Current Conditions
Temp-2.3 C
RH35 %
WindE 20 mph
RoadClosed
Maunakea Observatories Forecast
5 PM HST Wednesday 08 December (0300 UTC Thursday 9 December) 2021
Warning(s)
Increasing winds
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while scattered to broken high clouds fill in from the SW as the night progresses.
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C this evening and 2 C tomorrow morning. Winds will be from the ESE at 15-30 mph, while seeing will be near 0.8-0.9 arcseconds for the night. PW will start out near 2.5 mm, but may slip toward 1 mm by the end of the night.
Discussion
A well-defined inversion will continue to cap low-level moisture primarily near 7-8 thousand feet and ensure a dry and stable summit-level air mass through Saturday night. There is a possibility that building instability will deepen the low-level clouds field and increase the risk for periodic fog, ice and flurries at the summit for Sunday night. Daytime clouds will be minimal and short-lived through Saturday, but could pick up on Sunday and turn extensive for Monday.

Scattered to broken high clouds are expected to move in from the move in from the SW and may contribute to periods of extensive cloud cover for the night. These clouds will shift to the northern skies during the second half of the night and will slip off toward the east through tomorrow, leaving predominately clear skies for that night and Friday night. More high clouds are set to fill in from the west late Saturday, with thicker clouds perhaps developing in the area for Sunday night.

Precipitable water will start out near 2.5 mm for this evening, but may slip toward 1 mm by the end of the night, only to increase back to 3-4 mm probably for the remainder of the forecast period.

Despite fairly calm skies in the free atmosphere, an increase in boundary layer turbulence will likely contribute to poor seeing throughout the forecast period. An influx of moisture and instability may further degrade seeing for Sunday night.

Little change since the morning forecast...A relatively deep tight ridge will continue to fill in from the east, settling in to the north of the state probably well into next week. Subsidence associated with the ridge will help maintain a well-defined inversion primarily near 7-8 thousand feet and ensure a dry/stable summit-level air mass through at least Saturday night. Unfortunately, a fairly tight wind gradient along the southern flank of the ridge will persist overhead, which will keep winds near 20-25 mph probably throughout the forecast period. This will result in steady boundary layer turbulence and contribute to poorer than average seeing through the next 5 nights. PW may briefly slip toward 1 mm by the end of tonight, but an influx of minor mid-level moisture will result in a rebound in PW (toward 3-4 mm for the following 4 nights). Models continue to suggest that a weak upper-level trough will begin to destabilize the air mass a bit, which may help deepen the low-level cloud field late in the weekend. While previously fairly consistent, it looks like this projection is a bit overdone and reflected in the latest run. As such, the long-term odds on moisture at the summit has dropped a bit from the AM forecast.
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 Dec 08 - 8 PM40-608-90 / 02.5ESE/15-300.7-1.11.5-2.5
Thu Dec 09 - 2 AM40-608-90 / 02ESE/15-300.6-11-2
2 PM20-408-90 / 07.5ESE/10-20NaN1-2
8 PM0-20Clear0 / 02.5ESE/15-300.6-12-3
Fri Dec 10 - 2 AM0-10Clear0 / 02ESE/15-300.6-0.92.5-3.5
2 PM0-20Clear0 / 07E/15-30NaN2.5-3.5
8 PM0-10Clear0 / 02E/15-300.6-13-4
Sat Dec 11 - 2 AM0-20Clear0 / 01.5E/15-300.6-13-4
2 PM0-209-100 / 06NE/10-20NaN3-5
Sun Dec 12 - 2 AM10-309-100 / 01NE/15-300.6-13-4
2 PM40-604-520 / 55ENE/25-40NaN3-5
Mon Dec 13 - 2 AM20-404-1030 / 10-1ENE/20-350.7-1.33-5
2 PM60-804-1065 / 204ENE/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 Dec 08 - Thu Dec 09 17:53 19:01 5:27 6:36 N/A 22:54 32 22 01.5 -17 37
Thu Dec 09 - Fri Dec 10 17:53 19:02 5:28 6:36 N/A 23:51 42 22 53.1 -12 41
Fri Dec 10 - Sat Dec 11 17:53 19:02 5:28 6:37 N/A 0:45 53 23 41.3 -7 18
Sat Dec 11 - Sun Dec 12 17:54 19:02 5:29 6:38 N/A 1:37 63 0 27.2 -1 45
Sun Dec 12 - Mon Dec 13 17:54 19:03 5:29 6:38 N/A 2:27 72 1 11.8 3 45
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 9 December 2021.
Additional Information
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