Current Conditions
Temp4.2 C
RH31 %
WindWSW 5 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Tuesday 25 September (0300 UTC Wednesday 26 September) 2018
Warning(s)
Chance for fog/high humidity
Possibility for afternoon convection
Cloud Cover and Fog/Precipitation Forecast
There is a moderate chance for periods of fog and high humidity throughout the night; precipitation is unlikely.
Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C this evening and 3 C tomorrow morning for the night. Winds will be from the south at 5-15 mphwhile seeing will be near 0.7-0.8 arcseconds for the night. Precipitable water is expected to be in the 3-4 mm through the night.
Discussion
The atmosphere near the Big Island will remain a bit moist and unstable, which could allow for periods of fog and high humidity over the next 2 nights. There is a good chance that the inversion will rebuild near 5-6 thousand feet for Thursday night, then break down again for Friday night, only to quickly restrengthen near 6 thousand feet for the remainder of the weekend. Nonetheless, this may result in another round of high humidity and fog at the summit for Friday night; dry and stable conditions will prevail for Thursday and Saturday night and nighttime precipitation is unlikely throughout the forecast period. Extensive daytime clouds and isolated afternoon convection are possible over the next 2 days and on Friday, while daytime clouds will be minimal and short-lived for Thursday and Saturday.

Patches of mid/upper-level clouds may pass through/near the area for much of tonight, with more high clouds set to fill out of the south later tomorrow, eventually allowing a band of clouds to pass overhead, contributing to extensive cloud cover for tomorrow night. This band may shift toward the NW on Thursday, opening up skies a bit for that night. However, more broken high clouds are expected to fill in from the SE for Friday night, with additional cirrus exhaust drifting in from the south and SW on Saturday night.

There is a chance that PW will linger near 3 mm for tonight, increase to 4+ mm for the following 3 nights, then slip toward 2 mm through Saturday night.

A mixture of moisture and mid-level turbulence will likely contribute to poor/variable seeing probably through late tomorrow evening. There is a chance for a drying trend, which could allow seeing to improve through early Thursday morning and eventually settle in near 0.5-0.6 arcseconds for that night. However, an influx of moisture combined with boundary layer turbulence will result in another round of poor seeing for the next 2 nights.

Not much change since the morning forecast, though the odds on fog and expected PW did drop a bit for tonight...The early season low to the NNW of the state is expected to lift northward, leaving a low-level convergence band just west of the Big Island through early Thursday morning. This band will remain close enough to the area, and combined with an influx of tropical moisture from the SSE, will help erode the inversion and increase the risk for fog and high humidity at the summit mainly through late Wednesday morning. It may also allow for the development of afternoon convection particularly along the western and interior slopes of the Big Island over the next 2 days. A stabilizing trend is expected as this convergence band weakens and lifts off toward the NW and dry area moves in from the SE for Thursday. This may not only improve conditions, but may allow seeing to settle back in near 0.5-0.6 arcseconds for that night. However, this dry/stable area is likely the result of moisture being drawn toward the development of a tropical low to the SE around that time. This low will likely develop into a tight hurricane and pass ~500 km to the south of the state over the weekend and into the early part of next week. While this cyclone/hurricane is highly unlikely to directly impact the state, a developing outer rainband may scrape the Big Island and briefly erode the inversion, increasing the risk for moisture at the summit for Friday night. This band is set to pass, allowing the inversion to rebuild and dry/stable conditions to prevail for the remainder of the weekend, but a tight wind gradient between the northern periphery of the cyclone and the ridge to the north will help stir up boundary layer turbulence and contribute to poor seeing 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 Sep 25 - 8 PM20-406-1060 / 153.5SSE/5-150.6-0.93-4
Wed Sep 26 - 2 AM20-406-1050 / 103SSW/5-150.6-0.93-4
2 PM60-804-1075 / 307.5S/5-15NaN4-8
8 PM60-806-1060 / 103SSE/0-100.55-0.854-8
Thu Sep 27 - 2 AM60-806-1030 / 53ENE/0-100.4-0.74-6
2 PM40-606-1010 / 08.5ESE/0-10NaN3-5
8 PM20-406-90 / 03.5ENE/5-150.45-0.653.5-4.5
Fri Sep 28 - 2 AM10-307-90 / 03.5ESE/5-150.45-0.653.5-4.5
2 PM60-804-1075 / 406E/15-30NaN4-8
Sat Sep 29 - 2 AM60-806-1065 / 201.5E/25-400.7-1.14-8
2 PM60-808-1010 / 07ESE/25-40NaN3-6
Sun Sep 30 - 2 AM60-808-100 / 02.5ESE/20-350.6-12-3
2 PM40-609-100 / 08.5ESE/20-35NaN1.5-2.5
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 Sep 25 - Wed Sep 26 18:24 19:28 4:59 6:03 18:57 N/A 98 1 16.9 2 27
Wed Sep 26 - Thu Sep 27 18:23 19:27 4:59 6:03 19:36 N/A 94 2 06.3 7 01
Thu Sep 27 - Fri Sep 28 18:22 19:26 4:59 6:03 20:17 N/A 88 2 57.4 11 18
Fri Sep 28 - Sat Sep 29 18:21 19:25 4:59 6:03 21:00 N/A 80 3 50.6 15 03
Sat Sep 29 - Sun Sep 30 18:20 19:25 4:59 6:04 21:48 N/A 71 4 46.3 18 01
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Wednesday 26 September 2018.
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