winter weather operations seminar 2003-04. overview

Winter Weather Operations Seminar 2003-04


Overview

Criteria for Winter Storms Warnings

Criteria for Winter Storm Warnings:

SNOW 2 - 4” in 12 hour period (3” or more verifies)

3 - 5” in 24 hour period (4” or more verifies)

SLEET 1/2” covers ground

Ice Accumulation1/4" or more storm total ontrees or power lines or roads

Advisory Highlights:

SNOWnow 1” entire CWA

“BLACK ICE”cover with an advisory .

Minimum Probabilities for Winter Weather Issuances

MINIMUM Probabilities for Winter Weather Issuances:

Probabilities are for hazardous winter weather conditions developing; not precipitation probabilities

Warnings and advisories > 60% (likelihood) of conditions developing

Watches and "advisories may be needed" > 50% (good chance) of conditions developing

Outlooks > 30% (chance) of conditions developing

Users Needs

What NWS RAH's Users Need:

- Emergency Managers: 12-18 hours lead time (for essential winter storm preparations)

- School Officials: Issuances on time (initial decision on school closures are made by 5 AM)

- TV media graphics: Timely WSWs and AFDs (for producing TV graphics, displaying watches/warnings)

(for communicating the meteorology supporting winter storm issuance)

- Other forecasters: Early Preliminary AFD (for floating tentative solutions, setting the stage)

Fundamental Principles Guiding RAH’s Winter Storm Issuances

Fundamental Principals Guiding RAH's Winter Storm Issuances:

• Strive for ACCURACY

• Provide SUFFICIENT LEAD TIME for users to make essential preparations

• Resist the desire to be the "first with the worst“

• Do not succumb to pressure to issue excessive lead times when confidence is low.

• BE ON TIME with issuances

Impact of False Alarms and Excessive Lead Times

Impact of False Alarms and Excessive Lead Times:

False alarms diminish credibility resulting in "second guessing" by users making decisions

Longer lead times are subject to more forecast errors

Watch & Warning Critical Success IndexLead Time (hours) CSI

60 0.0048 0.1536 Source - Eastern Region ‘ 94 -‘01 0.3024 watch & warning verification data 0.4518 from the 12 original WSFOs 0.5512 0.60

Biggest contributor to CSI error's were from FARs

87% of the total CSI variance was explained by FARs.

Conclusion- Improve CSI by reducing FARs- Decrease FARs by targeting lead times adequate for essential preparations and

avoiding excessive lead times for low confidence events.

Warnings and Advisories

Best Practices for Warnings and Advisories

STRIVE for 12-18, not beyond 24

Exceptions:

Long holiday weekends may need longer lead times

Other circumstances such as “donut hole” in warning coverage

Warnings (Advisories) Lead Time (hrs - from onset of pcpn) Users need 12-18

High confidence 24

GENERALLY NOT RECOMMENDED > 24 (i.e., 36 hours)

Watches

Best Practices for Watches

STRIVE for 24, not beyond 36

Exceptions:

Long holiday weekends may need longer lead times

Other circumstances such as “donut hole” in watch coverage

Watches Lead Time (hours) RECOMMENDED 24

High confidence 36

GENERALLY NOT RECOMMENDED > 36 (i.e., 48 hours)

Users in RAH's CWA React to a Watch as a Signal to Prepare.

Outlooks

Outlooks Lead Time (hours)

RECOMMENDED 48 - 60

High confidence 72

GENERALLY NOT RECOMMENDED > 72 (i.e., days 4-7)

Best Practices for Outlooks

STRIVE for 48-60, not beyond 72

Exceptions:

Long holiday weekends may need longer lead times.

Other circumstances such as “donut hole” in outlook coverage

Warnings and Advisories

Winter Storm Targeted If High Generally Not Issuance Lead Time Confidence Recommended

Warnings Strive for 12-18 hours 24 hours > 24 hours

Watches Strive for 24 36 hours > 36 hours

Outlooks Strive for 48-60 hours 72 hours > 72 hours

Exceptions to the "generally not recommended time frame" (upper limit) include:

• Extended holiday weekends requiring longer lead times

• exceptionally high confidence storms (e.g., super storm of '93)

• A "doughnut hole" pattern (i.e., RAH is surrounded by issuances from other offices)

• Any "on the fence“ situations

Accuracy/Adequate Lead Time for Essential Preparation

A good outlook affords more time for issuing a better watch

A good watch affords more time for issuing a better warning

How Definitive Our Issuances Should Be

How Definitive Our Issuances Should Be:

WARNINGS Definitive/quantitative ACCUMULATION as....

rangecommon vs maximumwidespread vs localpredominant p-type emphasized

WATCHES Qualifier POTENTIAL for...possiblymay developdepends upon tracktiming uncertaintylocation uncertaintyp-type uncertainty

OUTLOOKS Well qualified CHANCE for...no numberssignificant snowsignificant icing

Other Principals Guiding RAH’s Winter Storm Issuances

Degree of forecaster confidence determines how far in advance and how definitive our issuances can be.


