Current Conditions
Temp3.7 C
RH83 %
WindW 0 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 20 October (0300 UTC Saturday 21 October) 2017
Warning(s)
Moderate/strong (tapering) winds
Chance for moisture on Sunday
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, but there is a possibility for thin isolated high clouds passing through the area during the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1.5 C tomorrow morning. Winds will be from the NE at 25-40 mph for today, diminishing to 15-30 mph 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 1.5-2 mm range for the second half.
Discussion
A fairly well-defined tradewind inversion will continue to cap low-level moisture below 9 thousand feet and ensure the summit remains dry and stable through at least midnight Saturday. Building moisture and instability will start to erode the inversion through Sunday, likely allowing the air mass to become very unstable and saturated for the early part of next week. Regardless, it will raise the stakes on fog, high humidity, ice and light flurries/rain at the summit for Sunday, Monday and Tuesday night. There is also a possibility for convection in the area and periods of heavy snow at the summit, mainly around Monday night. Daytime clouds will be minimal and short-lived for tomorrow, but will likely pick up on Sunday and turn very extensive for the early part of next week.

There is a possibility that thin bands of isolated high clouds will pass overhead and along the northern skies for tonight and tomorrow night, respectively. Thicker clouds are set to move in from the east and eventually develop in the area on Sunday, while more widespread clouds build in from the NW for the early part of next week. This will likely result in extensive cloud cover for Sunday night and probably overcast skies for the following 2 nights.

Precipitable water is expected to start out near 1 mm for this evening, briefly increase toward 2 mm by the end of the night, slip back toward 1-1.5 mm for tomorrow night, then jump to 4+ mm for the following 3 nights.

Moderate/strong summit-level winds will continue to stir up boundary layer turbulence and contribute to poor/bad seeing for tonight. Winds are set to rapidly taper through Saturday, allowing seeing to return toward more average-like values as light/moderate turbulence prevails in the free atmosphere for that night. An increase in upper-level turbulence/instability, moisture and boundary layer turbulence will likely degrade seeing once again for the following 3 nights.

Subtle/favorable changes have been made to the PW forecast for the next 2 nights...The deep ridge to the north is set to breakdown over the next 36 hours, but will continue to promote relative strong large-scale subsidence in the area through at least early Sunday morning. This subsidence will help maintain a well-defined inversion at or below 9 thousand feet and ensure a dry/stable summit-level air mass during that time. Winds will remain relatively strong for another 6 hours, then is expected to rapidly weaken (with the ridge) later in the night. Still, boundary layer turbulence will continue to be an issue for tonight. There is a chance that seeing will improve toward more average-like values as light/moderate mid-level turbulence associated with a decaying low moves through for tomorrow night. Remnant moisture along the eastern side of this low is also slated to move in on Sunday, and help slowly erode the inversion through that day. In addition, a sharp trough is expected to rapidly dig in from the NW, destabilizing the atmosphere and reorganize this moisture in the area as well as pull deep tropical moisture up from the south later that night. This could allow the atmosphere to become highly unstable and quite saturated for Monday and most of Tuesday. As a result, this will significantly raise the stakes on fog, high humidity, ice, rain/snow and extensive cloud cover or even overcast skies between Sunday evening and late Tuesday night. There is also a possibility for widespread convection in the area, very strong winds and periods of moderate/heavy snow particularly on Monday night. The bulk of this moisture is set to slip off toward the east and NE through Tuesday night, which should allow the air mass to stabilize and dry out by Wednesday afternoon.
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)
Fri Oct 20 - 8 PM0-209.5-100 / 02NE/25-400.8-1.21-1.5
Sat Oct 21 - 2 AM0-209.5-100 / 01.5ENE/15-300.6-11.5-2
2 PM0-209.5-100 / 08.5NE/5-15NaN1.5-2.5
8 PM0-209.5-100 / 03.5SE/5-150.55-0.751-1.5
Sun Oct 22 - 2 AM0-209.5-1010 / 03SSW/5-150.5-0.81-1.5
2 PM60-804-660 / 205SSW/10-20NaN3-6
8 PM60-804-775 / 400SSW/15-300.5-1.14-6
Mon Oct 23 - 2 AM80-1004-990 / 60-1SW/20-350.8-1.64-8
2 PM80-1004-1095 / 801S/25-40NaN10-15
Tue Oct 24 - 2 AM80-1004-1095 / 90-2SW/50-701-210-15
2 PM80-1004-1090 / 403SW/35-50NaN10-15
Wed Oct 25 - 2 AM60-805-860 / 151SSW/30-450.6-1.26-10
2 PM60-804-660 / 106WSW/15-30NaN4-8
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
Sat Oct 21 - Sun Oct 22 18:03 19:08 5:05 6:10 N/A 19:49 7 15 49.8 -15 10
Sun Oct 22 - Mon Oct 23 18:02 19:07 5:06 6:11 N/A 20:32 12 16 38.4 -17 30
Mon Oct 23 - Tue Oct 24 18:01 19:06 5:06 6:11 N/A 21:16 19 17 27.5 -19 05
Tue Oct 24 - Wed Oct 25 18:01 19:06 5:06 6:11 N/A 22:02 26 18 17.2 -19 52
Wed Oct 25 - Thu Oct 26 18:00 19:05 5:07 6:12 N/A 22:50 35 19 07.2 -19 47
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 23 October 2017.
Additional Information
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