Winter Outlook 2020-2021 - United States Coast Guard Briefing Prepared by: National Weather Service - United States ...
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Winter Outlook 2020-2021
United States Coast Guard
Briefing
Prepared by: National Weather Service
WFO Mount Holly, NJ
Outline • Winter 2019 – 2020 Review • Winter 2020 – 2021 Outlook • NWS Winter Weather Products
Temperatures Last Winter
2019–20 Winter Temperature Verification*
at Philadelphia
Observed Temp (Temp
Period
Departure)
December 38.7°F (+1.2)
January 38.9°F (+5.9)
February 40.8°F (+5.1)
March 48.9°F (+5.4)
NOAA Temperature Outlook Last
Winter Avg* 39.5°F (+4.0)
Winter*
(Issued Fall 2019) Dec-Mar Avg 41.8°F (+4.5)
*Note: Meteorological Winter is defined as Dec-Jan-Feb
Average Winter Temperatures
at PHL (Past 10 Winters; °F)
2019-2020: 39.5
2018-2019: 36.9
2017-2018: 36.9
2016-2017: 40.5 5 consecutive
2015-2016: 41.4 winters of
2014-2015: 32.6 above average
2013-2014: 33.0 temperatures,
and 7 of the
2012-2013: 38.2
last 10!
2011-2012: 40.7
2010-2011: 33.1
Avg (1981-2010): 35.5
Precipitation/Snowfall Last Winter
2019–20 Winter Precipitation/Snowfall
Verification at Philadelphia
Observed Precip Observed Snowfall
Period
(Precip Departure) (Snowfall Departure)
November 1.16” (-1.83”) T (-0.3”)
December 5.21” (+1.65”) 0.1” (-3.3”)
January 2.64” (-0.39”) 0.2” (-6.3”)
February 2.46” (-0.19”) T (-8.8”)
March 3.94” (+0.15”) 0.0” (-2.9”)
NOAA Precipitation Outlook Last April 3.75” (+0.19”) 0.0” (-0.5”)
Winter*
Winter Total* 10.31” (+1.07”) 0.3” (-18.4”)
(Issued Fall 2019)
Seasonal
19.16” (-0.42”) 0.3” (-22.1”)
Total**
*Notes: * Meteorological Winter is defined as Dec-Feb
* * Seasonal is defined as Nov-Apr
Average Seasonal Snowfall at PHL
(Past 10 Winters; inches)
2019-2020: 0.3
2018-2019: 17.1
2017-2018: 29.8
• An even split
2016-2017: 15.0 between above
2015-2016: 27.5 and below
2014-2015: 27.0 average years!
2013-2014: 68.0 • Last winter was
the second
2012-2013: 8.3
least snowy on
2011-2012: 4.0 record!
2010-2011: 44.0
Avg (1981-2010): 22.4
Seasonal Snowfall for
Philadelphia, PA (1973–2020)
80 78.7
75
70 68.0
65.5
65
1981-2010 Normal Seasonal Snowfall: 22.4"
60
54.9
55
Seasonal Snowfall (inches)
50
46.3
44.0
45
40.2
40
35.9
35
30.4
30 27.5 29.8
26.1 27.0
25.4 25.7
24.3 22.9
25 23.1
20 20.8 21.6 21.0
20.9 19.5
15 17.5 18.0
18.7 15.4 16.516.4 17.0 17.1
13.6 15.0 14.6 12.9 15.0
10 12.5 13.4
11.2
9.8
4.7 8.3
5
6.3
0.8 4.0 4.0
0
0.3
On average about 2 of every 3 winters feature below average
snowfall. Lots of “little” years with a few “big” years!
Seasonal Snowfall for
Wilmington, DE (1979–2020)
80
75 72.7
70
65
60
1981-2010 Normal Seasonal Snowfall: 20.2" 55.9 56.1
55
Seasonal Snowfall (inches)
50
46.0
45
40.0
40
35
30 26.9 27.0 28.0
24.925.1 25.4 25.4
25 23.4
22.1
20.3 20.5
20
19.9 18.8
15 17.7
15.9 14.915.614.2 15.7 16.1
14.7
10 12.1 13.1 12.6 12.6
11.0
8.3 8.5 9.2 9.0
5
3.5 T 2.4 5.2 5.2
0
0.9
1981-2010 Snowfall Climatology
Philadelphia Wilmington
# of Days Inches of # of Days Inches of
Month Month
it Snows Snowfall it Snows Snowfall
November 0.2 0.3 November 0.2 0.4
December 1.8 3.4 December 2.0 3.4
January 4.4 6.5 January 4.3 5.9
February 3.6 8.8 February 3.6 8.3
March 1.8 2.9 March 1.3 1.9
April 0.4 0.5 April 0.4 0.3
Annual Total 12.2 22.4 Annual Total 11.8 20.2
# of Days Inches of
Month
Dover it Snows Snowfall
November 0.0 0.2
December 0.9 2.9
January 2.2 4.6
February 1.9 7.7
March 0.3 0.3
April 0.0 0.0
Annual Total 5.3 15.7
1981-2010 Snowfall Climatology
Seasonal Forecasting:
A Sample of Major Indexes and Patterns
Used to Make Seasonal Forecasts
• ENSO (El Niño Southern Oscillation)
• NAO/AO (North Atlantic/Arctic Oscillation)
• Warm Octobers/Novembers (if both are warm,
winter tends to be warm)
• Local Research and Analogs
• Computer ModelsCurrent ENSO Status:
La Nina
SSTs are below average across the central and eastern Pacific near the equator. La
Nina conditions are present and expected to continue.Multi-Model ENSO Outlook
Typical La Nina Weather Pattern
North Atlantic Oscillation • The North Atlantic Oscillation (NAO) is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure between the Icelandic low and the Azores high. Changes in strength and position of the Icelandic low and the Azores high control the strength and direction of westerly winds and storm tracks across the North Atlantic. • A negative NAO is one of the best predictors for an East Coast trough (dip in the jet stream). This dip leads to colder temperatures and a greater threat of nor’easters. • Can’t be used for seasonal forecasting because the NAO is difficult to predict more than two weeks in advance. But it can and should be used for a shorter term forecast!
