# Graph conditional on day of the week

**URL:** <https://cylc.discourse.group/t/graph-conditional-on-day-of-the-week/1260>\
**Category:** Cylc Support\
**Created:** [November 6, 2025, 3:59pm UTC](https://cylc.discourse.group/t/graph-conditional-on-day-of-the-week/1260 "2025-11-06T15:59:25Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![gturek](https://avatars.discourse-cdn.com/v4/letter/g/a88e57/32.png) [@gturek](https://cylc.discourse.group/u/gturek)\
**Post date:** [November 6, 2025, 3:59pm UTC](https://cylc.discourse.group/t/graph-conditional-on-day-of-the-week/1260/1 "2025-11-06T15:59:25Z")

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Hi there!

I have the following situation:

```objectivec
PID = """ 
      forecast[-P1D] => forecast
      # except on thursdays when nowcast[-P1D] => forecast
"""      

```

How do I implement this condition?

Cheers!

---

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**Author:** ![hilary.j.oliver](https://yyz2.discourse-cdn.com/free1/user_avatar/cylc.discourse.group/hilary.j.oliver/32/4_2.png) [@hilary.j.oliver](https://cylc.discourse.group/u/hilary.j.oliver)\
**Post date:** [November 7, 2025, 3:12am UTC](https://cylc.discourse.group/t/graph-conditional-on-day-of-the-week/1260/2 "2025-11-07T03:12:18Z")

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Hi @gturek - try something like this - Hilary

```ini
[scheduler]
    allow implicit tasks = True
[scheduling]
    initial cycle point = 2025
    [[graph]]
        # on Wednesdays, run nowcast after previous forecast
        W-3T00 = "forecast[-P1D] => nowcast"
        # on Thursdays, run forecast after previous nowcast
        W-4T00 ="nowcast[-P1D] => forecast"
        # on the other days, run forecast after previous forecast
        T00 ! (W-4T00,W-3T00) = "forecast[-P1D] => forecast"

```

In 2025, 1 January was a Wednesday (nowcast day). Result (after `cylc graph 20250101 20250110`) :

 ![foo](https://global.discourse-cdn.com/free1/uploads/cylc1/original/1X/6ea60e4eec678fccab36b29479c8f4d7c184ba69.png)

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<div class="post-metadata">

**Author:** ![gturek](https://avatars.discourse-cdn.com/v4/letter/g/a88e57/32.png) [@gturek](https://cylc.discourse.group/u/gturek)\
**Post date:** [November 7, 2025, 8:53am UTC](https://cylc.discourse.group/t/graph-conditional-on-day-of-the-week/1260/3 "2025-11-07T08:53:30Z")

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Thanx Hilary, that’s a good starting point for me to experiment with. Cheers!