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Virginia, Mathews

Public Information Statement

Statement as of 11:00 AM EST on November 30, 2015

             winter preparedness week in Virginia
                 November 29- December 5, 2015

Today's topic - important winter atmosphere and ocean patterns.

... North Atlantic oscillation description...

The North Atlantic oscillation (nao) index is based on the surface
sea-level pressure difference between the subtropical (azores) high
and the subpolar low. The positive phase of the nao reflects
below-normal heights and pressure across the high latitudes of the
North Atlantic and above-normal heights and pressure over the
central North Atlantic, the eastern United States and western
Europe. The negative phase reflects an opposite pattern of height
and pressure anomalies over these regions. Both phases of the nao
are associated with basin-wide changes in the intensity and
location of the North Atlantic jet stream and storm track... and in
large-scale modulations of the normal patterns of zonal and
meridional heat and moisture transport... which in turn results in
changes in temperature and precipitation patterns often extending
from eastern North America to western and central Europe.

Strong positive phases of the nao tend to be associated with
above-normal temperatures in the eastern United States and across
northern Europe and below-normal temperatures in Greenland and
oftentimes across southern Europe and the middle east. They are
also associated with above-normal precipitation over northern
Europe and Scandinavia and below-normal precipitation over
southern and central Europe. Opposite patterns of temperature and
precipitation anomalies are typically observed during strong
negative phases of the nao. During particularly prolonged periods
dominated by one particular phase of the nao... abnormal height
and temperature patterns are also often seen extending well into
central Russia and north-central Siberia. The nao exhibits
considerable interseasonal and interannual variability... and
prolonged periods (several months) of both positive and negative
phases of the pattern are common.

... Pacific-North America index description...
the Pacific/ North American teleconnection pattern (pna) is one of
the most prominent modes of low-frequency variability in the
northern hemisphere extratropics. The positive phase of the pna
pattern features above-average heights in the vicinity of Hawaii
and over the intermountain region of North America... and
below-average heights located south of the Aleutian Islands and
over the southeastern United States. The pna pattern is associated
with strong fluctuations in the strength and location of the east
Asian jet stream. The positive phase is associated with an enhanced
east Asian jet stream and with an eastward shift in the jet exit
region toward the western United States. The negative phase is
associated with a westward retraction of that jet stream toward
eastern Asia, blocking activity over the high latitudes of the
North Pacific... and a strong split-flow configuration over the
central North Pacific.

The positive phase of the pna pattern is associated with
above-average temperatures over western Canada and the extreme
western United States... and below-average temperatures across the
south-central and southeastern U.S. The pna tends to have little
impact on surface temperature variability over North America during
Summer. The associated precipitation anomalies include above-average
totals in the Gulf of Alaska extending into the Pacific northwestern
United States... and below-average totals over the upper midwestern
United States.

Although the pna pattern is a natural internal Mode of climate
variability... it is also strongly influenced by the El Nino/southern
oscillation (enso) phenomenon. The positive phase of the pna pattern
tends to be associated with Pacific warm episodes (el nino)... and the
negative phase tends to be associated with Pacific cold episodes
(la nina).

... El Nino and La Nina...
the terms El Nino and La Nina have become commonplace in the weather
vocabulary since the 1980s. El Nino and La Nina are ocean phenomena
not weather phenomena. Most specifically... El Nino and La Nina
refer to whether Pacific Ocean sea surface temperatures along the
Equator between the West Coast of South America and the
international dateline are above or below normal. When they are
above normal... and El Nino is occurring. When they are below
normal... a La Nina is occurring.

Although they are ocean phenomena... El Nino and La Nina can have a
significant impact on the short term weather and climate on a global
scale. For example... when an El Nino is occurring... winds in the
upper levels of the atmosphere across the Caribbean Sea and western
tropical Atlantic are stronger than normal. This inhibits the
growth and intensity of Atlantic tropical storms and hurricanes. In
additions... Winters with moderate or strong el ninos are often
stormy on the U.S. West Coast... with flooding and landslides
commonplace in central and Southern California. This storminess
often extends across the southern U.S. And potentially the East
Coast of the U.S..

... The Alberta clipper... what?... where?... why?...
during most Winters... a large polar vortex establishes itself over
Hudson Bay Canada... and extends its influence southward into the
central and eastern parts of the U.S.. smaller scale low pressure
areas become embedded in the large circulation around the polar
vortex and drop southeastward into the U.S. From the Canadian
prairie provinces of Alberta and Saskatchewan.

Appropriately termed "alberta clippers"... these fast moving storm
systems usually precede a surge of cold polar or Arctic air... and
can produce bursts of significant snow along with strong winds. In
most instances... Alberta clippers produce limited precipitation in
Virginia due to their fast movement and resultant inability to tap
moisture from either the Atlantic Ocean or Gulf of Mexico. When
snow occurs with an Alberta clipper... it is usually on the order of
a dusting to four inches... I.E. A "nuisance" snow.

