Hi
Folks,
The focus of Friday map discussion for
1.
Mean/anomaly 500/200 hPa geopotential heights for 5-18 Oct'07.
2.
Integrated precipitable water for 0000 UTC 18,
3.
Mean/anomaly OLR for 20 Sep -
4.
GFS ensemble forecasts verifying 0000 UTC
5.
ECMWF 5-7 day forecasts verifying 0000 UTC
6.
SPC severe weather reports for 17-18 Oct'07.
7.
CPC mean/anomaly 30-day temperature time series for
8.
Normalized NH 30-day 200 hPa geopotential height and 850 hPa temperature
anomalies (R. Maue).
9.
DT pressure, shear (DT-850 hPa) and low-level vorticity images for 0000 UTC 13,
17 and
10.
850 hPa streamfunction and nondivergent wind for 0000 UTC
I.
Salient points:
1.
NH 500 hPa flow pattern was characterized by a wave number 4 pattern for the
last two weeks that was dominated by ridges over the east-central Pacific,
central and eastern NA/Canada, the
pattern.
2.
Beneath the eastern
tropics
of the western and central Pacific. The 30-day standardized 200 hPa
geopotential height anomalies ranged from 0.5-1.5 over eastern
3.
Mean/anomaly 200 hPa height anomalies over the
4.
The pattern of western/central Pacific ridging in the subtropics and
midlatitudes with a trough downstream near the east coast of
5.
Collectively, item's 1-4 suggest that transient disturbances embedded in the
anomalously strong Pacific jet should move ESE toward and through western
6.
Storms moving along the transient disturbance pathway identified in item 5
would be readily able to tap tropical moisture from the
7.
The integrated precipitable water field for 18, 20 Oct'07 shows a well-defined
plume of tropical moisture (PW values > 50 mm) that extends from the western
Caribbean and the Gulf of Mexico poleward to the Great Lakes and northeastern
US. This plume (aka freeway) of tropical moisture and
associated surge of tropical air contributed significantly to the favorable
larger-scale environment for severe weather earlier this week.
8.
An excerpt on Atlantic PV tails from the Friday map discussion post from
"At
00Z/9, a PV tail that ended with a weak PV maximum on the DT near 27 N and 70 W
is associated with a low-level vorticity maximum near 26 N and 66 W. The low-level
system proved to be non-developing, perhaps because of the relatively strong
westerly shear overhead (not shown). By 00Z/11, general ridging had occurred
over the west-central
ridge. Of
interest is the obvious decoupling of the lower-level and upper-level
disturbances as the former system is now near 30 N and 50 W, well to the ENE/E
of
its
position 48 h earlier."
Of interest is that the aforementioned
decoupled PV anomaly near 24 N and 52 W continued to move WSW before turning
/W/WNW/NW around the equatorward side of the eastern US upper-level ridge. At
0000 UTC 17 (20) Oct this cold-core PV anomaly can be found near 15 N and 78 W
(22 N and 87 W). High-resolution water vapor winds show a decided cyclonic
circulation near the northern part of the
map
for 0000 UTC 20 Oct'07 shows enhanced southeasterly flow across the
northwestern Caribbean and Yucatan Channel on the east side of the
aforementioned PV anomaly. This southeasterly airstream,
coinciding with the tropical moisture feed discussed above, turns more
southerly and southwesterly over the extreme eastern
9.
The future path of the PV anomaly mentioned in item 8) is of interest because
the deep tropical moisture feed associated with it carries the potential to
bring very heavy rains into parts of the southeastern US, where in many places
the rainfall is desperately needed, over the next couple of days.
10.
There is also some interesting forecast uncertainty with the next in a series
of transient disturbances forecast to reach the central US. The forecast uncertainty
is related to the strength and location of the cutoff cyclone forecast to form
over the lower Mississippi Valley by 60-84 h. Successive runs of the 0000 UTC
ECMWF, all verifying 0000 UTC 25 Oct'07, have moved the the
cutoff cyclone progressively further east from near the New Mexico/Arizona
border in the day 7 forecast to over Mississippi in the 5-day forecast. The
implications of this forecast uncertainty on the rainfall potential in the
Southeast, and perhaps another severe weather outbreak, are huge. An additional
precipitation wildcard is our aforementioned wandering PV anomaly that appears
to be heading toward the central Gulf coast, given the poleward-directed
tropical moisture plume currently in place to the east of this PV anomaly.