North Atlantic Oscillation
What has the recent pattern been?
Upper Level “Height” anomalies
L
H
HWhat do the Models Have for this Winter?
Model precipitation: Near AverageWhat do the Models Have for this Winter?
Model precipitation: Near AverageWhat do the Models Have for this Winter?
Model precipitation: Below AverageWhat do the Models Have for this Winter?
Model precipitation: Near AverageNOAA 2020-21 Winter Outlook
(Issued October 2020)So What Does This Mean? • The Climate Prediction Center (CPC) forecast, computer models, and local research support above average temperatures this winter. • Potential for lengthy stretches of above normal temperatures with brief but sharp cold shots. Less ice on the rivers as a whole. • Near average precipitation is expected based on a blend of the model output and CPC guidance, but snowfall is more likely to be below normal due to the above average temperatures. • There are many uncertainties involved in seasonal forecasting, much more than a 7 day forecast. This is especially true for snowfall. In our area, one or two storms can make an entire season!
Key Winter Weather Websites NWS Mount Holly Winter Webpage: www.weather.gov/phi/winter Briefings: https://www.weather.gov/media/phi/current_briefing.pdf (Also emailed to core partners) Hazardous Weather EM Dashboard: https://www.weather.gov/phi/emerman
Sample Product: Snowfall Forecast*
Uncertainty in Snowfall
Forecast:
As with previous storms this
winter, uncertainty exists in
the snowfall accumulation
forecast owing primarily to
critical timings of transitions
between snow, ice, and rain.
While confidence in exact
snowfall totals is medium,
confidence is higher on a
period of significant and
widespread travel impacts,
especially from mid to late-
morning through the early
evening.
*This product represents our official forecast for expected snowfallSample Product: Probabilistic Snowfall Forecast*
Low End Potential High End Potential
9 in 10 (90%) Chance of Higher 1 in 10 (10%) Chance of Higher
Snowfall Than Depicted Below Snowfall Than Depicted Below
*Goal this year: Less focus on these maps, more focus on descriptive impacts and uncertaintiesSample Product: Ice Accumulation Forecast*
Ice accumulation notes:
Icing of a few hundredths to
a tenth of an inch is
generally insufficient to
produce tree damage or
power outages, but any
amount of ice is capable of
creating very hazardous
road conditions.
*This product represents our official forecast for expected ice accumulationSample Product: Winter Precipitation Onset Time* *Expected start time of frozen (snow, sleet, freezing rain) precipitation
Sample Product: Coastal Flooding Map*
Minor flooding is possible with
Tuesday night’s high tide.
Moderate flooding is possible
along much of the NJ and DE
Middlesex coast with Wednesday and
Bucks
Mercer
Wednesday night’s high tide.
Monmouth
Minor flooding may reach
upper Delaware Bay and the
Ocean lower Delaware River on
Delaware Burlington Wednesday and Wednesday
night.
New Castle
Cecil This graphic shows the
Salem expected degree of flooding on
Atlantic the oceanfront, bays, and
Cumberland estuaries along the highlighted
Kent areas.
Kent
No Flooding
Caroline
Spotty Minor Flooding
Talbot
Minor Flooding
Sussex
Moderate Flooding
Major Flooding
*Available in briefing packages when coastal flooding is a concernReminder: NWS now issues Snow Squall Warnings!
• Polygon-based, similar to severe thunderstorm and tornado warnings
• Three Distinct Information Segments:
• Hazard Description (i.e. white-out conditions from heavy snow and blowing snow)
Source (radar, webcams, etc)
Impact (i.e. dangerous, life-threatening travel)
• WEA – ActivatedHow to Stay in Touch • NWS Mount Holly website – www.weather.gov/phi – Detailed local forecast available going out 7 days – Hourly weather graphs • CPC website: – http://www.cpc.ncep.noaa.gov/ – Hazards assessment – 8-14 day climate outlooks – Seasonal climate outlooks
Questions?
weather.gov/phi US National Weather Service
@NWS_MountHolly
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