BUG: HerbieLatest should get the latest forecast for a given valid time

[blaylockbk]

Discussed in #465

^{Originally posted by williamhobbs August 5, 2025}
This is somewhat related to #464.

In the examples, HerbieLatest can be used to get the latest forecast with a given lead time (including the default of fxx=0), https://herbie.readthedocs.io/en/stable/user_guide/tutorial/latest.html. Is there a way to get the latest forecast for a given valid time?

That seems like it would be useful, for example, if I want to know what the HRRR forecast is for tomorrow at noon local time. That's a little tricky, because I need to know how long it takes HRRR outputs to be available and I may need to remember which HRRR runs go out more than 18 hours.

I tried this:

today = pd.Timestamp.now(tz='US/Central').floor('1d')
noon_tomorrow = today + pd.Timedelta('36h')
print(noon_tomorrow)
H = HerbieLatest(model="hrrr", valid_date=noon_tomorrow)
H

but it gives me

2025-08-06 12:00:00-05:00
💔 Did not find ┊ model=hrrr ┊ product=sfc ┊ 2025-Aug-05 15:00 UTC F00
✅ Found ┊ model=hrrr ┊ product=sfc ┊ 2025-Aug-05 14:00 UTC F00 ┊ GRIB2 @ aws ┊ IDX @ aws

which is not what I was hoping for.

[williamhobbs]

I starting looking into this, and I'm not sure there's actually an issue with HerbieLatest - it appears to be that Herbie is not working like I expected when provided date and valid_date.

For example,

H = Herbie(date='2025-09-11 12:00', model="hrrr", valid_date='2025-09-12 16:00')

returns

✅ Found ┊ model=hrrr ┊ product=sfc ┊ 2025-Sep-11 12:00 UTC F00 ┊ GRIB2 @ aws ┊ IDX @ aws

Should that be F28 instead of F00?