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Minding the breadcrumbs...

Updated: Jun 14, 2019

With respect to the weather, there's no doubt that your attention to details can make the difference between an uneventful flight and one that you regret for the rest of your life. And as you get closer to your departure time, you should rely less on forecasts and more on observations.

Visibility is the king...key a close eye on it.

I thought this was an interesting case where none of the forecasts really picked up on a low IFR event until after the event was occurring. This event occurred on the evening of May 31, 2019 PDT in the SoCal area. For simplicity, let's look specifically at Van Nuys, CA (KVNY) here.

It's often not a bad idea to look at the previous days weather to see if a similar event occurred and when. Often when the weather is very homogeneous, persistence can be an excellent forecast. That is, you can expect the same event and timing will occur the following day. During the prior evening, the low IFR event didn't arrive until 0748Z when a SPECI was issued for a broken ceiling at 500 feet (BNK005) with a visibility of five statute miles as shown below (oldest observations are presented first). Notice the visibility is 10SM (or potentially better) throughout the entire morning and into the late afternoon and early evening on the previous day until the visibility started to drop around 0600Z.

KVNY 301851Z VRB04KT 10SM CLR 26/12 A2990 RMK AO2 SLP116 T02560117=

KVNY 301951Z 11006KT 10SM CLR 27/11 A2988 RMK AO2 SLP111 T02670111=

KVNY 302051Z 13008KT 090V160 10SM CLR 28/11 A2987 RMK AO2 SLP107 T02780111 58011=

KVNY 302151Z 12009KT 090V150 10SM CLR 28/10 A2986 RMK AO2 SLP102 T02780100=