Thickness fields are more reliable than details displayed in the forecast soundings

It is preferable to expand the threat area, rather than to retract storm locations previously included.

When confidence in the forecast process is low (high)- forecast wording should be less (more) specific- lead times can be more (less) conservative

- climatology should be more (less) weighted

Conservative fields (e.g., thickness, height) are more reliable (i.e., less run to run errors) than fields based upon parameterization schemes (e.g., qpf, omega)


Additional Principals Guiding RAH’s Winter Storm Issuances

Do not downgrade winter storm warnings while an event is unfolding or ongoing unless there is conclusive and overwhelming evidence to do so. There is little value in doing so since essential preparations have already been made

Ice accumulation from freezing rain is a self limiting process unless there is sustained low level cold air advection to offset warming due to latent heat release. Significant ice accumulation will not occur without a source (typically a cold air high to the north) of low level cold air.

For winter storm issuances and forecasts....words are important. Predominant p-types and their impact are not easily communicated through the GRID displays.

Quantitative descriptions combined with qualitative impacts such as “extremely damaging” ice accumulations of up to 3/4 of an inch will occur on trees and power lines” are most effective, but should be limited to warnings.

Forecast Confidence

Forecast Confidence:Confidence determines how far in advance and how definitive NWS issuances should be.

Gauging Confidence Confidence increases with positive answers to these factors:

- NWP models consistent model to model- Models consistent run to run (dprog/dt)- Model initializations fits observed data well- Model diagnostics reveal model solutions are handling key physical

processes well- Key meteorological features are well behaved - Model solutions and conceptual models based on past cases are

consistent- Consensus of agreement between NCEP and other offices- Key ingredients for the event are already in place- Key model parameters (e.g., qpf, thickness) are verifying well

Decision Maker

The decision maker:

- determines forecast for the critical period (s)- decides issuances- must stay focus on meteorology - puts out the early AFD- encouraged to float tentative solutions with others on staff- usually leads coordination call

- have enough staff on hand to do so- stratify forecast periods (critical vs non-critical)- others answer the majority of calls- others type issuances - others do input for WWA...GFE

Shelter the decision maker:


Criteria for Wind Chill Products

WIND CHILL THRESHOLDS

Wind Chill Advisory Zero to -10 degrees F triggers

Wind Chill Warning -15 to -25 degrees F triggers

Issuances are now via WSW’s instead of NPWs


Snowfall in Products

Days 4 to 7”CHANCE” wording only e.g., chance of snow, chance of rain or snow,

chance of ice, etc

Outlook (Days 2-3)Significant winter storm possible No specifics, just uncertainties

Watch (Late 2nd - 3rd periods)No specific amounts in text products Text should not lock into specific details in time and spaceP-types may still be an uncertaintyAmounts are given in Grids, RDF, AFM, PFM

Warning (1st to 2nd period)Predominant p-type emphasizedSpecifics now in text products Allow your ranges to expand with the degree of uncertaintyEmphasize common widespread amounts, not just local maximum amounts

WSW

• Our most critical winter weather issuance• Used by the Media to “create the map”• Must be out on time, before the ZFP

WSW - Technical Details

• Primary vehicle to describe the event– Issue, update, cancel

• Re-issue with each forecast package• Expiration time is time of next issuance

PNS• Use PNSRAH (SpotLES or county listing format) to issue

frequent, timely, and informative updates during winter weather events:snow, sleet, or ice accumulations p-type changesroad conditions / power outageschanges to precipitation ratesdevelopment of snow bandschanges to the location of principal boundaries between precipitation types (e.g, rain/snow, freezing rain/sleet)

• Activate Skywarn spotters and include NCSU student volunteers (SKYWARN will go into STANDBY taking 1-3 hourly reports of temp, p-type and accumulation)

• Keeping the public informed of real - time winter weather conditions as an event is in progress is vital to the protection of life and property and cited as one of our most valuable services by the TV media.

SPS• Winter Storm Outlook

• Emphasize big impact changes during winter storm event (eg. rain changing to snow and accumulating rapidly, ice accumulating on most roads with travel becoming hazardous)

• Can also be used to augment ZFP and NOW emphasizing the onset of the event or other special information in dangerous situations.

• In lieu of an outlook can be used to address event uncertainty

• Other Details of Interest:

• Update warnings every 8 hours• Update watches & outlooks every 12 hours• Prioritize SPS’s and PNS’s• Additional NOW”s only if time and resources• Do not cancel outlooks; use SPS to indicate risk has

diminished.

Coordination Guidelines

• Review WWE graphics as soon as they are posted• Early AFD – get out front and paste critical portions

into 12Planet• Use ISC in GFE• Proposed in WWA• Conference Call • Every reasonable effort to reach consensus

Suggested Timing

- Preliminary AFD – 1:30

- Conference call – 2:00

- Update AFD – 2:30

- WSW – 3:00


IFPS/GFE

GFE Winter Weather OpsMethodology

GFE Winter Weather Ops Methodology

• Start with most complicated portion first – get it out of the way

• Suggested: wx/pop first, then work your way up• Consider creative division of duties among staff:

– “A” does all storm grids, “B” does pre-storm grids, “C” does post-storm grids

– “A” does all wx/pop/QPF/sky grids, “B” and possibly “C” do all temp/wind/fire wx grids

– Other duty-allocation methods?– Definitive & early intra-office coordination a

must!


