An Overview of HPC Winter Weather Guidance for Three Warning Criteria Snowfall Events That Occurred During the Winter Season. A Review of the Goree/Younkin/Brown Snowfall Forecasting Technique: Case Study Jim Sieveking Winter Weather Workshop November 19 th 2008

Contents Review of Internal HPC Winter Weather Products Review of HPC Guidance for three warning snowfall events  15 December 2007  31 January - 1 February 2008  3-4 March 2008 How to Properly Use HPC Guidance A Review of the Goree/Younkin/Brown Snowfall Forecasting Technique Case Study Using Weather Event Simulator (WES)

HPC Internal Winter Weather Guidance

Winter Storm Event Review

Surface Low Track 12 UTC 15 December UTC 16 December 2007

Surface Map 00:00Z 16 December 2007

500mb Upper Air Analysis 12 UTC 15 December UTC 16 December 2007 L

850mb Upper Air Analysis 00:00Z 16 December 2007

700mb Upper Air Analysis 00:00Z 16 December 2007

DAY 2 DAY 3 DAY 2+3 HPC WWD GUIDANCE 06:00 UTC THURSDAY 12/13/07 DAY 2 = 12:00 UTC Friday - 12:00 UTC Saturday DAY 3 = 12:00 UTC Saturday - 12:00 UTC Sunday DAY 2+3 = 12:00 UTC Friday - 12:00 UTC Sunday

DAY 2+3 HPC WWD GUIDANCE 18:00 UTC THURSDAY 12/13/07 DAY 2 = 00:00 UTC Saturday - 00:00 UTC Sunday DAY 3 = 00:00 UTC Sunday - 00:00 UTC Monday DAY 2+3 = 00:00 UTC Saturday - 00:00 UTC Monday DAY 2 DAY 3 DAY 2+3

HPC WWD GUIDANCE 06:00 UTC FRIDAY 12/14/07 DAY 1 = 12:00 UTC Friday - 12:00 UTC Saturday DAY 2 = 12:00 UTC Saturday - 12:00 UTC Sunday DAY 1+2 = 12:00 UTC Friday - 12:00 UTC Sunday DAY 1 DAY 2 DAY 1+2

DAY 2+3 HPC WWD GUIDANCE 18:00 UTC FRIDAY 12/14/07 DAY 1 = 00:00 UTC Saturday - 00:00 UTC Sunday DAY 2 = 00:00 UTC Sunday - 00:00 UTC Monday DAY 1+2 = 00:00 UTC Saturday - 00:00 UTC Monday DAY 1+2 DAY 1 DAY 2 DAY 1+2

HPC WWD GUIDANCE 06:00 UTC SATURDAY 12/15/07 DAY 1 = 12:00 UTC Saturday - 12:00 UTC Sunday DAY 1

HPC WWD GUIDANCE 18:00 UTC SATURDAY 12/15/07 DAY 1 = 00:00 UTC Sunday - 00:00 UTC Monday DAY 1

Winter Storm Event Review

Surface Low Track 12 UTC 31 January UTC 1 February 2008

500mb Upper Air Analysis 12 UTC 31 January UTC 1 February 2008 L

850mb Upper Air Analysis L 00 UTC 1 February 2008

DAY 2 DAY 3 DAY 2+3 HPC WWD GUIDANCE 06:00 UTC TUESDAY 01/29/08 DAY 2 = 12:00 UTC Wednesday - 12:00 UTC Thurs DAY 3 = 12:00 UTC Thursday - 12:00 UTC Friday DAY 2+3 = 12:00 UTC Wednesday - 12:00 UTC Friday

DAY 2+3 HPC WWD GUIDANCE 18:00 UTC TUESDAY 01/29/08 DAY 2 = 00:00 UTC Thursday - 00:00 UTC Friday DAY 3 = 00:00 UTC Friday - 00:00 UTC Saturday DAY 2+3 = 00:00 UTC Thursday - 00:00 UTC Saturday DAY 2 DAY 3 DAY 2+3

HPC WWD GUIDANCE 06:00 UTC Wednesday 01/30/08 DAY 1 = 12:00 UTC Wednesday - 12:00 UTC Thur DAY 2 = 12:00 UTC Thursday - 12:00 UTC Friday DAY 1+2 = 12:00 UTC Wednesday - 12:00 UTC Friday DAY 1 DAY 2 DAY 1+2

