Maunakea Observatories Forecast
5 PM HST Tuesday 21 January (0300 UTC Wednesday 22 January) 2025
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Warning(s)
Moderate winds
Cloud Cover and Fog/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 WNW at 15-30 mph for today, switching to a more WSW direction through the night. Seeing will be near 0.8-1 arcsecond, while precipitable water is expected to be in the 1-1.5 mm range for the first half of the night and 0.8-1.2 mm range for the second half.
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Discussion
A fairly well-defined inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure a dry/stable summit-level air mass through at least Thursday night. There is a possibility that an influx of deeper low-level moisture and upper-level instability will weaken the inversion and increase the risk for fog, ice and high humidity at the summit for Friday and Saturday night; precipitation is unlikely. Daytime clouds will be minimal and short-lived through Thursday, but could turn extensive for Friday and over the weekend.
Skies will remain predominately clear for tonight, but a band of mid/upper-level clouds is set to sweep in from the NW and persist over the summit area contributing to periods of extensive cloud cover for tomorrow night. This band will shift just east of the Big Island by early Thursday evening, likely leaving mostly clear skies for that night. Mostly clear skies should prevail overhead for the following 2 nights, though high clouds could pass along the northern skies during that time.
Precipitable water is expected to linger near 1-1.25 mm for tonight, briefly jump toward 4 mm for tomorrow afternoon/evening, then slip toward 1 mm as that night progresses. There is a good chance that it will increase toward 1.5 mm for Thursday night and probably to 4 mm for the following 2 nights.
While there is a small chance for a brief dip in the winds early this evening, persistent boundary layer turbulence combined with bouts of free atmospheric turbulence will contribute to poor/bad seeing over the next 3 nights. Winds are set to subside on Friday, but an elevated/weak inversion and possibility for moisture will likely limit seeing from improving much for that night and over the weekend.
Changes have been made mainly to the PW forecast...Altough a short-wave trough approaching from the NW is expected to energize a low to the north of the state, the surface ridge will continue to sit over the Big Island and promote steady/strong large-scale subsidence in the area before weakening a bit around Friday. Nevertheless, this subsidence will help maintain a well-defined inversion primarily near 7 thousand feet and ensure a dry/stable summit-level air mass through at least Thursday night. The frontal band associated with this low is set to miss the Big Island, but associated gravity waves may pass over the summit area particularly for Wednesday and Thursday night. More significantly, a tight wind gradient along the southern flank of the low will likely keep winds at 20+ mph, enough to stir up boundary layer turbulence and contribute to poor/bad seeing over the next 3 nights. There is a chance that winds will briefly approach 50 mph, particularly as the low sags southward and intensifies for Wednesday night. The low will eventually retract, weaken and lift northward by early Friday morning, which should allow winds to taper over the weekend. However, there is a possibility that the departing low will draw moisture in from the tropics as the surface and mid-level ridge shifts off toward the east during that time. This could result in an erosion/weakening of the inversion, which could increase the risk for fog, ice and high humidity at the summit for Friday and Saturday night.
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5 Day Forecast Summary (Graphical Trend)
| HST |
Cloud |
Fog/Precip |
Temp |
Wind |
Seeing |
PW |
| Cover (%) |
Height (km) |
Probability (%) |
(Celsius) |
(Dir/MPH) |
(Arcseconds) |
(mm) |
| Tue Jan 21 - 8 PM | 0-10 | Clear | 0 / 0 | 0 | WNW/15-30 | 0.7-1.1 | 1-1.5 |
| Wed Jan 22 - 2 AM | 0-10 | Clear | 0 / 0 | -0.5 | WSW/15-30 | 0.8-1.2 | 0.8-1.2 |
| 2 PM | 60-80 | 6-10 | 0 / 0 | 3 | WSW/25-40 | NaN | 2-4 |
| 8 PM | 60-80 | 7-9 | 0 / 0 | -2 | W/30-45 | 1-2 | 2-4 |
| Thu Jan 23 - 2 AM | 50-70 | 7.5-9 | 0 / 0 | -2.5 | W/20-35 | 0.8-1.6 | 1-2 |
| 2 PM | 20-40 | 7-9 | 0 / 0 | 2 | SW/15-30 | NaN | 1-2 |
| 8 PM | 0-20 | Clear | 0 / 0 | -3 | SW/15-30 | 0.7-1.3 | 1.25-1.75 |
| Fri Jan 24 - 2 AM | 0-20 | Clear | 0 / 0 | -3 | SW/15-30 | 0.6-1 | 1.25-1.75 |
| 2 PM | 40-60 | 4-4.5 | 25 / 5 | 3 | SW/15-30 | NaN | 4-8 |
| Sat Jan 25 - 2 AM | 0-20 | Clear | 30 / 10 | -2 | WSW/5-15 | 0.5-0.9 | 3-5 |
| 2 PM | 60-80 | 4-5 | 60 / 20 | 3 | W/5-15 | NaN | 4-8 |
| Sun Jan 26 - 2 AM | 0-20 | Clear | 40 / 10 | -2.5 | WSW/0-10 | 0.6-1 | 3-5 |
| 2 PM | 0-20 | 4-5 | 60 / 15 | 3 | SW/10-20 | NaN | 4-8 |
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Rise and Set times for the Sun and Moon
| Night (HST) |
Sun Set |
Twilight End |
Twilight Beg |
Sun Rise |
Moon Rise |
Moon Set |
Illumination (%) |
RA |
DEC |
| Tue Jan 21 - Wed Jan 22 |
18:17 |
19:24 |
5:43 |
6:50 |
0:54 |
N/A |
44 |
14 24.5 |
-17 45 |
| Wed Jan 22 - Thu Jan 23 |
18:18 |
19:25 |
5:43 |
6:50 |
1:46 |
N/A |
35 |
15 11.8 |
-21 57 |
| Thu Jan 23 - Fri Jan 24 |
18:18 |
19:25 |
5:42 |
6:49 |
2:41 |
N/A |
26 |
16 02.4 |
-25 18 |
| Fri Jan 24 - Sat Jan 25 |
18:19 |
19:26 |
5:42 |
6:49 |
3:38 |
N/A |
18 |
16 56.3 |
-27 33 |
| Sat Jan 25 - Sun Jan 26 |
18:20 |
19:26 |
5:42 |
6:49 |
4:35 |
N/A |
11 |
17 53.1 |
-28 27 |
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Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 22 January 2025.
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Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
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