0.5°
CFSR analysis: 1–31 Oct 2007
250–150-hPa layer-averaged PV (black, PVU), irrotational wind (vectors, starting at 3 m s-1), relative humidity (gray shading, %) and wind speed (color shading, m s-1); 600–400-hPa layer-averaged ascent (red, every 5 x 10-3 hPa
s-1). Colored dots denote JMA best-track positions of TCs, where blue = TD, green = TS, red = TY, and purple = EC.
· WPAC:
1–15 Oct
7–22 Oct
15–31 Oct
· PAC:
1–15 Oct
7–22 Oct
15–31 Oct
· NAM:
1–15 Oct
7–22 Oct
15–31 Oct
0.5°
GFS Analysis: 15 Oct-4 Nov 2007
1000-500-hPa
thickness, SLP, 700-hPa absolute vorticity, 700-hPa wind
500-200-hPa
thickness, SLP, 300-hPa absolute vorticity, 300-hPa wind
·
Geopotential height, temperature, wind, upward motion at 925,
850,
700,
500,
300,
250,
and 200
hPa
· 700-hPa
geopotential height, wind, total column precipitable water
·
1000-500-hPa
thickness, SLP, 24-h SLP change
· Geopotential
height forecast errors
24-h forecast: 200,
500,
and 1000
hPa
48-h forecast: 200,
500,
and 1000
hPa
72-h forecast: 200,
500,
and 1000
hPa
·
140°-80°W
cross sections of wind, potential temperature, and vertical
motion
With Ertel PV: 15°N
17.5°N
20°N
22.5°N
25°N
27.5°N
30°N
32.5°N
35°N
With
relative vorticity: 15°N
17.5°N
20°N
22.5°N
25°N
27.5°N
30°N
32.5°N
35°N
1.0°
GFS Analysis: 15 Oct-4 Nov 2007
·
Streamfunction, nondivergent wind, full wind relative vorticity at
925,
300,
and 200
hPa
· Velocity potential, irrotational wind, full wind
divergence at 925,
300,
and 200
hPa
· Potential
temperature and wind on the 1.5-PVU surface (dynamic tropopause,
''DT''), and 925-850-hPa layer-averaged cyclonic relative vorticity
·
Pressure
on the DT, DT-to-850-hPa shear, and 925-850-hPa layer-averaged
cyclonic relative vorticity
· Ertel PV, pressure, and
winds on 340-K
and 350-K
isentropic surfaces
---
Friday
Map Discussion: 2 November 2007
All
Attachments
Hi
Folks,
The focus of the 2 Nov'07 Friday map discussion was on
tropical cyclone (TC) Noel and its extratropical transition (ET). The
discussion built off forecast uncertainties associated with the
track, intensity and ET of Noel as discussed in earlier posts to map
by Brian Colle, Ryan Torn, Mike Brennan, David Novak and myself.
The
following images are attached for reference:
1. WV mosaics for
selected times between from 0000 UTC 2 Nov and 1200 UTC 3
Nov'07:
Source:
http://cimss.ssec.wisc.edu/tropic/real-time/tpw2/global/main.html
Source:
http://www.rap.ucar.edu/weather/
2.
High-resolution WV winds for 1200 UTC 3 Nov'07:
Source:
http://cimss.ssec.wisc.edu/tropic2/
3.
GFS initialized SLP and 1000-500 hPa thickness analyses for 1200 UTC
3 Nov'07:
Source:
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/
4.
Dynamic tropopause (DT) analyses and forecasts for selected times
between 1200 UTC 2 Nov and 0000 UTC 4 Nov'07:
Source:
http://www.atmos.albany.edu/facstaff/rmctc/DTmaps/animSelect.php
5.
Bob Hart cyclone phase space diagrams updated as of 0600 UTC 4
Nov'07:
Source: http://moe.met.fsu.edu/cyclonephase/
6.
Buoy 44004 meteogram:
Source:
http://seaboard.ndbc.noaa.gov/
A
few salient points related to the attached images and associated
loops:
1. The many flavors of ET were on display with Noel.
The beginnings of dry slot development east of Noel and asymmetric
flow structure poleward of Noel could be seen in the WV imagery as
early as 18Z/2, even as the deep-layer (850 hPa to DT) shear remained
anticyclonic with an estimated thermal vorticity minimum immediately
over Noel within a broader anticyclonic shear environment.
2.
The passage of multiple troughs of different scale and intensity,
some of which interacted with Noel directly and some of which helped
to define the larger-scale environment poleward of the storm, played
a part of the ET process. For example, a trough passage across the
Northeast near 00Z/2 helped to pull tropical moisture poleward to
Atlantic Canada along an offshore baroclinic zone in its wake that
served
as a conduit for the future track of Noel.
