Current Conditions
Temp3.4 C
RH7 %
WindENE 2 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 18 June (0300 UTC Wednesday 19 June) 2019
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable through the night (though there is a chance for light patches of dissipating cirrus filling from the west by sunrise).
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C, with winds from the east at 5-15 mph and near 0.75-0.8 arcseconds. Precipitable water is expected to be in the 2.5-3.5 mm range for the night.
Discussion
The tradewind inversion will continue to cap low-level moisture primarily near 6-7 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain clear for tonight, but a band of scattered high clouds will begin to spread in from the west just after sunrise tomorrow and will gradually become slightly more widespread and perhaps thicker, which could lead to periods of extensive cloud cover for that night and Thursday night (that evening in particularl). There is a good chance that this band will sag southward on Friday, leaving only residual patches of mid-level clouds to slowly dissipate in the area for the weekend. (There is a slight possibility for light boundary layer turbulence mainly on Saturday.)

Precipitable water is expected to linger near 3 mm for the next 2 nights, then increase toward 3.5-4 mm for the following 2 nights and perhaps 4+ mm for Saturday night.

Increasing turbulence in the free atmosphere in the free atmosphere will likely contribute to poorer than average seeing into early Thursday evening. More laminar westerly flow will eventually build over the summit, allowing seeing to improve through Thursday night and eventually settle back in near 0.5-0.6 arcseconds for the following 2 nights.

Little change since the morning forecast...The SW tip of the mid/low-level ridge will continue to sit to the north of the state and promote steady large-scale subsidence in the area into next week, while the tropical upper-tropospheric trough (TUTT) retracts off toward the west over the next several days. Nevertheless, this subsidence will help maintain a well-defined inversion near 6-7 thousand feet and ensure the summit remains dry and stable throughout the forecast period. While there is a chance that the TUTT will gradually shift eastward later in the week, it will not be able to overcome the subsidence associated with the ridge. However, the SE edge of the TUTT, aka the sub-tropical jet, is expected to build in overnight, increasing turbulence in the free atmosphere and likely contributing to poorer than average seeing over the next 2-3 nights. The STJ will also begin to shuttle scattered high clouds into the area just after sunrise tomorrow. These clouds are set to organized into a band and become thicker through the day, liekly contributing to periods of extensive cloud cover for that night and into Thursday night. The STJ is expected to sag southward and become more zonally orientated as an upper-level low develops to the NW and the TUTT shifts subtly eastward around Friday morning. This may help clear the high clouds out of the area, allowing laminar westerly flow build in aloft and likely help improve seeing particularly for Friday and Saturday 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)
Tue Jun 18 - 8 PM0-5Clear0 / 02.5E/5-150.6-0.92.5-3.5
Wed Jun 19 - 2 AM0-20Clear0 / 02.5E/5-150.65-0.952.5-3.5
2 PM20-409.5-100 / 08NE/0-10NaN3-5
8 PM20-408.5-100 / 03NNE/0-100.65-0.952.5-3.5
Thu Jun 20 - 2 AM40-607-100 / 03NNW/0-100.6-0.92.5-3.5
2 PM60-807-100 / 08WSW/0-10NaN3-5
8 PM60-806-100 / 03W/5-150.55-0.853.5-4.5
Fri Jun 21 - 2 AM20-406-90 / 03WSW/5-150.5-0.73.5-4.5
2 PM0-20Clear0 / 07.5SSW/5-15NaN4-6
Sat Jun 22 - 2 AM0-20Clear0 / 02SSW/10-200.45-0.753-5
2 PM0-20Clear0 / 08WSW/10-20NaN4-6
Sun Jun 23 - 2 AM0-20Clear0 / 02.5W/5-150.45-0.654-8
2 PM0-20Clear0 / 07WSW/5-15NaN4-8
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
Tue Jun 18 - Wed Jun 19 19:13 20:27 4:19 5:34 20:24 N/A 96 19 36.6 -22 37
Wed Jun 19 - Thu Jun 20 19:13 20:27 4:20 5:34 21:13 N/A 91 20 29.6 -21 12
Thu Jun 20 - Fri Jun 21 19:13 20:27 4:20 5:34 21:57 N/A 84 21 20.4 -18 51
Fri Jun 21 - Sat Jun 22 19:13 20:28 4:20 5:34 22:38 N/A 77 22 08.9 -15 45
Sat Jun 22 - Sun Jun 23 19:14 20:28 4:20 5:34 23:16 N/A 68 22 55.5 -12 04
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 19 June 2019.
Additional Information
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