Latest Forecast for Mauna Kea Observatories
5 PM HST Wednesday 13 June (0300 UTC Thursday 14 June) 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 1.5 C, with light southerly winds and seeing near 0.5-0.6 arcseconds. Precipitable water is expected to be in the 1-1.5 mm range for the first half of the night and 1.25-1.75 mm range for the second half.

Graphical Summary

Discussion
The tradewind inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived for the remainder of the week, but could pick up for Monday.

Clear skies are expected for tonight, but there is a chance that stray patches of thin cirrus will occasionally drop down from the north and pass over/near the summit area over the next 4 nights. Still, cloud cover should rarely exceed 20% for any prolong periods during those nights.

Precipitable water is expected to mostly hang near 1.2-1.3 mm over the next 2 nights, trend toward 2 mm through Friday night and likely exceed 4 mm for Saturday and Sunday night.

Relatively calm skies will prevail in the free atmosphere as fairly laminar flow persists aloft, allowing for better than average seeing through most of Friday night. However, there is a possibility for periods of variability and/or degradation in seeing should summit-level winds die completely, particularly toward the end of tonight and for tomorrow night. An increase in boundary layer turbulence could contribute to a more significant deterioration in seeing for Saturday and especially Sunday night.

Subtle favorable changes have been made to the PW forecast....An upper-level trough passing overhead will not affect the stability of the atmosphere and will eventually give way to a deep ridge building in from the west late tonight, which will persist to the north into the early part of next week. Nonetheless, large-scale subsidence will persist in the area, which will help maintain a fairly well-defined inversion at or below 9 thousand feet and ensure the summit remains dry and stable throughout the forecast period. In addition, the deep ridge will prevent the sub-tropical jet from loitering in the area, allowing relatively calm skies to prevail in the free atmosphere probably throughout the forecast period. This combined with fairly laminar/weak flow aloft, will help minimize turbulence and likely permit for better than average seeing for at least the next 3 nights. However, there is a possiblity periods of variability and/or degradation in seeing should summit-level winds die completely, particularly toward the end of tonight and for tomorrow night. While a slight increase in winds should help mix the air mass up a bit and stabilize seeing for Friday night, winds may continue to climb and eventually stir up boundary layer turbulence, which could further degrade seeing for Saturday and especially Sunday night. There is a possibility mid-moisture revolving around a relatively deep upper-level low to the east will increase PW and RH late Sunday night and into the early part of next week.

Astronomical Observing Quality Guidance
05 pm HST Wednesday 13 June (03 UTC Thursday 14 June)CN2
08 pm HST Wednesday 13 June (06 UTC Thursday 14 June)CN2
11 pm HST Wednesday 13 June (09 UTC Thursday 14 June)CN2
02 am HST Thursday 14 June (12 UTC Thursday 14 June)CN2
05 am HST Thursday 14 June (15 UTC Thursday 14 June)CN2
08 am HST Thursday 14 June (18 UTC Thursday 14 June)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
08 pm HST
Wed 13 Jun
02 am HST
Thu 14 Jun
02 pm HST
Thu 14 Jun
08 pm HST
Thu 14 Jun
02 am HST
Fri 15 Jun
02 pm HST
Fri 15 Jun
08 pm HST
Fri 15 Jun
02 am HST
Sat 16 Jun
02 pm HST
Sat 16 Jun
02 am HST
Sun 17 Jun
02 pm HST
Sun 17 Jun
02 am HST
Mon 18 Jun
02 pm HST
Mon 18 Jun
06 UTC
Thu 14 Jun
12 UTC
Thu 14 Jun
00 UTC
Fri 15 Jun
06 UTC
Fri 15 Jun
12 UTC
Fri 15 Jun
00 UTC
Sat 16 Jun
06 UTC
Sat 16 Jun
12 UTC
Sat 16 Jun
00 UTC
Sun 17 Jun
12 UTC
Sun 17 Jun
00 UTC
Mon 18 Jun
12 UTC
Mon 18 Jun
00 UTC
Tue 19 Jun
Cloud Cover (%) 0 to 5 0 to 5 0 to 20 0 to 20 0 to 20 0 to 20 0 to 20 0 to 20 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 N/A 9.5-10 9.5-10 9.5-10 9.5-10 9.5-10 9.5-10 9.5-10 9.5-10 9-10 9.5-10
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 25/5
PW (mm, summit upward) 1 to 1.5 1 to 1.5 1 to 1.5 1 to 1.5 1 to 1.5 1 to 1.5 1.25 to 1.75 1.5 to 2 2 to 4 3 to 5 4 to 8 6 to 10 8 to 12
Mean Seeing (arcsecs) 0.55 ± 0.1 0.55 ± 0.15 N/A 0.6 ± 0.15 0.6 ± 0.15 N/A 0.55 ± 0.1 0.6 ± 0.1 N/A 0.65 ± 0.15 N/A 0.8 ± 0.2 N/A
Summit Temp (°C) 1.5 1.5 7.5 2.5 2.5 8 3.5 3.5 9 4 9 3 7
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)

S/5 to 15

S/5 to 15

WSW/0 to 10

NE/0 to 10

ENE/0 to 10

NE/0 to 10

NNE/5 to 15

ENE/5 to 15

NNE/10 to 20

NNE/10 to 20

NNE/20 to 35

NNE/20 to 35

NE/25 to 40


 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
Wed.Jun.13/Thu.Jun.14
19:11
20:25
4:19
5:33
6:35
19:26
1
6 06.1
19 50
Thu.Jun.14/Fri.Jun.15
19:12
20:26
4:19
5:33
N/A
20:30
4
7 09.6
20 03
Fri.Jun.15/Sat.Jun.16
19:12
20:26
4:19
5:33
N/A
21:31
10
8 12.4
18 49
Sat.Jun.16/Sun.Jun.17
19:12
20:26
4:19
5:33
N/A
22:26
18
9 13.1
16 19
Sun.Jun.17/Mon.Jun.18
19:13
20:27
4:19
5:33
N/A
23:16
27
10 10.9
12 48


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Thursday 14 June 2018.
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