Current Conditions
Temp3.0 C
RH8 %
WindE 9 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Wednesday 08 July (0300 UTC Thursday 9 July) 2020
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 5 C this evening and 3 C tomorrow morning. Winds will be from the SE at 5-15 mph, with seeing near 0.6-0.7 arcseconds. Precipitable water is expected to start out in the 0.8-1 mm range, but increase toward 2 mm as the night progresses.
Discussion
A fairly well-defined inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure the summit steers free of fog and precipitation throughout the forecast period. However, there is a possibility that an influx of moisture will push humidity toward 40-60% between late Wednesday night and early Friday evening. Daytime clouds will be minimal and short-lived through tomorrow, but could pick up for Thursday and Friday, then taper again for the weekend.

Skies will remain predominately clear throughout the forecast period, but there is a possibility for light dissipating cirrus particularly along the western skies late in the weekend.

Precipitable water is expected to start out below 1 mm for this evening, but increase toward 2 mm as the night progress and settle in the 3-4 mm range for Thursday night and the opening half of Friday night. It will slip toward 2 mm or less through Saturday night and probably sit near 1 mm for much of Sunday night.

Lingering low-level turbulence will contribute to another night of slightly poorer than average seeing for tonight. While this turbulence will subside for the remainder of the forecast period, another source of turbulence associated with building instability as well as an influx of moisture may limit much of an improvement for Thursday night. A drier more stable air mass will allow for more improvement and seeing to settle in near 0.5-0.55 arcseconds as turbulence in the free atmosphere increases over the weekend.

No change since the morning forecast...The lower half of the atmosphere will remain under the influence of the ridge to the NE, while the tropical upper-tropospheric trough (TUTT) continues to strengthen to the NW through the week. Nevertheless, the bulk of the instability associated with the TUTT will linger off near the western portion of the state, which will allow steady large-scale subsidence to prevail in the area during this time. This subsidence will help maintain a fairly distinct inversion near 8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. A dissipating tropical wave is still expected to spread minor widespread moisture through the area between late tonight and early Friday evening. This will result in an increase in summit-level humidity and PW toward 40-60% and 3-4 mm, respectively, during that time. There is a possibility that this moisture as well as a brief pocket of instability associated with the TUTT will have a negative impact on seeing for tomorrow night. Seeing is set to improve as the atmosphere dries and stabilizes thereafter, but the strengthening of the TUTT could help reestablish the sub-tropical jet overhead and increase free atmospheric turbulence 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 (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Wed Jul 08 - 8 PM0-5Clear0 / 05SE/5-150.5-0.80.8-1
Thu Jul 09 - 2 AM0-5Clear0 / 03SE/5-150.5-0.81-2
2 PM0-20Clear0 / 06.5SE/5-15NaN2-4
8 PM0-5Clear0 / 01.5ESE/5-150.5-0.73-4
Fri Jul 10 - 2 AM0-5Clear0 / 01ESE/5-150.5-0.73-4
2 PM0-20Clear0 / 06ESE/5-15NaN4-6
8 PM0-5Clear0 / 00.5ENE/5-150.45-0.653-4
Sat Jul 11 - 2 AM0-10Clear0 / 00NE/5-150.45-0.652-3
2 PM0-20Clear0 / 06NE/0-10NaN2-3
Sun Jul 12 - 2 AM0-209.5-100 / 01.5NE/0-100.4-0.61-2
2 PM0-209.5-100 / 07.5NE/5-15NaN1-2
Mon Jul 13 - 2 AM0-209.5-100 / 02ENE/0-100.4-0.60.8-1.2
2 PM0-209.5-100 / 07.5ESE/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
Wed Jul 08 - Thu Jul 09 19:15 20:28 4:27 5:40 22:05 N/A 81 22 49.9 -13 27
Thu Jul 09 - Fri Jul 10 19:15 20:28 4:27 5:40 22:42 N/A 73 23 36.3 -8 55
Fri Jul 10 - Sat Jul 11 19:15 20:28 4:28 5:40 23:16 N/A 64 0 20.7 -4 09
Sat Jul 11 - Sun Jul 12 19:14 20:27 4:28 5:41 23:49 N/A 55 1 04.2 0 42
Sun Jul 12 - Mon Jul 13 19:14 20:27 4:29 5:41 0:23 N/A 45 1 47.6 5 28
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 9 July 2020.
Additional Information
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