Latest Forecast for Mauna Kea Observatories
4 PM HST Wednesday 05 December (0300 UTC Thursday 6 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 C this evening and -0.5 C tomorrow morning. Winds will be from the SE at 10-20 mph, while seeing will be less than average at first, improving as the night progresses (0.6-0.7) arcsec. Precipitable water is expected to linger close to 1 mm, possibly deeping below, through the night.

Graphical Summary

Discussion
A well-defined inversion will continue to cap the little supply of low-level moisture at or below 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.

Summit skies will be predominantly clear through tonight and most of tomorrow. Some mid/high clouds will be visible along the northern horizon on Thursday night while sweeping quickly from the northwest to the northeast through Friday. Clear skies will follow for the weekend nights.

Precipitable water is expected to linger close to 1 mm tonight and to increase and linger close to 2 mm tomorrow evening and night, to then further increase and possible reach 3 mm on Friday night. It will quickly drop again on Saturday and will be close to 1 mm, with possible dips below, on Saturday and Sunday night.

Observing conditions will start to improve tonight although some residual boundary layer turbulence is likely to still result in average to less than average seeing, particularly during the first half of the night, improving as the night progresses. Observing conditions will further improve on Thursday and Friday night as winds at the surface taper, but minor moisture in the airmasses and some passing high clouds might minimally interfere then. Another round of boundary layer turbulence is exepcted instead over the weekend nights as winds at the surface will increase again in response to tightening pressure gradients in the area.

Not change since the morning forecast... The current weather scenario is dominated by a high pressure centered Northeast of the islands in the wake of a weakening front now Southeast of the State. The high pressure system is expected to sag southward in response to a trough passing far to the north through Thursday, which is likely to advect over some minimal cloud cover and moisture. Nonetheless, large-scale subsidence will still prevail and a new ridge is set to build in from the west over the weekend. As a result, this subsidence will easily maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. As winds at the surface decrease through today and tonight, seeing will improve accordingly through Friday, but some minor cloudiness and increase in PW could possibly degrade it or make it variable then. Drier and clearer conditions are expected for the weekend nights but surface winds might increase again then as surface pressure tighten and observing conditions could degrade some then.

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
Wed 05 Dec
02 am HST
Thu 06 Dec
02 pm HST
Thu 06 Dec
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
02 am HST
Sun 09 Dec
02 pm HST
Sun 09 Dec
02 am HST
Mon 10 Dec
02 pm HST
Mon 10 Dec
06 UTC
Thu 06 Dec
12 UTC
Thu 06 Dec
00 UTC
Fri 07 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
12 UTC
Sun 09 Dec
00 UTC
Mon 10 Dec
12 UTC
Mon 10 Dec
00 UTC
Tue 11 Dec
Cloud Cover (%) 0 to 5 0 to 5 0 to 10 0 to 20 10 to 30 10 to 30 10 to 30 0 to 20 0 to 10 0 to 10 0 to 10 0 to 10 0 to 10
Cloud Height (km) above sea level N/A N/A N/A 9-10 7-8 7-8 8-9 N/A N/A N/A N/A N/A N/A
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) 0.8 to 1.2 0.9 to 1.3 1.5 to 2.5 1.5 to 2 1.75 to 2.25 3.5 to 4.5 3 to 4 2.5 to 3.5 1 to 1.5 0.9 to 1.2 1 to 1.5 0.8 to 1.2 0.8 to 1.2
Mean Seeing (arcsecs) 1 ± 0.2 0.65 ± 0.15 N/A 0.6 ± 0.15 0.55 ± 0.15 N/A 0.55 ± 0.15 0.55 ± 0.15 N/A 0.9 ± 0.2 N/A 0.7 ± 0.2 N/A
Summit Temp (°C) 0 -0.5 4 2 0.5 4.5 0.5 0 3.5 -0.5 4 0.5 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)

ESE/10 to 20

SE/10 to 20

S/5 to 15

W/0 to 10

WSW/5 to 15

WNW/5 to 15

WNW/5 to 15

NW/5 to 15

NE/10 to 20

ENE/20 to 35

ENE/20 to 30

ENE/20 to 30

ENE/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
Wed.Dec.05/Thu.Dec.06
17:52
19:00
5:25
6:34
6:01
17:03
1
16 11.1
-16 53
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


Forecast issued by: Tiziana Cherubini
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Next update at 10 AM HST (2000 UTC) Thursday 6 December 2018.
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