Latest Forecast for Mauna Kea Observatories
5 PM HST Tuesday 23 February (0300 UTC Wednesday 24 February) 2021

Warnings
None

Cloud Cover and Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for light cirrus along the far northern skies mainly toward the second half of the night.

Summary of Key Meteorological Variables
Summit temperatures will be near -1.5 C this evening and -2 C tomorrow morning. Winds will be from the ENE at 5-15 mph for the first half of the night, increasing to 10-20 mph for the second half. Seeing will be near 0.5-0.6 arcseconds, while precipitable water is expected to be in the 1-1.2 mm range for the night.

Graphical Summary

Discussion
A fairly well-defined inversion will continue to cap low-level moisture near 8-9 thousand feet and ensure a dry/stable summit-level air mass through at least late Wednesday evening. There is a chance that building instability will begin to erode the inversion, deepen the marine layer and increase the risk for fog, ice and flurries at the summit for Thursday night. There is a small possibility that the inversion will recover a bit and decrease this risk for Friday night, but fresh instability could negate that recovery and increase this risk again for Saturday night. There is also a chance for isolated convection in the area mainly for Thursday and on Saturday. Daytime clouds will be minimal and short-lived through Wednesday, but will likely turn quite extensive for the remainder of the forecast period.

Skies overhead will remain predominately clear for the next 2 nights, but there is a possibility for light high clouds along the far northern skies during that time. Thicker patches of clouds may begin to develop in the area on Thursday and could contribute to periods of extensive cloud cover for that night. Some clearing is possible for Friday night, but more patches of thick clouds may flare up in the area again for Saturday night.

Precipitable water is expected to linger near 1-1.2 mm for tonight, slip toward 0.8-1 mm for tomorrow night, then jump toward 4+ mm for Thursday, Friday and Saturday night.

Calmer skies with deep/laminar westerly flow in the free atmosphere should allow seeing to settle in near 0.5-0.55 arcseconds over the next 2 nights. An increase in instability, available moisture and periods of free atmospheric turbulence will contribute to poor/bad seeing for Thursday, Friday and Saturday night.

Little change since the morning forecast...The mid/low-level ridge will continue to sit just north of the state and promote relatively strong subsidence in the area before rebounding northward in response to an upper-level trough passing through beginning late Wednesday night. Nevertheless, this subsidence will help maintain a fairly well-defined inversion near 8-9 thousand feet and ensure a dry/stable summit-level air mass through at least Wednesday evening. Upper-level diffluence and cold air will begin to builed into the area as the trough deepens over the state early Thursday morning. This will help erode the inversion and deep the marine/low-level cloud layer, essentially saturating the air mass below 18 thousand feet for that night. There is a chance that upper-level convergence will fill in over the Big Island as the trough axis slips eastward, perhaps allowing the air mass to briefly stabilize a bit for Friday night. However, another larger/sharper trough may quickly drift in from the west and destabilize the air mass again, effectively eroding the inversion and saturating the lower half of the atmospher probably for the remainder of the weekend. As a result, there is a high probability that extensive fog, ice and/or flurries will plague the summit for especially Thursday and Saturday night; there is a slight possibility for an improvement in conditions for Friday night. There is also a chance for the development of isolated convection in the area, particularly along the eastern as well as southeastern coasts, and perhaps within the Big Island plume to the west at virtually anytime after Wednesday night.

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
Tue 23 Feb
02 am HST
Wed 24 Feb
02 pm HST
Wed 24 Feb
08 pm HST
Wed 24 Feb
02 am HST
Thu 25 Feb
02 pm HST
Thu 25 Feb
08 pm HST
Thu 25 Feb
02 am HST
Fri 26 Feb
02 pm HST
Fri 26 Feb
02 am HST
Sat 27 Feb
02 pm HST
Sat 27 Feb
02 am HST
Sun 28 Feb
02 pm HST
Sun 28 Feb
06 UTC
Wed 24 Feb
12 UTC
Wed 24 Feb
00 UTC
Thu 25 Feb
06 UTC
Thu 25 Feb
12 UTC
Thu 25 Feb
00 UTC
Fri 26 Feb
06 UTC
Fri 26 Feb
12 UTC
Fri 26 Feb
00 UTC
Sat 27 Feb
12 UTC
Sat 27 Feb
00 UTC
Sun 28 Feb
12 UTC
Sun 28 Feb
00 UTC
Mon 01 Mar
Cloud Cover (%) 0 to 10 0 to 20 0 to 20 0 to 20 0 to 20 60 to 80 60 to 80 60 to 80 70 to 90 20 to 40 60 to 80 60 to 80 70 to 90
Cloud Height (km) above sea level N/A N/A N/A N/A N/A 4-8 4-8 4-8 4-5 4-5 4-8 4-8 4-8
Chance for Fog/Precip (%) 0/0 0/0 0/0 0/0 30/5 75/40 90/50 90/50 90/40 65/25 90/60 90/65 90/60
PW (mm, summit upward) 1 to 1.2 1 to 1.2 0.8 to 1.2 0.8 to 1 0.8 to 1 4 to 8 3.5 to 4.5 3.5 to 4.5 4 to 8 3 to 5 4 to 8 4 to 8 4 to 8
Mean Seeing (arcsecs) 0.6 ± 0.1 0.5 ± 0.1 N/A 0.5 ± 0.1 0.55 ± 0.15 N/A 0.9 ± 0.2 1.0 ± 0.3 N/A 0.9 ± 0.3 N/A 1.0 ± 0.3 N/A
Summit Temp (°C) -1.5 -2 3 -2.5 -3 -1 -4 -5 0 -4.5 -2 -5 -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)

ENE/5 to 15

ENE/10 to 20

E/10 to 20

E/10 to 20

ESE/10 to 20

ESE/10 to 20

ESE/15 to 25

E/15 to 25

S/5 to 15

SW/5 to 15

SW/5 to 15

WNW/0 to 10

NE/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
Tue.Feb.23/Wed.Feb.24
18:34
19:39
5:31
6:36
N/A
5:06
89
8 04.5
23 45
Wed.Feb.24/Thu.Feb.25
18:34
19:39
5:31
6:35
N/A
5:56
95
9 02.1
21 10
Thu.Feb.25/Fri.Feb.26
18:35
19:39
5:30
6:34
17:04
6:42
99
9 59.0
17 17
Fri.Feb.26/Sat.Feb.27
18:35
19:40
5:29
6:34
18:05
7:25
100
10 54.5
12 18
Sat.Feb.27/Sun.Feb.28
18:35
19:40
5:29
6:33
19:05
N/A
98
11 48.8
6 32


Forecast issued by: Ryan Lyman
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Next update at 10 AM HST (2000 UTC) Wednesday 24 February 2021.
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