Warm front into Tuscany: TAF, trend and an alternate that isn't there
You hold a VFR-only PPL with no night rating. Today's plan: LIME (Bergamo Orio al Serio) to LIRP (Pisa), 190 NM in a PA-28, cruise 5500 ft, endurance 3 h 10 min including a 45-min reserve, alternate LIRQ (Firenze, 40 NM east of Pisa). Off-blocks 12:30Z, ETA 14:20Z.
LIRP TAF, issued 05:00Z: 0806/0906 12008KT 9999 SCT025 BKN040 TEMPO 0812/0818 24012G22KT 6000 -RA BKN012 PROB30 0815/0820 2500 RA BKN008.
LIRQ TAF: 0806/0906 10008KT 6000 SCT015 BKN030 TEMPO 0810/0816 3500 BR BKN008.
METAR LIRP 081150Z: 12010KT 9999 SCT018 BKN030 13/10 Q1009. METAR LIME 081150Z: 15012KT 9999 FEW020 BKN045 14/09 Q1008; at 08:00Z LIME reported 09007KT Q1013.
A forecaster briefs you: the warm front lies about 40 NM west of Milano, moving east at 15 kt, with a rain band roughly 90 NM wide. No radar, no IFR clearance available.
1. Compare the LIRP TAF with your ETA and with the LIME observations. Is the front on schedule, and how much weight can you put on the good-weather base group?
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Work the timeline first. Your ETA of 14:20Z sits inside TEMPO 0812/0818 (6000 m, -RA, BKN012) and only 40 minutes before the PROB30 group of 2500 m and BKN008. The base group (9999, SCT025 BKN040) is only the most likely state, not a promise: TEMPO tells you the forecast expects a temporary but real deterioration in exactly your window, and PROB30 says a 30% chance of the worst case.
Now test the forecast against the trend. The TAF was issued seven hours before departure. At Milano the QNH fell 5 hPa between 08:00Z and 11:50Z – about 1.2 hPa/h – while the wind veered 090° to 150° and increased from 7 to 12 kt. That is the textbook pre-warm-frontal signature: falling pressure, veering and strengthening wind, thickening cloud. A 5 hPa fall in under four hours is a front that is close and moving, not a distant one.
Combining a 40 NM distance at 15 kt with that pressure trend, the front is probably one to two hours ahead of the briefing position – so the weather reaches Pisa around 13:30–14:30Z, at or just before your ETA, not after it.
2. Assume the front arrives at Pisa two hours earlier than the TAF suggests. What does that do to your fuel plan and to the validity of LIRQ as an alternate?
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Fuel first. Endurance 3 h 10 min with a 45-min reserve leaves 2 h 25 min of usable fuel. The trip is 1 h 50 min, so you have 35 minutes of slack before you touch the reserve – and that slack is the only thing you can spend on a missed approach and a diversion.
A diversion from Pisa to Firenze is 40 NM, roughly 20 minutes in a PA-28. Add 10 minutes for a hold or a second approach and you have consumed about 30 of the 35 minutes. That is not a margin; it is a coincidence. Any headwind, any delay on the ground, any vectoring and you land at Firenze inside your legal reserve.
Worse, the alternate itself fails. LIRQ's TEMPO 0810/0816 forecasts 3500 m in mist with BKN008 – below the VFR minima you need – and it covers the whole of your arrival window. An aerodrome that is forecast below your minima at your ETA is not an alternate; it is a second problem. So the honest picture is a destination with a TEMPO of BKN012 and 6000 m, and no usable alternate within fuel range.
3. Give your decision for the 12:30Z departure and the reasoning you would write on your plog.
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Decision: do not depart at 12:30Z on this plan.
The chain of reasoning: the front is running one to two hours ahead of the forecast; my ETA falls inside a TEMPO for BKN012 in rain; the only alternate is forecast below VFR minima for my entire window; and I am VFR-only, without radar, at 5500 ft in the boundary layer where the low cloud and rain will be. Delaying is not a fix either – the rain band is 90 NM wide at 15 kt, roughly six hours to clear Pisa, which puts any departure after nightfall, and I have no night rating.
On the plog I would write: alternate unusable – flight only if LIRP is VMC with margin at arrival. If I still wanted to go, the only defensible version is a decision-point flight: LIME stays east of the front, so set a hard gate 30 NM east of Pisa – if the current LIRP METAR is not at least SCT020/BKN040 and 8 km, turn back to Bergamo with the fuel to do it, and never press on hoping for a TEMPO to end early.