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Berks Winter Cast

Checklist For Perfect Winterstorms

Storm Checklist Key:

Extremely conducive for HSE in Berks (Red)

Significantly conducive for HSE in Berks (Blue)

Marginally conducive for HSE in Berks (Green)

Non conducive for HSE in Berks (Black)

Conduciveness to HSE in Berks not yet determined or relationship does not exist (Normal)

 

 

If you      L-I-K-E      S..N..O..W..     , you like to see RED’s;  BLUE’s are ok, but stay away from the GREEN’s and BOLDED BLACKS

 

 

NAO (usually our most important factor)

NAO positive

NAO neutral

NAO weak negative

NAO moderate negative

NAO negative (rapid rate of change from a recent neutral or positive or towards a neutral or positive state)

NAO strong negative—storm may be suppressed to the south of Philadelphia

 

50-50 Low

No 50/50 low

Weak 50/50 low

Classic 50/50 low

 

EPO

Negative

Neutral

Positive

 

PNA Index

Positive Trending Positive

Positive

Neutral

Negative (does energy undercut the trough on the west coast?)

 

QBO

            Value

            Values > +10.0

            Values Between +10.0 and -10.0

            Values < -10.0

            Trend

Falling-Neutral-Falling              =          32

            Rising-Neutral-Falling              =          13

            Rising-Neutral-Rising               =          3

            Rising                                      =          2

            Falling-Rising                          =          2

            Rising-Falling                          =          1

            Falling

 

Polar Vortex

Non-existent or located on other side of pole

Located just north of Great Lakes

Very weak or diffuse

Displaced into Northwestern Canada

Displaced east of Greenland

Located in North Central Canada

Located over Hudson Bay

Located in North Central, Mid-Western, or Southeastern United States

Located in southeastern Canada propagating northwest

 

Character of 500hPa Trough / Vorticity Maximum

Open-wave trough into a closed circulation or,

Open-wave trough or,

Cutoff low

 

Positively tilted trough

Neutral tilted trough

Negative tilted trough

            West of Appalachian

If a negatively tilted trough forms, it forms far enough north and/or east so that the ridge does NOT build into New England

            East of Appalachians

 

Increasing trough amplitude:  reaches moderate amplitude

Increasing trough amplitude:  reaches maximum amplitude

 

Vorticity maximum curves to the northeast after reaching the East Coast

Vorticity maximum curves to the northeast before reaching the East Coast

Upper level jet streak approaching base of trough near East Coast

Jet streak embedded within the upper-level confluent zone

If a negatively tilted trough forms, it forms far enough north and/or east so that the ridge does NOT build into New England

 

Jet Streaks Positions (3)

North, North, North

North, North, Near

North, Near, South

            Near, South, South

            South, South, South

 

Character/Location of Surface High Pressure (Arctic High)

No where to be found

Not strong enough or positioned wrong (<1020mb, east of Maine coast, east central Canada)

Good set up:  1. West of Maine coast and/or north of PA/NY state border.  2.  In extreme southeast Canada west of 65 degrees west Longitude or entrenched in Northern Plains/Midwest as a “banana high.”

 

Low Level Cold Air

Adequate

            1000 to 500 mb thickness < 5400m

            1000 to 850 mb <1300

 

            Other thickness values…

Suspect or inadequate

                        1000 to 500 mb thickness > 5400

                        1000 to 850 mb > 1300m

 

                        Other thickness values

 

Character of Surface Low Pressure

Characteristics of Surface Low Pressure (General)

Primary low pressure (no matter the type) passes over, north and/or west of Philadelphia

 

Characteristics of Surface Low Pressure (Miller “A”)

“Miller A” Gulf of Mexico or Southeast low that comes up the coast: tracks east of Cape Hatteras and moves north-northeast avoiding Delmarva Peninsula.

Miller A” Gulf of Mexico or Southeast low that comes up the coast: tracks west of Cape Hatteras and moves north-northeast or east-northeast avoiding Delmarva Peninsula.

“Miller A” Gulf of Mexico or Southeast low that comes up the coast: tracks west of Cape Hatteras and crosses Delmarva Peninsula.

 

Gulf or Southeast low cutter west of Appalachians with Atlantic coastal re-development:  tracks east   of Cape Hatteras and moves north-northeast avoiding Delmarva Peninsula.

Gulf or Southeast low cutter west of Appalachians with Atlantic coastal re-development:  tracks west of Cape Hatteras and moves north-northeast or east-northeast avoiding Delmarva Peninsula.

Gulf or Southeast low cutter west of Appalachians with Atlantic coastal re-development:  tracks west of Cape Hatteras and crosses Delmarva Peninsula.

           

 

“Double-barreled low”:  primary low dissipates and gives way to secondary (coastal) low

            “Double-barreled low”:  primary low stays in tact and starves secondary (coastal) low of

energy

 

Characteristics of Surface Low Pressure (Miller “B”)

“Miller B” clipper that re-develops off the mid-Atlantic or New England coast:  tracks south of Washington D.C and Dover, Delaware.

“Miller B” clipper that re-develops off the mid-Atlantic or New England coast:  tracks north of Washington D.C. and Dover, Delaware.

