Maunakea Weather Center

Maunakea Observatories Forecast
5 PM HST Thursday 07 December (0300 UTC Friday 8 December) 2023
Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while light cirrus pass mainly along the south and SE skies particularly during the second half of the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 4 C for this evening and 3.5 C tomorrow morning. Winds will be light and varialble, with seeing near 0.5-0.6 arcseconds for the night. Precipitable water is expected to linger in the 0.5-0.7 mm range through the night.

Discussion
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.

A stream of light cirrus passing along the southern skies will continue to creep northward into this evening, then will slip by along the SE coast of the Big Island later in the night. This stream is expected thicken and perhaps spread over the Big Island, contributing to periods of extensive cloud cover for between Friday afternoon and early Saturday evening. These clouds will abruptly shift eastward early Sunday morning, leaving clear skies for that night and the early part of next week.

Precipitable water is expected to linger in the 0.5-0.7 mm range for tonight, then increase and settle in near 0.7-0.9 mm probably for the remainder of the forecast period.Increasing shear in the free atmosphere will likely push seeing toward 0.5-0.6 arcseconds for tonight and there is a possibility that a brief passage of upper-level turbulence will further degrade seeing toward 0.6-0.7 arcseconds for tomorrow night and maybe into early Saturday evening. Lighter winds at and above the summit and a more stable upper air mass are expected to quickly build in and allow seeing to improve during the latter night, and perhaps settle in near 0.3-0.4 arcseconds for at least Sunday night. There is a possibility that stronger winds below the summit may contribute to a minor degradation and/or variation in seeing for Monday night.

Some changes have been made, mainly to the PW forecast...Although a trough passing to the far north is expected to squash the ridge southward, subside will still prevail near the Big Island well into next week. This subsidence will easily maintain a well-defined inversion primarily near 7 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Unfortunately, the passing trough is expected to dismantle the upper-level ridge over the next 24-36 hours and help the westerly ridge to expand southward over the next week or so. Strong upper-level SW flow along the eastern flank of the incoming trough will transport banding cirrus out of the tropics and over the eastern half of the Big Island particularly between tomorrow afternoon and early Saturday evening. This flow will also contribute to increasing shear and free atmospheric turbulence over the next 48 hours, resulting in more average-like seeing over the next 2-3 nights. The high clouds are expected abruptly shift eastward as the trough axis passes over the Big Island around midnight Saturday. This will not only open up summit skies, but allow lighter northerly flow along the western flank of the trough to fill in over the area for the remainder of the weekend. That could allow seeing to improve through Saturday night and even settle in around 0.3-0.4 arcseconds for Sunday night. The last two model runs have backed off an increase in mid-level flow, but still expect rather strong/deep low-level trades for Monday night. This could be enough to stir up minor ground layer turbulence and perhaps result in a slight degradation/variation in seeing during that night.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Thu Dec 07 - 8 PM10-309.5-100 / 04NE/0-100.45-0.650.5-0.7
Fri Dec 08 - 2 AM20-409.5-100 / 03.5SE/0-100.45-0.650.5-0.7
2 PM40-609-100 / 08SW/5-15NaN0.7-1.1
8 PM40-609-100 / 02.5NW/5-150.525-0.7750.6-0.8
Sat Dec 09 - 2 AM60-808-100 / 02.5W/5-150.525-0.7750.7-0.9
2 PM60-809-100 / 08W/0-10NaN0.8-1.2
8 PM40-609-100 / 03SSE/0-100.5-0.70.7-0.9
Sun Dec 10 - 2 AM20-409-9.50 / 02NE/5-150.4-0.60.7-0.9
2 PM0-20Clear0 / 08ENE/5-15NaN0.8-1.2
Mon Dec 11 - 2 AM0-5Clear0 / 02.5E/5-150.25-0.450.7-1
2 PM0-20Clear0 / 07.5ENE/5-15NaN0.8-1.2
Tue Dec 12 - 2 AM0-5Clear0 / 02.5NE/5-150.35-0.650.7-1
2 PM0-20Clear0 / 08NNE/0-10NaN0.8-1.2
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
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
Mon Dec 11 - Tue Dec 12 17:54 19:02 5:29 6:37 6:30 16:56 0 16 43.9 -26 04
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Friday 8 December 2023.
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