Jeffrey A. Chapman Philip N. Schumacher NOAA/NWS Sioux Falls, South Dakota

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The Forecast Winter Storm Warning issued by 21oo UTC 4/2/14 (some eastern areas issued a bit later)

The Outcome

Stage 4 Radar QPE 24h ending 1200 UTC 4/3/14 48 h ending 1200 UTC 4/4/14 24h ending 1200 UTC 4/4/14 Widespread Convection Mesoscale banding

1200 UTC 4/2/14 GFS QPF 24h ending 1200 UTC 4/3/1424h ending 1200 UTC 4/4/14 48 h ending 1200 UTC 4/4/14

1200 UTC 4/2/14 NAM QPF 24h ending 1200 UTC 4/3/1424h ending 1200 UTC 4/4/14 48 h ending 1200 UTC 4/4/14

 Dynamically similar at start of convection  GFS: more established with mid-level frontal boundary across NE hPa PV (PVU, shaded) and Mean Wind (m/s) 700 hPa Frontogenesis ( o C/100 km / 3h) GFS 18h forecast 03/06 UTC RAP analysis

 Defining area of mid- level frontogenesis from MN to NE hPa PV (PVU, shaded) and Mean Wind (m/s) 700 hPa Frontogenesis ( o C/100 km / 3h) GFS 24h forecast 03/12 UTC RAP analysis

 Intensification of mid-level frontal hPa PV (PVU, shaded) and Mean Wind (m/s) 700 hPa Frontogenesis ( o C/100 km / 3h) GFS 27h forecast 03/15 UTC RAP analysis

 Sharpening of mid- level frontal zone.  Start to identify wave pushing out into central High Plains hPa PV (PVU, shaded) and Mean Wind (m/s) 700 hPa Frontogenesis ( o C/100 km / 3h) GFS 30h forecast 03/18 UTC RAP analysis

 Rapid intensification of mid-level frontal boundary hPa PV (PVU, shaded) and Mean Wind (m/s) 700 hPa Frontogenesis ( o C/100 km / 3h) GFS 33h forecast 03/21 UTC RAP analysis

 PV advection established across the frontal boundary hPa PV (PVU, shaded) and Mean Wind (m/s) 700 hPa Frontogenesis ( o C/100 km / 3h) GFS 36h forecast 04/00 UTC RAP analysis

RAP Analysis  Widespread weak to moderately unstable conditions above frontal zone and across warm sector denoted by negative EPV 03/1200 UTC 500 hPa Omega (  b/s) hPa EPV (PVU) /700 hPa Fgen ( o C/100 km/3h) GFS 24h Forecast

RAP Analysis  Overall presence of instability is a result of relatively dry air above the frontal boundary  However, GFS forecast is more saturated over the front. 03/1200 UTC 500 hPa Omega (  b/s) hPa Sat. Deficit (g/kg) /700 hPa Fgen ( o C/100 km/3h) GFS 24h Forecast

RAP Analysis  Widespread weak to moderately unstable conditions above frontal zone denoted by negative EPV 03/1500 UTC 500 hPa Omega (  b/s) hPa EPV (PVU) /700 hPa Fgen ( o C/100 km/3h) GFS 27h Forecast

RAP Analysis  GFS forecast remains more saturated above the frontal zone.  More organized and more mature mid- level lift in GFS forecast. 03/1500 UTC 500 hPa Omega (  b/s) hPa Sat. Deficit (g/kg) /700 hPa Fgen ( o C/100 km/3h) GFS 27h Forecast

RAP Analysis  Presence of continued instability in both the GFS forecast and RAP analysis. 03/1800 UTC 500 hPa Omega (  b/s) hPa EPV (PVU) /700 hPa Fgen ( o C/100 km/3h) GFS 30h Forecast

RAP Analysis  RAP analysis finally shows moistening of the layer above the front.  GFS forecast closing on trend of slower saturation in RAP. 03/1800 UTC 500 hPa Omega (  b/s) hPa Sat. Deficit (g/kg) /700 hPa Fgen ( o C/100 km/3h) GFS 30h Forecast

700 hPa Wind (m/s) and hPa PV (PVU) RAP Analysis 03/0600 UTC 03/0600 UTC RAP PV and Residual Wind (RAP-GFS) GFS 18h Forecast

700 hPa Wind (m/s) and hPa PV (PVU) RAP Analysis 03/0900 UTC 03/0900 UTC RAP PV and Residual Wind (RAP-GFS) GFS 21h Forecast

hPa RAP PV and 700 hPa Residual Wind (RAP-GFS) 03/1200 UTC03/0900 UTC 03/1500 UTC03/1800 UTC

 Forecast neutral to slightly less northward transport of moisture through Iowa 700 hPa Meridional Moisture Transport (g kg -1 m s -1 ) RAP analysis 03/06 UTC GFS 18h forecast RAP-GFS 03/06 UTC

 GFS - northward displacement of stronger meridional transport E NE/W IA 700 hPa Meridional Moisture Transport (g kg -1 m s -1 ) RAP analysis 03/09 UTC GFS 21h forecast RAP-GFS 03/09 UTC

 Maturing of the meridional transport couplet. 700 hPa Meridional Moisture Transport (g kg -1 m s -1 ) RAP analysis 03/12 UTC GFS 24h forecast RAP-GFS 03/12 UTC

 Forecast meridional transport returning toward neutral anomaly central plains 700 hPa Meridional Moisture Transport (g kg -1 m s -1 ) RAP analysis 03/15 UTC GFS 27h forecast RAP-GFS 03/15 UTC

 Forecast meridional transport returned to neutral, six hours delayed from analysis 700 hPa Meridional Moisture Transport (g kg -1 m s -1 ) RAP analysis 03/18 UTC GFS 30h forecast RAP-GFS 03/18 UTC

Results/Conclusions Despite an adequate model large-scale forecast, a delay in snowfall development within a mesoscale band resulted in a poor forecast. Convective development across Missouri/Illinois does appear to have an impact on development of the mesoscale snow band across eastern Nebraska, southeast South Dakota, northwest Iowa and Minnesota. The internal PV anomaly resulting from fairly widespread convection diverted the wind flow/moisture transport into the developing mesoscale band. However, larger-scale models failed to produce this anomaly. Lack of PV anomaly with convection can be used as a “flag” that adjustments to forecasts will likely be needed.

Results/Conclusions Two questions arise from the current work 1) Is there something with the current parameterized convection which does not allow development of the diabatic PV anomaly? 2) Would running a model with explicit convection eliminate this problem?

Future Work High-resolution WRF local modeling Control Run to reproduce “reality” Alter model physics to remove latent heating to allow diagnosis of impact of convection

Questions and Comments?