11%	6101
April	1st to 10th	Day	47% 10% 16% 19% 7% 1	2520
	11th to 20th	Day	46% 7% 17% 19% 10% 1	2696
	21st to end	Day	46% 9% 14% 23% 8% 1	2940
May	1st to 10th	Day	39% 8% 16% 24% 12% 2	8227
	11th to 20th	Day	47% 10% 15% 21% 7%	8777
	21st to end	Day	45% 10% 15% 20% 10% 1	10306
June	1st to 10th	Day	48% 8% 14% 19% 9% 1	3360
	11th to 20th	Day	54% 9% 12% 18% 7%	3360
	21st to end	Day	43% 9% 17% 22% 9% 1	3360
July	1st to 10th	Day	35% 8% 17% 22% 16% 2	7162
	11th to 20th	Day	36% 8% 15% 28% 12% 1	7153
	21st to end	Day	35% 7% 20% 31% 7%	7339
August	1st to 10th	Day	34% 9% 16% 34% 7%	4524
	11th to 20th	Day	37% 9% 18% 24% 11%	4512
	21st to end	Day	42% 7% 22% 23% 5%	4747
September	1st to 10th	Day	39% 7% 20% 27% 7% 1	2400
	11th to 20th	Day	41% 8% 18% 25% 8%	2367
	21st to end	Day	42% 9% 17% 22% 9% 1	2186
October	1st to 10th	Day	46% 7% 20% 20% 6%	3280
	11th to 20th	Day	49% 7% 15% 24% 4	2982
	21st to end	Day	47% 7% 22% 20% 4	3142
November	1st to 10th	Day	59% 5% 14% 17% 5% 1	1574
	11th to 20th	Day	55% 6% 16% 15% 8%	1470
	21st to end	Day	57% 6% 13% 15% 7% 2	1444
December	1st to 10th	Day	66% 7% 12% 10% 5%	2020
	11th to 20th	Day	62% 6% 15% 12% 4	2324
	21st to end	Day	41% 8% 14% 26% 9% 1	3058
January	1st to 10th	Night	60% 6% 9% 14% 9% 1	9367
	11th to 20th	Night	47% 6% 15% 18% 12% 1	9378
	21st to end	Night	49% 9% 19% 17% 6%	9375
February	1st to 10th	Night	57% 6% 14% 13% 10%	2940
	11th to 20th	Night	55% 6% 11% 19% 8% 1	2801
	21st to end	Night	53% 7% 15% 18% 7% 1	2162
March	1st to 10th	Night	48% 8% 14% 18% 12%	5496
	11th to 20th	Night	48% 9% 14% 19% 9%	5438
	21st to end	Night	41% 10% 12% 24% 13%	5116
April	1st to 10th	Night	48% 9% 14% 18% 10% 1	2100
	11th to 20th	Night	48% 8% 14% 19% 10% 1	1872
	21st to end	Night	45% 9% 11% 24% 10% 1	1680
May	1st to 10th	Night	43% 6% 11% 27% 11% 1	4688
	11th to 20th	Night	45% 11% 13% 23% 8%	4070
	21st to end	Night	38% 11% 20% 19% 8% 3	3870
June	1st to 10th	Night	47% 8% 12% 22% 11% 1	1260
	11th to 20th	Night	52% 10% 14% 20% 5%	1260
	21st to end	Night	43% 9% 17% 20% 10%	1260
July	1st to 10th	Night	39% 9% 15% 25% 11% 1	2690
	11th to 20th	Night	39% 8% 15% 24% 13%	2684
	21st to end	Night	35% 9% 20% 29% 7%	3193
August	1st to 10th	Night	31% 9% 19% 35% 6%	2601
	11th to 20th	Night	37% 9% 15% 28% 10% 1	2601
	21st to end	Night	41% 8% 25% 20% 6% 1	3156
September	1st to 10th	Night	42% 8% 19% 23% 7% 1	2000
	11th to 20th	Night	38% 7% 19% 26% 9%	2033
	21st to end	Night	44% 8% 15% 20% 11% 1	2210
October	1st to 10th	Night	49% 8% 17% 18% 8%	3920
	11th to 20th	Night	40% 7% 16% 29% 7%	4167
	21st to end	Night	50% 8% 18% 19% 6%	4652
November	1st to 10th	Night	57% 6% 13% 17% 6% 1	2923
	11th to 20th	Night	57% 7% 12% 15% 8%	3150
	21st to end	Night	57% 8% 12% 16% 6% 1	3176
December	1st to 10th	Night	58% 8% 15% 14% 6%	5380
	11th to 20th	Night	64% 7% 14% 11% 5%	6087
	21st to end	Night	47% 8% 13% 25% 6% 1	8140

