# Presentation: 729299

## 10.2 High Impact Sub-Advisory Snow Events: The Need to Effectively Communicate the Threat of Short Duration High Intensity Snowfall

- Gregory A. DeVoir
- NOAA/NWS State College, PA
- January 13, 2004

- 20th Conference on Weather Analysis and Forecasting
- SESSION 10: PUBLIC FORECAST AND WARNING ISSUES

## NWS Tiered Forecasting Approach

- When potentially hazardous weather conditions are expected, routine forecast products are headlined and complimented with specific event-driven Watches, Warnings, Advisories or Special Weather Statements (SPSs).

## Warnings are ideally preceded by Watches, alerting to the potential threat to life and property well in advance of impending weather events.

- NWS Tiered Forecasting Approach

## Our Goal: To provide sufficient lead time so that preventative actions can be taken to mitigate the impacts of adverse weather conditions.  Save lives and property.

In most instances of hazardous weather, the tiered forecast product approach works well. User groups are informed well ahead of time in the majority of significant events.

- In most instances of hazardous weather, the tiered forecast product approach works well. User groups are informed well ahead of time in the majority of significant events.

- NWS Tiered Forecasting Approach

## However, a small number of events occur annually which fail to meet Advisory (and/or) Warning criteria, yet still pose a significant hazard.

- NWS Tiered Forecasting Approach

## Sub-Advisory Events

- Not confined to cold-season phenomena.
- Patchy Dense Fog.
- Approaching-severe Thunderstorms.
- Non-severe wind gusts.
- Many occur during the winter season, where a combination of precipitation intensity, duration and type, along with fluctuations in wind and temperature present a multitude of hazards.

## Occurring in short-lived bursts or squalls of snow, total snow accumulation is a secondary concern.  

Severe impact is created by blinding snowfall, rapidly deteriorating road conditions, and increasing driver anxiety and confusion.

The terms “high intensity”, “high impact” and “sub-advisory” are used here to describe such events.  

- Severe impact is created by blinding snowfall, rapidly deteriorating road conditions, and increasing driver anxiety and confusion.
- The terms “high intensity”, “high impact” and “sub-advisory” are used here to describe such events.

- Sub-Advisory Snowfall

## Central PA SnowAdvisory/Warning Criteria

- In central Pennsylvania, Winter Weather Advisory snow criteria is met when an average of at least 2 to 4 inches of snow accumulates in a 12-hour period
- A “midpoint” value of 3 inches or more is required.
- Warning criteria is reached when 6 inches of snow or more falls within a 12-hour period (again, a midpoint value).

## High Impact Sub-Advisory Snowfall

- In areas which receive substantial annual snowfall, forecasts calling for one to two inches of snow do not typically arouse substantial public concern.
- For this reason, the NWS does not headline its forecasts for such amounts in these areas.

## However, snow falling at a high intensity       (bursts or squalls), with 1-2” amounts in a    1 to 2 hour period, greatly magnifies the public impact. 

When snowfall rates are high, yet advisory criteria are not met, advisories typically are not issued and the public is not aware of the potential impact of the snowfall. 

- When snowfall rates are high, yet advisory criteria are not met, advisories typically are not issued and the public is not aware of the potential impact of the snowfall.

- High Impact Sub-Advisory Snowfall

## Slide 11

## An Ongoing Forecast Problem...

- The NWS predicts weather. But clearly, there are numerous other factors that affect the outcome of a short burst of snow in a few hours.
- Road conditions, air and road surface temperatures, as well as how drivers act and respond to available information and road conditions are factors the NWS cannot control.

## 
NOAA strategic plan, mission goal 4:

  "Support the Nation's commerce with information for safe, efficient, and environmentally sound transportation.“

To fulfill its mission, the NWS must do all it can to ensure its users are informed of all impending weather hazards. Critical short-term weather information must reach our customers.

- NOAA strategic plan, mission goal 4:
-   *"Support the Nation's commerce with information for safe, efficient, and environmentally sound transportation.“*
- To fulfill its mission, the NWS must do all it can to ensure its users are informed of *all *impending weather hazards. Critical short-term weather information must reach our customers.

