Maunakea Weather Center

Maunakea Observatories Forecast
5 PM HST Friday 23 February (0300 UTC Saturday 24 February) 2024
Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while patches of mid/upper-level clouds spread in from the west and/or develop in the area throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 3 C this evening and 1 C tomorrow morning. Winds will be from the WSW at 10-20 mph for this evening, switching to a more WNW direction through the night. Seeing will be near 0.5-0.6 arcseconds, while precipitable water is expected to start out near 1 mm, but will increase toward 4 mm as the night progresses.

Discussion
A well-defined inversion will continue to cap low-level moisture at or below 9 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

A narrow band of mid/upper-level clouds is expected to spread in from the west and/or develop near/over the summit area for tonight then will shift off toward the east just after sunrise tomorrow. Another patch of quick-moving cirrus is projected to fill in from the WSW and briefly pass over Big Island for tomorrow night. Clear skies will prevail for Sunday and Monday night, but there is a chance that light dissipating cirrus will spread in from the west for Tuesday night.

Precipitable water is expected to start out near 1 mm for this evening, but will trend toward 4 mm through the night. There is a good chance that it will dip toward 3-3.5 mm by late tomorrow morning through that night, then dip into the 2-3 mm range for Sunday night, and settle in probably around 1.5 mm for the following 2 nights.

Despite steady upper-level shear in the free atmosphere, light/calm winds at the summit combined with mainly laminar westerly flow overhead should allow seeing to settle in around 0.4-0.5 arcseconds for at least tonight. A subtle increase in upper-level flow could result in a slight degradation toward 0.5-0.55 arcseconds for the next 3 nights. Strong westerly flow (> 100 mph) aloft could further degrade seeing for the early part of next week

No change since the morning forecast...While an omega-like pattern (with a low to the NW, a ridge to the north and another low to the NE) will continue set up NE Pacific into early next week, large-scale/steady subsidence associated with the mid/surface ridge will govern the state throughout the forecast period. This subsidence will easily sustain a well-defined inversion at or below 9 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. While the westerly jet will remain quite active/intense, it will maintain a fairly zonal orientation and split into two further west of the Dateline. The latter will result in a more shallow jet overhead, which will allow for relatively calm winds near summit-level probably well into next week. The strength of the jet will still promote steady moderate/strong upper-level shear, which will likely keep seeing in around 0.5-0.6 arcseconds through at least the weekend. However, the low to the NW will continue to draw moisture/clouds out the tropics, which is expected to be shuttled eastward (via the jet overhead) and towards the stronger low intensifying to the NE over the next 24-30 hours. This will result in an increase in CC and PW mainly over the early half of the weekend. PW and CC should improve as the low to the NW weakens and loses access to tropical moisture during the second half of the weekend. There is a good chance that the low to the NE will strengthen the southern portion of the westerly jet early next week. This could result in upper-level westerly flow around 120-130 mph, which will contribute to significant shear and probably a subtle degration in seeing (toward 0.6-0.65 arcseconds) for Monday and Tuesday night.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Fri Feb 23 - 8 PM0-207-80 / 03WSW/10-200.45-0.651-2
Sat Feb 24 - 2 AM10-306-80 / 01WNW/10-200.45-0.652-4
2 PM20-408-90 / 05WNW/5-15NaN2-4
8 PM40-607-90 / 0-0.5NW/5-150.5-0.73-4
Sun Feb 25 - 2 AM30-508-90 / 0-0.5NW/5-150.45-0.653-4
2 PM0-20Clear0 / 04N/5-15NaN3-5
8 PM0-5Clear0 / 0-1NNE/5-150.45-0.652.5-3.5
Mon Feb 26 - 2 AM0-5Clear0 / 0-1.5NE/5-150.45-0.652-3
2 PM0-20Clear0 / 03NE/0-10NaN1.5-2.5
Tue Feb 27 - 2 AM0-5Clear0 / 0-2NE/0-100.525-0.7751-1.5
2 PM0-20Clear0 / 03W/0-10NaN1-2
Wed Feb 28 - 2 AM0-208-90 / 0-2.5W/0-100.475-0.7251-1.5
2 PM0-208-90 / 03NW/0-10NaN1-2
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
Sat Feb 24 - Sun Feb 25 18:34 19:39 5:31 6:36 18:45 N/A 99 11 13.6 7 43
Sun Feb 25 - Mon Feb 26 18:34 19:39 5:31 6:35 19:33 N/A 97 11 56.1 2 05
Mon Feb 26 - Tue Feb 27 18:35 19:39 5:30 6:34 20:20 N/A 92 12 38.3 -3 37
Tue Feb 27 - Wed Feb 28 18:35 19:40 5:29 6:34 21:08 N/A 87 13 21.2 -9 14
Wed Feb 28 - Thu Feb 29 18:36 19:40 5:28 6:33 21:58 N/A 79 14 05.6 -14 33
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 26 February 2024.
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