Latest Forecast for Mauna Kea Observatories
5 PM HST Wednesday 15 November (0300 UTC Thursday 16 November) 2017

Warnings
None

Cloud Cover and Precipitation Forecast
There is a small chance for evening fog/ice; precipitation is not expected and skies will remain clear for the night.

Summary of Key Meteorological Variables
Summit temperatures will be near -0.5 C this evening and -1 C tomorrow morning. Winds will be from the WNW at 5-15 mph, with seeing near 0.7-0.75 arcseconds. Precipitable water is expected to linger in the 3-4 mm range for the night.

Graphical Summary

Discussion
While the tradewind inversion will continue to restrengthen near 8-10 thousand feet, there is a small possibility for fog/ice early this evening; precipitation is not expected and relatively dry/stable air mass will prevail for the remainder of the forecast period. Daytime clouds will become minimal and short-lived for tomorrow, but may pick up again on Friday and over the weekend, then taper for the early part of next week.

The banding high clouds to the south are expected to retreat back to the tropics, leaving clear skies for tonight. However, another band may briefly set up along the southern skies for tomorrow night, then also slip off toward the SE on Friday. Isolated patches of high clouds are set to spread in from the west on Friday and Saturday night, while another band of clouds develop along the SE skies during the second half of the weekend. The latter is not expected to have much of an impact on cloud cover.

Precipitable water is expected to slip into the 3-4 mm range for tonight, 2.5-3.5 mm range for tomorrow night, settle in near 2 mm for Friday and Saturday night, the perhaps slip toward 1 mm through Sunday night.

While winds are set to diminish for the next 2 nights, patches of mid/upper-level turbulence moving through will likely contribute to poorer than average seeing for tonight. Calmer skies should allow seeing to improve toward slightly better than average values for tomorrow night, but significant boundary layer turbulence will likely result in poor/bad seeing for the following 3 nights.

Changes have been made to the PW forecast......A quasi-stationary large-scale trough will linger to the NE of the state and prohibit the eastward advancement of the mid/low-level ridge to the NW probably well into next week. Fortunately, the state will remain on the more stable side of the trough, while an embedded short-wave trough shifts further eastward, allowing the ridge to expand a bit over the next 12-24 hours. This will help further stabilize/dry out the air mass, rebuild the inversion near 8-10 thousand feet and ensure the summit steers free of fog/precipitation throughout most of tonight (though there is a very small risk for early evening fog/ice) and probably the remainder of the forecast period. It no longer appears that PW will dip below 3 mm as a band of mid-level moisture persists over or just south of the Big Island through the night, then slowly detrains into the surrounding atmosphere over the remainder of the week. Seeing will also not benefit from patches of turbulence moving through the area in the wake of the SWT for tonight. There is a chance for an improvement in seeing as this turbulence shifts off toward south for tomorrow night. However, another SWT is expected to reinforce/expand the large-scale trough to the NE over much of the weekend. While this probably won't have much of an impact of the stability of the atmosphere, it could significantly increase in summit-level winds, which will likely stir up boundary layer turbulence and contribute to poor/bad seeing during that time.

Astronomical Observing Quality Guidance
05 pm HST Wednesday 15 November (03 UTC Thursday 16 November)CN2
08 pm HST Wednesday 15 November (06 UTC Thursday 16 November)CN2
11 pm HST Wednesday 15 November (09 UTC Thursday 16 November)CN2
02 am HST Thursday 16 November (12 UTC Thursday 16 November)CN2
05 am HST Thursday 16 November (15 UTC Thursday 16 November)CN2
08 am HST Thursday 16 November (18 UTC Thursday 16 November)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
08 pm HST
Wed 15 Nov
02 am HST
Thu 16 Nov
02 pm HST
Thu 16 Nov
08 pm HST
Thu 16 Nov
02 am HST
Fri 17 Nov
02 pm HST
Fri 17 Nov
08 pm HST
Fri 17 Nov
02 am HST
Sat 18 Nov
02 pm HST
Sat 18 Nov
02 am HST
Sun 19 Nov
02 pm HST
Sun 19 Nov
02 am HST
Mon 20 Nov
02 pm HST
Mon 20 Nov
06 UTC
Thu 16 Nov
12 UTC
Thu 16 Nov
00 UTC
Fri 17 Nov
06 UTC
Fri 17 Nov
12 UTC
Fri 17 Nov
00 UTC
Sat 18 Nov
06 UTC
Sat 18 Nov
12 UTC
Sat 18 Nov
00 UTC
Sun 19 Nov
12 UTC
Sun 19 Nov
00 UTC
Mon 20 Nov
12 UTC
Mon 20 Nov
00 UTC
Tue 21 Nov
Cloud Cover (%) 0 to 5 0 to 5 0 to 20 10 to 30 10 to 30 0 to 20 0 to 20 10 to 30 10 to 30 0 to 20 0 to 20 0 to 20 0 to 20
Cloud Height (km) above sea level N/A N/A 9.5-10 9.5-10 9.5-10 N/A 9.5-10 9.5-10 9.5-10 N/A N/A N/A N/A
Chance for Fog/Precip (%) 20/0 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) 3 to 4 3 to 4 3 to 4 2.5 to 3.5 2 to 3 2 to 3 1.5 to 2.5 1.5 to 2.5 2 to 4 1.5 to 2.5 1 to 2 1 to 2 1 to 2
Mean Seeing (arcsecs) 0.75 ± 0.15 0.7 ± 0.1 N/A 0.55 ± 0.1 0.6 ± 0.15 N/A 0.9 ± 0.2 1.2 ± 0.3 N/A 1.5 ± 0.5 N/A 1.2 ± 0.3 N/A
Summit Temp (°C) -0.5 -1 4 -1 -1.5 2 -2 -3 1 -4 1 -4 3
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/5 to 15

WNW/5 to 15

WNW/5 to 15

W/10 to 20

W/10 to 20

W/20 to 35

WSW/25 to 40

WSW/35 to 50

WSW/40 to 60

WSW/40 to 60

WSW/40 to 60

W/30 to 45

W/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.Nov.15/Thu.Nov.16
17:52
18:59
5:15
6:22
4:53
16:27
4
14 02.8
-7 32
Thu.Nov.16/Fri.Nov.17
17:51
18:58
5:15
6:23
5:44
17:06
1
14 49.8
-11 12
Fri.Nov.17/Sat.Nov.18
17:51
18:58
5:16
6:23
6:34
17:46
0
15 37.3
-14 23
Sat.Nov.18/Sun.Nov.19
17:51
18:58
5:16
6:24
7:25
18:28
1
16 25.4
-16 57
Sun.Nov.19/Mon.Nov.20
17:51
18:58
5:17
6:24
N/A
19:12
3
17 14.3
-18 47


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Thursday 16 November 2017.
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