SKY CONDITION - missing "VV" type

[Vipersf]

Currently there are four types of clouds being considered in the code:
export type MetarCloudCode = "FEW" | "SCT" | "BKN" | "OVC"

However, as per Weather.gov, a fifth type exists being "VV":

"Cloud amount and height: CLR (no clouds detected below 12000 feet); FEW (few); SCT (scattered); BKN (broken); OVC (overcast); followed by 3-digit height in hundreds of feet; or vertical visibility (VV) followed by height for indefinite ceiling."

For obvious reasons, CLR is not considered relevant; yet the VV one (being rather closely linked to OVC) is.

Do I understand correctly that this is currently not implemented? If so, would it be possible to implement this?

[fboes]

@Vipersf I like the idea. Parsing is simple, but how do you propose to represent the result in the JavaScript-Object?

Is there an example how CheckWx handles this (as the structure is supposed to be compatible)? I could not find an example at https://www.checkwxapi.com/metar

[gstarch]

Perhaps useful to refer to page 12 of this document: https://static.e-publishing.af.mil/production/1/af_a3/publication/afman15-124/afman15-124.pdf

1.3.7. Cloud and Obscuration Group (NsNsNshshshsCC). Report as often as necessary to
indicate all forecast cloud layers up to the first overcast layer. Arrange groups in ascending
order of cloud bases AGL (e.g., lowest base first). (T-0)
1.3.7.1. Cloud Amount (NsNsNs). The cloud amount is given as sky clear (SKC = no
clouds); few (FEW = trace to 2/8ths); scattered (SCT = 3/8ths to 4/8ths); broken (BKN =
5/8ths to 7/8ths); or overcast (OVC = 8/8ths). Follow the three-letter abbreviations with
the height of the base of the cloud layer (mass) hshshs without a space (e.g., FEW100,
SCT250). The summation principle applies. This principle states that the sky cover at any
level is equal to the summation of the sky cover of the lowest layer, plus the additional sky
cover at all successively higher layers, up to and including, the layer being considered. Do
not assign a sky cover to a layer less than a lower layer (e.g., SCT015 FEW020 should be
SCT015 BKN020).
1.3.7.2. When the sky is totally obscured, encode VVhshshs, where VV is the indicator
and hshshs is the vertical visibility in hundreds of feet (e.g. VV002).
1.3.7.3. Ceiling Height (hshshs). A ceiling is the height above the earth’s surface of the
lowest layer reported as broken or overcast; or the vertical visibility into an indefinite
ceiling. Consider all layers and obscuring phenomena to be opaque.
1.3.7.4. Indefinite Ceiling (VVhshshs). The vertical visibility measured in feet, into a
surface-based total obscuration, which hides the entire celestial dome (8/8ths).
1.3.7.5. Surface-Based Partial Obscuration. When forecasting a surface-based partial
obscuration, encode as FEW000, SCT000, or BKN000 as appropriate to indicate a surfacebased partial obscuration. Code as a remark the obscuring phenomena and the applicable
layer. For example, FG SCT000 would indicate the w’w’ weather element causing the
obscuration is caused by fog and layer amount is SCT. Include the amount of partial
obscuration in your sky cover summation computation. Do not consider surface-based
partial obscurations as a ceiling.
1.3.7.6. Variable Sky Condition. If two or more significant sky conditions alternate
frequently from one to the other, describe the situation with a TEMPO group; do not use
variable sky condition remarks.
AFMAN15-124 16 JANUARY 2019 13
1.3.7.7. Height of Cloud Base (hshshs). Forecast the height of the base of each sky cover
layer in hundreds of feet AGL using the reportable layers defined in Table 1.3.

It's the foggy season now, so measured VV is common on days when normal cloud obscuration cannot be assessed in octas. I will look for examples when I see this.