California radar image
2 min read

Business calls today, and you need to get from your home base in Santa Barbara, California (KSBA) to San Francisco (KSFO) for an important meeting. There’s a bit of fog on the coast of California, but you are instrument-rated and current. Your airplane today is a well-equipped Piper Arrow, with dual Garmin 430W GPS/NAV/COMs, an HSI, autopilot and your trusty Garmin 696 portable GPS with XM datalink weather.

A look at the weather shows no major systems, just a weak low easing east out of California:

US surface analysis

The satellite image shows a few lines of clouds, but mostly at low levels:

West coast satellite

The radar doesn’t show any convective activity, but there is some precipitation in the San Francisco area:

California radar image

The freezing level is fairly high today, and en route MEAs should allow for a 6,000 ft. cruising altitude that is forecast to be ice-free:

Icing airmets

The Current Icing Potential (CIP) tool from backs up the AIRMET, with an ice-free forecast even at 7,000 ft:

Current Icing Potential

You should have a decent ride today, as well, with no pilot reports of turbulence.

But if icing isn’t much of a concern, the ceiling and visibility may be. Your departure is generally reporting good weather, but with the usual California fog bank rolling in:

METAR KSBA 150053Z 26011KT 10SM FEW009 13/11 A3009 RMK AO2 SLP188 FOG BANK
    ON SHR SE-SW T01280106 $=

The forecast is excellent:

TAF KSBA 142340Z 1500/1524 24008KT P6SM SCT007
     FM150200 VRB03KT P6SM SKC
     FM151000 VRB03KT P6SM SCT015
     FM151400 VRB03KT P6SM BKN015
     FM151800 16006KT P6SM SCT025 BKN040
     FM152100 23007KT P6SM BKN250=

Weather at your destination is cloudy with light rain, but certainly well above minimums for any of the approaches:

METAR KSFO 150132Z 15007KT 4SM -RA BR SCT013 SCT026 OVC035 14/12 A3009 RMK
    AO2 P0002= (SPECI)
METAR KSFO 150056Z 15008KT 4SM -RA BR SCT013 BKN026 OVC033 14/12 A3008 RMK
    AO2 RAB2357 SLP187 P0003 T01390122=
METAR KSFO 142356Z 16010KT 9SM BKN016 BKN027 OVC070 14/12 A3008 RMK AO2
    RAE48 SLP185 P0001 60017 T01440117 10144 20139 53001=

The forecast at San Francisco calls for continuing light rain and layered clouds:

TAF AMD KSFO 150118Z 1501/1606 15008KT P6SM SCT015 BKN025 OVC035
     TEMPO 1501/1502 4SM -RA BR BKN015
     FM150200 21010KT P6SM SCT015 BKN025 OVC040 TEMPO
     1502/1504 6SM -RA
     FM150400 22007KT P6SM BKN015 OVC025
     FM150700 15004KT P6SM OVC015
     FM152000 20012KT P6SM SCT015 BKN025 PROB30 1520/1524 6SM
     -RA BKN015
     FM160000 23013G19KT 6SM -RA BR OVC020=

For real weather geeks, the Skew-t Log-P diagram for Oakland, California shows more details:

Oakland Skew-t Log-p

So do you go or cancel? Why?

John Zimmerman
16 replies
  1. zane
    zane says:

    First off, I really like these thought experiments. I would worry about this one a bit, but I would go, considering the equipment, the weather, and my knowledge of the area. Let me say that again – I am familiar with that airspace – I would definitely not go in those weather conditions if I had never been into SFO before, as it is very busy Bravo airspace with terrain nearby. Also, in an Arrow, why SFO and not San Carlos or Hayward? Much less chance of getting spun on approach or stuck in a holding pattern… Thanks again for another great Go or No go!

  2. Mike
    Mike says:

    If, I was an experienced pilot I would do it. Vis is 6 clouds are still above mins. Since I am not familiar with the airspace out west, I would have to take Zane’s word for it as well as what I hear from others and advice an experienced pilot to go for it with caution and tell an inexperienced pilot to put it off for another day.