3. The
evolution of Noel and its subsequent ET exposed uncertainties and
limitations with the ET definition. One "classical" ET
definition is that it represents the physical process that results in
the transformation of a warm-core TC into a cold-core extratropical
cyclone (EC). Asymmetries in total precipitable water, cloud
distribution and deep convection that are consistent with increasing
vertical wind shear and the beginnings of ET were already present by
18Z/2. In this context a fairly rapid ET occurred in the 12 h period
ending 00Z/3.
4. However, the GFS sea level pressure (SLP) and
1000-500 hPa thickness initialized analysis for 12Z/3 clearly shows a
closed 576 dam closed thickness contour is still colocated with the
storm. On the mesoscale the storm still appears to be warm core.
However, on the synoptic scale the thermal ridge (trough) lies just
to the northeast (to the southwest) of the storm as is characteristic
of a baroclinic system and EC. The storm-scale 1000-500 hPa warm core
shown in the 12Z/3 GFS initialized analysis is also consistent the
850 hPa to DT mesoscale thermal ridge (anticyclonic shear) and
thermal vorticity minimum seen in the DT analysis for this time. It
is not until 00Z/4 that there is a clear signature of a mesoscale
thermal trough (cyclonic shear) and thermal vorticity maximum
immediately to the southwest of now EC Noel. On the synoptic scale,
however, EC Noel now lies between the downstream thermal ridge and
the upstream thermal trough as is characteristic of any TC that has
gone through an ET worthy of the name.
5. Cyclone phase space
(CPS) diagrams obtained from Bob Hart's web link for the 06Z/4 GFS
run can be used to shed some light on the Noel ET. The CPS diagram
comparing the 900-600 hPa thermal wind versus the 900-600 hPa
storm-relative thickness symmetry shows that in the lower troposphere
that Noel passed from the symmetric warm core to asymmetric warm core
phase around 06Z/2 as an asymmetric structure was developing in the
precipitable water pattern around Noel. By 06Z/4 (denoted by the "C"
in CPS), Noel was crossing the boundary from asymmetric warm core to
asymmetric cold core on its way (in forecast mode now) to an ordinary
baroclinic EC. The CPS diagram for the 900-600 hPa thermal wind
versus the 600-300 hPa thermal wind shows that Noel was never a deep
warm core system. It was moderate warm core at the outset, consistent
with a Cat 1 at its best, and was already shallow warm core by
12Z/2.
6. Explosively deepening oceanic ECs can also have
shallow warm cores in what otherwise are classic baroclinic
environments. An example is the first Presidents' Day storm (PSD1) of
19 Feb.79. Figure 11 from Bosart (1981) shows the presence of a
1000-700 hPa thermal ridge over the cyclone center at 12Z/19 at which
time the cyclone was deepening rapidly. Shallow warm-core storms such
as Noel and PSD1 illustrate what should be obvious to any veteran
TC/EC watchers: Cyclones of all types inhabit a rich spectrum of
baroclinic and barotropic phase space and seldom, if ever, can be
categorized as 100% pure baroclinic or barotropic systems.
The
Presidents' Day Snowstorm of 18-19 February 1979: A Subsynoptic-Scale
Event
Lance F. Bosart
Monthly Weather Review
Volume 109,
Issue 7 (July 1981) pp. 1542-1566
7. On the synoptic scale,
and in agreement with the transition of symmetric cloud/WV structure
to an asymmetric structure, Noel experienced a fairly rapid ET in the
6-12 h period ending 18Z/2-00Z/3. However, on the storm scale the ET
began later (after 00Z/3) and was mostly complete by 06Z/4. Clearly,
the process of ET, and the timing and duration of ET, is scale
(horizontal and vertical) and time dependent.
8. Noel passed
just to the east of buoy 44004 (38.5 N and 70.4 W) as it accelerated
northeastward to Nova Scotia. A meteogram from 44004 show elements of
both a TC and an EC. Although the SLP trace lacks the accelerating
"V-shaped" pressure fall of a classic TC, a TC-like
well-defined radius of maximum wind is present present, but it is
broad (~800 km based on a storm forward speed of ~20 m/s) as is often
more characteristic of an oceanic cyclone. Of obvious interest is how
Noel might have evolved as it accelerated north-northeastward had it
been able to track farther westward over the corridor of highest
SSTs.
9. A fascinating and unresolved aspect of the Noel ET is
the role of the weak upper-level trough over the southeastern US that
appears to initiate the ET process. At 00Z/2 this trough appears as a
weak PV tail that extends from West Virginia to northern Louisiana.
By 12Z/2 the axis of this trough is approaching the coastal waters
from North Carolina to Georgia. In the 12 h period ending 00Z/3 the
trough and PV
tail/anomaly develops the classic "S"
shape of a system associated with the early stages of cyclogenesis.