DAY 2+3 HPC WWD GUIDANCE 18:00 UTC Wednesday 01/30/08 DAY 1 = 00:00 UTC Thursday - 00:00 UTC Friday DAY 2 = 00:00 UTC Friday - 00:00 UTC Saturday DAY 1+2 = 00:00 UTC Thursday - 00:00 UTC Saturday DAY 1+2 DAY 1 DAY 2 DAY 1+2

HPC WWD GUIDANCE 06:00 UTC THURSDAY 01/31/08 DAY 1 = 12:00 UTC Thursday - 12:00 UTC Friday DAY 1

HPC WWD GUIDANCE 18:00 UTC THURSDAY 01/31/08 DAY 1 = 00:00 UTC Friday - 00:00 UTC Saturday DAY 1

Total Snowfall 1 February 2008

Winter Storm Event Review

Surface Low Track 12 UTC 3 March UTC 4 March 2008

500mb Upper Air Analysis 12 UTC 3 March UTC 4 March 2008 L

850mb Upper Air Analysis L 12 UTC 4 March 2008

DAY 2 DAY 3 DAY 2+3 HPC WWD GUIDANCE 06:00 UTC SATURDAY 03/01/08 DAY 2 = 12:00 UTC Sunday - 12:00 UTC Monday DAY 3 = 12:00 UTC Monday - 12:00 UTC Tuesday DAY 2+3 = 12:00 UTC Sunday - 12:00 UTC Tuesday

DAY 2+3 HPC WWD GUIDANCE 18:00 UTC SATURDAY 03/01/08 DAY 2 = 00:00 UTC Monday - 00:00 UTC Tuesday DAY 3 = 00:00 UTC Tuesday - 00:00 UTC Wednesday DAY 2+3 = 00:00 UTC Monday - 00:00 UTC Wed DAY 2 DAY 3 DAY 2+3

HPC WWD GUIDANCE 06:00 UTC SUNDAY 03/02/08 DAY 2 = 12:00 UTC Monday - 12:00 UTC Tuesday DAY 3 = 12:00 UTC Tuesday - 12:00 UTC Wednesday DAY 2+3 = 12:00 UTC Monday - 12:00 UTC Wed DAY 2 DAY 3 DAY 2+3

HPC WWD GUIDANCE 18:00 UTC SUNDAY 03/02/08 DAY 1 = 00:00 UTC Monday - 00:00 UTC Tuesday DAY 2 = 00:00 UTC Tuesday - 00:00 UTC Wednesday DAY 1+2 = 00:00 UTC Monday - 00:00 UTC Wed DAY 1 DAY 2 DAY 1+2

DAY 2+3 HPC WWD GUIDANCE 06:00 UTC Monday 03/03/08 DAY 1 = 12:00 UTC Monday - 12:00 UTC Tuesday DAY 2 = 12:00 UTC Tuesday - 12:00 UTC Wednesday DAY 1+2 = 12:00 UTC Monday - 12:00 UTC Wed DAY 1+2 DAY 1 DAY 2 DAY 1+2

HPC WWD GUIDANCE 18:00 UTC MONDAY 03/03/08 DAY 1 = 00:00 UTC Tuesday - 00:00 UTC Wednesday DAY 1

HPC WWD GUIDANCE 06:00 UTC Tuesday 03/04/08 DAY 1 = 12:00 UTC Tuesday - 12:00 UTC Wednesday DAY 1

” ICE ACCUMULATION >0.25” ICE ACCUMULATION 0.5” SLEET ACCUMULATION Less Than 3 Inches Inches 6 -9 Inches 9 – 12 Inches Greater Than 12 Inches Snowfall Accumulation March Winter Storm Accumulation St. Louis Farmington Salem Godfrey Steelville Virden Greenville Red Bud

How To Properly Use HPC Guidance

WINTER FORECASTING GUIDANCE GFS SREF HPC Winter Weather Products ECWMF NAM WRF CANADIAN COLLABORATION

WFO FORECAST ≠ HPC GUIDANCE Use HPC winter weather products as GUIDANCE! Understand HPC’s weaknesses

HPC Forecast Consistency? Flip Flop

WWD BLENDER “{2007/12/13 04:50} hpc_wwd: I used a blend of: 12z ecwmf 12z ecwmf ensemble mean 21z srefmean 00z canadian regional gem draft hpc qpf 12z nam 12z gfs, and nam/srefmean/ecwmf for thermal profiles.”

