Current Conditions
Temp1.8 C
RH70 %
WindENE 8 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Thursday 16 August (0300 UTC Friday 17 August) 2018
Warning(s)
High humidity
Chance for fog/rain and convection
Cloud Cover and Fog/Precipitation Forecast
There is a high risk for fog, high humidity and light rain throughout the night. A band of scattered to broken thick clouds will continue to pass over, occasionally redeveloping in the area 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 light and from the SW, with seeing near 0.9-1 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
Discussion
The inversion will remain rather weak/indistinct as weak instabiilty and mid/low-level moisture persists in the area through Sunday morning. Consequently, humidity is expected to linger in the 60-80% range and there is moderate/high risk for periods of fog and light rain at the summit over the next 3 nights. There is also a possibility for isolated convection in the area, particularly during the afternoon and early morning hours. The inversion is set to rebuild near 6-7 thousand feet through Sunday, which should reduce the risk for moisture at the summit for that night and at least the opening half of Monday night. However, incoming deep moisture could erode the inversion and increase this risk again by early Tuesday morning. Extensive daytime clouds are expected through Saturday, then will begin to taper for Sunday and especially Monday, only to possibily pick up again on Tuesday.

A band of broken thick clouds will continue to sit over the summit and periodically flare up/redevelop, contributing to periods of extensive cloud cover probably into Saturday evening. This band will begin to breakup and shift northward early Sunday morning, likely leaving clear skies for that night and the early part of Monday night. However, more thick clouds may begin to move in from the ESE by early Tuesday morning.

Precipitable water is expected to exceed 4 mm through Sunday night, but may slip toward 3 mm for part of Monday night.

Despite relatively calm skies and mostly laminar WSW flow in the free atmosphere, an abundance of mid/low-level moisture and eventually instability in the area will likely contribute to poor/bad seeing over the next 4 nights. These is a possibility that drier more stable summit-level conditions could allow seeing to improve toward average-like values for Sunday night. However, a possible increase in boundary layer turbulence may degrade seein once again through Monday night.

Models are backing off the extent of the moisture in the area, but keep the inversion rather weak...Widespread (albiet weak) instability associated with the tropical upper-tropospheric trough (TUTT) to the NW, combined with the absence of a prominent ridge, will keep the inversion rather weak/indistinct and allow the atmosphere near the Big Island to remain rather saturated as deep moisture continues to fill in from the SW into Saturday night. As a result, there is a moderate/high risk for fog and light rain at the summit as humidity lingers near 60-80% for the next 3 nights. Thick scattered/broken clouds will also continue to flow in from the SW and there is a chance that these clouds will flare up, particularly during the afternoon/evening and again near sunrise. Isolated convection may also develop along the Big Island slopes, especially during the afternoon hours. A deep ridge is set to fill in from the SE, weakening and shifting the TUTT off toward the NE on Sunday. This should help clear out summit skies and reinstill large-scale subsidence in the area, which should rebuild the inversion and diminish the risk for moisture at the summit through that night and for Monday evening. However, models suggest that TC Lane will approach from the SE during the latter night. While it still far out in the forecast to anticipate the storm's impact on the state, there is a good chance that widespread tropical moisture surrounding the storm will bring another round of inoperable conditions/skies to the summit around Tuesday and Wednesday (and perhaps into Thursday/Friday).

Please note: There will no forecasts tomorrow, August 17, in observance of Statehood Day. The regular forecast schedule will resume on Monday, August 20.
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)
Thu Aug 16 - 8 PM70-904-990 / 602.5SW/0-100.8-1.210-15
Fri Aug 17 - 2 AM60-804-985 / 402SW/0-100.7-1.110-15
2 PM80-1004-1090 / 605SSW/0-10NaN10-15
8 PM70-904-885 / 502SSE/0-100.7-1.110-15
Sat Aug 18 - 2 AM50-704.5-880 / 352SSE/0-100.6-18-12
2 PM80-1004-890 / 606ESE/5-15NaN8-12
8 PM60-804.5-875 / 302.5E/5-150.7-1.18-12
Sun Aug 19 - 2 AM40-605-870 / 152E/5-150.6-0.98-12
2 PM20-404-540 / 108ENE/5-15NaN4-8
Mon Aug 20 - 2 AM0-20Clear15 / 03NE/10-200.45-0.754-6
2 PM0-20Clear0 / 09NE/15-30NaN3-5
Tue Aug 21 - 2 AM20-405-840 / 103.5ENE/20-350.6-12-4
2 PM80-1004-1075 / 255ENE/25-40NaN4-8
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
Sat Aug 18 - Sun Aug 19 18:57 20:05 4:47 5:54 N/A 0:47 60 16 28.1 -17 47
Sun Aug 19 - Mon Aug 20 18:56 20:04 4:47 5:54 N/A 1:32 69 17 18.7 -19 51
Mon Aug 20 - Tue Aug 21 18:56 20:03 4:48 5:55 N/A 2:18 78 18 09.8 -21 01
Tue Aug 21 - Wed Aug 22 18:55 20:02 4:48 5:55 N/A 3:07 85 19 01.1 -21 15
Wed Aug 22 - Thu Aug 23 18:54 20:01 4:48 5:55 N/A 3:56 91 19 52.1 -20 33
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 17 August 2018.
Additional Information
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