Maunakea Weather Center

Maunakea Observatories Forecast
5 PM HST Thursday 28 March (0300 UTC Friday 29 March) 2024
Warning(s)
None

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 -1 C, with light northerly winds through the night. Precipitable water is expected to start out near 4 mm, but could dip to 3 mm or less by the end of the night.

Discussion
A well-defined inversion will continue to cap low-level moisture at or below 8 thousand feet well into next week, while a drier mid-level air mass builds into the area over the next 3-6 hours. This will help drop summit-level humidity toward 20% by this evening and ensure the summit steers free of fog and precipitation through the next 5 nights. Daytime clouds will be minimal and short-lived through Monday, but could pick up for Tuesday.

Skies overhead will remain predominately clear for tonight, while a narrow band of cirrus quickly fills in from the west late tomorrow afternoon, passing mainly along the southern skies for that night and into Saturday. This band will quickly sag further southward near sunset on Saturday, leaving mostly clear skies again for the remainder of the weekend and through Monday night.

Precipitable water is expected to start out near 4 mm for this evening, but could dip below 3 mm or less by the end of the night and continue to trend toward 1-1.5 mm through Friday night. There is a good chance that PW will settle in the 1-1.5 mm range for Saturday night, then slip to 0.8 mm or less for the following 2 nights.

Mostly calm/stable skies with light winds at and above the summit, combined with a drier mid-level air mass should allow seeing to settle in around 0.45-0.5 arcseconds for tonight. There is a chance for an increase in low-level turbulence as deep easterly flow increases in the 10-20 thousand feet layer, which could result in a degradation in seeing (to 0.6-0.65 arcseconds) for Friday night. These winds will taper as laminar westerly flow sets up in the free atmosphere, which will likely allow seeing to settle back in around 0.4-0.5 arcseconds for the following 3 nights.

No change since the morning forecast...A deep mid/surface ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area into next week. This subsidence will easily negate passing rather shallow upper-level troughs, help maintain a well-defined inversion at or below 8 thousand feet and ensure the summit steers free of fog and precipitation through the next 5 nights. Residual mid-level moisture lingering in the area will continue to detrain into the surrounding air mass and/or shift off toward the SE, which should allow summit-level humidity to drop to 20% by the start of the night. PW will be a little slower to respond, but could slip to 3 mm by the end of the night, dip into the 1-1.5 mm range for Friday and Saturday night, then settle in below 1 mm, as very dry mid/upper-level air builds into the area for the following 2 nights. Any moisture will have little impact on seeing, which could dip toward 0.4-0.5 arcseconds as relatively light/variable winds and a generally stable/calm air mass prevails in the free atmosphere for tonight. However, deep easterly winds are set to pick up below 20 thousand feet as the ridge to the north expands in response to a passing of a short-wave trough on Friday. While its unlikely summit-level winds will top 20 mph for any prolong period, the deep easterlies could stir up low-level dynamic turbulence and contribute to average/poor seeing for Friday night. The deep easterly winds will subside again as the mid-level portion of the ridge retracts toward the NE, while a shallow sub-tropical jet sets up just over or south of the Big Island over the weekend and into next week. While this could result in an increase in upper-level shear (near 25-30K feet), it should have little impact on seeing, which will probably settle back in around 0.4-0.5 arcseconds after Friday 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 Mar 28 - 8 PM0-5Clear0 / 0-1N/0-100.4-0.63-4
Fri Mar 29 - 2 AM0-5Clear0 / 0-1N/0-100.35-0.552.5-3.5
2 PM0-20Clear0 / 04.5NE/5-15NaN1.5-2.5
8 PM0-208-90 / 00NE/10-200.5-0.81-1.5
Sat Mar 30 - 2 AM10-308-90 / 0-0.5ENE/10-200.5-0.71-1.5
2 PM20-408-100 / 05.5NE/5-15NaN1-2
8 PM0-209-100 / 00.5NNE/5-150.4-0.61-1.5
Sun Mar 31 - 2 AM0-5Clear0 / 00NNE/5-150.35-0.551-1.5
2 PM0-20Clear0 / 05.5NE/0-10NaN1-1.5
Mon Apr 01 - 2 AM0-5Clear0 / 00E/0-100.35-0.550.6-1
2 PM0-20Clear0 / 05.5S/0-10NaN0.8-1.25
Tue Apr 02 - 2 AM0-20Clear0 / 00S/5-150.4-0.60.6-1
2 PM60-804-560 / 202.5SSE/10-20NaN3-6
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 Mar 28 - Fri Mar 29 18:44 19:49 5:04 6:09 21:39 N/A 84 15 29.6 -22 45
Fri Mar 29 - Sat Mar 30 18:44 19:49 5:03 6:08 22:35 N/A 76 16 22.8 -26 06
Sat Mar 30 - Sun Mar 31 18:45 19:50 5:02 6:07 23:34 N/A 67 17 19.5 -28 14
Sun Mar 31 - Mon Apr 01 18:45 19:50 5:01 6:06 0:33 N/A 57 18 18.9 -28 51
Mon Apr 01 - Tue Apr 02 18:45 19:50 5:00 6:05 1:30 N/A 46 19 19.3 -27 50
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday April 1 2024.
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