Maunakea Observatories Forecast
5 PM HST Tuesday 14 January (0300 UTC Wednesday 15 January) 2025
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Warning(s)
Moderate (tapering) 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 -1 C, with winds from the NNE at 20-35 mph for this evening, easing to 10-20 mph for the morning hours. Seeing will start out near 1 arcsecond, but could improve to 0.5-0.6 arcseconds as the night progresses. PW is expected to be in the 1.25-1.75 mm range for the first half of the night, increasing to 1.5-2.5 mm for the second half.
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Discussion
The tradewind inversion is set to restrengthen near 6-7 thousand feet and, combined with a relatively dry/stable mid-level air mass, will ensure the summit steers free of fog/precipitation through Wednesday night. There is a possibility that the inversion will weaken as pockets of mid-level moisture and instability pass through the area, increasing the risk for fog, ice and high humidity over the following 2 nights; precipitation is unlikely. The inversion is set to rebuild again near 6-7 thousand feet by late Saturday morning, allowing dry/stable conditions to return to the summit for that night. Daytime clouds will be minimal and short-lived for tomorrow, but could turn extensive for Thursday and Friday, only to taper again for the weekend.
Clear skies will prevail for tonight, but patches of mid/upper-level clouds may pass along the northern skies, occasionally passing overhead for Wednesday and Thursday night. These clouds will shift off toward the east and/or lift northward on Friday, leaving clear skies for the weekend.
Precipitable water is expected to start out near 1.25 mm for this evening, but will increase toward 2.5 mm by the end of the night, and settle in around 4 mm for much of the following 3 nights. There is a good chance that PW will trend back to 1 mm through Saturday night.
While boundary layer turbulence will likely contribute to poor seeing for this evening, diminishing summit-level winds, combined with relatively laminar northerly flow in the free atmosphere should allow seeing to settle in near 0.5-0.6 arcseconds for tomorrow morning/evening. However, another round of boundary layer turbulence will probably contribute to poor/bad seeing for the remainder of the forecast period.
Minimal change since the morning forecast...The eastern edge of a mid-level ridge will linger overhead before weakening and shifting off toward the SW as a new trough build in from the NW early Thursday morning. Nevertheless, large-scale subsidence associated with the ridge is expected to rebuild a fairly distinct inversion near 6-7 thousand feet and ensure a dry/stable summit-level air mass over the next 2 nights. Summit-level winds are also set to taper as the ridge flattens out a bit, in anticipation of the approaching trough over the next 12-24 hours. This could allow for calmer skies and an improvement in seeing through tonight and into tomorrow evening. However, westerly flow along southern flank of the approaching trough will help strengthen summit-level winds again beginning early Thursday morning and may contribute another round of strong boundary layer turbulence (and thus poor/bad seeing) between late that evening and Saturday evening. There is also a possibility that instability associated with trough will weaken the inversion and, combined with pockets of moisture/clouds along the northern skies, could allow for periods of fog, ice and high humidity at the summit for Thursday and Friday night. The inversion is set to recover again as the trough shifts eastward and a new ridge builds in from the west by early Saturday morning. This will help reinstill large-scale subsidence in the area and ensure a dry/stable summit-level air mass over much of the weekend.
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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 14 - 8 PM | 0-10 | Clear | 0 / 0 | -1 | NNE/20-35 | 0.7-1.1 | 1.25-1.75 |
| Wed Jan 15 - 2 AM | 0-10 | Clear | 0 / 0 | -1 | NNE/10-20 | 0.45-0.75 | 1.5-2.5 |
| 2 PM | 0-20 | Clear | 0 / 0 | 4 | N/5-15 | NaN | 2-4 |
| 8 PM | 0-20 | 6-8 | 0 / 0 | -1 | NW/5-15 | 0.4-0.6 | 3-4 |
| Thu Jan 16 - 2 AM | 0-20 | 6-8 | 0 / 0 | -2 | NW/15-30 | 0.6-0.9 | 3.5-4.5 |
| 2 PM | 60-80 | 4-8 | 25 / 5 | 1 | NW/15-30 | NaN | 4-6 |
| 8 PM | 10-30 | 5-8 | 40 / 10 | -4 | WNW/15-30 | 0.7-1.3 | 3-5 |
| Fri Jan 17 - 2 AM | 10-30 | 5-8 | 50 / 10 | -5 | WNW/20-35 | 0.8-1.6 | 3-5 |
| 2 PM | 60-80 | 4-7 | 75 / 25 | 0 | WNW/25-40 | NaN | 4-6 |
| Sat Jan 18 - 2 AM | 0-20 | Clear | 50 / 10 | -3 | NW/30-45 | 1-2 | 3-5 |
| 2 PM | 0-20 | Clear | 0 / 0 | 4 | N/25-40 | NaN | 2-3 |
| Sun Jan 19 - 2 AM | 0-10 | Clear | 0 / 0 | 0 | N/20-30 | 0.7-1.3 | 1-2 |
| 2 PM | 0-20 | Clear | 0 / 0 | 5 | NNW/10-20 | NaN | 1-2 |
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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 14 - Wed Jan 15 |
18:13 |
19:21 |
5:42 |
6:50 |
18:59 |
N/A |
97 |
9 10.5 |
20 11 |
| Wed Jan 15 - Thu Jan 16 |
18:13 |
19:21 |
5:42 |
6:50 |
19:56 |
N/A |
93 |
10 00.9 |
15 10 |
| Thu Jan 16 - Fri Jan 17 |
18:14 |
19:22 |
5:42 |
6:50 |
20:49 |
N/A |
87 |
10 47.6 |
9 38 |
| Fri Jan 17 - Sat Jan 18 |
18:15 |
19:22 |
5:42 |
6:50 |
21:39 |
N/A |
80 |
11 31.8 |
3 52 |
| Sat Jan 18 - Sun Jan 19 |
18:15 |
19:23 |
5:42 |
6:50 |
22:28 |
N/A |
72 |
12 14.4 |
-1 56 |
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Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 15 January 2025.
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Additional Information
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