Finally, the 6-day GFS ensemble 500 hPa height forecast verifying 0000 UTC
II.
Inferences, speculations and science issues:
1. Can
the persistent ridging over the central and eastern US for the last couple of
months be related be related to tropical heating anomalies over the Indian Ocean
and western Pacific, downstream of which a strong has been anchored in the
subtropics and middle latitudes over the central Pacific?
2.
Can the reduction in the (apparent) number of early autumn cold pools over
northwestern
3.
Can the formation of persistent ridges at relatively high middle latitudes help
to ensure an anomalous poleward transport of deep tropical moisture on the western
flanks of these ridges as has been observed the last few days?
4.
What are the physical processes responsible for the formation of deep tropical
moisture pathways well into middle latitudes?
5.
Are deep tropical moisture pathways more sensitive to midlatitude dynamical
process and/or tropical thermodynamic processes?
6.
As the climate continues to warm how will the "second" severe weather
season change in the autumn? Is it reasonable to argue that there should be an
increase in future autumnal severe weather outbreaks over North America based
on increased deep tropical moisture when a trough is present over the western
US?
7.
Is there any reason to expect that upper-level troughs will become more common
in autumn in a future warmer climate with a corresponding increase in severe weather
activity downstream over central and eastern North America in conjunction with
more robust deep tropical moisture plumes?
8.
Can a first order estimate of future convective mode and frequency be obtained
by constructing CAPE/shear phase space diagrams from multi-centennial integrations
of sophisticated climate models.
9.
Will there be fewer positively tilted upper-level troughs in autumn, a
requirement for a poleward flux of angular momentum, in response to a weaker
meridional temperature gradient in a future climate and, if so, will the
frequency of cutoff cyclones increase at somewhat higher latitudes?
10.
Can climate models be used to make first-order estimates of how the mix of
large-scale flow regimes will change in a future warmer world and, if so, can anything
be said about changes in the future frequency and behavior of transient
disturbances associated with individual large-scale flow regimes?
http://cimss.ssec.wisc.edu/tropic/real-time/tpw/mainTPW.html
(CIMMS precipitable water;
http://amsu.cira.colostate.edu/gpstpw/
(CIRA blended precipitable water)
http://www.atmos.albany.edu/facstaff/rmctc/DTmaps/animSelect.php
(McTaggart-Cowan UA GFS animation builder)
http://www.coaps.fsu.edu/~maue/extreme/
(Ryan Maue's Extreme Weather Page)
http://www.spc.noaa.gov (
http://www.cpc.ncep.noaa.gov/products/global_monitoring/temperature/global_temp_accum.shtml
(Global temperature Time Series from
the CPC)
http://www.cdc.noaa.gov/map/ (ESRL/PSD
map room)
http://www.atmos.albany.edu/student/greenstein/EC%20ewall%200z.htm
(Matt Greenstein's ECMWF forecasts)
http://www.meteo.psu.edu/%7Egadomski/ewallmref.html
(
.........................
A
sign of the Apocalypse: Weather Channel music is now for sale online.
Lance
Response
from Paul Roundy:
Hi,
Lance and All. . .
In
looking for connections between convective events in the tropics and mid-latitude
weather patterns, it is helpful to examine how the tropical anomalies evolved
with time through the period of interest.
I'm presently constructing a website for tracking the recent evolution
of modes of tropical convection in real time.
The site is more comprehensive than others because it includes the
influence of climate processes such as ENSO, the
Http://www.atmos.albany.edu/facstaff/roundy/waves/
select
the link "Recent Evolution of OLR Modes".
The
first panel represents the linear sum of the OLR anomalies associated with the
different OLR modes shown in the other panels.
Active convection is suggested in blue shades. The panel titles give the leading modes plotted
in the panels.
Winds
are estimated by regression onto the OLR modes and are at 850 hPa. The long
barb in the lower left of each figure is 10 m/s.
Now
to my point: The major OLR anomalies
that contributed to the 30-day mean were largely contributed by ENSO (panel e),
the MJO (panel c), equatorial Rossby waves (panel b), and the
Incidentally,
looping the maps over the last month reveals the different modes that recently
contributed to a nice westerly wind burst over the equatorial west
Pacific. Multiple modes contributed to
the longevity and intensity of the burst.
A Kelvin wave developed in the
Paul