Transcript Slide 1

Polar Vortex
• The polar vortex is analyzed at 500 millibars. The
polar vortex occurs above the core of the coldest polar
air. Since frigid air is dense, heights are lower aloft
because cold air has a lower thickness than warmer
air.
• At the surface of the polar air mass will be high
pressure, but low heights will occur aloft at 500 mb
since the air is compacted due to high density air near
the surface.
Polar Vortex cont.
• The polar vortex can often be located over Canada
since the coldest surface air is often found over high
latitude icy/land locations. The polar vortex aloft
propagates toward where the polar air mass moves.
The vortex often moves very slowly or is stationary,
and its position determines what part of the USA the
Arctic air will invade.
• When the vortex is centered over the Hudson Bay, as
shown above, arctic air usually plunges south over the
Dakotas and the northern Plains. If the vortex center
shifts to the east, the core of the Arctic air invasion
usually shifts east with it.
Polar Vortex cont.
There are many regions where the polar vortex can be located
for it to be marginally conducive for East coast snowstorms.
Most important is that the PV is on our side of the northern
hemisphere and away from the pole (displaced).
December 2006:
Trace of snow in
Philadelphia.
Temperatures
were 5.3 degrees
above normal.
Polar Vortex cont.
• However, in my opinion, the polar vortex is best
situated in southeastern Canada just prior to an East
Coast snowstorm. However, for a storm to come up
the coast the PV needs to weaken and/or move out of
the way (northward,northwestward, or backwards
diving south and east of the pumping PNA ridge).
Otherwise the storm will be suppressed to the south.
North Hudson Bay, Canada is also a favorable
position just prior to a snowstorm.
• Just keep it away from the Great Lakes region or just
above it. In this position, short waves have trouble
slowing down and digging (thoughts courtesy of Dave
Tolleris).
Polar Vortex cont.
More…Polar Vortex Evolution
Polar Vortex Evolution
Polar Vortex Evolution
Polar Vortex Evolution
Polar Vortex Evolution
Polar Vortex Evolution
Get that PV
out of the
way! Now
we are
finally open
for
business.
“PV” Meet “50”, “50” Meet “SW”:
Shall We Dance?
“PV” Meet “50”, “50” Meet “SW”:
Shall We Dance?
“PV” Meet “50”, “50” Meet “SW”:
Shall We Dance?
Hooking Up: Combining Energy (Moving
Air Meets Moisture)
I absolutely
love the
position of
this 850 mb
low. It is to
the south
of PHL but
not too far
away…and
it’s moving
ENE or NE.
Very good
sign if this
model
comes to
fruition.
Hooking Up: Combining Energy (Moving
Air Meets Moisture)
Good snowstorm
dynamics.
Comma head and
dry slot. Keep that
dry slot south. We
would need a
WSW to ENE
dynamic to keep
the comma head
on us for the
maximum amount
of time minimizing
the impact of the
dry slot.
Polar Vortex and 50-50 Low (Blizzard of
2006)
HM (Polar Vortex-January 28, 2007 Post)
When the PV enters Canada and drops into lower Canada in
early FEB there are going to be some rules to consider....
1) Do not be fooled that the PV will easily race back out of here
the following week. As long as the PACIFIC pattern remains
favorable, the PV cannot escape. This is explained in the next
point.
2) AS the PV continues to revolve around, remember that AJ
and PJ s/w will continue to also pivot around like pendulums.
They also affect the PV position significantly so. Well think
about it. If AJ s/w off the PV continue to amplify down on the
west side, and amplify b/c of the continued PNA ridge (they
slide down) then it will pull the PV down. So essentially what
happens is, the PV continues to revolve. She is stuck!
HM (Polar Vortex-January 28, 2007 Post)
3) The CLOSE PVs of N. hemisphere dont cut it! OR I should
say..they do CUT IT! A block that is! What will happen is a block
will pinch off into the NW territories / alaska and perhaps even
lobe into the north pole. This feature will put a lid on any
movement back into the pole, where the pv likes to be ideally!
A period to watch for SECS would be FEB 10-12 when the PV
moves into east canada (the revolution sequence brings it here
but soon retrograding) ... this setup of the PV allows any mid
latitude s/w to amplify but move off the east coast rather than
cut inland. Depending upon how exactly things shape up this
period will determine the severity of the storm, what type and if
it even exists. But this is an early heads up...
A post coming soon about the threat at DAY 5-6...
JB On The Polar Vortex and Setting Up the
East Coast for a Snowstorm (Jan 30, 2007)
Bust the southern stream comes through from
the west, build pressures in Canada and get
the vortex to pull away and you have a
chance for storms that can go to town. IF
YOU WANT DEEPENING SURFACE AND
ALOFT, THERE HAS TO BE SOME KIND OF
PRESSURE RISE SURFACE AND ALOFT
FIRST SO THERE CAN BE THE CHANGE
NEEDED TO PRODUCE A STORM THAT
DOESN'T JUST RUN AWAY AT 50 MPH LIKE
THIS ONE IS GOING TO.