- An Ongoing Forecast Problem...

## Across the U.S., the frequency of sub-advisory snow events increases as one moves north, and towards areas downwind of the Great Lakes. 

The following slide contains data extracted from Cember and Wilks (1993), indicates % of and # of days of:
 	Snowfall > 1”
 	Snowfall > 4”
 	1” < Snowfall < 4”

- The following slide contains data extracted from Cember and Wilks (1993), indicates % of and # of days of:
-  	Snowfall > 1”
-  	Snowfall > 4”
-  	1” < Snowfall < 4”

- High Impact Sub-Advisory Snowfall - Frequency

## Nov 8-15

**Dec 1-15**

**Jan 1-31**

**Feb 15-28**

**Mar 24-31**

**Cember and Wilks 1993**

## On average, throughout the winter months, sub-advisory snowfalls occur 3 to 4 times as often as snow Advisory/Warning events.

Assessing and communicating the character (intensity, duration) of snowfall on these days becomes much more important than predicting actual amounts.

- Assessing and communicating the character (intensity, duration) of snowfall on these days becomes much more important than predicting actual amounts.

- High Impact Sub-Advisory Snowfall – Cember and Wilks

## High Impact Sub-Advisory Snowfall

-  The timing of snowfall intensity and duration in relation to traffic volume (PENNDoT, 2001), including time of day and day of week, is critical to determining potential public impact.
-  Impacts are greatly magnified during periods of higher traffic volume,
-    especially weekday rush hours and weekend afternoons.

## Predictability of Events

- Increased computational resources and better tools (computer models, satellite and radar imagery) enable forecasters to diagnose more meso- and smaller-scale weather phenomena and instabilities than ever before.
- Operational application of snow microphysics concepts - Waldstreicher (2001) showed how BUFKIT and snow microphysics concepts can be applied operationally to better identify and more accurately predict the timing of heavier snow bursts.

## Cross-Hair Signature Waldstreicher (2001)

## Recent Examples in/near PA

- 22 February 2001 – 2 to 3 inches of snow in less than 2 hours throughout mid-Atlantic states, including Washington, D.C. area.
- 28 December 2001 - Lake Effect Snow Squall (Loganton, PA).
- 5 January 2003 – 1 to 3 inches of snow in less than 3 hours across south central PA (midday Sunday following church services).

## In each of these examples, snow amounts were accurately forecast well ahead of time.

Yet, for each example, the impact was out of proportion with the volume of the snowfall.

INTENSITY was the biggest factor, along with traffic volume and subsequent road conditions, leading to multiple fatal chain reaction accidents.

- Yet, for each example, the impact was out of proportion with the volume of the snowfall.
- INTENSITY was the biggest factor, along with traffic volume and subsequent road conditions, leading to multiple fatal chain reaction accidents.

- Recent Examples in/near PA

## Slide 22

## NOWCASTs were in effect for all of these events, but...

NOWCASTs have a limited audience (NWS websites, NOAA Weather Radio, sporadic AM/FM radio stations).

Many did not receive critical short term forecast information. 

- NOWCASTs have a limited audience (NWS websites, NOAA Weather Radio, sporadic AM/FM radio stations).
- Many did not receive critical short term forecast information.

