Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Wednesday 09 October 2019

Warnings
Fog and ice
Chance for convection and flurries/rain
Increasing winds

Cloud Cover and Precipitation Forecast
Extensive fog, ice, thick clouds/convection and/or flurries/rain are expected to plague the summit through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 6 C this afternoon, 1 C this evening and -1 C tomorrow morning. Winds will be from the SE at 15-30 mph for today, increasing to 25-40 mph through the night. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively, through the night.

Graphical Summary

Discussion
Deep moisture filling into the area, combined with weak instability to the NW are expected to erode the inversion and allow extensive fog, ice and/or periods of light rain/flurries to plague the summit for tonight and at least the opening half of tomorrow night. The moisture is set to quickly shift off toward the NNW through Friday, which will help rebuild the inversion near 7 thousand feet and ensure the summit remains dry and stable for the weekend. Extensive daytime clouds are expected over the next 2 days, then will taper on Friday and become minimal and short-lived over the weekend and early part of next week.

Patches of thick clouds are expected to fill in from the SE, contributing to extensive cloud cover or even overcast skies for tonight and the early part of tomorrow night. These clouds will push off toward the NW during the latter night, opening up skies for much of the weekend. However, there is a chance for isolated patches of light/thin cirrus in the area, particularly to the NW during the early part of the weekend.

Precipitable water is expected to exceed 4 mm for the next 2 nights, slip toward 1-1.25 mm for Friday night, then settle in near 2-3 mm for the following 2 nights.

Boundary layer turbulence combined with poor/wet summit conditions will result to bad seeing over the next 2 nights. The air mass is set to stabilize and dry out on Friday, but light/moderate boundary layer turbulence may limit seeing from improving beyond average-like values for the remainder of the forecast period.

A low developing to the far NW, combined with a new deep ridge forming to the NE will strengthen southerly flow over the Big Island, which will advect an old tropical wave through the area over the next 36 hours. Moisture and instability associated with wave (in addition to weak instability provided by the low), is expected to erode the inversion through the afternoon and allow the air mass near the Big Island to turn very saturated, contributing to inoperable summit conditions for tonight and at least the opening half of tomorrow night. There is also a relatively high risk that convection will move in from the SE and/or develop mainly along the SE slopes of the Big Island during this period. In addition, a tight wind gradient between the low and ridge will also increase winds toward 30-40 mph mainly for much of tomorrow. Conditions are set to improve as the moisture is drawn toward the low to the NW and the deep ridge to NE reinstill strong large-scale subsidence in the area through Friday. While this will help rebuild the inversion and ensure dry/stable summit conditions for the weekend, a relatively tight wind gradient will still prevail in the area during that time. This will keep winds near 20 mph, enough to stir up light boundary layer turbulence and keep seeing more average-like values (or slightly poorer over the weekend.

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
Wed 09 Oct
08 pm HST
Wed 09 Oct
02 am HST
Thu 10 Oct
02 pm HST
Thu 10 Oct
08 pm HST
Thu 10 Oct
02 am HST
Fri 11 Oct
02 pm HST
Fri 11 Oct
08 pm HST
Fri 11 Oct
02 am HST
Sat 12 Oct
02 pm HST
Sat 12 Oct
02 am HST
Sun 13 Oct
02 pm HST
Sun 13 Oct
02 am HST
Mon 14 Oct
00 UTC
Thu 10 Oct
06 UTC
Thu 10 Oct
12 UTC
Thu 10 Oct
00 UTC
Fri 11 Oct
06 UTC
Fri 11 Oct
12 UTC
Fri 11 Oct
00 UTC
Sat 12 Oct
06 UTC
Sat 12 Oct
12 UTC
Sat 12 Oct
00 UTC
Sun 13 Oct
12 UTC
Sun 13 Oct
00 UTC
Mon 14 Oct
12 UTC
Mon 14 Oct
Cloud Cover (%) 60 to 80 80 to 100 80 to 100 80 to 100 80 to 100 60 to 80 20 to 40 0 to 20 0 to 20 0 to 20 0 to 10 0 to 20 0 to 10
Cloud Height (km) above sea level 4-8 4-9 4-10 4-10 4-9 5-9 4-4.5 9.5-10 9.5-10 N/A N/A N/A N/A
Chance for Fog/Precip (%) 90/60 100/90 100/95 100/95 95/75 75/25 25/5 0/0 0/0 0/0 0/0 0/0 0/0
PW (mm, summit upward) 6 to 10 10 to 15 10 to 15 10 to 15 10 to 15 8 to 12 2 to 4 1 to 1.5 1 to 1.5 1 to 2 2 to 3 2 to 3 2 to 3
Mean Seeing (arcsecs) N/A 1.5 ± 0.5 1.5 ± 0.5 N/A 1.5 ± 0.5 1.0 ± 0.3 N/A 0.75 ± 0.15 0.7 ± 0.15 N/A 0.7 ± 0.15 N/A 0.7 ± 0.15
Summit Temp (°C) 6 1 -1 4 -1 0 8 3 3.5 10 4 9 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)

SE/15 to 30

SE/20 to 35

SE/25 to 40

SE/25 to 40

SE/25 to 40

SE/15 to 30

E/10 to 20

ENE/15 to 25

ENE/15 to 25

ESE/15 to 30

E/15 to 25

ENE/15 to 30

NE/15 to 25


 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.Oct.09/Thu.Oct.10
18:12
19:16
5:02
6:06
N/A
3:54
89
22 46.3
-12 33
Thu.Oct.10/Fri.Oct.11
18:11
19:16
5:02
6:06
N/A
4:43
94
23 31.9
-8 22
Fri.Oct.11/Sat.Oct.12
18:10
19:15
5:02
6:07
17:03
5:31
98
0 16.8
-3 50
Sat.Oct.12/Sun.Oct.13
18:10
19:14
5:03
6:07
17:38
6:19
100
1 01.5
0 52
Sun.Oct.13/Mon.Oct.14
18:09
19:13
5:03
6:07
18:12
7:09
100
1 46.9
5 35


Forecast issued by: Ryan Lyman
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Next update at 5 PM HST Wednesday 09 October (0300 UTC Thursday 10 October) 2019.
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