The Over Forecast Advisory Event on St. Patricks Day Weekend 2013 NOAA’s National Weather Service Ron W. Przybylinski Science and Operations Officer Fred Glass Lead Forecaster National Weather Service – St. Louis

Topics to be Presented Upper level pattern over the Central United States from 1200 UTC 0316 to 1200 UTC 3/ mb, 500 mb 850 mb patterns from the initial 00 Hour Forecast (700 am 3/16/2013) NAM model. Surface pattern was also used for the NAM forecasts. 12 and 24 Hour Forecasts of the Surface and Upper level patterns (for 700 PM 3/16 and for 700 am Sunday 3/17/2013 St. Pats Day. HPC (now WPC) snow forecasts for March 17 th Saint Patricks Day.. Upper level pattern over the Central United States from 1200 UTC 0316 to 1200 UTC 3/ mb, 500 mb 850 mb patterns from the initial 00 Hour Forecast (700 am 3/16/2013) NAM model. Surface pattern was also used for the NAM forecasts. 12 and 24 Hour Forecasts of the Surface and Upper level patterns (for 700 PM 3/16 and for 700 am Sunday 3/17/2013 St. Pats Day. HPC (now WPC) snow forecasts for March 17 th Saint Patricks Day..

Topics to be Presented. Precipitation Types from the NAM and GFS using the 1200 UTC Model run (700 am Saturday) 3/16/2013 Model soundings – from the NAM and GFS from the 1200 UTC (03/16/13) Model run. Viewing forecast soundings every 12 hours and 30 Hr Forecast - 18 UTC Comparisons of the model soundings with AMDAR (aircraft sounding data) sounding. Commercial aircraft taking off and landing from Lambert field. We will survey model sounding performance issues to the AMDAR Soundings Precipitation Types from the NAM and GFS using the 1200 UTC Model run (700 am Saturday) 3/16/2013 Model soundings – from the NAM and GFS from the 1200 UTC (03/16/13) Model run. Viewing forecast soundings every 12 hours and 30 Hr Forecast - 18 UTC Comparisons of the model soundings with AMDAR (aircraft sounding data) sounding. Commercial aircraft taking off and landing from Lambert field. We will survey model sounding performance issues to the AMDAR Soundings

Where are we at?

300 mb Upper Air pattern NAM 00Hr Forecast – VT 1200 UTC (700 am) MB Upper Level Jet extended from eastern South Dakota through the eastern Great Lakes region.

500 MB Pattern (18 Kft) 00 Hr NAM Forecast VT 1200 UTC (700 am 3/16) Mean Upper Level Flow from the west-northwest. Weak disturbances from over the Rocky Mountains

850 MB Analysis (5 Kft) 00 Hr Forecast VT 1200 UTC (700 am) 3/16/13 L L 850 mb trough moving through Missouri at this time

Surface Analysis (NAM) 1200 UTC 00Hr Forecast (700 am cdt) Cold frontal boundary extended from surface low over SE Indiana through southern Missouri and into northern Oklahoma.

Soundings AMDAR Sounding-1314 UTC (813 AM CDT) Aircraft ascending to the southeast from Lambert field. NAM Model Sounding for STL Valid Time 1200 UTC (700 am cdt). 00 Hr Forecast Sounding.

Soundings AMDAR Sounding – 1314 UTC (813 AM CDT) Aircraft ascending to the southeast from Lambert Field. GFS Model Sounding at 1200 UTC (700 AM CDT at STL. 00 Hr Forecast Sndg..

NAM-GFS Model Precipitation Type NAM Model PTYPE 00 Hr Fcst VT 1200 UTC AM CDT Saturday morning. GFS Model PTYPE 00 Hr Fcst VT 1200 UTC AM CDT Saturday morning

WPC Forecasts WPC WWD Day 2 Forecast: Issued at 1727 UTC

WPC Forecasts WPC WWD Day1: Valid 1200 UTC : Issued at 0523 UTC (1223 AM)

WPC Forecast WPC WWD Days 1 and 2. Valid 0000 UTC Issued at 1806 UTC (106 PM Saturday)

300 MB Upper Air Pattern (NAM 12 Hr Forecast) VT 0000 UTC Strong Upper-Level Jet Core extends across the Lower Great Lakes region. Area to watch out for Upper-level Divergence is right entrance region of the ULJ (Dr. Jim Moore)

500 MB Pattern (18 Kft) NAM Fcst VT 0000 UTC 12 Hr Fcst (700 PM Sat) 500 mb pattern shows nearly zonal flow pattern with major 500 mb trough moving across the Great Lakes. Weak distrubances over the central and southern Rockies.

850 MB Pattern (5 kft) NAM Fcst VT 0000 UTC 0317 – 700 PM Sat Eve. Colder air continues to seep southward towards Missouri and the southern Half of Illinois. 850 mb 0° C isotherm entering NE MO

Surface Analysis – NAM 12 Hr Forecast VT 0000 UTC (700 PM Sat Evening Cold front is now well south of Missouri from West Virginia to an area of low pressure over west Texas.

