Current Conditions
Temp4.2 C
RH15 %
WindNW 28 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 21 November (0300 UTC Saturday 22 November) 2014
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable through the night. The banding high clouds passing to the south is expected to retract a bit during the second half of the night, but there is still a possibility that scattered high clouds will stray over the summit.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this afternoon and 0 C for the night. Winds will be from the ESE at 20-35 mph for today, easing to 10-20 mph as the night progresses. Seeing will start out near 0.8 arcseconds but improve toward 0.6 arcseconds as winds subside. Precipitable water is expected to be in the 0.8-1 mm range for the night.
A well-defined inversion will continue to cap low-level moisture at or below 8 thousand feet and keep the mid/summit-level air mass dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

The banding high clouds passing to the south is expected to retract back toward the tropics through the night, then shift northward again perhaps passing over the southern half of the Big Island for tomorrow night. Nonetheless, there is a possibility that scattered high clouds will stray over the summit area from time to time. These clouds are slated to shift further southward through Sunday and eventually eastward late Monday morning. This will leave clear skies for the early part of next week.

Precipitable water is expected to linger near 0.8-0.9 mm through the weekend, increase to 1.25 mm for Monday night and probably 1.5 mm for Tuesday night.

While lingering boundary layer turbulence will contribute to poor seeing for this evening, winds are slated to subside allowing seeing to improve toward average-like values by the end of the night and perhaps 0.4-0.5 arcseconds for tomorrow night. There is a very good chance that mid-level turbulence will start to build into the area, degrading seeing near sunrise Sunday and likely contribute to poor seeing for that night and perhaps Monday night as well. This source of turbulence is expected to subside on Tuesday, allowing seeing to slip back toward 0.4-0.5 arcseconds for that night.

Changes have been made to the fog and CC forecast...A passing trough will continue to shift eastward and flatten out, allowing the mid-level ridge to the north of the state to regain control of the atmosphere and promote steady/strong large-scale subsidence in the area probably throughout the forecast period. This will help to rebuild a well-defined tradewind inversion at or below 8 thousand feet and ensure a dry and stable summit during that time. Summit-level winds are also slated to subside, reducing boundary layer turbulence and allow seeing to improve toward 0.6 arcseconds by the end of the night and hopefully 0.4 arcseconds for tomorrow night. The sub-tropical jet will continue to set up to the south and transport banding high clouds along the southern skies through most of the weekend. The jet has progressed further nortward than previously expected, but should retreat subtly southward as the night progresses. Unfortunately, A new developing mid/upper-level trough passing to the north may drag the jet back northward and could bring more organized high clouds over the Big Island area for tomorrow night. Skies will open up again as the trough weakens and shifts the jet off to the SE through Sunday night. While it appears that this trough will pass to far to the north to really affect the stability of the atmosphere, turbulence associated with the trough will likely degrade seeing for Sunday and Monday night. Seeing should improve as the lingering turbulence subsides and zonal flow prevails aloft by Tuesday 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)
Fri Nov 21 - 8 PM20-409-100 / 00E/15-300.6-10.8-1
Sat Nov 22 - 2 AM10-309-100 / 00ENE/10-200.5-0.70.8-1
2 PM10-309-100 / 07ENE/5-15NaN0.8-1.2
8 PM30-508.5-100 / 02E/10-200.4-0.50.7-0.9
Sun Nov 23 - 2 AM40-608-100 / 01SE/10-200.4-0.60.7-0.9
2 PM40-609-100 / 07W/10-20NaN0.8-1.2
8 PM0-209.5-100 / 02W/10-200.6-0.90.7-0.9
Mon Nov 24 - 2 AM0-20Clear0 / 02WNW/10-200.6-0.90.7-0.9
2 PM0-20Clear0 / 08.5W/10-20NaN1-2
Tue Nov 25 - 2 AM0-10Clear0 / 03.5WNW/10-200.5-0.81-1.5
2 PM0-20Clear0 / 08.5NW/5-15NaN1-2
Wed Nov 26 - 2 AM0-10Clear0 / 03.5NW/5-150.35-0.551.25-1.75
2 PM0-20Clear0 / 09NNE/5-15NaN1-2
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
Sun Nov 23 - Mon Nov 24 17:51 18:58 5:19 6:26 N/A 19:23 4 17 42.2 -18 41
Mon Nov 24 - Tue Nov 25 17:51 18:58 5:19 6:27 N/A 20:21 10 18 40.4 -18 04
Tue Nov 25 - Wed Nov 26 17:51 18:58 5:20 6:28 N/A 21:21 18 19 38.5 -16 22
Wed Nov 26 - Thu Nov 27 17:51 18:59 5:20 6:28 N/A 22:21 27 20 35.7 -13 41
Thu Nov 27 - Fri Nov 28 17:51 18:59 5:21 6:29 N/A 23:21 38 21 31.6 -10 12
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 24 November 2014.
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