Once secondary low pressure develops it tracks East or East-Northeast

Once secondary low pressure develops it tracks Northeast, North-Northeast, or North

Secondary low goes through rapidly deepening phase at the surface, in reference to the 850mb low, and in reference to the 500mb low

Secondary low does NOT go through a rapidly deepening phase at the surface

 

700 hPa Low Strength and Track

Track

North of Philadelphia

Over or near Philadelphia

South of Philadelphia

 

            Strength (“Comma-head”)

            Closed low north and/or west of PHL

            Closed low near PHL

            Closed low south and/or east of PHL

Comma-head (backlash) signature located north of PHL

            Comma-head signature located near PHL

            Comma-head signature south of PHL

 

850 hPa Low Strength and Track

850 hPa Low Strength

Open low

Closed low

 

850 hPa Low Track

Too far inland for all the NE, even mountains

Too far inland for Interstate-95 cities to stay all snow: tracks between Atlantic coast and Appalachian

Mountains

Good for New England only:  tracks between New York City and Philadelphia

Good for Northern Mid-Atlantic and New England by passing to the south and east of Philadelphia and

moving in a general easterly direction

Good for lower Mid-Atlantic: Washington D.C. to Richmond, Virginia:  tracks near Virginia and North

Carolina border.

Too far south for Interstate-95 cities

           

South and east of closed low

0 to 60nm northwest of closed low

60 to 240 nm northwest of closed low

            240 + nm northwest of closed low

-5 C isotherm bisects the heavy snow

-2C to -8 C for moderate snow

 

Snowstorm Dynamics

            Overrunning snow only

            Storm snow only

            Wrap around snow only

Overrunning snow and storm snow

            Storm snow and wrap around snow

            Overrunning snow and wrap around snow

            Overrunning snow, storm snow, and wrap around snow

           

            Mesoscale Phenomena

CSI

            Inverted troughs

            Banded snowfall

            Negative EPV

            Dry slot

            Mid-level frontogenesis

            Gravity waves

 

Local Climatology

El Nino versus La Nina

                        Strong El Nino

                        Moderate El Nino

                        Weak El Nino

                        Weak La Nina

                        Moderate La Nina

                        Strong La Nina

 

ENSO Trend

            Stable strong El Nino

Stable moderate El Nino

Stable weak El Nino

Weakening strong El Nino

Weakening moderate El Nino

            Weakening weak El Nino

            Strengthening El Nino

            Stable neutral

            Weakening weak La Nina

            Weakening moderate La Nina

            Weakening strong La Nina

            Stable weak La Nina

            Stable moderate La Nina

            Stable strong La Nina

 

Teleconnections

 

MJO

MJO Phase

            Phase 1

            Phase 2

            Phase 3

            Phase 4

            Phase 5

            Phase 6

            Phase 7

            Phase 8

 

Southeast Ridge

            Strong SE Ridge

            Moderate SE Ridge

            Weak SE Ridge

            Displaced SE Ridge

            No SE Ridge

 

Ocean Temperatures

            Temperatures generally >45

            Temperatures generally between 40 and 45

            Temperatures generally between 35 and 40

            Temperatures generally between 30 and 35

            Temperatures generally < 30

 

Computer Models (GFS, NAM. ECMWF; GGEM, UKMET)

            Excellent agreement on storm dynamics

            Good agreement on storm dynamics

            Fair agreement on storm dynamics

            Poor agreement on storm dynamics

 

Weekend Rule

            Snowstorm event commences on a Friday

            Snowstorm event commences on a Saturday

Snowstorm event commences on a Sunday

            Snowstorm event commences on a Monday

           

Moon Phases Just Prior to or At the Beginning of a Storm

            New Moon Phase

            Waxing Crescent

            First Quarter

            Waxing Gibbous

            Full Moon

            Waning Gibbous

            Last Quarter

            Waning Crescent

 

Forecasting Exact Snowfall Amounts

 

Miscellaneous

 

 

The Pre-Cyclonic Environment Prior to Big East Coast Snowstorms (Don S.)

An upper-level trough over eastern Canada. 

An upper-level ridge over the western United States/Canada (PNA+). 

Sometimes unimpressive short-waves: Prior to the development of heavy snowfall, many cyclone-producing troughs are poorly defined only 1-2 days before the snow events and have not yet consolidated into a significant short-wave trough in the eastern United States.

Major pattern changes: In some instances, major snowstorms occur as a part of major changes to the larger-scale circulation pattern.  In particular, the snowstorm of 5-7 February 1978 occurred as part of a dramatic change in the circulation regime across North America that saw a blocking pattern emerge with an upper cutoff anticyclone over north-central Canada and a cutoff low over the northeastern United States and southeastern Canada.  The January “Blizzard of ‘66” also occurred in a period of major upper-level circulation change.  With the President’s Day Storm of February 1979, a major circulation change also occurred but not in the same manner as during either February 1978 or January 1966. This storm occurred during a transition from a persistent large-scale circulation pattern that brought extremely cold temperatures to the northeastern United States to one that became more zonal as the storm exited the East Coast, signaling the end of the cold regime.

 

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