Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 03 December (0300 UTC Friday 4 December) 2020

Warnings
None

Cloud Cover and Precipitation Forecast
There is a small risk for periods of fog and high humidity mainly for early this evening; precipitation is not expected. There is a chance for patches of high clouds and mid-level clouds along the northern and southern skies, respectively, through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this evening and 0.5 C tomorrow morning. Winds will be from the SE at 15-25 mph, with seeing near 0.7-0.75 arcseconds. Precipitable water is expected to exceed 4 mm for the night.

Graphical Summary

Discussion
The tradewind inversion will remain a bit weak/elevated, which could allow for periods of fog and high humidity mainly for early this evening. The inversion is set to quickly restrengthen as the night progresses, becoming well-established near 7 thousand feet and will ensure a dry/stable summit-level air mass for the following 4 nights. There is a possibility for a some limited afternoon clouds at the summit through the weekend, then will become minimal and short-lived for the early part of next week.

There is a chance for residual patches of high clouds along the northern skiesfor much of tonight. In addition, mid-level clouds begin to fill in from the SE as the night progresses, then will linger along the southern skies through the weekend. Cloud cover should not exceed 25% for any prolong period and clear skies are expected for Monday night.

Precipitable water is expected to linger near or exceed 4 mm through the weekend, then could trend toward 2 mm through Monday night.

A mixture of light boundary layer turbulence as well as mid-level turbulence will contribute to poor seeing through the next 5 nights.

No change since the morning forecast...Mid/low-level winds are set to switch to a more SE direction as a relatively flat ridge to the north continues to split and shift off toward the east and west. While the ridge will still promote large-scale subsidence in the area well into next week the SE winds will advect mid/low-level moisture, which could negate this subsidence over the next 12-18 hours. This may result in a minor erosion of the inversion, which could lead to fog/high humidity at the summit mainly for early this evening. The bulk of the low-level moisture will slide westward as the night progresses, but patches of mid-level clouds associated with an inverted trough to the south will move from the SE during that time. The trough is set to weaken thereafter, but the mid-level clouds may persist in the area well into the weekend. In addition, a tight wind gradient between the ridge to the NE and dissipating trough will likely keep summit-level winds around 20 mph, enough to stir up boundary layer turbulence probably throughout the forecast period. There is also a possibility that mid-level turbulence/instability along the northern fringe of the trough will also contribute to some degradation in seeing, mainly over the weekend.

Astronomical Observing Quality Guidance
Seeing/CN2 Images are not available today. Sorry for the inconvenience.
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
08 pm HST
Thu 03 Dec
02 am HST
Fri 04 Dec
02 pm HST
Fri 04 Dec
08 pm HST
Fri 04 Dec
02 am HST
Sat 05 Dec
02 pm HST
Sat 05 Dec
08 pm HST
Sat 05 Dec
02 am HST
Sun 06 Dec
02 pm HST
Sun 06 Dec
02 am HST
Mon 07 Dec
02 pm HST
Mon 07 Dec
02 am HST
Tue 08 Dec
02 pm HST
Tue 08 Dec
06 UTC
Fri 04 Dec
12 UTC
Fri 04 Dec
00 UTC
Sat 05 Dec
06 UTC
Sat 05 Dec
12 UTC
Sat 05 Dec
00 UTC
Sun 06 Dec
06 UTC
Sun 06 Dec
12 UTC
Sun 06 Dec
00 UTC
Mon 07 Dec
12 UTC
Mon 07 Dec
00 UTC
Tue 08 Dec
12 UTC
Tue 08 Dec
00 UTC
Wed 09 Dec
Cloud Cover (%) 10 to 30 0 to 20 10 to 30 10 to 30 10 to 30 10 to 30 0 to 20 0 to 20 0 to 20 0 to 20 0 to 20 0 to 10 0 to 20
Cloud Height (km) above sea level 6-9 5-9 5-7 5-6 5-6 5-6 5-6 5-6 5-6 5-6 N/A N/A N/A
Chance for Fog/Precip (%) 30/0 10/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0 0/0
PW (mm, summit upward) 4 to 6 4 to 6 4 to 8 4 to 6 4 to 6 4 to 8 4 to 6 4 to 6 4 to 8 4 to 6 3 to 5 2 to 4 1 to 2
Mean Seeing (arcsecs) 0.75 ± 0.2 0.7 ± 0.2 N/A 0.7 ± 0.2 0.8 ± 0.2 N/A 0.8 ± 0.2 0.9 ± 0.2 N/A 0.9 ± 0.2 N/A 0.7 ± 0.2 N/A
Summit Temp (°C) 1 0.5 5 0.5 0.5 5 0.5 0 5 -0.5 4 -1.5 4
Wind Dir/Speed (mph)
    Summit (615 hPa)
    19,000 ft (500 hPa)
    24,500 ft (400 hPa)
    31,000 ft (300 hPa)
    35,000 ft (250 hPa)
    40,000 ft (200 hPa)
    46,000 ft (150 hPa)
    54,000 ft (100 hPa)

SE/15 to 25

SE/15 to 25

ESE/10 to 20

ESE/15 to 25

ESE/15 to 25

SE/10 to 20

ESE/15 to 25

ESE/15 to 25

E/10 to 20

ENE/15 to 25

ENE/10 to 20

ENE/10 to 20

E/10 to 20


 Rise and Set times for the Sun and Moon
Night (HST)
Sun Set
Twilight End
Twilight Beg
Sun Rise
Moon Rise
Moon Set
Illum (%)
RA
Dec
Thu.Dec.03/Fri.Dec.04
17:52
19:00
5:25
6:33
20:39
N/A
84
8 08.4
23 37
Fri.Dec.04/Sat.Dec.05
17:52
19:00
5:25
6:34
21:36
N/A
76
9 03.8
21 10
Sat.Dec.05/Sun.Dec.06
17:52
19:01
5:26
6:34
22:35
N/A
66
9 57.8
17 35
Sun.Dec.06/Mon.Dec.07
17:52
19:01
5:26
6:35
23:33
N/A
56
10 50.4
13 02
Mon.Dec.07/Tue.Dec.08
17:53
19:01
5:27
6:35
0:31
N/A
45
11 41.9
7 45


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Friday 4 December 2020.
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