Current Conditions
Temp4.9 C
RH10 %
WindN 0 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 22 May (0300 UTC Tuesday 23 May) 2017
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 3.5 C this evening and 3 C tomorrow morning. Winds will be from the ENE at 5-15 mph, with seeing around 0.55-0.6 arcseconds. Precipitable water is expected to be in the 2.5-3.5 mm range for the night.
Discussion
A fairly well-defined tradewind inversion will continue to cap low-level moisture near 7-8 thousand feet and ensure the summit remains dry and stable through at least Thursday night. There is a chance that building instability will weaken the inversion and increase the risk for fog and high humidity at the summit for Friday night; precipitation is unlikely. Daytime clouds will be minimal and short-lived through Thursday, but could pick up for Friday and over the weekend.

Broken high clouds will continue to pass over and especially along the southern skies contributing to extensive cloud cover before pushing off toward east early tomorrow afternoon. Although this should help open up skies for most of that night, thin cirrus may pass along the northern skies early Wednesday morning, while banding may also scrape the southern half of the Big Island for that night. Clear skies will prevail for Thursday evening, but scattered to broken high clouds are set to drift in from the west and may contribute to another round of extensive cloud cover for much of Friday and over the weekend.

Precipitable water is expected to linger near 3 mm for tonight, briefly slip toward 1.5-2 mm for tomorrow night, then increase to 3-4 mm for Wednesday and Thursday night and probably 4+ mm for Friday night.

Relatively laminar westerly flow will prevail in the free atmosphere, likely allowing seeing to settle in near 0.5-0.6 arcseconds for the next 3 nights. A gradual increase in upper-level instability, combined with light boundary layer turbulence, could degrade seeing toward 0.65-0.7 arcseconds for Thursday and Friday night.

Very little change since the morning forecast...Although the mid-level ridge will remain rather weak/indistinct probably through most of the week, the persistent low-level ridge to the north will continue to instill steady large-scale subsidence in the area during this time. This subsidence will help maintain the tradewind inversion near 7-8 thousand feet and ensure a dry/stable summit-level air mass through at least Thursday night. There is a possibility that the tropical upper-troposperic trough (TUTT) very gradually rebuilding far to the west will begin to migrate eastward and destabilize the air mass later in the week. This instability may help erode/weaken the tradewind inversion, which could lead to periods of fog/high humidity at the summit by Friday night. Right now, the odds are on the small side, but that could change as the TUTT deepens in the area later in the weekend. Nevertheless, the TUTT and especially its slowly strengthening southern counterpart, the sub-tropical jet (STJ), will send scattered to broken high clouds through the area over much of the week. Fortunately, the STJ will remain relatively deep (vertically), allowing laminar flow to persist above the summit, which should result in minimal turbulence in the free atmosphere and better than average seeing over the next 3 nights. Summit-level winds may pick up once the STJ begins to pick up steam, which may stir up minor boundary layer turbulence and degrade seeing a bit for Thursday and Friday night.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Mon May 22 - 8 PM60-808.5-100 / 03.5ENE/5-150.5-0.72.5-3.5
Tue May 23 - 2 AM60-808-100 / 03ENE/5-150.45-0.652.5-3.5
2 PM40-608-90 / 07ENE/5-15NaN2-3
8 PM0-20Clear0 / 02E/5-150.45-0.651.5-2
Wed May 24 - 2 AM10-309.5-100 / 01.5SE/5-150.45-0.651.5-2
2 PM30-509-100 / 06W/0-10NaN2-4
8 PM50-709-100 / 00.5W/0-100.4-0.63-4
Thu May 25 - 2 AM40-609-100 / 00WSW/5-150.45-0.653-4
2 PM0-20Clear0 / 05.5WNW/10-20NaN3-5
Fri May 26 - 2 AM20-409.5-100 / 00.5WNW/15-250.5-0.83-4
2 PM60-808-1040 / 104WNW/15-25NaN4-8
Sat May 27 - 2 AM60-808-1025 / 50W/10-200.5-0.94-6
2 PM0-209-1060 / 154NW/10-20NaN6-10
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 May 22 - Tue May 23 19:03 20:15 4:22 5:34 3:58 N/A 9 1 53.7 6 26
Tue May 23 - Wed May 24 19:04 20:16 4:22 5:34 4:48 N/A 3 2 50.5 10 43
Wed May 24 - Thu May 25 19:04 20:16 4:21 5:33 5:41 18:14 1 3 49.9 14 23
Thu May 25 - Fri May 26 19:04 20:17 4:21 5:33 6:38 19:20 1 4 51.5 17 04
Fri May 26 - Sat May 27 19:05 20:17 4:21 5:33 N/A 20:26 4 5 54.3 18 33
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 23 May 2017.
Additional Information
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