Add cycle-specific forecast lengths for GFS

dev/parm/config/gfs/yaml/defaults.yaml

@@ -17,6 +17,10 @@ base:
   DO_METP: "YES"
   FHMAX_GFS: 120
   FHMAX_HF_GFS: 48
+  FHMAX_GFS_00: 384
+  FHMAX_GFS_06: 180
+  FHMAX_GFS_12: 384
+  FHMAX_GFS_18: 180
   FCST_BREAKPOINTS: ""
   DO_GSISOILDA: "NO"
   DO_LAND_IAU: ".false."

dev/workflow/CYCLE_SPECIFIC_FORECAST_LENGTHS.md

@@ -0,0 +1,89 @@
+# Cycle-Specific Forecast Lengths for GFS
+
+## Overview
+
+This feature allows the Global Forecast System (GFS) to run different forecast cycles (00z, 06z, 12z, 18z) to different output lengths. This helps save compute time by running shorter forecasts for some cycles while maintaining longer forecasts for others.
+
+## Configuration
+
+To enable cycle-specific forecast lengths, add the following parameters to your configuration YAML file (e.g., `dev/parm/config/gfs/yaml/defaults.yaml`):
+
+```yaml
+base:
+  FHMAX_GFS_00: 384  # 16 days for 00z cycle
+  FHMAX_GFS_06: 180  # 7.5 days for 06z cycle
+  FHMAX_GFS_12: 384  # 16 days for 12z cycle
+  FHMAX_GFS_18: 180  # 7.5 days for 18z cycle
+```
+
+These values override the default `FHMAX_GFS` for their respective cycles.
+
+## How It Works
+
+### Cycledef Generation
+
+When cycle-specific FHMAX values are defined, the workflow generates separate Rocoto cycledefs for each cycle:
+- `gfs_00` - Runs at 00z
+- `gfs_06` - Runs at 06z
+- `gfs_12` - Runs at 12z
+- `gfs_18` - Runs at 18z
+
+The standard `gfs` cycledef is still generated for compatibility.
+
+### Task Generation
+
+Tasks that depend on forecast length automatically detect cycle-specific FHMAX values:
+
+- **Product Generation Tasks** (atmos_prod, ocean_prod, ice_prod):
+  - When FHMAX values differ across cycles, separate metatasks are created
+  - Example: `gfs_atmos_prod_00`, `gfs_atmos_prod_06`, etc.
+  - Each metatask runs only for its designated cycle with appropriate forecast hours
+
+- **UPP Tasks** (atmupp, goesupp):
+  - Similar behavior to product tasks
+  - Cycle-specific versions created when needed
+
+### Backward Compatibility
+
+When cycle-specific FHMAX values are not defined or are all the same, the system uses the standard implementation with a single metatask, maintaining full backward compatibility.
+
+## Example: Operational-like Setup
+
+16-day forecasts for synoptic cycles (00z, 12z) and 7.5-day forecasts for intermediate cycles (06z, 18z):
+
+```yaml
+base:
+  INTERVAL_GFS: 6      # Run GFS every 6 hours
+  FHMAX_GFS: 120       # Default fallback (5 days)
+  FHMAX_HF_GFS: 48     # High-frequency output to 48 hours
+  FHMAX_GFS_00: 384    # 16 days for 00z
+  FHMAX_GFS_06: 180    # 7.5 days for 06z
+  FHMAX_GFS_12: 384    # 16 days for 12z
+  FHMAX_GFS_18: 180    # 7.5 days for 18z
+```
+
+## Implementation Details
+
+### Code Locations
+
+- **Configuration**: `dev/parm/config/gfs/yaml/defaults.yaml`
+- **Cycledef Generation**: `dev/workflow/rocoto/gfs_cycled_xml.py`
+- **Forecast Hour Utilities**: `dev/workflow/rocoto/tasks.py`
+- **Task Generation**: `dev/workflow/rocoto/gfs_tasks.py`
+
+### Forecast Hour Calculation
+
+For each cycle, forecast hours are determined by:
+1. Check if `FHMAX_GFS_<cyc>` exists in configuration
+2. If yes, use that value; otherwise fall back to `FHMAX_GFS`
+3. Generate forecast hour list using high-frequency and standard intervals
+
+Example for 00z with FHMAX_GFS_00 = 384:
+- Hours 0-48: Every 3 hours (high-frequency)
+- Hours 48-384: Every 6 hours (standard)
+- Total: 73 forecast hours
+
+Example for 06z with FHMAX_GFS_06 = 180:
+- Hours 0-48: Every 3 hours (high-frequency)
+- Hours 48-180: Every 6 hours (standard)
+- Total: 39 forecast hours

dev/workflow/rocoto/gfs_cycled_xml.py

@@ -79,6 +79,28 @@ def get_cycledefs(self):
             interval_gfs_str = timedelta_to_HMS(interval_gfs)
             strings.append(f'\t<cycledef group="gfs">{sdate_gfs_str} {edate_gfs_str} {interval_gfs_str}</cycledef>')
 
+            # Create cycle-specific cycledefs for GFS (00z, 06z, 12z, 18z)
+            # This allows different forecast lengths for different cycles
+            if interval_gfs <= to_timedelta('6H'):
+                for cyc in ['00', '06', '12', '18']:
+                    # Find first occurrence of this cycle hour at or after sdate_gfs
+                    cyc_hour = int(cyc)
+                    sdate_cyc = sdate_gfs.replace(hour=cyc_hour)
+                    if sdate_cyc < sdate_gfs:
+                        # Move to next day if we're past this hour
+                        sdate_cyc = sdate_cyc + to_timedelta('24H')
+                    # Find last occurrence at or before edate_gfs
+                    edate_cyc = edate_gfs.replace(hour=cyc_hour)
+                    if edate_cyc > edate_gfs:
+                        # Move back a day if we're past the end date
+                        edate_cyc = edate_cyc - to_timedelta('24H')
+
+                    if sdate_cyc <= edate_cyc:
+                        sdate_cyc_str = sdate_cyc.strftime("%Y%m%d%H%M")
+                        edate_cyc_str = edate_cyc.strftime("%Y%m%d%H%M")
+                        interval_cyc_str = timedelta_to_HMS(to_timedelta('24H'))
+                        strings.append(f'\t<cycledef group="gfs_{cyc}">{sdate_cyc_str} {edate_cyc_str} {interval_cyc_str}</cycledef>')
+
             date2_gfs = sdate_gfs + interval_gfs
             date2_gfs_str = date2_gfs.strftime("%Y%m%d%H%M")
             if date2_gfs <= edate_gfs: