Current Conditions
Temp-0.9 C
RH8 %
WindNNE 20 mph
Mauna Kea Observatories Forecast
5 PM HST Wednesday 20 January (0300 UTC Thursday 21 January) 2021
Chance for fog/ice
Cloud Cover and Fog/Precipitation Forecast
There is a small risk for periods of fog, ice and high humidity throughout the night; precipitation is unlikely. Broken relatively thick clouds will continue to block most of the sky throughout the night.
Summary of Key Meteorological Variables
Summit temperatures will be near -1.5 C, with winds from the ENE at 10-20 mph for the night. Seeing will be near 0.8-0.9 arcseconds, while precipitable water is expected to exceed 4 mm for the night.
Although the inversion is set to strengthen a bit near 7-9 thousand feet over the next 24-36 hours, persistent mid-level moisture passing near/over the summit area, strengthening easterly winds and occasionally a weakening/lifting of the inversion (mainly over the weekend) could contribute to periods of fog, ice and/or high humidity at virtually any time over the next 5 nights, Friday night in particular; precipitation is unlikely. Some afternoon clouds are possible throughout the forecast period, especially for Saturday and Sunday, then should taper for next week.

Broken thick clouds will continue to pass over/near the summit and contribute to block most of the sky for tonight. These clouds will begin to shift to the eastern skies and break up a bit, opening up more than 50% of the sky for the following 3 nights. However, more widespread broken clouds are set to develop in the area and will likely blanket summit skies for Sunday night.

Precipitable water is expected to exceed 4 mm for tonight, then could dip toward 3.5-4 mm for the remainder of the forecast period.

Despite relatively light flow aloft, residual moisture will likely contribute to poor seeing for tonight. While the air mass may stabilize and perhaps dry out, an increase in boundary layer turbulence will prohibt an improvement or even further degrade seeing for the remainder of the forecast period.

Not that much change since the morning forecast..The mid/upper-level trough sitting over/near the Big Island is expected to shift eastward, while a deposited mid-level low to the SW slowly dissipates over the next several days. While this could help to stabilize the air mass as a tight mid-level ridge takes shape to the NE, residual moisture/clouds from the trough/low will continue to linger in the area contributing to overcast skies and may also allow for periods of fog, ice and high humidity at the summit for tonight. The bulk of the clouds will shift eastward with the trough, perhaps opening up skies more than 50% of the sky for the next 3 nights. However, summit-level winds are expected to pick up as a the ridge strengthens in response to the dissipation of the low. This could significantly increase boundary layer turbulence and contribute to poor/bad seeing for the remainder of the forecast period. In addition, residual moisture from the low could get caught up in the deep ESE flow and scrape the southern half of the Big Island, which could increase the risk for fog/ice at the summit mainly between early Friday evening and Sunday afternoon. Although this moisture will eventually slide off toward the NW as a low takes form near the dateline early next week, widespread high clouds may develop over and/or drift in from the west and contribute to overcast skies for Sunday and Monday night.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Wed Jan 20 - 8 PM70-906-1025 / 5-1.5ENE/10-200.6-14-8
Thu Jan 21 - 2 AM60-806-920 / 5-1.5ENE/10-200.6-14-6
2 PM60-804.5-830 / 103NE/15-30NaN3-5
8 PM20-406-820 / 5-1.5E/20-350.7-1.13-4
Fri Jan 22 - 2 AM10-306-7.515 / 5-2.5E/25-400.8-1.23-4
2 PM40-604.5-740 / 102E/25-40NaN4-6
8 PM20-405-730 / 5-3E/25-400.9-1.53.5-4.5
Sat Jan 23 - 2 AM20-405-740 / 10-4ESE/25-400.8-1.43.5-4.5
2 PM60-804-865 / 301SE/20-35NaN4-6
Sun Jan 24 - 2 AM30-506-830 / 5-3SE/20-350.7-1.33-5
2 PM60-807-1050 / 251.5SSE/20-35NaN4-6
Mon Jan 25 - 2 AM80-1007-1020 / 5-3E/10-350.7-1.13-5
2 PM80-1004-1025 / 101SE/10-20NaN4-8
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
Wed Jan 20 - Thu Jan 21 18:16 19:24 5:43 6:50 N/A 1:10 54 2 21.5 10 27
Thu Jan 21 - Fri Jan 22 18:17 19:24 5:43 6:50 N/A 1:59 64 3 06.8 14 50
Fri Jan 22 - Sat Jan 23 18:18 19:25 5:43 6:50 N/A 2:51 73 3 54.3 18 40
Sat Jan 23 - Sun Jan 24 18:18 19:25 5:43 6:49 N/A 3:44 81 4 44.6 21 46
Sun Jan 24 - Mon Jan 25 18:19 19:26 5:42 6:49 N/A 4:39 88 5 37.8 23 56
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 21 January 2021.
Additional Information
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