Maunakea Weather Center

Maunakea Observatories Forecast
5 PM HST Wednesday 06 December (0300 UTC Thursday 7 December) 2023

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 C tomorrow morning. Winds will be light and from the ENE at 5-15 mph for this evening, switching to a more SE direction as the night progresses. Seeing will be near 0.4 arcseconds, while precipitable water is expected to be in the 0.5-0.7 mm range for the night.

A very distinct inversion near 7 thousand feet, combined with a dry/stable mid/upper-level air mass will ensure the summit steers free of fog and precipitation through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Skies will remain predominately clear through probably through at least Thursday evening. There is chance that a batch of scattered cirrus will quickly move in from the south and pass along the SE skies early Friday morning. More organized cirrus will quickly follow suit that afternoon/evening and is expected to move over the Big Island, contributing to extensive cloud cover (or even overcast skies) for much of Friday night and much of Saturday night. These clouds are expected to abrutly shift eastward late Sunday morning, leaving clear skies again for that night.

Precipitable water is expected to settle in around 0.6 mm for the next 2 nights, then increase back toward 1-1.5 mm for Friday and Saturday night, then drop back toward 1 mm or less for Sunday night.

Very light predominately easterly flow at and above the summit, combined with a dry/stable air mass will allow seeing to settle in near 0.4 arcseconds for another night. Upper-level westerly flow is set to pick up early tomorrow, resulting in an increase free atmospheric turbulence and a degradation (toward 0.6 arcseconds) in seeing for Thursday and especially Friday night. Flow aloft is expected to weaken, which should help diminish free atmospheric turbulence and allow seeing to improve back toward 0.4-0.5 arcseconds for Saturday and Sunday night.

No change since the morning forecast...A deep ridge will continue to sit to the north of the state and stretch across most of the Pacific before sagging briefly southward in response to a weak trough passing through the area around Friday/Saturday, only to rebound back northward over the weekend. Nevertheless, strong/steady subsidence associated with the ridge will prevail near the Big Island, which will help maintain a very well-defined inversion near 7 thousand feet and ensure a dry/stable summit-level air mass probably into next week. The depth, positioning and shape of the ridge will also initially keep the westerly jet flowing west to east well to the north of the state for another 12-18 hours. This will allow mostly clear/calm skies to prevail in the free atmosphere, and combined with deep/light easterly flow associated with the ridge, should keep seeing near 0.4 arcseconds for tonight. Upper-level westerly flow is projected to increase as the incoming weak passing trough expands the westerly jet southward beginning Thursday. This will could increase free atmospheric shear, and result in a degradation in seeing (toward 0.55-0.6 arcseconds) over Thursday night and especially Friday night. While the trough is not expected to affect the stability of the atmosphere, it could drag banding high clouds in from the south contribute to extensive cloud cover at the summit between late Friday afternoon and around midnight Saturday. These clouds are set to push off toward the east with the passing of the trough axis on Sunday morning, allowing clear skies to prevail overhead for that night. Seeing should also improve as the westerly jet retracts northward and lighter flow builds in aloft late Saturday night and particularly for Sunday night.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Wed Dec 06 - 8 PM0-5Clear0 / 03ENE/0-100.35-0.450.5-0.7
Thu Dec 07 - 2 AM0-5Clear0 / 02SE/0-100.35-0.450.5-0.7
2 PM0-20Clear0 / 08N/0-10NaN0.6-1
8 PM0-5Clear0 / 03.5NE/0-100-10.5-0.7
Fri Dec 08 - 2 AM0-209.5-100 / 03.5SSE/0-100.45-0.650.5-0.7
2 PM20-409-100 / 08SW/5-15NaN0.6-1
8 PM40-608-100 / 02.5NW/5-150.475-0.7251-1.5
Sat Dec 09 - 2 AM60-808-100 / 02.5W/5-150.475-0.7251-1.5
2 PM80-1008-100 / 08WNW/0-10NaN1-2
Sun Dec 10 - 2 AM40-608-90 / 02N/0-100.4-0.61-1.5
2 PM0-20Clear0 / 08NNE/5-15NaN1-2
Mon Dec 11 - 2 AM0-5Clear0 / 03NNE/5-150.3-0.50.7-1.1
2 PM0-20Clear0 / 09NE/10-20NaN1-1.5
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
Wed Dec 06 - Thu Dec 07 17:52 19:01 5:26 6:34 1:51 N/A 29 12 37.1 -2 31
Thu Dec 07 - Fri Dec 08 17:52 19:01 5:26 6:35 2:40 N/A 21 13 20.4 -8 10
Fri Dec 08 - Sat Dec 09 17:53 19:01 5:27 6:36 3:32 N/A 13 14 05.7 -13 36
Sat Dec 09 - Sun Dec 10 17:53 19:02 5:27 6:36 4:28 N/A 7 14 54.3 -18 37
Sun Dec 10 - Mon Dec 11 17:53 19:02 5:28 6:37 5:27 N/A 3 15 46.9 -22 53
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Thursday 7 December 2023.
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