HPC Blender Approach Just Click On Status To See the Concoction HPC WWD forecaster used the following blend as a starting point grid: NOTE: Each component in the blend was given equal weighting Day 1 graphic last updated at Mon Nov 3 16:13:13 UTC 2008 using the following blend settings: QPF BLEND 12Z GFS %40 12Z NAM %30 00Z ECM %30 PTYPE BLEND 12Z GFS %20 12Z NAM %50 09Z SREF Mean %30

HPC Blender Approach NAM ECWMF GFS CAUTION: This approach often leads to an unrealistic snowfall forecast, with increased areal coverage and lower snowfall amounts than what actually verifies. This approach is heavily biased toward model QPF. 33% OF EACH

Beware of the HPC East Coast Bias

Heavy Snowfall Forecasting Technique Goree/Younkin/Brown Goree, P.A., and R.J.Younkin, 1966: Synoptic Climatology of Heavy Snowfall over the Central and Eastern United States. Monthly Weather Review, 94, 11, Brown, R.F., and R.J. Younkin, 1970: Some Relationships Between 850-Millibar Lows and Heavy Snow Occurrences Over the Central and Eastern United States. Monthly Weather Review, 98,5,

 Goree and Younkin (1966) study contained a data set for two winter seasons – which supplied them with 50 winter storm events that: Produced heavy snow (4 inches in 12 hours) over a 14,384nm 2 area. Were associated with deepening and occluding surface low-pressure systems. Had a movement of the 500mb vorticity maxima in a direction north of east (44 of the 50 cases)  Brown and Younkin (1970) study contained a data set for two winter seasons – which supplied them with 81 winter storm events that: Produced heavy snow (4 inches in 12 hours) over a 17,982nm 2 area. Had a discernable 850mb low center that moved northeast and deepened during the 12hr heavy snowfall event Heavy Snowfall Forecasting Technique Goree/Younkin/Brown So let us assume for this technique to properly work, you must have: 1.A 500mb vorticity maxima that is moving northeast 2.A deepening/occluding surface low pressure system 3.A discernable 850 low center that tracks northeast and deepens with time 4.Thermal profile is conducive for snowfall and moisture is available

Goree and Younkin, 1966 The most favorable location of heavy snow with respect to the 500mb vorticity maxima is 2.5 Latitude Degrees (~150 Nautical Miles) to the left of its path.

Heavy Snow Occurs: 2.5 Degrees or 150 nm left of the track of the vorticity maxima. Slightly downstream from where the curvature changes from cyclonic to anticyclonic When the 500mb trough or low is deepening Goree and Younkin, 1966

Brown and Younkin, 1970 The initial 850mb center of the 12 hour study revealed that the -5°C isotherm nearly bisects the observed subsequent 12-hr heavy snowfall area.

Brown and Younkin, 1970 The most favorable location of heavy snow with respect to the 850mb low track is roughly 90 Nautical Miles to the left of its path.

Heavy Snow Occurs: 1.5 degrees or 90 nm to the left of the track of the 850mb low When the mean circulation deepens significantly * The “initial” -5°C degree isotherm is a good indicator for heavy snowfall axis in the following 12 hours. Brown and Younkin, 1970

Goree/Younkin/Brown Technique Step 1: Plot the track of the 850 mb low pressure. Draw a parallel line 90 nm to the cold side of the track. Step 2: Plot the track of the 500 mb vorticity maximum. Draw a line parallel to this track and 2.5 degrees of latitude (~150nm) to the cold side of the track. Step 3: Evaluate the location of the -5 o C 850 mb temperature compared to the tracks plotted in Steps 1 and 2. Step 4: Assess the warm air advection, lift and moisture available along the track over time. Step 5: Based on the results of Steps 1 through 4, determine the axis of heaviest snowfall and the relative intensity along the track. 90nm 150nm

Technique Application: Weather Event Simulator Scenario (12Z 31 January 2008) *12-24 Forecast Weather Event Simulator – 500mb Evolution – MSLP Comparison – 850mb Low Track Comparison – 850mb Temperature (Looking for -5°C) – Trowal Structure? – QPF/Snowfall Differences Applying the Empirical Technique – 500mb Vorticity Maxima Track Consensus – 850 Low Track Consensus – 850mb “Initial” Temperature – Compare Technique to HPC and Observed Snowfall

500mb Vorticity Maxima

850mb Low Track Initial Temperature (°C) At 00Z Feb 1 st

Putting It All Together -5°C 0°C

HPC Forecast

Observed Snowfall

You Be The Judge

Regional Distance Scale 1.5°1.0°2.0°2.5°3.0° Regional Distance Scale 1.5°1.0°2.0°2.5°3.0° Regional Distance Scale 1.5°1.0°2.0°2.5°3.0° Regional Distance Scale 1.5°1.0°2.0°2.5°3.0°