• Stress accuracy for predicting predominant ptype by using 6-hour long grid boxes (wx, pop, & qpf)

• Shorter intervals (3-hour long grids or even hourly) can be used in 1st period if there is high confidence in: – the forecast– a significant sociological impact associated with

ptype change• Make sure all times of PoP boxes line up with wx

and qpf grids… otherwise you’ll have inconsistencies!


• There are a few different options for constructing Wx grids:

1) Determine p-type corridors ahead of time, sketching it out on a map as we’ve always done, then manually construct PoP grids, & use edit areas and “Common Values” dropdown menu or Pickup Value GUI to assign Wx to corridors.

• Plus: More control of Wx, with specificity regarding type(s) and coverage/probability.

• Minus: A lot of clicking; can be confusing if it’s a long duration event with a lot of mixes and probabilities; have to ensure a match between PoP and Wx.



2) BostonWinterWxTool (with Wx being edited, right-click to bring up smart tool menu & select). This uses several other grids, including thickness grids, to construct Wx based on the TRENDS partial thickness technique.

• Plus: Convenient in that it uses grids done already; ensures correlation with PoP so there are no inconsistencies.

• Minus: Can create a huge mess of Wx (tests with very simple setups still yielded 10 or more areas with differing Wx/probability), making zone groupings very difficult; leads to very long ZFP text & the need for extensive postprocessing; have to complete QPF, QPF-6hr, PoP, T, and two thickness grids before running; busy GUI.



3) All_Wx_Tool – still being tested, but shows promise.

• Plus: Ensures correlation with PoP so there are no inconsistencies; works by allowing you to choose a mix, then puts in probability of that mix using PoP grids.

• Minus: Still may not yield the kind of wording you want; not very sophisticated as it doesn’t improve much on Pickup method.


• Promoted approach: Start with PoP…

…filling in using edit areas and “Assign Value” (right-click on map to select)


• Make use of “Select Homogeneous Area” (right-click menu) to make edit areas


• Once you have your PoP, click on corresponding Wx grid, do Pickup Value, and Assign Value.


• Select Homogeneous Area on your next PoP area…


• …and click on Wx and Assign Value of the next weather selection.


• Finally, Select Homogeneous Area to make the last edit area…


• …and assign the weather mix.


• Using the pickup window may seem cumbersome with all of the clicking, but this will enable you to select a PREDOMINANT P-TYPE, with lesser chances of other p-types.

Make use of the “Mix” or “Or” buttons to further refine p-type descriptions.


• You can also use the Common Values menu. With desired edit area selected, put the cursor on the color scale (top of map), right-click, and choose Select Common Values. Follow the dropdown menus until you reach your desired weather type.


• Then, to start layering p-types, you must change the Weather Edit Mode to “Combine” rather than “Replace”. Do a right-click on the map (not the color scale) to get to this option.


• With edit area selected (done using Select Homogeneous Area on the already-defined area of Wx) and “Combine” on, you can then layer, say, a Chc IP- atop your Def ZR-.


• With edit area selected (done using Select Homogeneous Area on the already-defined area of Wx) and “Combine” on, you can then layer, say, a Chc IP- atop your Def ZR-… giving you these results.

End of GFE Winter Weather Ops

Methodology

BostonWinterWxTool: Example

PoP

BostonWinterWxTool

QPF

BostonWinterWxTool

1000-850 mb

thickness

BostonWinterWxTool

850-500 mb

thickness

BostonWinterWxTool

The GUI

BostonWinterWxTool

The resulting

Wx


WWA

WWA

New and Improved ???

Changing duration will not change product expiration

Must edit ProdExp using arrows

Important: Edit text in AWIPSText window first…spell check and then copy into WWA Descriptive or Synopsis window.

WWA upgrade allowsyou to edit text in transmit window


WWE


Aviation

Aviation Forecasting

Winter Weather Concerns

Reduced Visibility, Low Ceilings, and Icing are major factors in 70 percent of fatal accidents.

Icing

Clear – FZRA, FZDZ – adds significant weight, reduced aerodynamic performance

Rime – Fog/Cloud droplets – reduced aerodynamic performance

Mixed

Couple of Points to Keep in MindMost Important Portion of the TAF is the 2-6 hour Forecast

Amendments to update for current conditions are not forecasts. We must be alert for Amendments in this period!

CAD does not follow diurnal cycles – be sure that the meteorological reasoning concurs with your improving trend.

Keep it simple beyond 12 hours. Remember, the users are required to use the lowest value in the time period. You are not helping them out by adding Prob/Tempo/Becmg groups, especially in the later periods.

Good Bye

winter weather operations seminar 2003-04. overview

Documents

lead times adequate

sufficient lead time

advisories winter storm

hours users

stage slide

overview slide

advisories best practices

good chance of conditions