Current Conditions
Temp1.8 C
RH28 %
WindSSE 9 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Monday 24 September (0300 UTC Tuesday 25 September) 2018
Cloud Cover and Fog/Precipitation Forecast
There is a slight risk for short-lived fog and high humidity toward the end of the night; precipitation is not expected and skies will remain predominately clear.
Summary of Key Meteorological Variables
Summit temperatures will be near 4 C this evening and 3.5 C tomorrow morning. Winds will be from the south at 5-15 mph, with seeing near 0.6-0.65 arcseconds. Precipitable water is expected to be in the 2-2.5 mm range for the night.
While the inversion will start out fairly well-established near 6-7 thousand feet for this evening, it is expected to lift toward 12 thousand feet by sunrise tomorrow, breakdown further for that night, then restrengthen through Wednesday and into Thursday, only to weaken again on Friday. Consequently, there is a risk for fog and high humidity throughout some portions of the forecast period (mainly Tuesday/Wednesday night and perhaps Friday night); with the possible exception of Tuesday night precipitation is unlikely through the next 5 nights. Daytime clouds will be minimal and short-lived for today and perhaps Thursday, but could turn extensive for the Tuesday, Wednesday and Friday. There is also a possibility for afternoon convection along the slopes, mainly for tomorrow and Wednesday.

Skies will remain predominately clear for tonight, but a patch of mid/high clouds of clouds may drift in from the south through tomorrow night, a more organized band of clouds sets up (SSW to NNE) over the summit for Wednesday night. This band may lift toward the NW through Thursday night, opening up skies a bit for Friday.

Precipitable water is expected to linger near 2-2.5 mm for tonight, then will increase to 4+ mm probably for the next 4 nights.

There is a possibility that a patch of mid/upper-level turbulence passing through the area will contribute to more average-like somewhat variable seeing for tonight. An influx of moisture/instability may contribute to poorer than average seeing mainly for Tuesday night, but a drying/stabilizing trend should help improve seeing through Wednesday night and especially Thursday night. Some degradation in seeing is possible due to an increase in boundary layer turbulence for Friday night.

Not much change since the morning forecast, though the odds on fog/high humidity increased a tad....A fairly deep ridge to the east is expected to shift subtly eastward as the low to the NW strengthens and broadens eastward before taking off toward the north late in the week. While the low is not expected to directly impact the stability of the atmosphere near the Big Island, it could draw patches of tropical moisture over/near the area, contributing to a weakening of the inversion between sunrise tomorrow and Thursday morning. This could increase the risk for periods of fog and high humidity at the summit, and may allow for the development of afternoon convection, primarily along the western and perhaps southern slopes for Tuesday and Wednesday. A drier air mass may fill into the area as the low's associated low-level convergence band takes on a more SW to NE orientation and slides off toward the west around Thursday. While this could help reset the inversion and diminish the risk for fog/high humidity at the summit for that night, another patch of moisture associated with a tropical wave may make a push through the area and briefly weaken/lift the inversion, increasing this risk once again for Friday night. This tropical wave (combined with other favorable conditions), may help spawn a tropic cyclone/hurricane in the Central Pacific later in the week, which right now is set to pass well south of the Big Island late in the weekend and should pose little threat (with the possible exception of a slightly tighter wind gradient) to the summit.
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 Sep 24 - 8 PM0-20Clear10 / 04SSE/5-150.5-0.82-2.5
Tue Sep 25 - 2 AM0-20Clear30 / 53.5S/5-150.45-0.752-2.5
2 PM60-804-975 / 258SSE/10-20NaN4-8
8 PM20-406-1050 / 102.5S/10-200.6-16-10
Wed Sep 26 - 2 AM20-406-1065 / 203SSW/5-150.6-0.96-10
2 PM60-804-1080 / 308SE/5-15NaN6-10
8 PM60-808-1040 / 103.5SE/5-150.5-0.83-5
Thu Sep 27 - 2 AM60-808-1030 / 53.5SE/5-150.5-0.73-5
2 PM60-808-1010 / 08SE/5-15NaN4-8
Fri Sep 28 - 2 AM40-608-1010 / 03.5SE/5-150.45-0.654-6
2 PM60-804-865 / 209ESE/5-15NaN4-8
Sat Sep 29 - 2 AM20-406-860 / 153.5E/15-300.5-0.93-6
2 PM40-606-810 / 08E/20-35NaN4-6
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
Mon Sep 24 - Tue Sep 25 18:25 19:29 4:58 6:03 18:19 6:53 100 0 28.7 -2 10
Tue Sep 25 - Wed Sep 26 18:24 19:28 4:59 6:03 18:57 N/A 98 1 16.9 2 27
Wed Sep 26 - Thu Sep 27 18:23 19:27 4:59 6:03 19:36 N/A 94 2 06.3 7 01
Thu Sep 27 - Fri Sep 28 18:22 19:26 4:59 6:03 20:17 N/A 88 2 57.4 11 18
Fri Sep 28 - Sat Sep 29 18:21 19:25 4:59 6:03 21:00 N/A 80 3 50.6 15 03
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 25 September 2018.
Additional Information
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