Current Conditions
Temp3.9 C
RH87 %
WindSSW 0 mph
Mauna Kea Observatories Forecast
5 PM HST Friday 13 September (0300 UTC Saturday 14 September) 2019
High humidity and fog
Chance for rain and thunderstorms
Cloud Cover and Fog/Precipitation Forecast
There is a high risk for extensive fog, high humidity and light rain at the summit through the night. Broken mid/upper-level clouds will continue to pour in from the SW, contributing to extensive cloud cover through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 1 C, with winds from the WSW at 5-15 mph for the night. Seeing will be near 0.8-1 arcseconds, while precipitable water is expected to exceed 4 mm through the night.
The inversion is set to fall apart as instability and moisture builds into the area late this afternoon, allowing the atmosphere to turn quite saturated over the next 2 nights. There is a chance that the inversion will begin to rebuild near 8 thousand feet around sunrise on Sunday, but mid-level moisture is expected to persist in the area through that night, perhaps even into the following 2 nights. Consequently, high humidity will likely remain an issue throughout the forecast period, and there is a high risk for extensive fog and light rain at the summit mainly over the next 2 nights (this risk will subside thereafter). Extensive daytime clouds are expected through the weekend, then will begin to taper for the early part of next week. There is also a possibility for afternoon convection along the slopes, mainly for tomorrow and perhaps Sunday.

Broken thick mid/upper-level clouds will continue to spread in from the SW, contributing to extensive cloud cover for at least the next 2 nights, probably most of Sunday night. These clouds will begin to breakdown during the latter night, leaving residual patches of mid-level clouds in the area, while thin strands of cirrus continue to fill in from the SW for the early part of next week.

Precipitable water is expected to exceed 4 mm through the next 5 nights.

Persistent mid/summit-level moisture, combined with periods of instability and upper-level turbulence will contribute to poor/bad seeing over the next 3 nights. There is a chance that seeing will improve (toward more average-like values) with conditions for Monday and Tuesday night.

No change since the morning forecast...A fairly deep mid/upper-level low to the NNE of the state will continue to undercut the mid-level ridge as it progresses westward before weakening and lifting northward around the early part of next week. Unfortunately, this westward shift of the low will allow the air mass to become more unstable, while deep mid/low-level moisture drifts in from the south over the next 12-24 hours. As a result, the inversion is expected to fall apart late this afternoon while the atmosphere becomes quite saturated probably for the next 2 nights. This will likely allow extensive fog, high humidity and perhaps light rain to plague the summit during this time. There is also a possibility for the development of convection in the area, particularly to the north and over the interior slopes during the afternoon over the next 3 days. There is a chance that the inversion will begin to rebuild again as the low shifts subtly northward and an upper-level ridge builds to the south around Sunday afternoon/evening. However, very weak mid-level winds will likely allow moisture to persist in the area into the early part of next week. Consequently, humidity may continue to linger in the 60-80% range for at least Sunday night and perhaps even the following 2 nights, which could result in more short-lived fog during those nights (though the odds will fall). A dry/stable air mass is expected to return to the summit, once the mid-level ridge takes shape to the NE around the middle part of next week, if not sooner.
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 Sep 13 - 8 PM70-904-890 / 651WSW/5-150.7-1.18-12
Sat Sep 14 - 2 AM80-1004-995 / 751W/5-150.7-1.18-12
2 PM80-1004-1095 / 904WSW/5-15NaN10-15
8 PM80-1004-1095 / 851WNW/0-100.9-1.510-15
Sun Sep 15 - 2 AM80-1004-1090 / 801WNW/0-100.9-1.510-15
2 PM80-104-1090 / 755E/0-10NaN10-15
8 PM60-804.5-1075 / 502E/5-150.7-1.310-15
Mon Sep 16 - 2 AM40-605-1065 / 402S/5-150.7-1.110-15
2 PM60-804-765 / 356.5NNE/5-15NaN8-12
Tue Sep 17 - 2 AM20-405-740 / 203ENE/5-150.5-0.96-10
2 PM40-604-760 / 308.5E/5-15NaN4-8
Wed Sep 18 - 2 AM10-306-730 / 103E/10-200.4-0.84-6
2 PM0-204-4.55 / 010.5E/10-20NaN3-6
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
Sat Sep 14 - Sun Sep 15 18:34 19:39 4:56 6:00 19:02 N/A 98 0 29.9 -2 38
Sun Sep 15 - Mon Sep 16 18:33 19:38 4:56 6:01 19:36 N/A 95 1 14.5 2 01
Mon Sep 16 - Tue Sep 17 18:32 19:37 4:56 6:01 20:11 N/A 90 1 59.8 6 36
Tue Sep 17 - Wed Sep 18 18:32 19:36 4:57 6:01 20:47 N/A 84 2 46.3 10 57
Wed Sep 18 - Thu Sep 19 18:31 19:35 4:57 6:01 21:26 N/A 76 3 34.8 14 53
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 16 September 2019.
Additional Information
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