HM (February 2, 2007)
Where exactly the PV(s) set up and how exactly the
pacific behaves will make all the difference for what
happens in the FEB 9-11 period and thereafter.
You cannot expect a huge displaced PV to hang
around forever... it either has to reload or go away
eventually b/c it is not in it's natural environment to just
"chill" ... So it will be common to hear the avg joe
forecast milder wx as we progress into mid feb... well
duh.... but that doesnt mean DEC 06 into early JAN 07
wx again... and it may just increase our snow chances,
removing that shearing PV out.
HM (February 2, 2007)
FIRST ticket item would be FEB 9-11 period as the PV splits
and moves east. Once piece settling in the "50-50" position
(potentially, although it will be moving in and out) and another
moving back into the north/greenland. This is called reload and
it's a signal for potential east coast storm. The key player is the
PV in SE canada and how much pacific energy undercuts the
ridge and moves into the SW USA/plains. For now, I keep the
SECS alert on for this period b/c the stj s/w can easily move
east---and if GIVEN THE RIGHT ROOM and TIMING w/ the PV-- could yield a significant winter storm for many east of the
rockies. If the PV is slow to move, it will crush it (ie 00z EURO)
... if the STJ s/w is too slow and the PV zips out of here, it could
be a rainstorm. You get the idea... plenty of ideas.
February 5, 2007
Polar Vortex, 50-50 Low, and the NAO
As stated on my last two posts this snowstorm threat comes
about because the West Coast Ridge is fracturing as it
gets battered by energy coming in from the Pacific. The
northern end of the Ridge over northwestern Canada breaks off
as a bubble of positive height anomalies -- high pressure in the
jet stream-- which moves into north central Canada. This forces
the huge PV to move into southeastern Canada and to stays
in place. The PV which typically is situated over Hudson's Bay
is now displaced to the south. Because the vortex is displaced
over southeastern Canada it acts JUST as the 50/50 Low
would in setting up a strong confluence zone in the PJ. It is
the confluence zone which allows the cold High pressure over
Eastern and Central Canada to build.
Polar Vortex, 50-50 Low, and the NAO
Without the blocking features somewhere over
Greenland or eastern Canada--- such as a - NAO or
50/50 Low -the cold HIGH pressure area over the
Great Lakes or southeastern Canada will often slide
out to sea during the East coast storm which is one
reasons why in the big cities of the Northeast snow
changes to rain. BUT in major snowstorms however
the blocking does exist over eastern Canada and High
pressure is trapped so the cold air is held in place and
mostly precipitation over the Northeast even the big
cities falls the snow.
Jets and Vortex (Feb 8, 2007)
Now that we have the
synoptic pattern
down... we have
another problem. In
order to get this
system to come
further N up the coast
so the best / heavy
snows get into the
northern Mid Atlantic
and New England....
Jets and Vortex (Feb 8, 2007)
…the northern branch of
the Jet stream that is to
say the PJ -- is going to
have to drop in and
PHASE with the short
wave in the southern
branch or the STJ. The
problem is that none of
the medium-range
models over the last
several days are showing
this happening.
Jets and Vortex (Feb 8, 2007)
The vortex over southeastern
Canada is so big and so powerful
that the winds are very strong
circulating around it. It is these
strong winds In the PJ which
creates the confluence zone and
allows the cold High pressure to
move across the West Canada
border or just to the north. But on
the other hand these very strong
wings around the vortex are
prohibiting any sort of phasing by
the northern branch. The velocities
are simply to strong to allow the PJ
to phase.
Jets and Vortex (Feb 8, 2007)
Here Note the BLOCK-strong Positive 500
MB heights over north
central Canada which
traps the PV over far SE
Canada .... and
the interaction between
the BLOCK and
the PV keeps
the winds coming around
in the PJ vortex over the
Great Lakes very strong
.
Polar Vortex (DT on 2-5-09)
-Do We Get a Storm on Presidents Day Weekend of 2009?“When I state NO POLAR VORTEX on my map in Post #8 I am NOT stating
this as a negative factor.
In fact I am stating as a positive factor.
in some situations having a Huge PV and or one that is DISPLACED to the
south can act as a 50/50 Lo and help set up your confluence zone and
possible phasing event.
In this case the lack of deep solid large 500 MB vortex that can be called a
PV is VEEEEERY good for those east coast snow lovers.
ALSO... in the WHAT COULD GO WRONG? Department.
Next Monday and Tuesday when the Midwest deep south and Mid Atlantic is
basking in 50s and 60s and a strong se Ridge
we MUST see a 500 Low develop over SE Canada.”