However... if the polar vortex is strong enough... and its influence
extends southward into the deep South... Strong Alberta clippers can
become major weather events for Virginia and other parts of the mid
Atlantic region. In these situations... the Alberta clipper taps
the available moisture sources from the Atlantic Ocean and Gulf of
Mexico. The surface low redevelops and intensifies near the mid or
South Atlantic coast... and becomes a full blown Nor'easter. The
ensuing Nor'easter spreads heavy snow... (sometimes rain near the
coast) and strong winds up the East Coast... producing major travel


Governor Terry mcauliffe has declared the week of November 29 to
December 5, 2015 as winter preparedness week in Virginia. The
National Weather Service /NWS/ offices serving Virginia... in
cooperation with the Virginia department of emergency
management... will send public information statements over the NOAA
weather wire service each day through Saturday at approximately 11
am. These statements will focus on different aspects of winter
weather in the mid Atlantic region... and preparedness actions the
public should take for the upcoming winter season.

Below is a link to the NOAA winter outlook for 2015-16.


Additional information on winter weather preparedness can be
obtained on-line through the Virginia department of emergency
management home Page. The url is (in lower case):


In addition... the ready Virginia and ready North Carolina web
sites haves been developed to aid virginians and north carolinians
in their overall disaster preparedness. The urls are:

    http://www.Vaemergency.Gov/readyvirginia /English version/
    http://www.Vaemergency.Gov/listovirginia /Spanish version/
    http://readync.Org/ /English version/
    http://listonc.Org/ /Spanish version/

Up-to-date weather information is also available on-line from the
following National Weather Service sites (all urls in lower case):

NWS Wakefield - http://weather.Gov/akq
NWS Sterling - http://weather.Gov/lwx
NWS Blacksburg - http://weather.Gov/rnk
NWS Charleston WV - http://weather.Gov/rlx
NWS Morristown TN - http://weather.Gov/mrx
NWS Raleigh NC - http://weather.Gov/rah

National Weather Service winter weather awareness home Page -


Bill sammler
warning coordination meteorologist
NOAA/National Weather Service
Wakefield VA

Weather Severe Map
Alabama - Flood Warning , Areal Flood Watch , Record Report , Public Information Statement
Arizona - Freeze Warning, Freeze Watch , Special Statement
Arkansas - Flood Warning , Record Report , Public Information Statement
California - High Surf Advisory , Frost Advisory , Special Statement , Record Report , Public Information Statement
Colorado - Public Information Statement
Connecticut - Special Statement
Florida - Coastal Hazard Statement , Beach Hazard Statement , Public Information Statement
Georgia - Flood Warning , Areal Flood Watch , Hydrologic Statement , Public Information Statement
Hawaii - High Surf Advisory , Wind Advisory
Idaho - Air Stagnation Advisory , Record Report , Public Information Statement
Illinois - Flood Warning , Flood Advisory , Public Information Statement
Iowa - Winter Weather Advisory , Winter Storm Warning , Public Information Statement
Kentucky - Record Report
Louisiana - Flood Warning , Record Report , Public Information Statement
Maryland - Freezing Rain Advisory , Public Information Statement
Massachusetts - Special Statement
Michigan - Special Statement
Minnesota - Winter Weather Advisory , Winter Storm Warning , Public Information Statement
Mississippi - Flood Warning
Missouri - Flood Warning , Public Information Statement
Montana - Public Information Statement
Nebraska - Winter Weather Advisory , Winter Storm Warning
New York - Special Statement
North Carolina - Areal Flood Watch , Special Statement , Record Report , Public Information Statement
North Dakota - Winter Weather Advisory
Oklahoma - Flood Warning , Record Report , Public Information Statement
Oregon - Air Stagnation Advisory , Record Report
Pennsylvania - Freezing Rain Advisory
South Carolina - Flood Warning , Areal Flood Watch , Public Information Statement
South Dakota - Winter Storm Warning , Winter Weather Advisory
Tennessee - Flood Warning , Areal Flood Watch , Hydrologic Statement , Record Report
Texas - Flood Warning , Flood Warning, Areal Flood Warning , Record Report , Public Information Statement
Virginia - Areal Flood Watch , Special Statement , Hydrologic Statement , Record Report , Public Information Statement
Washington - Air Stagnation Advisory , Record Report
West Virginia - Record Report , Public Information Statement
Wisconsin - Winter Weather Advisory , Special Statement , Public Information Statement
Wyoming - High Wind Warning , Special Statement , Record Report
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