Current Conditions
Temp2.7 C
RH36 %
WindW 6 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 24 June (0300 UTC Tuesday 25 June) 2019
Warning(s)
High humidity
Chance for fog
Cloud Cover and Fog/Precipitation Forecast
There is a small/moderate chance for fog as humidity lingers in the 60-80% range through the night; precipitation is unlikely. Scattered to broken patches of thick clouds will persist along the western skies and may spill in overhead throughout the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 2.5 C this evening and 2 C tomorrow morning. Winds will be from the NNW at 15-25 mph for today, weakening to 10-20 mph through the night. Seeing will be near 0.8-0.9 arcseconds, while precipitable water is expected to exceed 4 mm through the night.
Discussion
Although the inversion will remain fairly well intact near 7-8 thousand feet over much of the next 4 nights, deep mid/upper-level moisture scraping the western half of the Big Island will keep humidity in the 60-80% range (occasionally higher, mainly between late Tuesday night and Thursday afternoon) and could allow for periods of fog and light rain at the summit during that time. The air mass is set to dry out and stabilize as the inversion strengthens, which will ensure the summit steers free of fog, high humidity and precipitation by Friday night. Extensive daytime clouds are expected through Thursday and there is a possibility for afternoon convection along the interior/western slopes of the Big Island through Thursday. Daytime clouds will become minimal and short-lived again for Friday and over the weekend.

Scattered to broken thick clouds will persist along the western skies and will likely spill in overhead through the next 4 nights, particularly between late tomorrow night and early Thursday morning. These clouds will begin to breakdown and retract further westward through Thursday night, leaving predominately clear skies for Friday night.

Precipitable water is expected to exceed 4 mm through Thursday night, then slip back into the 2-3 mm range for Friday night.

Despite relatively weak/uniform winds in the free atmosphere, an abundance of moisture will likely contribute to turbulent skies and poor/bad seeing over the next 3-4 nights. A dry/stable atmosphere combined with light/deep easterlies will allow seeing to improve through Thursday night and perhaps settle back in near 0.4-0.5 arcseconds for Friday night.

Little change since the morning forecast...While the SW tip of low-level ridge will continue to sit over the state, a rather deep mid/upper-level low/trough will persist to the NW before weakening and lifting off toward the north, allowing the mid-level ridge to rebuild early Friday morning. Subsidence associated with the low-level ridge will help maintain a portion of the inversion near 7-8 thousand feet, but deep moisture and clouds rotating around the eastern flank of the low/trough will scrape the Big Island, contributing to high humidity/PW and perhaps periods of fog/rain at the summit over the next 4 nights. There is a strong possibility that the odds on fog/rain at the summit will increase as a short-wave trough digs in from the NW, reinforcing the low and subtly shifting it eastward a tad between late tomorrow night and Thursday afternoon. This may also weaken the inversion a tad and increase the risk for afternoon convection along the western and interior slopes of the Big Island during that time. The risk for moisture at the summit, afternoon convection and extensive cloud cover is expected to diminish as the low/trough weakens and the mid-level ridge expands to the NE early Friday morning. Deeper subsidence associated with the ridge will rebuild a very well-defined inversion near 7-8 thousand feet, ensuring the summit steers free of fog/precipitation by that night and into 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)
Mon Jun 24 - 8 PM50-705-930 / 102.5NNW/15-250.7-1.16-10
Tue Jun 25 - 2 AM30-505-830 / 102NNW/10-200.6-16-10
2 PM70-904-965 / 306W/5-15NaN8-12
8 PM40-605-940 / 152SW/5-150.6-18-12
Wed Jun 26 - 2 AM60-804.5-960 / 302WSW/5-150.8-1.28-12
2 PM80-1004-1090 / 605.5SW/10-20NaN10-15
8 PM60-804.5-865 / 402.5SW/5-150.8-1.28-12
Thu Jun 27 - 2 AM50-704.5-860 / 202.5SW/5-150.8-1.28-12
2 PM60-804-865 / 157SW/5-15NaN8-12
Fri Jun 28 - 2 AM20-404.5-625 / 52E/5-150.5-0.84-8
2 PM0-20Clear0 / 08ENE/5-15NaN3-6
Sat Jun 29 - 2 AM0-20Clear0 / 03ENE/5-150.4-0.62-3
2 PM0-20Clear0 / 08.5ENE/5-15NaN2-3
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
Mon Jun 24 - Tue Jun 25 19:14 20:28 4:21 5:35 0:27 N/A 49 0 25.1 -3 32
Tue Jun 25 - Wed Jun 26 19:14 20:28 4:21 5:35 1:02 N/A 40 1 09.6 1 02
Wed Jun 26 - Thu Jun 27 19:14 20:28 4:21 5:35 1:38 N/A 30 1 55.2 5 37
Thu Jun 27 - Fri Jun 28 19:14 20:28 4:22 5:36 2:17 N/A 22 2 42.5 10 03
Fri Jun 28 - Sat Jun 29 19:15 20:29 4:22 5:36 2:58 N/A 14 3 32.5 14 07
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 25 June 2019.
Additional Information
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