Current Conditions
Temp3.9 C
RH8 %
WindNNW 0 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Wednesday 24 April (0300 UTC Thursday 25 April) 2019
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 3 C this evening and 2.5 C tomorrow morning. Winds will north at 5-15 mph, with seeing near 0.5-0.55 arcseconds. Precipitable water is expected to be in the 1-1.25 mm range for the night.
A strong well-defined inversion will continue to cap low-level moisture primarily near 7 thousand feet and ensure the summit remains dry and stable through Friday night. There is a possibility that the inversion will begin to to breakdown as instability and moisture build into the area, which could increase the risk for fog and ice at the summit through Saturday night and into Sunday night; precipitation is unlikely. Daytime clouds will be minimal and short-lived through Saturday, but could turn extensive for Sunday and Monday.

Skies will remain predominately clear for tonight, but a narrow band of cirrus is set to move in from the west and pass overhead for tomorrow night. After a brief clearing on Friday, more high clouds are expected to fill in from the SW early Saturday morning, with perhaps thicker clouds building in and/or developing overhead for Saturday and especially Sunday night.

Precipitable water is expected to be in the 1-1.25 mm range for tonight, increase toward 1.25-1.75 mm for tomorrow night, 3-4 mm for Friday night and probably 4+ mm for the following 2 nights.

Relatively calm skies at and above the summit, combined with a very stable atmosphere should allow for better than average seeing probably into at least Friday evening. There is a chance that an increasing turbulence will begin to degrade seeing through Friday night, and perhaps eventually lead to poor seeing as instability builds into to the area for the following night. Moisture and/or boundary layer turbulence may further deteriorate seeing for Sunday night.

Little change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area before decaying in response to a passing late season trough during the second half of the weekend and early part of next week. Nonetheless, this subsidence will help maintain a well-defined inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass through at least Friday night. In addition, flow aloft will remain fairly light and zonal, which shoudl result in predominately calm skies and allow for better than average seeing to prevail probably into early Friday evening. The sub-tropical jet is set to strengthen and build in from the SW as the trough begins to develop to the northwest on Friday. Initially, the STJ will increase turbulence in the free atmosphere and shuttle high clouds in from the SW as early as that night. This could result in an increase in cloud cover and deterioration in seeing during that time. The STJ will grow increasingly stronger and deeper as the trough closes into the area through Saturday. This will not further result in more clouds/turbulence, but the trough could begin to destabilize the air mass and deepen the low-level cloud flow for the remainder of the weekend. That may allow for the development of fog/ice at the summit for Saturday and Sunday night, as well as increase the risk for afternoon convection along the slopes on Sunday and Monday.
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 Apr 24 - 8 PM0-5Clear0 / 03N/5-150.45-0.651-1.25
Thu Apr 25 - 2 AM0-5Clear0 / 02.5N/5-150.4-0.61-1.25
2 PM0-20Clear0 / 08NW/5-15NaN1-2
8 PM20-409-100 / 02.5WNW/5-150.4-0.61.25-1.75
Fri Apr 26 - 2 AM10-309-100 / 02WNW/5-150.45-0.651.25-1.75
2 PM0-20Clear0 / 07SSW/0-10NaN2-3
8 PM20-409.5-100 / 02SW/5-150.45-0.653-4
Sat Apr 27 - 2 AM40-609-100 / 01SSW/5-150.5-0.73-4
2 PM60-809-100 / 05SW/5-15NaN3-4
Sun Apr 28 - 2 AM60-807-1040 / 10-1SW/15-300.55-0.953-5
2 PM60-804-875 / 253WSW/15-30NaN4-8
Mon Apr 29 - 2 AM40-604.5-875 / 20-3WSW/15-300.7-1.34-8
2 PM60-804-875 / 253WSW/20-35NaN4-8
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 Apr 24 - Thu Apr 25 18:52 20:00 4:40 5:48 23:52 N/A 64 19 22.4 -22 18
Thu Apr 25 - Fri Apr 26 18:52 20:00 4:39 5:47 0:40 N/A 54 20 14.3 -21 10
Fri Apr 26 - Sat Apr 27 18:53 20:01 4:38 5:46 1:24 N/A 45 21 04.2 -19 08
Sat Apr 27 - Sun Apr 28 18:53 20:01 4:38 5:46 2:05 N/A 36 21 52.2 -16 20
Sun Apr 28 - Mon Apr 29 18:53 20:02 4:37 5:45 2:44 N/A 27 22 38.6 -12 53
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 25 April 2019.
Additional Information
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