Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Thursday 29 October 2020

Warnings
Strong winds
Fog, ice and high humidity
Chance for convection and flurries

Cloud Cover and Precipitation Forecast
There is a high risk for periods of fog, ice and high humidity throughout the night. A narrow band of thin cirrus will continue to pass over/near the summit through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this afternoon and -2 C for the night. Winds will be from the WSW at 30-45 mph, while seeing will exceed 1 arcsecond. Precipitable water is expected to be in the 2-3 mm range for the night.

Graphical Summary

Discussion
While the air mass will continue to gradually dry out, persistent instability will prohibit the inversion from restrengthening and will likely allow for more periods of fog, high humidity and ice at the summit probably through the weekend (the odds will slowly subside after tonight); nighttime precipitation is unlikely. There is a good chance that the atmosphere will stabilize and the inversion will restrengthen on Monday, which will significantly decrease the stakes on moisture at the summit for Monday night. Extensive daytime clouds and afternoon convection along the Big Island slopes are possible through Sunday, then will taper for the early part of next week.

A narrow band of thin cirrus will continue to fill out of the WSW and pass over/near the summit for tonight, then sag southward for tomorrow night. More organized widespread high clouds are expected to set up along the SE skies for the latter part of Friday night and especially Saturday night. These clouds will shift further eastward on Sunday, leaving clear skies for that night, but may spread back toward the NW and shift over the summit for Monday night.

Precipitable water is expected to linger primarily in the 2-3 mm range through the next 5 nights.

A mixture of boundary layer turbulence, free atmospheric turbulence and/or persistent instability will contribute to poor/bad seeing for the next 3-4 nights. There is a good chance that seeing will dramatically improve as the atmosphere stabilizes and mid-level flow tapers for Monday night.

The low to the north will north will remain quasi-stationary/steady for another 24 hours, then will begin to lift off toward the NE as a short-wave trough digs in from the NW over the weekend. While the bulk of the moisture is expected to slide to the north and/or flare up to the east of the Big Island, persistent instability associated with both the low/trough will keep the inversion rather weak/indistinct through much of the weekend. This could allow for more periods of fog, ice and high humidity at the summit over the next 3-4 nights. While nighttime precipitation is unlikely, there is still a chance that isolated convection will develop in the area, which could deposit light flurries at the summit at virtually anytime. The odds will favor the afternoon hours as the land heats up and helps fire off convection along the Big Island slopes. There is a chance that stronger than normal winds above 10 thousand feet (associated with a tight wind gradient along the southern flank of the low/trough) will help promote additional mixing and reduce the risk for afternoon convection a bit. On the flip side, these winds will stir up significant boundary layer turbulence and contribute to bad seeing over the next 3 nights. Winds are set to subside as the incoming trough lifts off toward the NE on Sunday, but the inversion may not begin to take shape until the ridge rebounds and strengthens to the north early next week.

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
02 pm HST
Thu 29 Oct
08 pm HST
Thu 29 Oct
02 am HST
Fri 30 Oct
02 pm HST
Fri 30 Oct
08 pm HST
Fri 30 Oct
02 am HST
Sat 31 Oct
02 pm HST
Sat 31 Oct
08 pm HST
Sat 31 Oct
02 am HST
Sun 01 Nov
02 pm HST
Sun 01 Nov
02 am HST
Mon 02 Nov
02 pm HST
Mon 02 Nov
02 am HST
Tue 03 Nov
00 UTC
Fri 30 Oct
06 UTC
Fri 30 Oct
12 UTC
Fri 30 Oct
00 UTC
Sat 31 Oct
06 UTC
Sat 31 Oct
12 UTC
Sat 31 Oct
00 UTC
Sun 01 Nov
06 UTC
Sun 01 Nov
12 UTC
Sun 01 Nov
00 UTC
Mon 02 Nov
12 UTC
Mon 02 Nov
00 UTC
Tue 03 Nov
12 UTC
Tue 03 Nov
Cloud Cover (%) 60 to 80 20 to 40 20 to 40 60 to 80 10 to 30 0 to 20 60 to 80 10 to 30 10 to 30 60 to 80 0 to 20 40 to 60 40 to 60
Cloud Height (km) above sea level 4-10 8-10 9-10 4-10 9-10 9.5-10 4-10 9.5-10 9.5-10 4-8 N/A 9-10 9-10
Chance for Fog/Precip (%) 95/60 90/30 75/25 95/60 75/25 60/15 90/50 60/10 50/10 75/40 40/5 25/5 0/0
PW (mm, summit upward) 4 to 8 2 to 3 2 to 3 4 to 8 2 to 3 2 to 3 4 to 8 2.5 to 3.5 2.5 to 3.5 4 to 8 2 to 3 3 to 6 2 to 3
Mean Seeing (arcsecs) N/A 1.5 ± 0.5 1.5 ± 0.5 N/A 1.5 ± 0.5 1.5 ± 0.5 N/A 1.3 ± 0.5 1.1 ± 0.4 N/A 0.85 ± 0.25 N/A 0.55 ± 0.15
Summit Temp (°C) 1 -2 -2 3 -1 -1.5 1 -2 -2.5 4 1 4 1
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)

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/30 to 45

WSW/25 to 40

W/20 to 35

W/10 to 20

SSW/5 to 15

S/5 to 15

SE/5 to 15


 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.Oct.29/Fri.Oct.30
17:58
19:03
5:08
6:13
16:56
5:50
99
1 36.2
5 16
Fri.Oct.30/Sat.Oct.31
17:57
19:03
5:08
6:14
17:29
6:39
100
2 20.6
10 03
Sat.Oct.31/Sun.Nov.01
17:57
19:02
5:09
6:14
18:04
7:29
99
3 06.5
14 29
Sun.Nov.01/Mon.Nov.02
17:56
19:02
5:09
6:15
18:41
N/A
97
3 54.3
18 21
Mon.Nov.02/Tue.Nov.03
17:56
19:02
5:09
6:15
19:22
N/A
93
4 44.3
21 27


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Thursday 29 October (0300 UTC Friday 30 October) 2020.
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