20082009 Winter Seminar

1
2008-2009 Winter Seminar
Snowy scene in Efland, NC on February 14, 2008
photo courtesy of Russell Bullock
2
Motivation for our Training Session Today- The
past couple of winters have been rather quiet
2007-2008 KRDU 0.5 snow KGSO 4.0
snow2006-2007 KRDU 1.6 snow KGSO 0.8
snow2005-2006 KRDU T snow KGSO 1.3
snow2004-2005 KRDU 0.9 snow KGSO 1.7
snow2003-2004 KRDU 14.9 snow KGSO 18.5 snow
3
Winter Weather Forecast Philosophy Degree of
forecaster confidence determines how far in
advance and how definitive our issuances can
be.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) weightedIt is preferable to expand the
threat area, rather than to retract storm
locations previously included.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)Thickness fields are more reliable
than details displayed in the forecast soundings
- nomogram
4
Forecast Confidence Confidence determines how
far in advance and how definitive NWS issuances
should be. Let users know what principal
factors determine confidence level via AFDs and
to a lesser degree WSWs
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 - Ensembles
5
Winter Weather Forecast Philosophy Winter Storm
Targeted If High Generally Not Issuance
Lead Time Confidence
Recommended Warnings Strive for
12-18 hours 24 hours gt 24
hours Watches Strive for 24
36 hours gt 48
hours Exceptions to the "generally not
recommended time frame" 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
6
Extended Forecast PhilosophyDay 7Do not
introduce snow/icing potential in Day 7Days
4-6Limit your probabilities to chance (no
slight chance, likely or categorical)The
following are required before introducing chance
of wintry p-types Two or more consecutive
model(s) runs showing similar potential Majority
of medium range models (GFS, GEM, ECMWF, UKMET,
NOGAPS) are supporting the potential for p-type
problems. NCEP guidance PoPs are at least
40Avoid including details about possible phase
changes keep it simple. Never forecast amounts
nor include light or heavyExpress an
appropriate degree of uncertainty (e.g., chance
of rain or snow) Day 3Do not use categorical
terms"Likely" should be reserved for situations
with a high degree of confidence (i.e. not just
a perfect prog solution from one model).Avoid
forecasting exact amounts.Limit details to any
possible phase changes.
7
Winter Weather Forecast Philosophy Principals
Guiding RAHs Winter Storm IssuancesUpdate
warnings every 6-8 hours watches outlooks
every 12 hoursUse preferred hazard valid times
) 4am, 6am, 9am, noon, 4pm, 6pm, 9pm and
midnight.)Segment WSWs when appropriate by
ptype or QPFAvoid canceling WSWs at the onset
(place your bets and let it ride)
8
(No Transcript)
9
WSW Layout (What? Where? When?)
...WINTER STORM WARNING FOR TODAY THROUGH
FRIDAY... A WINTERY MIX OF SNOW AND SLEET WILL
OVERSPREAD CENTRAL NORTH CAROLINA FROM THE SOUTH
TODAY. THROUGH SATURDAY MORINING LOCATIONS FROM
ALBEMARLE TO ASHEBORO AND BURLINGTON NORTH ACROSS
THE TRIAD CAN EXPECT 4 TO 6 INCHES OF SNOW MIXED
WITH SOME SLEET. OTHER LOCATIONS IN THE SANDHILLS
AND PIEDMONT FROM WADESBORO AND ROCKINGHAM NORTH
TO THE TRIANGLE CAN EXPCET 3 TO 5 INCHES OF SNOW
MIXED WITH SOME SLEET. PRECIPITATION RATES WILL
INCREASE THIS AFTERNOON ACROSS TRIAD AND
NORTHWEST WHERE NEARLY ALL SNOW IS EXPEDTED WITH
LITTLE SLEET. IN THE EASTERN PIEDMONT AND
SANDHILLSA MIXTURE OF SNOW AND SLEET DOMINATE
BEFORE MIXING WITH SOME RAIN LATE TONIGHT. SNOW
AND SLEET WILL BECOME MORE INTERMITTENT LATE
TONIGHT. HOWEVER A SECOND ROUND OF HEAVIER MIXED
PRECIPITATION IS EXPECTED FRIDAY MORNING BEFORE
TAPERING OFF TO FREEZING DRIZZLE OR FLURRIES
FRIDAY AFTERNOON. IN THE WAKE OF THE SNOW AND
SLEET TEMPETURES WILL REMAIN WELL BELOW FREEZING
INTO SATURDAY. TRAVEL IN THE WARNING AREA WILL
LIKELY BECOME DIFFICULT FROM MID AFTERNOON TODAY
THROUGH FRIDAY NIGHT. PEOPLE PLANNING TRAVEL
SHOULD CHECK THE LATEST WEATHER AND ROAD
CONDITIONS...AND EXPECT TRAVEL DELAYS. TRAVEL
HEADING WEST INTO THE WESTERN PIEDMONT MAY NEED
TO BE POSTPONED OR CANCELED BECAUSE OF HEAVY SNOW
ACCUMULATIONS. SOME OF THE HEAVIEST SNOW AND
SLEET WILL OCCUR IN THE MID TO LATE AFTERNOON
HOURS IMPACTING LOCAL COMMUTERS. UNCERTAINTY
REMAINS WITH EXPECTED PRECIPITATION AMOUNTS FROM
THIS STORM. UNIFORM COVERAGE IS NOT LIKELY AND
SOME LOCATIONS COULD RECEIVE MORE SLEET AND SNOW
THAN CURRENTLY FORECAST.
P-type and QPF
Timing and Duration
Impacts
Confidence / What Ifs
10
Allowable WSW Headlines

• Policy take 4, but this time for the better!

11
January 19th Raleigh Gridlock (Advisories for
below criteria events, but of high impact rare
Instances) Communicate possible impacts in AFDs
and WSWs
12
(No Transcript)
13
Winter Weather Advisory for Black Ice

• Handled in a similar fashion to Dense Fog.
• Issued as the conditions are developing and just
  prior to high travel times.
• Issued in advance (up to 8 hours?) only in cases
  where confidence is high.
• Cases where black ice is very limited and only a
  few isolated areas could have ice use the SPS.

...WINTER WEATHER ADVISORY IS IN EFFECT UNTIL 9
AM EST WEDNESDAY... THE NATIONAL WEATHER SERVICE
IN RALEIGH HAS ISSED A WINTER WEATHER ADVISORY
FOR BLACK ICE.
14
(No Transcript)