Correlations between Correlations between NAM forecasts of banded NAM forecasts of banded

snow ingredients and snow ingredients and snowfall, for a broad snowfall, for a broad

spectrum of snow eventsspectrum of snow events

Mike Evans and Mike JurewiczMike Evans and Mike JurewiczNOAA/NWS Binghamton, NYNOAA/NWS Binghamton, NY

PurposePurpose

Many case studies have shown Many case studies have shown utility of looking at certain key utility of looking at certain key dynamical ingredients prior to dynamical ingredients prior to major, banded snow events.major, banded snow events.

Question: What about smaller Question: What about smaller events: can the same conceptual events: can the same conceptual models applied to big events be models applied to big events be applied to smaller events? applied to smaller events?

OutlineOutline

Review of conceptual models Review of conceptual models regarding banding associated regarding banding associated with major storms and moderate with major storms and moderate storms.storms.

Our findings.Our findings. Now what?Now what?

Heavy Banded Snowfall Conceptual Heavy Banded Snowfall Conceptual Model (from Nicosia and Grumm)Model (from Nicosia and Grumm)

Frontogenesis and Stability (from Frontogenesis and Stability (from Novak et al.)Novak et al.)

Frontogenesis (shaded) and saturated equivalent potential temperature (contoured)

Novak et al. summarized Novak et al. summarized these findings by listing 3 key these findings by listing 3 key ingredients for snow ingredients for snow banding…banding…

FrontogenesisFrontogenesis Reduced stabilityReduced stability MoistureMoisture

Next Question… What about Next Question… What about “moderate” events?“moderate” events?

Forecasters are using these Forecasters are using these parameters – especially at short parameters – especially at short rangesranges

What we’ve doneWhat we’ve done

Examine 27 cases (maximum Examine 27 cases (maximum snowfall from 4 to 39 inches).snowfall from 4 to 39 inches).

Look for existence of the Look for existence of the ingredients.ingredients.

Look for relationships between Look for relationships between the magnitude, depth and the magnitude, depth and persistence of the ingredients and persistence of the ingredients and snowfall.snowfall.

Findings related to Findings related to magnitude of key magnitude of key ingredientsingredients Ingredients identified by Novak et. al. also Ingredients identified by Novak et. al. also

exist in smaller storms.exist in smaller storms. Significant correlations were found between Significant correlations were found between

event max snowfall and 12-hr forecast event event max snowfall and 12-hr forecast event maximum Fn convergence and event maximum Fn convergence and event maximum upward vertical motion.maximum upward vertical motion.

No significant correlation was found between No significant correlation was found between event max snowfall and 12-hr forecast event event max snowfall and 12-hr forecast event minimum geostrophic EPV. minimum geostrophic EPV.

Correlations with max snowfall decreased Correlations with max snowfall decreased rapidly from 12 hour forecasts to 24 hour rapidly from 12 hour forecasts to 24 hour forecasts.forecasts.

Findings related to depth Findings related to depth and persistence of key and persistence of key ingredientsingredients Significant correlations were found between max Significant correlations were found between max

snowfall and depth and persistence of Fn convergence snowfall and depth and persistence of Fn convergence and negative geostrophic EPV.and negative geostrophic EPV.

Better correlations were found between max snowfall Better correlations were found between max snowfall and depth and persistence of parameters that and depth and persistence of parameters that combined ingredients (* Signature).combined ingredients (* Signature).

No ingredient or combination parameter correlated No ingredient or combination parameter correlated better with max snowfall than depth and persistence better with max snowfall than depth and persistence of omega < -8 µbsof omega < -8 µbs-1-1

Depth and persistence of key ingredients are all Depth and persistence of key ingredients are all strongly correlated to depth and persistence of strongly correlated to depth and persistence of upward vertical motion.upward vertical motion.

Correlations between max snowfall and depth and Correlations between max snowfall and depth and persistence of key ingredients all decreased persistence of key ingredients all decreased significantly between 12 and 24 hours.significantly between 12 and 24 hours.

More findings…temporal More findings…temporal trends in EPVtrends in EPV

A strong correlation was found between A strong correlation was found between max snowfall and the magnitude of max snowfall and the magnitude of negative EPV, 3 hours prior to the most negative EPV, 3 hours prior to the most intense banding.intense banding.

A strong correlation was found between A strong correlation was found between max snowfall and the change in EPV, max snowfall and the change in EPV, from 3 hours prior to the most intense from 3 hours prior to the most intense banding, to the time of most intense banding, to the time of most intense banding (EPV increased rapidly in major banding (EPV increased rapidly in major events).events).

More findings… More findings… microphysicsmicrophysics

No correlation between max No correlation between max snowfall and depth of the snowfall and depth of the dendrite zone.dendrite zone.

Strong correlation between max Strong correlation between max snowfall and magnitude, depth snowfall and magnitude, depth and persistence of omega in the and persistence of omega in the dendrite zone.dendrite zone.

Final question – can we show Final question – can we show benefits of looking at benefits of looking at ingredients vs. just looking ingredients vs. just looking at omega?at omega? We can’t prove that examining depth and We can’t prove that examining depth and

persistence of ingredients or combinations of persistence of ingredients or combinations of ingredients, ingredients, at a point over the entire at a point over the entire time of the stormtime of the storm, provides any , provides any improvement over examination of depth and improvement over examination of depth and persistence of strong model omega.persistence of strong model omega.

However, there is evidence that the However, there is evidence that the magnitude of certain ingredients magnitude of certain ingredients at key at key timestimes (during the most intense banding), (during the most intense banding), correlates more closely with event total correlates more closely with event total snowfall than does model omega. snowfall than does model omega.

Now what?Now what?

Complete a draft of a paper, Complete a draft of a paper, submit to ER Scientific Service submit to ER Scientific Service Division (late May).Division (late May).

Develop teletraining (fall, 2007).Develop teletraining (fall, 2007).