Current Conditions
Temp5.3 C
RH17 %
WindNE 10 mph
RoadOpen (4x4)
Mauna Kea Observatories Forecast
5 PM HST Friday 25 May (0300 UTC Saturday 26 May) 2018
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while broken high clouds continue to spread in from the SW through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 4.5 C this evening and 4 C tomorrow morning. Winds will be from the ENE at 10-20 mph, with seeing near 0.55-0.6 arcseconds. Precipitable water is expected to be in the 3-4 mm range for the night.
Discussion
A well-defined tradewind inversion will continue to cap low-level moisture at or below 10 thousand feet and ensure the summit remains dry and stable through the next 5 nights. Daytime clouds will be minimal and short-lived through the weekend, but could pick up as mid-level moisture moves through the area for the early part of next week.

Broken high clouds will continue to drift in from the west, contributing to extensive cloud cover for tonight. More organized widespread clouds will slip in from the SW for tomorrow night, with thicker clouds following suit late Sunday and into the early part of next week. These clouds will likely contribute to mostly overcast skies beyond tonight.

Precipitable water is expected to linger in the 3-4 mm range for tonight, then increase to 4-6+ mm for the remainder of the forecast period.

Relatively calm skies and laminar westerly flow in the free atmosphere should allow for better than average seeing for the next 2 nights. Increasing shear/turbulence in the free atmosphere will likely degrade seeing toward more average-like values for Sunday night and perhaps slight worse for the following 2 nights.

Little change since the morning forecast...The mid/low-level ridge will continue to sit to the north of the state, before being displaced eastward as a relatively deep tropical upper-tropospheric trough (TUTT) strengthens to the NW late in the weekend and for the early part of next week. Nonetheless, the ridge will promote steady/strong large-scale subsidence in the area, which will negate the weak instability associated with the TUTT, maintain a fairly well-defined inversion at or below 10 thousand feet and ensure the summit steers free of nighttime fog and precipitation throughout the forecast period. In addition, an upper-level low to the WNW and embedded in the TUTT will continue to send broken high clouds into the area and is expected to dig southward over the next 12-24 hours. While this southward progression may actually help kink the sub-tropical jet a bit and shift it northward, the low/STJ will be able to tap into more organized/widespread mid/upper-level clouds and transport it over the summit contributing to mostly overcast skies after tonight. The low/TUTT will remain too far from the summit to affect the stability of the atmosphere, but there is a good chance that the sub-tropical jet will strengthen and move back over the summit area as the low shifts subtly eastward late in the weekend and for the early part of next week. This could result in an increase in free atmospheric turbulence/shear and thus degrade seeing during that time. There is also a possibility that the STJ will gain access to mid-level moisture, which could raise the stakes on daytime clouds and increase summit-level humidity toward 60-70% for the early part of next week.

Please Note: There will be no forecasts on Monday, May 28, in observance for Memorial Day; the normal forecast schedule will resume on Tuesday, May 29.


HST CC (%) CLD HGT (km) Fog Prob (%) Prcp Prob (%) Temp (C) Wind (dir/mph) Seeing (asec) PW (mm)
---------------------------------------------------------------------------------------------------------------------------------------
05/25/2018 2000 70-90 8.5-10 0 0 4 60/10-20 0.5-0.7 3-4
05/26/2018 0200 80-100 8-10 0 0 3.5 60/10-20 0.45-0.65 3-4
05/26/2018 1400 80-100 8-10 0 0 8.5 45/10-20 NaN 3-6
05/26/2018 2000 80-100 8-10 0 0 3 30/10-20 0.45-0.65 4-6
05/27/2018 0200 70-90 8-10 0 0 2.5 30/10-20 0.5-0.7 4-6
05/27/2018 1400 80-100 7-10 0 0 7 0/10-20 NaN 4-8
05/27/2018 2000 80-100 7-10 0 0 2 0/5-15 0.55-0.75 4-8
05/28/2018 0200 80-100 6-10 0 0 1 315/5-15 0.6-0.8 4-8
05/28/2018 1400 80-100 6-10 20 5 6 240/5-15 NaN 4-8
05/29/2018 0200 80-100 6-10 0 0 0.5 150/10-20 0.6-0.9 4-8
05/29/2018 1400 80-100 6-10 15 5 5 135/10-20 NaN 4-8
05/30/2018 0200 80-100 6-10 0 0 0 150/5-15 0.6-0.9 4-8
05/30/2018 1400 80-100 6-10 25 5 6 60/0-10 NaN 4-8
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 May 25 - 8 PM70-908.5-100 / 04ENE/10-200.5-0.73-4
Sat May 26 - 2 AM80-1008-100 / 03.5ENE/10-200.45-0.653-4
2 PM80-1008-100 / 08.5NE/10-20NaN3-6
8 PM80-1008-100 / 03NNE/10-200.45-0.654-6
Sun May 27 - 2 AM70-908-100 / 02.5NNE/10-200.5-0.74-6
2 PM80-1007-100 / 07N/10-20NaN4-8
8 PM80-1007-100 / 02N/5-150.55-0.754-8
Mon May 28 - 2 AM80-1006-100 / 01NW/5-150.6-0.84-8
2 PM80-1006-1020 / 56WSW/5-15NaN4-8
Tue May 29 - 2 AM80-1006-100 / 00.5SSE/10-200.6-0.94-8
2 PM80-1006-1015 / 55SE/10-20NaN4-8
Wed May 30 - 2 AM80-1006-100 / 00SSE/5-150.6-0.94-8
2 PM80-1006-1025 / 56ENE/0-10NaN4-8
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 May 25 - Sat May 26 19:04 20:17 4:21 5:33 N/A 4:04 90 13 49.5 -6 31
Sat May 26 - Sun May 27 19:05 20:17 4:21 5:33 N/A 4:44 95 14 39.0 -10 44
Sun May 27 - Mon May 28 19:05 20:18 4:20 5:33 17:26 5:25 98 15 29.0 -14 26
Mon May 28 - Tue May 29 19:06 20:18 4:20 5:33 18:18 6:09 100 16 19.7 -17 27
Tue May 29 - Wed May 30 19:06 20:19 4:20 5:33 19:10 N/A 99 17 11.1 -19 39
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 29 May 2018.
Additional Information
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