Marginal VFR at Mountain View

Total endurance remaining is 12 gal ÷ 9.0 gph ≈ 1.33 hours (80 minutes).

14 CFR 91.151 requires enough fuel to reach the first point of intended landing plus 30 minutes at normal cruise for day VFR (45 minutes at night, which does not apply to a recreational pilot, who may not fly at night). Thirty minutes at 9 gph is 4.5 gallons, so the fuel actually available for navigation is 12 − 4.5 = 7.5 gallons ≈ 50 minutes.

• To Mountain View: 50 nm at 95 kt = 0.53 hr ≈ 4.8 gallons. Arrival fuel ≈ 7.2 gallons, or about 48 minutes of endurance.
• That is legal on the 91.151 arithmetic - but only barely, and it counts the destination as the first point of intended landing.

The moment the weather makes the destination doubtful, the honest planning question changes: can the airplane fly to the destination, then to an alternate, then 30 minutes? Mountain View to Cedar Valley is roughly 30 nm, about 2.9 gallons. That total is 4.8 + 2.9 + 4.5 = 12.2 gallons against 12 aboard. The answer is no - continuing and then diverting would put the airplane on the ground below the required reserve, in worsening weather, with a passenger aboard.

On paper, yes. In Class E airspace below 10,000 feet, VFR requires 3 statute miles visibility and cloud clearance of 1,000 above, 500 below, and 2,000 horizontal. The report shows 4 miles and a ceiling of 1,800 feet above ground, so a pilot at 1,300 feet above ground would be exactly 500 feet below the cloud deck.

But that legal minimum is a knife edge:

• Terrain. The field elevation is 3,400 feet and the ridge is 2,900 feet. The cloud base is about 5,200 feet MSL. Descending through that gap, with a 2,900-foot ridge in the way, leaves almost no vertical room and no room to turn back if the ceiling drops another few hundred feet.
• Trend. Temperature 14 and dew point 13 means a 1 °C spread - saturation is imminent, and fog or a lowering ceiling is likely, not merely possible.
• Wind. 18 gusting 26 across a ridge produces mechanical turbulence and downdrafts on the lee side; a 4-mile visibility in rain reduces the time to recognize and escape.
• The trap. "4 miles and 1,800 feet" is exactly the kind of report that invites a pilot to press on and end up scud-running. Legal minimums assume an engine that keeps running and a missed approach that can be flown visually.

For a recreational pilot with limited instrument time and a passenger aboard, this is below any reasonable personal minimum, regardless of the FAR numbers.

Divert now to Cedar Valley. It is 25 nm south, about 16 minutes and 2.4 gallons at the current groundspeed. That leaves roughly 9.6 gallons, or just over an hour, which covers the diversion plus the 30-minute reserve with real margin - and it goes to better weather rather than worse.

Execution:

• Turn south immediately, before the ridge; do not "take a look" at Mountain View first. A look costs 10–12 minutes and 2 gallons the airplane cannot spare.
• Note the time and fuel at the diversion so the reserve calculation is based on actuals, not the preflight plan.
• Get a current briefing on the ground at Cedar Valley and make the passenger phone ahead; the family event is not a factor in the fuel or weather decision, and saying that out loud helps.
• Do not launch toward Mountain View later the same day unless the ceiling and visibility have clearly improved and the fuel is topped off.

The judgment error to avoid is treating the destination as fixed because of the passenger and the event. The two variables that have already failed - fuel and weather trend - are both irreversible in flight. Diverting early costs an hour; diverting late, or not at all, is the classic sequence behind VFR-into-IMC and fuel-exhaustion accidents.