- Recent Examples in/near PA

## Last week - January 6, 2004

## January 6, 2004

**NATIONAL WEATHER SERVICE STATE COLLEGE PA**
**1036 AM EST TUE JAN 6 2004**
**PAZ005-006-011-012-017>019-025>028-034-035-037-041-045-046-061730-**
**BEDFORD-BLAIR-CAMERON-CLEARFIELD-FULTON-HUNTINGDON-JUNIATA-MCKEAN-MIFFLIN-NORTHERN CENTRE-NORTHERN CLINTON-NORTHERN LYCOMING-POTTER-SOUTHERN CENTRE-SOUTHERN CLINTON-SOUTHERN LYCOMING-TIOGA-**
**1036 AM EST TUE JAN 6 2004**
**...ARCTIC COLD FRONT TO TRIGGER LOCALIZED HEAVY SNOW SQUALLS...**
**BITTER COLD ARCTIC AIR...SOME OF THE COLDEST OF THE SEASON...WILL SPILL INTO CENTRAL PENNSYLVANIA DURING THE DAY TODAY. ACCOMPANYING THE COLD FRONT WILL BE SNOW SHOWERS AND EVEN SOME**** LOCALLY**** ****HEAVY SQUALLS.**
**SOME OF THE HEAVIER SQUALLS COULD DROP A QUICK COATING TO AN INCH OR TWO OF SNOW. THIS WILL ****CAUSE ROAD CONDITIONS TO DETERIORATE RAPIDLY IN SOME LOCATIONS.**** GUSTY WINDS COULD ALSO CAUSE BLOWING AND DRIFTING OF ANY NEW SNOW THAT FALLS...REDUCING VISIBILITIES TO NEAR ZERO AT TIMES. **
**$$**
**LA CORTE**

## January 6, 2004

**PENNDOT Roadway Weather Information System (RWIS)**

## SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1122 AM EST TUE JAN 6 2004

PAZ012-019-026>028-035>037-041-042-045-046-049-050-056-063-061715-
CUMBERLAND-FRANKLIN-FULTON-HUNTINGDON-JUNIATA-MIFFLIN-NORTHERN
CLINTON-NORTHERN LYCOMING-PERRY-SNYDER-SOUTHERN CENTRE-SOUTHERN
CLINTON-SOUTHERN LYCOMING-SULLIVAN-TIOGA-UNION-
1122 AM EST TUE JAN 6 2004

...ARCTIC COLD FRONT TRIGGERING LOCALIZED HEAVY SNOW SQUALLS...

BITTER COLD ARCTIC AIR...SOME OF THE COLDEST OF THE SEASON...WILL
SPILL INTO CENTRAL PENNSYLVANIA DURING THE DAY TODAY. ACCOMPANYING
THE COLD FRONT WILL BE SNOW SHOWERS AND EVEN SOME LOCALLY HEAVY
SQUALLS.

SOME OF THE HEAVIER SQUALLS COULD DROP A QUICK COATING TO AN INCH OR
TWO OF SNOW. THIS WILL CAUSE ROAD CONDITIONS TO DETERIORATE RAPIDLY
IN SOME LOCATIONS. GUSTY WINDS COULD ALSO CAUSE BLOWING AND DRIFTING
OF ANY NEW SNOW THAT FALLS...REDUCING VISIBILITIES TO NEAR ZERO AT
TIMES.

MULTIPLE VEHICLE ACCIDENTS HAVE ALREADY BEEN REPORTED IN SOME OF THE
SQUALLS OVER PARTS OF WESTERN AND CENTRAL PENNSYLVANIA.

$$

**NATIONAL WEATHER SERVICE STATE COLLEGE PA**
**1122 AM EST TUE JAN 6 2004**
**PAZ012-019-026>028-035>037-041-042-045-046-049-050-056-063-061715-**
**CUMBERLAND-FRANKLIN-FULTON-HUNTINGDON-JUNIATA-MIFFLIN-NORTHERN**
**CLINTON-NORTHERN LYCOMING-PERRY-SNYDER-SOUTHERN CENTRE-SOUTHERN**
**CLINTON-SOUTHERN LYCOMING-SULLIVAN-TIOGA-UNION-**
**1122 AM EST TUE JAN 6 2004**
**...ARCTIC COLD FRONT TRIGGERING LOCALIZED HEAVY SNOW SQUALLS...**
**BITTER COLD ARCTIC AIR...SOME OF THE COLDEST OF THE SEASON...WILL**
**SPILL INTO CENTRAL PENNSYLVANIA DURING THE DAY TODAY. ACCOMPANYING**
**THE COLD FRONT WILL BE SNOW SHOWERS AND EVEN SOME LOCALLY HEAVY**
**SQUALLS.**
**SOME OF THE HEAVIER SQUALLS COULD DROP A QUICK COATING TO AN INCH OR**
**TWO OF SNOW. THIS WILL CAUSE ROAD CONDITIONS TO DETERIORATE RAPIDLY**
**IN SOME LOCATIONS. GUSTY WINDS COULD ALSO CAUSE BLOWING AND DRIFTING**
**OF ANY NEW SNOW THAT FALLS...REDUCING VISIBILITIES TO NEAR ZERO AT**
**TIMES.**
**MULTIPLE VEHICLE ACCIDENTS HAVE ALREADY BEEN REPORTED**** IN SOME OF THE**
**SQUALLS OVER PARTS OF WESTERN AND CENTRAL PENNSYLVANIA.**
**$$**

