Current Conditions
Temp-0.6 C
RH97 %
WindW 0 mph
RoadClosed
Mauna Kea Observatories Forecast
5 PM HST Friday 20 April (0300 UTC Saturday 21 April) 2018
Warning(s)
Chance for fog, ice and high humidity
Cloud Cover and Fog/Precipitation Forecast
There is a moderate/high risk for fog, ice, high humidity mainly during the early portion of the night; precipation is unlikely. Banding high clouds will continue to pass overhead, contributing to mostly overcast skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 0 C for this evening and 1 C tomorrow morning. Winds will be from the NE at 10-20 mph, while seeing will likely exceed 1 arcsecond. Precipitable water will start out near 4 mm, but will slip toward 3 mm through the night.
Discussion
Although the upper air mass is expected to rapidly dry out around sunset today, residual low-level moisture and instability may keep the inversion elevated and could allow for more fog, ice, high humidity particularly during the early portion of the night. The inversion is set to restrengthen near 7-8 thousand feet through tomorrow and ensure the summit remains dry/stable for the remainder of the forecast period. Daytime clouds will taper for tomorrow and become minimal and short-lived for Sunday and early part of next week.

Banding high clouds will continue to stream over the summit, contributing to mostly overcast skies for tonight. There is a chance that this stream will break up a bit, but extensive cloud cover will remain an issue until this band sags southward for Monday night. Unfortunately, this band may return northward, increasing cloud cover once again for Tuesday night.

Precipitable water will start out near 4 mm, but will slip toward 3 mm through the night and likely settle in near 2-3 mm for following 3 nights, then drop toward 1 mm for Tuesday night.

Strong turbulence in the free atmosphere, combined with lingering moisture/instability will result in bad seeing for tonight. While the air mass is set to stabilize/dry for subsequent nights, persistent turbulence in the free atmosphere will still contribute to poorer than average seeing for tomorrow night. There is a possibility that calmer skies will allow seeing to improve toward more average-like seeing for Sunday and Monday night, while laminar (albeit strengthening) flow aloft could help further improve seeing for Tuesday night.

Little change since the morning forecast...An embedded short-wave trough in the large scale tropical upper-tropospheric trough (TUTT) will continue to shift eastward and weaken, allowing the TUTT to retreat westward and a new mid-level ridge to build in from the west through the night and into tomorrow. Unfortunately, abundant/residual low-level moisture in the area could allow for more periods of fog, ice and high humidity at the summit especially during the early portion of the night Eventually, large-scale subsidence associated with the building ridge will help restrengthen the inversion over the course of tomorrow and ensure the summit remains dry and stable for the remainder of the forecast period. However, the sub-tropical jet is expected to linger in the area and shuttle banding high clouds overhead through the weekend. While there is a possibility that the STJ will briefly shift southeastward, allowing skies to open up to the north and perhaps overhead for Monday night, the jet is set to expand westward and broaden/strengthen, bringing a fresh band of high clouds overhead for Tuesday night. This expansion may actually help reduce turbulence in the free atmosphere (though laminar westerly flow) and could allow seeing to improve (toward average/good values) by Tuesday 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)
Fri Apr 20 - 8 PM80-1007-1075 / 150NE/10-200.8-1.63.5-4.5
Sat Apr 21 - 2 AM80-1008-1050 / 101NE/10-200.7-1.32.5-3.5
2 PM80-1009-1040 / 106NE/10-20NaN3-6
8 PM70-909-100 / 02NE/10-200.6-12-3
Sun Apr 22 - 2 AM70-908.5-100 / 01.5ENE/10-200.6-0.92-3
2 PM60-808-100 / 08NE/10-20NaN2-3
8 PM60-808-100 / 03NE/10-200.55-0.752.5-3.5
Mon Apr 23 - 2 AM60-808-100 / 02.5NE/10-200.5-0.72.5-3.5
2 PM20-408-90 / 07NE/10-20NaN2-3
Tue Apr 24 - 2 AM10-308-90 / 02NNE/5-150.5-0.82-3
2 PM20-409-100 / 07NNW/5-15NaN1-2
Wed Apr 25 - 2 AM50-709-100 / 01.5NW/5-150.45-0.650.9-1.3
2 PM60-808.5-100 / 06.5NW/5-15NaN1-2
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
Fri Apr 20 - Sat Apr 21 18:51 19:58 4:43 5:50 N/A 23:53 33 6 45.7 20 04
Sat Apr 21 - Sun Apr 22 18:51 19:58 4:42 5:50 N/A 0:51 44 7 46.1 19 21
Sun Apr 22 - Mon Apr 23 18:51 19:59 4:41 5:49 N/A 1:44 55 8 45.4 17 25
Mon Apr 23 - Tue Apr 24 18:52 19:59 4:41 5:48 N/A 2:34 66 9 42.8 14 24
Tue Apr 24 - Wed Apr 25 18:52 20:00 4:40 5:47 N/A 3:19 76 10 38.1 10 34
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 23 April 2018.
Additional Information
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