Does fxx=0 means actual weather reading?

[yinghawl]

Hi all,

I am fairly new to using Herbie to analyze historical weather data. Does the following code (fxx=0) query the actual weather data for 2021-01-01 12:00?

H = Herbie(
    "2021-01-01 12:00",
    model="hrrr",
    product="sfc",
    fxx=0
)

Thanks,
Anson

[blaylockbk]

Hi @yinghawl,

In Herbie, the fxx variable is the forecast lead time.

fxx=0 represents F00, which is the forecast with zero hours lead time, also known as the "analysis." So yes, fxx=0 will query the weather analysis valid at the time you specify.

---

If you were to set DATE="2021-01-01 12:00", and fxx=6 (meaning F06), then you are asking for the 6 hour forecast of the model initialized at 12:00 UTC. The data would represent data valid at 18:00 (6 hours after 12:00).

[rthedin]

Hi Brian,
Thanks for creating and maintaining Herbie. I have a related question, also using HRRR data.

Using the example you gave, I can do
Herbie(valid_date='2021-01-01 12:00', model='hrrr', product='sfc', fxx=6)
and Herbie will print "Found 2021-Jan-01 06:00 UTC F06 [HRRR] [product=sfc] GRIB2 file from aws and index file from aws."

From the information printed, it seems like Herbie gave me data of a 6 hour forecast initialized at 6AM, so data at 12PM. That appears to be contradict what you just said-- I was expecting to see some info on 18:00. What am I missing here?

[blaylockbk]

Herbie accepts arguments for date or valid_date.

• date represents the model initialization time
• valid_date represents the datetime the data is valid

Herbie/herbie/archive.py

Lines 250 to 258 in b96ce71

	if date is not None:
	# User supplied `date`, which is the model initialization datetime.
	self.date = pd.to_datetime(date)
	self.valid_date = self.date + timedelta(hours=self.fxx)
	else:
	assert valid_date is not None, "`date` or `valid_date` is required."
	# User supplied `valid_date`, which is the model valid datetime.
	self.valid_date = pd.to_datetime(valid_date)
	self.date = self.valid_date - timedelta(hours=self.fxx)

If you want the data valid at 18z from the model initialized at 12z you would do

Herbie(date='2021-01-01 12:00', model='hrrr', product='sfc', fxx=6)

or

Herbie(valid_date='2021-01-01 18:00', model='hrrr', product='sfc', fxx=6)

[rthedin]

That makes sense. Thanks for the quick response!