Maunakea Weather Center

Maunakea Observatories Forecast
5 PM HST Monday 18 March (0300 UTC Tuesday 19 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 1.5 C this evening and 1 C tomorrow morning. Winds will be from the WNW at 5-15 mph, with seeing near 0.4-0.5 arcseconds for the night. Precipitable water is expected to be in the 0.8-1 mm range for the first half of the night and 0.6-0.8 mm range for the second half.

Discussion
A well-defined tradewind inversion will continue to cap low-level moisture at or below 8 thousand feet and ensure the summit remains dry/stable through the next 5 nights. Daytime clodus will be minimal and short-lived into the weekend.

Skies will remain predominately clear for tonight, but a band of patchy mid/upper-level clouds are expected to move in from the NW and pass through the area for Tuesday and Wednesday night. These clouds will shift eastward by late Thursday morning, leaving predominately clear skies for that night as well as Friday night.

Precipitable water is expected to start out near 1 mm for this evening, but will trend toward 0.6 mm as the night progresses, only to jump to 1.5-2 mm for much of Tuesday night, and probably 3-4 mm for Wednesday night. There is a good chance that PW will decrease toward 1 mm through Thursday night, and settle in around 0.6-0.7 mm for Friday night.

Decreasing winds at summit-level, combined with mostly calm/stable skies and laminar westerly flow in the free atmosphere should allow seeing to settle in near 0.4-0.45 arcseconds for much of the next 3 nights. There is a possibility for increasing low-level dynamic turbulence, which could begin to degrade seeing late Thursday night, while strengthening boundary layer turbulence will likely contribute to bad seeing for Friday night.

No change since the morning forecast...Although the mid-level ridge will remain rather indistinct for the next several days, the surface ridge to the NE will continue to promote steady large-scale subsidence in the area into the weekend. In addition, a broad but shallow westerly jet will maintain a rather zonal orientation across much of the Pacific, minimizing instability near the Islands until the development of an upper-level trough in the area over the next few days. Fortunately, this developing trough is expected to coincide with the rebuilding of the mid-level ridge filling in from the NW late in the week. Nevertheless, subsidence associated with the surface ridge will easily maintain a well-defined inversion at or below 8 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Mostly calm skies with laminar westerly flow in the free atmosphere should allow seing to settle in around 0.4-0.45 arcseconds for at least the next 3 nights. The aforementioned developing trough will initially remain rather weak/indistinct, but could bring mid/upper-level clouds/moisture to the area, resulting in an increase in CC/PW mainly around Wednesday. The bulk of this moisture is actually expected to slide eastward as the trough gradually deepens over the state around Thursday/Friday. Still, instability associated with developing trough is not expected overcome subsidence from the surface to the NE and the building mid-level ridge to the NW until perhaps an upper-level low spawns just south of the state late in the weekend. There is a very good chance that a tight wind gradient will form along the SE flank of the mid-level ridge and the mid-level reflection of the trough beginning Friday. This will likely conribute to an increase in winds, which will stir up boundary layer turbulence and result in bad seeing for much of the weekend.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Mon Mar 18 - 8 PM0-5Clear0 / 01.5WNW/5-150.4-0.60.8-1
Tue Mar 19 - 2 AM0-5Clear0 / 01WNW/5-150.35-0.450.6-0.8
2 PM0-20Clear0 / 05.5WSW/5-15NaN1-2
8 PM0-207.5-80 / 00WSW/5-150.3-0.51.5-2
Wed Mar 20 - 2 AM10-307.5-80 / 0-1SW/5-150.3-0.41.5-2
2 PM20-406.5-7.50 / 03.5WSW/5-15NaN2-4
8 PM20-406.5-7.50 / 0-2WSW/0-100.35-0.553-4
Thu Mar 21 - 2 AM30-506.5-7.50 / 0-3W/0-100.35-0.553-4
2 PM10-306.5-70 / 00N/5-15NaN2-4
Fri Mar 22 - 2 AM0-10Clear0 / 0-3.5NNE/10-200.45-0.751-2
2 PM0-20Clear0 / 00NNE/15-30NaN1-2
Sat Mar 23 - 2 AM0-5Clear0 / 0-4NE/25-400.8-1.60.7-1.1
2 PM0-20Clear0 / 06ENE/35-50NaN0.6-1
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
Mon Mar 18 - Tue Mar 19 18:41 19:46 5:13 6:17 N/A 3:21 71 7 49.5 26 09
Tue Mar 19 - Wed Mar 20 18:42 19:46 5:12 6:16 N/A 4:04 80 8 41.7 23 09
Wed Mar 20 - Thu Mar 21 18:42 19:46 5:11 6:16 N/A 4:42 87 9 30.7 19 10
Thu Mar 21 - Fri Mar 22 18:42 19:47 5:10 6:15 N/A 5:16 93 10 16.9 14 26
Fri Mar 22 - Sat Mar 23 18:43 19:47 5:09 6:14 N/A 5:48 97 11 01.0 9 09
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 19 March 2024.
Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products