VV001 and Indefinite Ceilings Explained

Most METAR cloud groups name a layer and a height: BKN012 is a broken deck at 1,200 feet with clear air above it. A VV group is different. It says the sky is obscured and there is no distinct layer to measure, only a depth you can see up into. VV001 reports an indefinite ceiling with vertical visibility of 100 feet, a classic LIFR signature in fog or heavy precipitation. Reading it correctly is the difference between expecting a low deck you can climb through and recognizing a near-zero-ceiling obscuration.

This guide covers the VV### format, why it appears, what "indefinite ceiling" means, and how a low VV drives the flight category. It is part of the METAR field guide.

The VV### format

A vertical visibility group is the letters VV followed by three digits. As with every cloud height in a METAR, the digits are hundreds of feet above ground level:

VV001    vertical visibility 100 ft
VV004    vertical visibility 400 ft
VV010    vertical visibility 1,000 ft

So VV001 is 100 feet, VV004 is 400 feet, and VV010 is 1,000 feet. The encoding is identical to a layer height like BKN001, which is why the two look similar at a glance. The difference is the meaning of the number, not the math.

A normal layer group such as BKN or OVC tells you the base of a cloud deck. A VV group tells you how far up you can see into a sky that has no measurable base at all.

Why VV appears: the sky is obscured

A VV group is reported when the sky is obscured and no distinct cloud layer can be measured. Instead of cloud bases at a defined height, the observer or the automated sensor sees a column of restricted air, and the only thing that can be measured is how far up vertical visibility extends before it is lost.

This happens when the obscuring phenomenon reaches the ground and fills the airspace above the field:

• Dense fog that extends well overhead.
• Heavy snow filling the column with falling and blowing crystals.
• Other surface-based obscurations thick enough to hide any layer structure.

In each case there is no "bottom of a cloud" to report, because the restriction starts at the surface. The VV figure is the practical answer to "how high can you see straight up before it goes white."

What "indefinite ceiling" means

The ceiling formed by a VV group is called an indefinite ceiling. The word indefinite is doing real work. With a BKN or OVC deck, the ceiling height is the base of a definite layer: there is structured cloud at that altitude and clearer air below it. With VV, there is no defined layer, so the "ceiling" is just the height at which vertical visibility runs out inside the obscuration.

That distinction matters operationally. A definite ceiling implies you could break out into clear air on top at a known height. An indefinite ceiling makes no such promise. You are inside the obscuration the whole way up to the VV figure, and the air above it is unknown from this group alone.

VV counts as a ceiling

For flight-category purposes, the ceiling is the lowest BKN, OVC, or VV layer. Vertical visibility is the third member of that list. A VV group is a ceiling at its stated height, exactly the way a broken or overcast layer is.

FEW and SCT are never ceilings, but VV always is. This is the rule that catches people: because VV001 does not say BKN or OVC, it is tempting to skip it when hunting for the ceiling. Do not. It is the ceiling, and usually the lowest one in the report. For the full list of which groups form a ceiling and which do not, see FEW, SCT, BKN, OVC: which layers are a ceiling.

How a low VV reads as IFR or LIFR

Once you treat VV as the ceiling, the flight category follows directly from the standard thresholds. The worst of ceiling and visibility wins:

A VV group puts the ceiling at its height in hundreds of feet:

• VV001 is a 100-foot ceiling: below 500, so LIFR.
• VV004 is a 400-foot ceiling: still below 500, so LIFR.
• VV007 is a 700-foot ceiling: between 500 and below 1,000, so IFR.

Because the obscurations that produce a VV group, dense fog and heavy snow, also crush surface visibility, the visibility value usually pushes the same direction. The two restrictions reinforce each other, which is why a low VV is such a reliable IFR or LIFR marker. Full thresholds for both ceiling and visibility are in VFR, MVFR, IFR, LIFR.

Contrast with a normal BKN or OVC ceiling

Put the two side by side:

KXYZ 121753Z 18004KT 1/4SM FG VV001 12/12 A2998

Here VV001 is the ceiling: an indefinite 100-foot ceiling in fog, with visibility down to a quarter mile. Both the ceiling and the visibility are deep in LIFR territory, and there is no defined layer to climb through.

KXYZ 121753Z 18004KT 6SM BR BKN008 OVC020 12/10 A2998

Here the lowest ceiling is BKN008, a definite broken layer at 800 feet, with an overcast deck at 2,000 above it. The 800-foot ceiling reads IFR, but it is a structured layer: there is clearer air below it and a known top region. The difference is not just the height. VV001 says you are inside the obscuration, while BKN008 says there is a defined deck with measurable air around it.

Decode the obscured sky in one step

When a report shows VV###, read it as an indefinite ceiling: the sky is obscured, vertical visibility extends only to that many hundreds of feet, and it counts as the ceiling for the flight category. A low VV almost always lands in IFR or LIFR, and it pairs with low surface visibility from the same fog or snow.

To see it labeled instantly, paste the raw report into wxdecoder and the VV group is read as the ceiling, with the resulting flight category shown alongside the raw text. wxdecoder is for situational awareness, not an official briefing. Next, read which layers count as a ceiling to lock in the rule.

Last updated June 29, 2026