Date: 201909
Local time of day: 1801-2400
Location: SEA.Airport, WA
Flight conditions: IMC
Weather elements / visibility: Rain; Snow; Thunderstorm; Turbulence
Light: Night
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E S46
ATC / advisory: TRACON S46
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Contributing factors: Company Policy; Procedure; Weather
Primary problem: Procedure

Narrative: Experienced lightning strike on descent to SEA at about 9;000 MSL. No systems abnormalities observed; landed normally. For the second time in a week; SEA experienced a significant convective event when there had been nothing of the sort in the TAF all day; right up until it hit. Before departure from ZZZ; WSI (Weather Services International) radar just some precipitation tops in the mid-twenties; but they were all green. We were dispatched with a BFI alternate and about 1;000 lbs of extra fuel for ATC; some of which was consumed by an overburn of about 600 lbs? In addition; uncharacteristically for ZZZ; we burned through most of our taxi fuel; too - so we didn't have much extra to play with.About 100 NM north of CYYJ; Dispatch gave us a heads-up that there were reports of 'heavy rain and moderate turbulence' from aircraft departing on the BANGR. At this point we could see on the 160-mile scan that there was significant convective activity west and southwest of SEA; and threatening to encroach on the MARNR arrival routing and the airport itself. In hindsight; going from that position direct to HUH so as to approach SEA from the northeast would have worked well. It seemed that we were the first to come in off the MARNR for a while; the only PIREPS were those passed on from Dispatch on ride and precipitation.Still talking to CZVR; we continued on the MARNR; hoping that the weather was upper-level and that we'd be able to slip under it. The light was dusky and we could see some of it; but inconclusively. By the time we were talking to Seattle Center; the Associated Threat; AT; 'dots' were starting to show up; but the returns were still diffuse green and yellow; with sporadic reds that we could easily evade. Still no current PIREPS coming from our routing. However; now the line was painting pretty much solid from OLM all the way to just south of BLI. I had transited areas of low altitude AT dots before; under similar circumstances; with no issues. In fact; I've even been literally mocked by ATC for hesitating to do so. FO (First Officer) and I discussed options. Arrival fuel was showing 6.8. BFI after missed approach showed 5.7; PAE showed 5.2. But SEA was clearly under imminent thunderstorm threat; followed very soon thereafter by both BFI and PAE; due to the orientation of the line of weather and the direction it was moving. We'd be in a bad position if we burned the fuel to get around the weather and then all 3 of those stations closed up. FO suggested; and we were cleared; direct NEHOS. That shortened our routing significantly; and took us across what appeared to be a fairly thin spot in the line. Once talking to Seattle Approach; we could hear aircraft on the HAWKS arrival; that routing was closing up?? A company aircraft requested an east downwind due to observed lightning west of the field. The ride through the band of weather; which was not more than about 15 miles wide; actually wasn't too bad - light to moderate turbulence with heavy rain and snow. The TAT (True Air Temperature) was about +12. No hail. We only sporadically lost ground contact. The lightning strike sounded like a loud 'THUNK!' and was accompanied by a bright blue flash.No subsequent systems abnormalities were indicated. As soon as we got through the weather the visibility was excellent. We picked up the field on about a 15 mile final and the ride was smooth the rest of the way to the runway - in spite of a significant shower just a few miles west of final approach. It was impossible to tell what part of the aircraft got hit. Up front we felt like it was the front - but in the back everybody's opinions varied. It seemed like everybody felt like it was right where they were sitting. Had the TAF been accurate I would have had more fuel. WHAT IS WITH THE FORECAST INACCURACY IN SEATTLE LATELY?? Operationally; in hindsight; even a late decision to circumvent the weather to the north probably would have been prudent?? But that would have carried the risk of having to make a low-fuel beeline for BLI if SEA; BFI; and PAE all closed up - which was clearly a threat.




Synopsis: B737 Captain reported continuously receiving inaccurate weather forecasts for the Seattle area.