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	11% 10% 18% 37% 18% 5%	220
	11th to 20th	Day	16% 11% 22% 30% 16% 3	220
	21st to end	Day	10% 13% 29% 31% 15% 3	242
February	1st to 10th	Day	10% 11% 18% 35% 20% 5%	220
	11th to 20th	Day	8% 13% 23% 31% 19% 6%	283
	21st to end	Day	10% 12% 21% 34% 19% 3	401
March	1st to 10th	Day	9% 9% 25% 34% 18% 6%	540
	11th to 20th	Day	10% 7% 25% 33% 18% 7%	540
	21st to end	Day	12% 8% 26% 29% 20% 5%	594
April	1st to 10th	Day	7% 10% 27% 32% 16% 7%	540
	11th to 20th	Day	12% 11% 22% 33% 17% 6%	532
	21st to end	Day	14% 12% 23% 28% 16% 7%	540
May	1st to 10th	Day	15% 12% 26% 28% 16% 3	549
	11th to 20th	Day	13% 8% 21% 30% 21% 7%	780
	21st to end	Day	15% 7% 23% 27% 21% 7%	1072
June	1st to 10th	Day	14% 11% 27% 29% 15% 4	990
	11th to 20th	Day	21% 8% 20% 25% 21% 5%	990
	21st to end	Day	14% 6% 19% 26% 24% 10%	990
July	1st to 10th	Day	15% 5% 22% 30% 22% 6%	917
	11th to 20th	Day	12% 6% 25% 29% 21% 8%	912
	21st to end	Day	12% 8% 21% 31% 20% 8%	878
August	1st to 10th	Day	13% 9% 18% 27% 22% 11%	527
	11th to 20th	Day	9% 11% 29% 27% 16% 7%	517
	21st to end	Day	14% 8% 25% 27% 16% 10%	583
September	1st to 10th	Day	17% 10% 22% 24% 19% 8%	530
	11th to 20th	Day	17% 7% 24% 24% 22% 7%	530
	21st to end	Day	15% 13% 33% 20% 14% 5%	530
October	1st to 10th	Day	16% 14% 24% 26% 16% 5%	530
	11th to 20th	Day	19% 12% 21% 28% 16% 4	367
	21st to end	Day	18% 13% 28% 22% 14% 6%	344
November	1st to 10th	Day	17% 9% 28% 27% 16% 3	220
	11th to 20th	Day	17% 9% 24% 34% 14% 2	220
	21st to end	Day	13% 11% 27% 32% 11% 5%	220
December	1st to 10th	Day	13% 10% 26% 34% 13% 5%	220
	11th to 20th	Day	12% 12% 25% 34% 15% 3	220
	21st to end	Day	14% 5% 17% 39% 16% 9%	242
January	1st to 10th	Night	14% 7% 24% 35% 17% 3	1160
	11th to 20th	Night	13% 11% 28% 32% 14% 2	1144
	21st to end	Night	16% 13% 29% 29% 11% 1	995
February	1st to 10th	Night	16% 9% 23% 30% 18% 4	840
	11th to 20th	Night	12% 8% 27% 33% 18% 1	824
	21st to end	Night	8% 9% 26% 36% 17% 4	692
March	1st to 10th	Night	8% 8% 30% 32% 19% 3	840
	11th to 20th	Night	14% 7% 26% 38% 14% 2	840
	21st to end	Night	13% 6% 24% 35% 21% 2	924
April	1st to 10th	Night	9% 7% 30% 37% 15% 2	840
	11th to 20th	Night	12% 8% 25% 35% 18% 1	624
	21st to end	Night	11% 9% 32% 30% 18%	420
May	1st to 10th	Night	14% 7% 31% 34% 12% 1	420
	11th to 20th	Night	12% 6% 29% 35% 17% 1	414
	21st to end	Night	15% 6% 23% 33% 21% 2	455
June	1st to 10th	Night	15% 8% 26% 30% 21%	420
	11th to 20th	Night	21% 5% 21% 29% 22% 2	420
	21st to end	Night	15% 4 25% 32% 22% 3	420
July	1st to 10th	Night	12% 4 21% 39% 23% 1	390
	11th to 20th	Night	14% 5% 21% 35% 22% 3	388
	21st to end	Night	10% 4 21% 36% 24% 4	438
August	1st to 10th	Night	12% 4 19% 32% 31% 4	398
	11th to 20th	Night	8% 4 27% 36% 23% 2	396
	21st to end	Night	13% 4 25% 36% 20% 1	597
September	1st to 10th	Night	14% 6% 23% 36% 20% 2	800
	11th to 20th	Night	14% 6% 22% 36% 21% 3	800
	21st to end	Night	17% 11% 27% 30% 13% 2	800
October	1st to 10th	Night	17% 8% 30% 31% 14% 1	800
	11th to 20th	Night	12% 9% 28% 36% 12% 2	800
	21st to end	Night	17% 11% 33% 30% 8% 1	880
November	1st to 10th	Night	20% 7% 27% 31% 13% 2	873
	11th to 20th	Night	17% 11% 31% 30% 9% 1	1050
	21st to end	Night	16% 10% 27% 35% 11% 2	1064
December	1st to 10th	Night	14% 9% 29% 34% 11% 2	1160
	11th to 20th	Night	15% 8% 28% 32% 14% 3	1160
	21st to end	Night	14% 6% 25% 36% 17% 2	1276

Page generated at 2026-06-28 00:10:47. Version ac07

Copyright © 2026 Attilla Danko.