  3. Brian
    Brian says:

    Am I the only one who thinks this information is insufficient? I would check METARs and TAFs at airports along the route for a more complete picture.

    And I could be wrong, but I believe it would be illegal to file and fly with this limited information. The forecast ceiling breaks the 1-2-3 rule for most of the day, so wouldn’t you need to check the TAF for an alternate airport before departing?

    Since I am familiar with the area, I would check the forecast at Hayward, Oakland, and Concord for choosing an alternate. Hayward and Oakland are right across the bay; Concord is a bit further east across a low range that tends to block the fog. All three are reasonably close to BART stations to get a ride into San Francisco.

    I would ONLY make a go decision if airports along my route were above minimums in case I needed to divert, and if I had a favorable forecast at one of those alternates.

  4. Larry Baum
    Larry Baum says:

    Being from the east and with what was presented, this would be a go for me given the aircraft and equipment presented. I immediately wondered what the Metars and TAFs were for the enroute and surrounding airports. That information would be quite helpful and something I would definitely factor into my final decision. Brian asked the same questions and he and Zane bring in local knowledge which also can be incredibly useful.

    Keep these Go or No Go articles coming. They are great exercises.

  5. mark neumann
    mark neumann says:

    Being from the Bay Area, I know SFO goes to 1 runway in these conditions, which causes a lot of flight delays.

    Palo Alto, SJC, Hayward, or Oakland maybe.

  6. Stan
    Stan says:

    Before deciding, I would want more information. I would look at the winds and temperatures aloft. Surface winds listed in METARs and TAFs can be very different from winds aloft. Also, it only takes about 15 degrees to pick up ice from induction. Maybe the Skew-t Log-P diagram answers the question about winds and temps, but I admit I don’t know how to read it. I would also check the turbulence chart on to see if turbulence may be forecasted. I agree with Brian that I would make sure I had a REALISTIC alternate to go to with a lot more than minimum fuel reserves in these conditions.

  7. Terry Scott
    Terry Scott says:

    I see avwxworkshhops has a lot of nice things said about it on the internet and I do hope the guy figures out his wife unplugged it when she was vacuming.

    Do like the GO/NO gos though, don’t ever think I’ll fly into anywhere near there or as busy but the logic applies for every chock removal.

  8. gregg reynolds
    gregg reynolds says:

    I’d go after checking conditions at airports along the route and likely selecting KSQL versus KSFO for destination.

  9. John Fonville
    John Fonville says:

    Yes, I would go; however, if my wife was to be
    the passenger I would not. She does not like IFR flying. One needs to consider more than just the

  10. Matt Warmerdam
    Matt Warmerdam says:

    If you are instrument rated, why not go? There are so many divert options with significantly different micro climates, you could fly north to Gnoss Field KDVO and find blue skies while SFO is socked in. Or the East Bay like Hayward. Many viable alternates.

    Having to change your plans in route is not an emergency, this is not a risky endeavor. For an airplane to be a useful tool we have to actually get aboard and use them if the only downside to the outcome is you might not get to your first choice. Nothing described in this situation is unreasonable risk, just potential for inconvenience.

    • Peter T
      Peter T says:

      As a native California pilot I would absolutely GO. And would even do it single pilot, though only because I’ve travelled that route a hundred times, IFR and VFR. There are tons of alternates in the Central Valley if any trouble develops along the way, and plenty of alternates in the Bay Area. Concord and Livermore are over the hills, out of the coastal influence on a day like this.
      Agree with Matt that there is no unreasonable risk, so the only qualification I would make to my GO decision is to go *if* I am flexible in where I land and how I get to where I need to go, and what time I need to be there. If it’s truly an important business meeting I may decide to take United Express, but otherwise it sounds like a great day for using that IFR ticket.
      PS: for those not from the area, John was naturally using a hypothetical destination – you’d never fly your Arrow into SFO.

  11. Claudia
    Claudia says:

    I’d say lets go. However I would consider landing in San Carlos as it’s outside the class B airspace and close enough to drive into San Francisco for the meeting. I would hate to have to hold around the big jets.

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