Maunakea Weather Center

Maunakea Observatories Forecast
6 AM HST (1600 UTC) Wednesday 29 May 2024

Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while broken high clouds build in from the west, contributing to extensive cloud cover as the night progresses.

Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon, 3 C this evening and 2 C tomorrow morning. Winds will be from the WNW at 10-20 mph, with seeing near 0.6-0.7 arcseconds for the night. Precipitable water is expected to exceed 4 mm throughout the night.

Despite humidity near 50-60%, a well-defined inversion will continue to cap the limited supply of organized low-level moisture near 7-8 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Some minor afternoon clouds are possible mainly through tomorrow, then will become minimal and short-lived again for the remainder of the week.

Scattered to broken mid/upper-level clouds will continue to drift in from the west and could contribute to periods of extensive cloud cover over the next 3 nights, particularly between midnight and Friday morning. These clouds will pass off toward the east, leaving residual mid-level clouds in the area for Friday night. Mostly clear skies will prevail overhead for the weekend.

Precipitable water is expected to linger near or exceed 4 mm throughout much of the forecast period.

Although mostly laminar WNW flow will prevail in the free atmosphere, winds at and/or just above the summit will likely contribute to low-level and/or boundary layer turbulence, which may result in average/poor seeing over the next 2 nights. There is a good chance that winds will subside and allow seeing to improve through Friday night and probably settle in near 0.5 arcseconds as predominately light winds and stable skies prevail above the summit over the weekend.

A deep surface ridge will persist in NE Pacific and continue to promote strong/steady subsidence in the area through the week. This subsidence will easily offset the instability associated with the tropical upper-tropospheric trough (TUTT) lingering to the west, maintain a well-defined tradewind inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. Unfortunately, the mid-level ridge will initially remain rather indistinct, allowing the sub-tropical jet (STJ) to deepen into the mid-level portion of the atmosphere over the next 48 hours. While mostly laminar WNW flow will prevail in the free atmosphere, flow at and especially just above the summit may remain 20-25 mph, which could stir up light dynamic turbulence and contribute to slightly poorer than average seeing over the next 2 nights. An upper-level low to the NW and embedded within the TUTT will have no impact on the stability of the atmosphere, but will continue to send mid/upper-level moisture into the STJ and over the summit during that time. This will likely result in extensive cloud cover and high PW (as well as humidity) through at least Thursday night. There is a very good chance that skies will begin to open up, while PW slowly declines as the low shifts just east of the state over the weekend. This will also allow the mid-level ridge to restrengthen to the NE, resulting in a more shallow STJ, lighter winds at the summit (and probably above) and thus likely improvement in seeing during that time.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Wed May 29 - 2 PM40-606-70 / 08WNW/10-20NaN6-10
8 PM50-708-100 / 03WNW/10-200.525-0.7756-10
Thu May 30 - 2 AM70-908-100 / 02WNW/10-200.525-0.7754-8
2 PM80-1007.5-100 / 08WNW/15-30NaN4-8
8 PM80-1007-100 / 03WNW/15-300.6-0.94-6
Fri May 31 - 2 AM60-807-100 / 02WNW/15-300.6-0.94-6
2 PM40-607-80 / 07.5WNW/10-20NaN4-8
8 PM20-407-80 / 02.5NW/10-200.475-0.7254-6
Sat Jun 01 - 2 AM10-307-100 / 02NNW/5-150.45-0.654-6
2 PM0-20Clear0 / 07NNE/0-10NaN4-6
Sun Jun 02 - 2 AM0-10Clear0 / 01.5S/0-100.4-0.63-5
2 PM0-20Clear0 / 06.5SSE/5-15NaN4-6
Mon Jun 03 - 2 AM0-10Clear0 / 00.5SSE/5-150.375-0.6253-5
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 May 29 - Thu May 30 19:06 20:19 4:20 5:33 0:33 N/A 53 22 38.0 -12 45
Thu May 30 - Fri May 31 19:07 20:20 4:20 5:33 1:12 N/A 41 23 28.9 -6 20
Fri May 31 - Sat Jun 01 19:07 20:20 4:19 5:32 1:50 N/A 30 0 18.9 0 22
Sat Jun 01 - Sun Jun 02 19:07 20:21 4:19 5:32 2:28 N/A 20 1 09.2 7 03
Sun Jun 02 - Mon Jun 03 19:08 20:21 4:19 5:32 3:08 N/A 12 2 01.0 13 20
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 29 May (0300 UTC Thursday 30 May) 2024.
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