**MULTI-VEHICLE ACCIDENT HAS **
**OCCURRED ON I-80 IN CENTRE **
**COUNTY **
**                   ****State police say a multi-vehicle accident has occurred in the westbound lanes of Interstate-80 near Bellefonte in Centre County. At least three medical helicopters have been called to the scene. Details about the accident and the extent of injuries are not yet available. **

- January 6, 2004

## January 6, 2004

**CDT PHOTO/MICHELLE KLEIN**** **

**CDT PHOTO/NIKI DESAUTELS**** **

**CDT PHOTO/MICHELLE KLEIN**** **

**Photo Credits:           **
**Centre Daily Times (CDT)  and AP**

**CDT PHOTO/NIKI DESAUTELS**** **

**AP PHOTO**

**AP PHOTO**

## 
High Intensity, Sub-Advisory snow events  should be headlined or covered by Special Weather Statements (SPSs). NWS forecasters can exercise subjective judgment in the issuance of Advisories and Warnings (NWS Directives).  

Consistently appropriate forecast terminology needed to ensure the responsiveness of DOT agencies and road crews (i.e. snow bursts/squalls vs. generic snow shower wording).

- High Intensity, Sub-Advisory snow events  should be headlined or covered by Special Weather Statements (SPSs). NWS forecasters can exercise subjective judgment in the issuance of Advisories and Warnings (NWS Directives).
- Consistently appropriate forecast terminology needed to ensure the responsiveness of DOT agencies and road crews (i.e. snow bursts/squalls vs. generic snow shower wording).

- How Can We Better
- Communicate the Threat?

## Education and Outreach – Partnerships with state police, DOT and other local agencies is essential.

Intelligent Transportation Systems (ITS) such as Highway Advisory Radio systems and remotely queued variable text roadside signs can directly reach highway travelers with critical weather information. 

- Intelligent Transportation Systems (ITS) such as Highway Advisory Radio systems and remotely queued variable text roadside signs can directly reach highway travelers with critical weather information.

- How Can We Better
- Communicate the Threat?

## How Can We Better 

- Communicate the Threat?

- NWS State College is actively pursuing additional partnerships with PENNDOT and law enforcement agencies regarding the recent and previous I-80 incidents.
- Hope to expand existing RWIS infrastructure through existing partnerships with Penn State and PENNDOT, and make this data available to travelers in real time.

## Conclusion

- High Intensity, Sub-Advisory snowfall *can* be a significant threat to life and property. The timing of such events is critical to their resulting impact.
- More accurate assessment of snowfall character (intensity and duration) along with heightened efforts to partner with state and local agencies to more efficiently deliver this information will better serve our users.

## 
To support the NOAA Strategic Mission, the NWS must do all it can to ensure its users are informed of all  impending weather hazards.  

Progress in this area will decrease loss of life and property on our nation’s highways, and move the NWS closer to our organizational goal of becoming America’s “No Surprise” Weather Service.

Questions?

- To support the NOAA Strategic Mission, the NWS must do all it can to ensure its users are informed of *all  *impending weather hazards.
- Progress in this area will decrease loss of life and property on our nation’s highways, and move the NWS closer to our organizational goal of becoming America’s “No Surprise” Weather Service.
- Questions?

- Conclusion