NWS Albany Winter NWS Albany Winter Weather Forecast Tools: Weather Forecast Tools: For Your ConsiderationFor Your Consideration

John S. QuinlanJohn S. QuinlanSenior MeteorologistSenior Meteorologist

NWS Albany, NY NWS Albany, NY

Things we will coverThings we will cover

• Ensemble Forecasts (courtesy of Neil Stuart)

• Winter Weather Smart Tools• Lake Effect

PSU Collaborative Research PSU Collaborative Research and Weather Data Model and Weather Data Model

Ensemble Graphics on NWSEnsemble Graphics on NWShttp://http://nws.met.psu.edu/ensemblesnws.met.psu.edu/ensembles

/index.html/index.html

The The meridionalmeridional component of the wind, V, is considered positive when component of the wind, V, is considered positive when the wind in blowing from south to north. A south wind has a posithe wind in blowing from south to north. A south wind has a positive tive meridionalmeridional component while a north wind has a negative component while a north wind has a negative meridionalmeridionalcomponent. The zonal component of the wind, U, is considered poscomponent. The zonal component of the wind, U, is considered positive itive when the wind is blowing from west to east. Thus, a west wind hawhen the wind is blowing from west to east. Thus, a west wind has a s a positive zonal component and an east wind a negative zonal positive zonal component and an east wind a negative zonal component.component.

Valentine’s Day StormValentine’s Day Storm• Forecast guidance

– Anomalies– Ensembles– Plumes– NCEP/HPC– Observational data

• Forecast process and considerations

• What happened

Anomalies and Plumes Anomalies and Plumes –– 2 to 3 2 to 3 day lead timeday 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 Ensemble probabilities for ≥≥1.00” 1.00” liquid equivalentliquid equivalent

Widespread region of ≥ 90% probability of ≥ 1.00” of liquid

equivalent

Unusual consistency in the spread

Other guidance and observationsOther 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?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

NWS Albany Winter Weather NWS Albany Winter Weather Smart ToolsSmart Tools

• PType Nomogram Tool• Pcpn Type from Thickness• Box Weather Tool• Car Snow Amt

PTypePType NomogramNomogram ToolTool

• Uses model partial thickness to create a 2-D mapping of location of the precipitation types expected using the TRENDS technique. The results are displayed in a DESCRETE "Nomogram" grid.

The Universal Partial Thickness The Universal Partial Thickness NomogramNomogram

The vertical axis is the 1000-850 mb thicknessand the horizontal axis is the 850-700 mb thickness.

H1000H1000--H850 ThicknessH850 Thickness

H850H850--H700 ThicknessH700 Thickness

PTypePType NomogramNomogram

PcpnPcpn Type from ThicknessType from Thickness

• Computes the Wx grid based on model partial thicknesses as defined by the TRENDs technique from NWS Raleigh. The possibility exists to take a percentage blend of the Eta and GFS models to derive the forecast thickness values. Options also exists to adjust the critical layer thickness values to allow for a "warming" or "cooling" of the selected model to correct for model errors.

PcpnPcpn Type from ThicknessType from Thickness

Box Weather ToolBox Weather Tool

• All-encompasing weather tool with many forecaster options complete with internal grid consistency checks. Precipiation type is derived from the partial thickness method.

Surface Temperature ForecastSurface Temperature Forecast

Probability of PrecipitationProbability of Precipitation

QPF ForecastQPF Forecast

Box Box WxWx ToolTool

Car Snow AmtCar Snow Amt

• Determines ratio based on temperature, ascent, and RH from model fields. The derived snowratio is then multiplied by the QPF field to yield a snow amount.

Car Snow AmtCar Snow Amt

Lake Effect Snow IngredientsLake Effect Snow Ingredients(from Greg Byrd and Tom (from Greg Byrd and Tom NiziolNiziol))

• Instability• Fetch• Wind Shear• Upstream Moisture• Upstream Lakes• Synoptic-scale Forcing• Orography/Topography• Snow/Ice Cover on the Lake

InstabilityInstability

WFOWRF 5KM Resolution CRWFOWRF 5KM Resolution CR

Lake Effect SnowLake Effect Snow(some local considerations from (some local considerations from NiziolNiziol and Snyder)and Snyder)

• In most cases only 4 of 34 zones can reach warning criteria and an additional 8 zones can reach advisory criteria.

• The further you are away from the lake the more likely you will need some synoptic forcing to produce significant lake effect (>0.5”/hr) snow. Vort maxes are the most frequent mechanism.

• Surface-H8 Flow needs to be at least 15-20 kts, otherwise fetch is significantly decreased.

• Surface-H8 Flow needs to be cyclonic or at least straight. Anticyclonic flow is detrimental to lake effect.

• Strong synoptic sinking (neg vv values below -3) suppresses lake effect (this has more of an impact on initialization than when lake effect is shutting down).

• Low-level (below 8000 feet) inversions are the death of many potential lake effect events. If the cap is 5000-8000 feet you will have mainly flurries with squalls more likely as inversion heights increase above 8000 feet. Below 5000 feet you will likely experience stratocumulus and scattered flurries.