Latest Forecast for Mauna Kea Observatories
5 PM HST Thursday 06 December (0300 UTC Friday 7 December) 2018

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain clear, dry and stable through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 0.5 C, with light westerly winds for the night. Seeing will be near 0.55-0.6 arcseconds, while precipitable water is expected to be in the 1.5-2 mm range throughout the night.

Graphical Summary

Discussion
A well-defined tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear for tonight, but scattered mostly thin high clouds are expected to fill in from west and pass over/near the summit area between tomorrow afternoon and early Saturday evening. While these clouds will shift southward during the latter night, there is still a possibility that banding high clodus will set up to the south and be visible from the summit for Sunday and especially Monday night.

Precipitable water is expected to increase to 1.5-2 mm for tonight and 2-3 mm for tomorrow night, then settle back in near 0.6-0.8 mm range for the next 3 nights.

Calmer low-level skies with moderate turbulence in the free atmosphere will likely allow seeing to settle in near 0.55-0.6 arcseconds for the next 2 nights. There is a good chance for an increase in boundary layer turbulence and perhaps free atmospheric turbulence, while will contribute to poorer than average seeing for Saturday, Sunday and Monday night.

Little change since the morning forecast...The mid-level ridge is expected to briefly sag southward as a trough passes to the far north, then will rebound northward as a new ridge fills in from the west over the weekend. Nonetheless, large-scale subsidence will prevail in the area, which will help maintain a well-defined inversion near 7-8 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Winds will respond to the southward progression of the ridge, which will significantly reduce boundary layer turbulence and likely allow seeing to improve toward 0.5-0.6 arcseconds over the next 2 nights. Mid-level moisture embedded in the ridge is expected to increase PW toward 1.5-2.5 mm during this time. Seeing and PW are set to trend in opposite directions (degrading and decreasing, respectively) as the ridge shifts northward over the weekend. Very dry air along the southern portion of the ridge, should help PW settle back in near 0.6-0.8 arcseconds for Saturday, Sunday and Monday night. However, deep somewhat stronger easterly flow along this edge of the ridge will likely increase boundary layer turbulence again, and contribute to poorer than average seeing during that time.

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 06 Dec
02 am HST
Fri 07 Dec
02 pm HST
Fri 07 Dec
08 pm HST
Fri 07 Dec
02 am HST
Sat 08 Dec
02 pm HST
Sat 08 Dec
08 pm HST
Sat 08 Dec
02 am HST
Sun 09 Dec
02 pm HST
Sun 09 Dec
02 am HST
Mon 10 Dec
02 pm HST
Mon 10 Dec
02 am HST
Tue 11 Dec
02 pm HST
Tue 11 Dec
06 UTC
Fri 07 Dec
12 UTC
Fri 07 Dec
00 UTC
Sat 08 Dec
06 UTC
Sat 08 Dec
12 UTC
Sat 08 Dec
00 UTC
Sun 09 Dec
06 UTC
Sun 09 Dec
12 UTC
Sun 09 Dec
00 UTC
Mon 10 Dec
12 UTC
Mon 10 Dec
00 UTC
Tue 11 Dec
12 UTC
Tue 11 Dec
00 UTC
Wed 12 Dec
Cloud Cover (%) 0 to 5 0 to 5 0 to 20 10 to 30 20 to 40 10 to 30 0 to 20 0 to 5 0 to 20 0 to 20 0 to 20 10 to 30 0 to 20
Cloud Height (km) above sea level N/A N/A 9.5-10 9.5-10 9-10 8-9 8.5-9 N/A N/A 9.5-10 9-10 9-10 9-10
Chance for Fog/Precip (%) 0/0 0/0 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) 1.25 to 1.75 1.25 to 1.75 2 to 4 2 to 3 2 to 3 1 to 2 0.6 to 0.8 0.6 to 0.8 0.8 to 1.2 0.6 to 0.9 0.8 to 1.2 0.6 to 0.9 0.8 to 1.2
Mean Seeing (arcsecs) 0.6 ± 0.1 0.55 ± 0.1 N/A 0.55 ± 0.1 0.6 ± 0.1 N/A 0.8 ± 0.2 0.8 ± 0.2 N/A 0.75 ± 0.2 N/A 0.7 ± 0.15 N/A
Summit Temp (°C) 0.5 0.5 5 0 -0.5 4.5 -0.5 -0.5 5 1 5 1 6
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)

WNW/0 to 10

WSW/0 to 10

WNW/5 to 15

NW/5 to 15

N/5 to 15

NE/15 to 30

NE/15 to 30

ENE/15 to 30

ENE/15 to 30

ENE/15 to 30

ENE/15 to 30

E/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.06/Fri.Dec.07
17:52
19:01
5:26
6:34
6:55
17:48
0
17 02.6
-19 24
Fri.Dec.07/Sat.Dec.08
17:52
19:01
5:26
6:35
7:48
18:36
1
17 54.5
-20 58
Sat.Dec.08/Sun.Dec.09
17:53
19:01
5:27
6:36
N/A
19:25
4
18 46.4
-21 33
Sun.Dec.09/Mon.Dec.10
17:53
19:02
5:28
6:36
N/A
20:15
9
19 37.6
-21 08
Mon.Dec.10/Tue.Dec.11
17:53
19:02
5:28
6:37
N/A
21:06
15
20 27.8
-19 48


Forecast issued by: Ryan Lyman
Contact Us - (808) 932-2323
Hours: Mon-Fri 8 AM - 5 PM HST (1800-0300 UTC)

For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.

Next update at 10 AM HST (2000 UTC) Friday 7 December 2018.
Please call or email to be placed on the Mauna Kea Weather Bulletin email list.