Post on 20-Jan-2016
Forecast Challenges Associated with the Valentine’s Day, St. Patrick’s Day
and Tax Day Nor’easters of 2007
Neil A. Stuart
NWS Albany, NY
NROW 9
Valentine’s Day Storm
• Forecast guidance– Anomalies– Ensembles– Plumes– NCEP/HPC– Observational data
• Forecast process and considerations
• What happened
Anomalies and Plumes – 2 to 3 day lead time
} {
3-4 SD below normal 3+ days
in advance, increased to 4-5
SD closer to onset of storm
Clustering between 1.5”
and 2.4”
Ensemble probabilities for ≥1.00” liquid equivalent
Widespread region of ≥ 90% probability of ≥ 1.00” of liquid
equivalent
Unusual consistency in the spread
Other guidance and observations
HPC WWD forecasts temporal consistency with
axis of heaviest snow
Wind profile at boundary layer suggested warming
and period of mixed precipitation at Albany
Verified with 1800 UTC observed sounding
What Happened?
•Widespread 20-42” of snow Capital Region of NY and north and west
•NESIS Category 3 – ranked near Blizzard of ’78 in SE New England
•I-80 shut down in PA due to accidents in mixed precipitation
•Many planes stranded on runways for hours at JFK airport
•35 deaths
Surface low track across southeastern New
England, analog to some of the biggest snows in
upstate NY
Band of snow produced 4”-6” per hour
St. Patrick’s Day Storm
• Forecast guidance– Anomalies– Ensembles– Plumes– NCEP/HPC– Observational data
• What happened
Anomalies
3-4 SD below normal
Only 1-2 SD below normal in U direction,
but 3-5 SD above normal in V direction, with NE U.S. in RRQ
AnomaliesDeterministic operational GFS and NAM show 4-5 SD below normal – not
dampened by 15+ ensemble members
Deterministic and ensemble upper level wind
anomalies barely 2 SD below normal
Ensemble probabilities of 1.00” of liquid equivalent and plume guidance
Widespread region of ≥ 90% probability of ≥ 1.00” of liquid
equivalent, however, note western edge
Most clustering between 1.0”
and 2.5”
}{
Other guidance and observationsHPC WWD consistently kept the axis of heaviest snow in the Catskills and
northern New England
Extremely tight 850 hPa thermal gradient across southern NY and New England
Extremely tight boundary layer thermal gradient
contributed to very strong frontogenesis
What Happened?
•18-30” of snow in the Catskills with a foot or more over much of interior New England and New York
•NESIS Category 2
•10 deaths – all due to traffic accidents
Surface low tracked across southeastern
New England, similar to Valentine’s Day Storm
Primary heavy snow band in Catskills, note much
less reflectivity than Valentine’s Day Storm
Tax Day/Patriots Day Storm
• Forecast guidance– Anomalies– Ensembles– Plumes– Observational data
• What happened
Anomalies – Forecasted
U wind anomalies at 850 hPa forecasted to be
3-5 SD below normal
V wind anomalies at 850 hPa forecasted to be 3-4 SD above normal
U wind anomalies at 250 hPa 2-3 SD
below normal
MSLP anomalies of 4-5 SD below normal
Anomalies – Observed
U and V wind anomalies at 850 hPa U > 5 SD below normal
U wind anomalies at 250 hPa between 3 and 4 SD below normal
MSLP anomalies > 5 SD below normal
Ensemble probabilities of 2.00” of liquid equivalent and plume guidance
Ensemble probabilities of ≥ 2.00” of liquid equivalent were > 50%, with MREF the
highest and most widespread
SREF shows more spread, but both ensembles show virtually all members supporting ≥ 2.00”
of liquid equivalent
} {Clustering of plumes between 1.5” and 3.5”
of liquid equivalent
Other observations – What Happened
•Widespread flooding in southern NY and the mid-Atlantic states
•Severe coastal flooding and erosion from NJ through southern and eastern New England
•50 MPH wind gusts along the mid-Atlantic and New England coasts
•50 MPH or greater winds in the higher elevations of VT causing widespread tree and property damage
•IRS allowed 2 more days to file tax returns
•156 MPH gust at Mt. Washington
•Worst Weather in history of Boston Marathon
•$180 million damages in NJ, second only to Hurricane Floyd
Nearly isothermal at Albany, NY - Winds ≥ 50 KT
above the surface
Strong warm advection and deep winds ≥ 50 KT
Strong deep southeast winds ≥ 50 KT
Lessons from all three storms• Ensemble guidance and derived products are revolutionizing
forecasting
• New tools and products are allowing for unprecedented lead times for warning of high impact events
• POD ≥ 90%, FAR ≤ 20%, lead time for Watches ≥ 48 hours, Warnings ≥ 24 hours
• Anomalies showing departures from normal distinguishes high vs. low potential storm impact in extended ranges (2+ days prior to onset)
• Recognizing signals in ensemble means and spreads, and in anomaly displays helps quantify forecaster confidence
• Ensemble means and spreads help quantify uncertainty and temporal trends/consistency from run to run
• Probabilities for liquid equivalent rainfall amounts quantify confidence levels for corresponding snow amounts
Lessons from all three storms• Plume diagrams depict
– A range of liquid equivalent rainfall amounts– Precipitation types– Mean and maximum amounts of each precipitation type– Clustering near certain values and precipitation types helps quantify
confidence in those values• Despite advances in data analysis, assimilation and visualization,
some important user groups are not benefiting– PA interstate closed due to multiple accidents – Jets stranded on runways for 10+ hours in NYC– 67 deaths attributed to all three storms
• How can meteorologists help users to reduce the societal impacts of major winter storms like the 2007 storms?– Need to communicate forecast information in a manner understood by the
most user groups– Need to educate users on how to best use current forecast products and
services– Need to coordinate with users to best tailor current and future products
for their needs
Improving predictions and communication = Better preparation for weather-related hazards =
Reduced societal impacts!
Thank you for your attention!
• Real-time ensembles, anomalies, plumes and probabilities can be found at: http://eyewall.met.psu.edu
Questions?
http://www.sip.ucar.edu/wasis