Currently there is a ridge at the surface over Colorado and a
center of low pressure over the southern tip of Hudson Bay in N.
Ontario. Over the next 24 hours the high will drift southeastward,
and the surface low will push northward along the eastern shoreline
of Hudson Bay. In the upper
atmosphere, tomorrow will see a ridge
building from Idaho SE to the Texas Panhandle, with a cutoff low
over southern Hudson Bay and the axis of a trough through Michigan
and through the mid-west just east of the Mississippi.
Near the surface, low level winds will be from the south along the
southern portion of the flight, shifting to northerly along the
northern portion of the flight. Currently, there is snow over
NE Ontario, associated with wrap-around conditions of the surface
low. By tomorrow morning and evening, the surface low will be
shifting
Northward, and the wrap around precipitation
field will be moving
eastward, however, there is still a chance of precipitation lingering
over the Winnipeg and Norhouse regions, and possibly along the
southern shore of Hudson Bay as far west as the York region.
Any
precipitation over these regions should fall as rain tomorrow.
Sundays
high temperature over Winnepeg will be around 10C (50F), while at
Churchill it should be above freezing, reaching about 5C but falling
below
freezing overnight, ~-3C.
The ridge over the southern portion of the flight will preclude any
significant strat/trop
exchange along the southern portion of the flight tomorrow.
Cross sections E-W
through Boulder
for tomorrow morning show no enhanced PV values over the region,
and warmer air in the advancing ridge is evidenced by the concave-up
feature of the
potential temperature surfaces. N-S cross sections through Boulder
for tomorrow evening
show that as the aircraft flies north, it will cross the polar
jet stream very near the Canadian
border, seen as the region of enhanced wind velocity (yellow)
SW of Lake Winnepeg.
There will be some strat/trop exchange near this boundary, however,
given
the lack of troughing in this region, the influence will be confined
to the extreme
upper portion of the troposphere, around 300hPa, or near the 320K potential
temperature surface. If fact, this has come to be a very familiar
scenario,
we are under a relatively strong ridge at the surface (retreating eastward
with time), and the advancing edge of an upper-level ridge. There
is a very strong
cut-off upper level low in the mid-troposphere off the west coast,
seen in the
water vapor imagery as a vortex rolling
up, interleaving dry and moist air. This feature
has a high PV signature. Transport from this region has
the potential to
advect exchanged ozone. We see evidence of high total column
ozone amounts in
the
CIMSS GOES total ozone product, while this reflects the column, these
regions
of enhanced column ozone associated with a cut-off low are regions
of active
strat/trop exchange.
Trajectories suggest the possibility of air from around this upper-level
vortex
over the Pacific today arriving in the upper-troposphere over Boulder
tomorrow,
which could lead to layers of either/or both enhanced upper level moisture
(high
cirrus), and dry layers of enhanced ozone. see boulder_16utc_high.gif
At lower levels over Boulder, you will see air arriving around
the back of the surface high from
across the SW from S. California and Arizona.
boulder-16utc_low.gif
Further along the flight, we see the lower level flow become more northerly
in
origin, with air over S.Dakota originating over Montana, Idaho and
Oregon. pierre_17utc_low.gif
At the upper levels we again see air arriving from over the west-coast
and the Pacific
Ocean, and in the upper-troposphere (~8km) there is the possibility
of intercepting air
advected from the cut-off low feature in the Pacific.
pierre_17utc_high.gif
Over Winnipeg, you will come under the influence of the surface low
over NW Ontario,
and the lower level transport will be from the N and E, having wrapped
around the low.
Winnepeg will be on the very western edge of the precipitation shield
associated with
this low pressure center. Light snow is possible in association
with this flow, however,
most of this "weather" will be to the east of the flight track.
winnipeg_19utc_low.gif
At the upper levels above Winnipeg, transport is from the NW,
across Alaska and the
Northwest Territories.
winnipeg_19utc_high.gif
As the flight continues North with time, the back trajectories over
Norway House indicate
that transport even in the upper-troposphere is influenced by the upper-level
cut-off
low the Southern Hudson Bay region. The upper level low and surface
low are very
nearly stacked, and become more so with time over the next day (Monday),
evidence of
an occluding system. This results in the very different origin
of the air at upper levels over
Norway House, relative to Winnipeg. You will see air which
has crossed Hudson Bay
at high elevation, having come across the Northern part of the upper-level
low, and from
a region of low tropopause.
norwayhouse_20utc_high.gif
In the lower troposphere, you will also see trajectories arriving from
the NNE, and these
will have crossed Hudson Bay over the previous 24-48 hours. It
may be possible to observe
the advection air with a chemical signature representing this region
where you have seen
extensive ozone depletion on previous flights.
norwayhouse_20utc_low.gif
Similarly, low level flow over Churchill will be arriving from over
NW Hudson Bay,
and the NW shoreline. Again, this could deliver or advect the
signature of air from near
the surface over the Bay. In general, the Northerly origin of
these air parcels from near
Arctic latitudes over the last 48 hours and current soundings showing
a low level subsidence
inversion over Churchill suggest that you may see elevated layers
around 900mb and
above, these could reflect Arctic pollution layers. churchill_21utc_low.gif
In the upper troposphere the transport will again advect the signature
of air around the
upper level low over S. Hudson Bay, with transport across the top of
this low feature (from
a region of low tropopause). churchill_21utc_high.gif
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* Happy Mothers Day from the Happy Mother of two growing boys
:-)
