Current Conditions
Temp8.3 C
RH13 %
WindWSW 10 mph
RoadOpen (4x4)
Maunakea Observatories Forecast
630 AM HST (1630 UTC) Wednesday 20 October 2021
Warning(s)
None
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 8 C this afternoon, 3 C this evening and 2.5 C tomorrow morning. Winds will be from the NW at 10-20 mph for today, switching to a more northerly direction and decreasing to 5-15 mph through the night. Seeing will be around 0.45-0.5 arcseconds, while precipitable water is expected to be in the 3-4 mm range for the first half of the night and 2-3 mm range for the second half.
Discussion
A distinct inversion will continue to cap low-level moisture near 5-6 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies overhead will remain clear for tonight, but there is a possibility that patches of slow-moving high clouds will develop overhead for tomorrow night. More isolatd to scattered may move in from the SE for Saturday night; clear skies will prevail for Friday and Sunday night.

Precipitable water is expected to start out near 4 mm for this evening, but could slip toward 2 mm by the end of the night and drift into the 1.5-2 mm range for tomorrow night, only to rebound back to 2-3 mm for Friday, Saturday and Sunday night.

Flow at and above the summit is set to subside and become quite laminar, and combined with stable conditions should allow seeing to improve toward 0.45-0.5 arcseconds for tonight. There is a good chance seeing will settle in around 0.4 arcseconds as flow aloft becomes very light for Thursday and the opening part of Friday night. However, increasing mid-level turbulence may contribute to a minor degradation in seeing over the weekend.

The mid/surface ridge will start out displaced to the NW for the next 12 hours, but is expected to slowly progress eastward before shifting off toward the west coast later next week. Nevertheless, strong subsidence associated with the ridge will help maintain a well-defined inversion near 5-6 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. A weak quite shallow upper-level trough is set to develop overhead through the night, but is not expected to affect the stability of the atmosphere during its tenure. And while it may help develop patches of high clouds in to the area for tomorrow night, weak flow embedded in the trough axis will minimize dynamic turbulence in the free atmosphere for the next 2-3 nights. This, combined with a dry/stable air mass will allow seeing to settle in around 0.4-0.45 arcseconds during most of this time. There is a chance that mid-level turbulence will increase as the trough deepens a tad (while also shifting westward), which may contribute to a very minor degradation in seeing over the weekend.
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 (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Wed Oct 20 - 2 PM0-20Clear0 / 08NW/10-20NaN3-6
8 PM0-10Clear0 / 03NNW/10-200.4-0.63-4
Thu Oct 21 - 2 AM0-10Clear0 / 02.5N/5-150.35-0.552-3
2 PM10-308-90 / 07NE/0-10NaN2-3
8 PM0-208-90 / 01.5ENE/0-100.3-0.51.5-2
Fri Oct 22 - 2 AM0-208-90 / 01ESE/0-100.275-0.5251.5-2
2 PM0-20Clear0 / 07SSE/5-15NaN2-4
8 PM0-10Clear0 / 02ESE/0-100.3-0.52.5-3.5
Sat Oct 23 - 2 AM0-10Clear0 / 02ESE/0-100.4-0.62.5-3.5
2 PM0-209-100 / 08ESE/5-15NaN2-4
Sun Oct 24 - 2 AM10-309-100 / 03E/0-100.45-0.652-3
2 PM0-209-100 / 09NNE/5-15NaN2-3
Mon Oct 25 - 2 AM0-10Clear0 / 03.5NE/5-150.4-0.61.5-2.5
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 Oct 20 - Thu Oct 21 18:03 19:08 5:05 6:10 18:09 7:25 99 2 22.6 11 41
Thu Oct 21 - Fri Oct 22 18:03 19:08 5:05 6:10 18:45 N/A 97 3 09.3 16 19
Fri Oct 22 - Sat Oct 23 18:02 19:07 5:06 6:11 19:22 N/A 93 3 57.6 20 15
Sat Oct 23 - Sun Oct 24 18:01 19:06 5:06 6:11 20:03 N/A 87 4 47.6 23 17
Sun Oct 24 - Mon Oct 25 18:01 19:06 5:06 6:11 20:47 N/A 80 5 39.2 25 17
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 20 October (0300 UTC Thursday 21 October) 2021.
Additional Information
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This message is also available at the MKWC road conditions page.
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