Soundings at 700 PM Sat Evening AMDAR Sounding at 2309 UTC (639 PM CDT). Aircraft ascending from Lambert field to the southeast. NAM Model Sounding at 0000 UTC 0317 (700 PM CDT Saturday evening). 12 Hr Fcst

Soundings AMDAR Sounding at 2309 UTC (609 PM CDT ) Aircraft ascending from Lambert field to the southeast. GFS Model Sounding at 0000 UTC (700 PM CDT Saturday evening (12 Hr Fcst)

Model Precipitation Type NAM PCPN TYPE – 12 Hr Fcst VT 0000 UTC (700 PM CDT Saturday evening). GFS PCPN TYPE – 12 Hr Fcst VT 0000 UTC 0317 (700 PM CDT Saturday evening).

300 MB Upper Level Pattern (Jet Stream level). NAM 24 Hr Fcst VT 1200 UTC Sat

500 MB Pattern NAM Fcst – 24 Hr Fcst VT 1200 UTC (700 am CDT Sat Morning) 500 MB Flow continues to remain Zonal Flow Missouri and Illinois. Weak distrubance moving east over northern Texas while stronger trough moving ESE over Idaho.

850 MB Pattern (NAM 24 Hr Fcst) VT 1200 UTC (700 AM CDT Sat Morning 850 MB Frontal boundary extends from 8H Low over OK through West Virginia. Really cold air centered over Great Lakes region.

Surface Pattern (NAM 24 Hr Fcst) VT 1200 UTC (700 AM Sat Morning) Surface forecast pattern from the NAM showed the surface front sliding further south across central Arkansas and southern Tennessee. High Pressure moving southeast into the western Great Lakes region.

Soundings AMDAR Sounding at 1333 UTC 833 AM Sunday Aircraft was in descent into Lambert Field from the South-southeast. NAM Model Sounding at 1200 UTC 24 Hr Fcst VT 1200 UTC for St. Louis. (700 am Sunday).

Soundings AMDAR Sounding at 1333 UTC Aircraft was on descent into Lambert Field from the South-Southeast. Low-level winds are easterly. GFS Model Sounding at 1200 UTC. 24 Hr Forecast (VT 1200 UTC) 700 am CDT Saturday morning.

Model Precipitation Type NAM Model Precipitation Type 24 Hr Foreast (1200 UTC – 700 am Sunday) GFS Model Precipitation Type 24 Hr Forecast (1200 UTC – 700 am Sunday).

North-South Cross-section of Upper Level Jet, Ageo Wind and Vertical Motion NAM 24 Hr Fcst - Strong vertical motion is noted in the ‘Right Entrance Region of the Upper-Level Jet (Thermally Direct Circulation). Arrows pointing to areas of strongest vertical motion.

Soundings AMDAR Sounding at 1844 UTC (104 PM CDT). Aircraft descent from the East into Lambert Field. (Note the SE flow below 700 mb) NAM Sounding at 1800 UTC (100 PM CDT Saturday Hr Fcst Valid time 1800 UTC

North-South Cross-section of the Upper Level Jet, Ageo winds, Model Vertical Motion Field NAM 30 Hour Fcst VT 1800 UTC- Strong Vertical Motion Field is located again to the right side of the Upper Level Jet – between STL and MEM. (Thermally Direct Circulation – Entrance Region ULJ)

What Happened on St. Pats Day

Day 1 Precipitation Totals Valid 1200 UTC – (Monday Morning) STL

Summary Reviewed the large-scale environment from the NAM model beginning at 1200 UTC Saturday through 1200 UTC Sunday Both the NAM and GFS Model Soundings showed a slightly cold bias in the lower levels this case (at or below 800 mb) compared to AMDAR soundings. NAM and GFS model soundings did not capture the southeast flow at lower-levels compared to AMDAR Soundings at the 30 Hour Fcst from 0316 model run. The highest precip totals occurred in the Right Entrance Region of the Upper level Jet across southeast Missouri through southern Indiana. (Note location of Upper level Divergence centers.) Reviewed the large-scale environment from the NAM model beginning at 1200 UTC Saturday through 1200 UTC Sunday Both the NAM and GFS Model Soundings showed a slightly cold bias in the lower levels this case (at or below 800 mb) compared to AMDAR soundings. NAM and GFS model soundings did not capture the southeast flow at lower-levels compared to AMDAR Soundings at the 30 Hour Fcst from 0316 model run. The highest precip totals occurred in the Right Entrance Region of the Upper level Jet across southeast Missouri through southern Indiana. (Note location of Upper level Divergence centers.)

Summary Continued The NAM and GFS Precipitation Type Forecast provided direction for the 12 through 30 hour forecast preiod in showing sleet and some freezing drizzle while snow remained to the north of STL. Some Caution might be advised with the AMDAR soundings in some cases. Check more than one ascent aircraft if possible. Forecasters need to survey all available real and model data and question WPC snow forecasts when flip-flop snow forecasts are received at the local offices. The NAM and GFS Precipitation Type Forecast provided direction for the 12 through 30 hour forecast preiod in showing sleet and some freezing drizzle while snow remained to the north of STL. Some Caution might be advised with the AMDAR soundings in some cases. Check more than one ascent aircraft if possible. Forecasters need to survey all available real and model data and question WPC snow forecasts when flip-flop snow forecasts are received at the local offices.