Latest Forecast for Mauna Kea Observatories
5 PM HST Tuesday 12 January (0300 UTC Wednesday 13 January) 2021

Warnings
Chance for fog and ice

Cloud Cover and Precipitation Forecast
There is a high risk for periods of fog, ice and flurries as summit-level humidity increase 80% or more for the night. Patches of summit/low-level clouds are also expected to spread in from the SE for the night.

Summary of Key Meteorological Variables
Summit temperatures will be near -0.5 C this evening and -1.5 C tomorrow morning. Winds will be from the SSW at 5-15 mph, with seeing near 0.8-0.9 arcseconds. Precipitable water is expected to exceed 4 mm for the night.

Graphical Summary

Discussion
An influx of moisture below 15 thousand feet will continue to erode the inversion, raising summit-level humidity to 80% or more and signficantly increasing the risk for periods of fog, ice and light flurries at the summit for the next 2 nights. The air mass is expected to gradually dry out beginning late Thursday morning, which will help to diminish this risk for that night and eventually allow dry/stable conditions to return to the summit as the inversion becomes well-established near 7-8 thousand feet for Friday and Saturday night. Daytime clouds are expected to turn extensive with the possibility for afternoon convection for tomorrow, then taper for Thursday and become minimal and short-lived for Friday and over the weekend.

Patches of summit/low-level clouds are expected to spread in from the SE and linger in the area through tomorrow night. These clouds will push back off toward the east and disperse through Thursday, leaving predominately clear skies for the remainder of the forecast period.

Precipitable water is expected to linger near or exceed 4 mm through Thursday night, trend toward 3 mm for Friday night and probably 2 mm for Saturday night.

An increase in moisture and an elevated/indistinct inversion will likely contribute to poor/variable seeing for the next 2 nights. Seeing is set to improve as the air mass dries out through Thursday, and eventually settle in near 0.55-0.6 arcseconds as moderate turbulence prevails in the free atmosphere as early as the second half of Thursday night as well as Friday and Saturday night.

Little change since the morning forecast...The mid/low-level ridge will continue to move off to the east as a fast-moving developing trough/low develops to the NW digs toward the state. SE winds brodering the incoming trough and departing ridge will begin to advect mid/low-level moisture to the south into the area over the next 3-6 hours. This moisture combined with instability associated with the incoming low/trough will erode the inversion probably by this evening and allow the atmosphere below 15-16 thousand feet to become mostly saturated through Thursday morning. This will significantly raise the stakes on extensive fog, high humidity, ice and light flurries at the summit over the next 2 nights. While the bulk of the dynamic instability associated with the low/trough will pass to the north, there is an chance that calmer winds at and below the summit will limit mixing and allow for afternoon convection along the Big Island sloes mainly for tomorrow. The lack of winds will also slow the detrainment process, once the trough/low passes to the NE on Thursday, which could allow for more period of fog, high humidity and light ice at the summit for that night. The westerly trough is set to dip further southward on Friday, which will help to further dry out the air mass by that night. In addition, the mid/low-level ridge is projected to return over the state by that evening, re-establish strong widespread subsidence in the area and rebuild the inversion near 7-8 thousand feet 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
08 pm HST
Tue 12 Jan
02 am HST
Wed 13 Jan
02 pm HST
Wed 13 Jan
08 pm HST
Wed 13 Jan
02 am HST
Thu 14 Jan
02 pm HST
Thu 14 Jan
08 pm HST
Thu 14 Jan
02 am HST
Fri 15 Jan
02 pm HST
Fri 15 Jan
02 am HST
Sat 16 Jan
02 pm HST
Sat 16 Jan
02 am HST
Sun 17 Jan
02 pm HST
Sun 17 Jan
06 UTC
Wed 13 Jan
12 UTC
Wed 13 Jan
00 UTC
Thu 14 Jan
06 UTC
Thu 14 Jan
12 UTC
Thu 14 Jan
00 UTC
Fri 15 Jan
06 UTC
Fri 15 Jan
12 UTC
Fri 15 Jan
00 UTC
Sat 16 Jan
12 UTC
Sat 16 Jan
00 UTC
Sun 17 Jan
12 UTC
Sun 17 Jan
00 UTC
Mon 18 Jan
Cloud Cover (%) 0 to 20 10 to 30 60 to 80 20 to 40 10 to 30 20 to 40 0 to 20 0 to 20 0 to 20 0 to 5 0 to 20 0 to 5 0 to 20
Cloud Height (km) above sea level 4-5 4-5 4-7 4-8 4-4.5 4-4.5 N/A N/A N/A N/A N/A N/A N/A
Chance for Fog/Precip (%) 75/30 90/40 95/65 90/60 90/30 65/20 30/5 15/0 0/0 0/0 0/0 0/0 0/0
PW (mm, summit upward) 4 to 8 4 to 8 4 to 8 4 to 8 4 to 6 4 to 8 4 to 6 4 to 6 3 to 6 3 to 4 2 to 4 2 to 3 1.5 to 2.5
Mean Seeing (arcsecs) 0.8 ± 0.2 0.9 ± 0.2 N/A 0.9 ± 0.2 0.75 ± 0.15 N/A 0.7 ± 0.15 0.6 ± 0.1 N/A 0.55 ± 0.1 N/A 0.6 ± 0.1 N/A
Summit Temp (°C) -0.5 -1.5 3 -1 -1 5 0 0 5.5 1 6 0.5 5
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)

SSW/5 to 15

SSW/5 to 15

W/10 to 20

WNW/5 to 15

SSE/0 to 10

WNW/0 to 10

NE/0 to 10

W/0 to 10

NNE/5 to 15

ENE/5 to 15

ENE/5 to 15

E/5 to 15

SW/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.Jan.12/Wed.Jan.13
18:11
19:19
5:42
6:50
7:29
18:02
0
19 54.3
-23 54
Wed.Jan.13/Thu.Jan.14
18:12
19:20
5:42
6:50
N/A
19:03
2
20 52.2
-21 37
Thu.Jan.14/Fri.Jan.15
18:13
19:20
5:42
6:50
N/A
20:03
6
21 46.6
-18 14
Fri.Jan.15/Sat.Jan.16
18:13
19:21
5:42
6:50
N/A
20:59
11
22 37.3
-14 02
Sat.Jan.16/Sun.Jan.17
18:14
19:22
5:42
6:50
N/A
21:53
18
23 25.0
-9 19


Forecast issued by: Ryan Lyman
Contact Us - (808) 932-2323
Hours: Mon-Fri 8 AM - 5 PM HST (1800-0300 UTC)

For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.

Next update at 10 AM HST (2000 UTC) Wednesday 13 January 2021.
Please call or email to be placed on the Mauna Kea Weather Bulletin email list.