It is hypothesized that the impact of this smaller-scale upper-level
trough and PV anomaly was to initiate the ET process by developing
asymmetries in the precipitable water structure and satellite cloud
signatures, and to help reduce the moderate deep warm-core symmetric
structure of Noel to a weak shallow warm-core
structure.
Friday
Map Discussion: 9 November 2007: Parts I, II, and III
Part
I Attachments
Part
II Attachments
Part
III Attachments
1-12 Nov 2007: Noel
1.0°
GFS Analysis:
·
Ertel PV,
pressure, and winds on 315,
325,
335,
and 345-K
isentropic surfaces
·
250-hPa
wind speed, 1000-500-hPa thickness, and SLP (courtesy Jay
Cordeira)
·
Pressure
on the DT, DT-to-850-hPa shear, and 925-850-hPa layer-average
cyclonic relative vorticity
0.5°
GFS Analysis:
·
Potential
temperature on the DT, 850-hPa absolute vorticity, and cloud liquid
water content (courtesy Eyad Atallah at McGill University)
Part
I:
Hi Folks,
Part I of Friday map discussion for 10
Nov'07 focused on the European wind storm of 8-9 Nov'07. This storm
featured widespread gale-to storm-force winds over the North Sea, the
extreme eastern part of the UK and over portions of northern France,
Belgium, the Netherlands and Germany. The storm deepened to ~975 hPa
beneath strong northwesterly flow as it moved E/ESE from the vicinity
of Iceland just before 0000 UTC 8 Nov to just north of Denmark by
0000 UTC 9 Nov. The strongest winds occurred to the SW of the track
of the storm where the sea level pressure gradient was strongest
between the deepening cyclone and a 1036+ hPa anticyclone situated to
the west of the UK.
A comparison of NCEP/OPC analyzed North
Atlantic surface analyses and GFS-initialized automated analyses
revealed that the storm formed shortly after 0000 UTC 5 Nov. It was
manifest as a weak closed circulation with an estimated central
pressure of ~1010 hPa near 40 N and 60 W at 1200 UTC 5 Nov in advance
of a moderate cold-core trough that was crossing the mid-Atlantic
coast. Storm formation occurred along the warm side of a moderate
1000-500 hPa thickness gradient left behind in the wake of TC/EC
Noel. Ex-TC and now EC Noel, still showing signs of being warm
core, was located near 60 N and 58 W at 1200 UTC 5 Nov. Subsequently,
the storm moved NE and weakened slightly. By 0000 UTC 7 Nov it was
manifest as a weak 1014 hPa surface trough near 57 N and 42 W.
Noteworthy, however, was that the weak surface trough was becoming
situated beneath the equatorward entrance region of an
anticyclonically curved 250 hPa jet stream at this time.
By
1200 UTC 7, deepening was under way as evidenced by the appearance of
a closed 1008 hPa cyclone near 62 N and 28 W to the SW of Iceland. At
this time the now-deepening surface cyclone was passing poleward of a
1036+ hPa anticyclone situated near 48 N and 13 W. At 0000 8 Nov,
1200 UTC 8 Nov and 0000 UTC 9 Nov the storm was located near 62 N and
11 W (~985 hPa), 61 N and 3 E (~975 hPa), and 59 N and 10 E (~975
hPa), respectively. During the rapid deepening phase the storm
graduate became associated with the poleward exit region of the next
upstream jet.
Loops of potential temperature and winds on the
dynamic tropopause (DT) and 925-850 hPa relative vorticity (selected
images are attached) obtained from the McTaggart-Cowan GFS animation
builder (link given below) established that the storm was influenced
by two DT disturbances (PV anomalies). The first was the
aforementioned disturbance that crossed the mid-Atlantic coast. This
disturbance remained weak and induced no deepening as the storm moved
NE toward Iceland by 0000 UTC 7 Nov. Deepening began in earnest,
however, after 1200 UTC 7 Nov as the second DT disturbance, this one
of arctic origin that had broken away from an arctic vortex over
extreme northeastern Canada, began to interact with the surface storm
as it was moving eastward just south of Iceland.
The second DT
disturbance is best seen at 0000 UTC 8 Nov as it is breaking away to
the ESE of the core arctic vortex over extreme northeast Canada. At
issue is to what extent secondary ridging on the DT in the Davis
Strait and southern Greenland area at this time may have distorted
the arctic vortex over extreme northeastern Canada sufficiently to
enable a piece of the vortex to break away to the E/ESE and
induce
rapid storm deepening downstream as a result. The observed ridging
over the Davis Strait and southern Greenland was occurring ahead of a
moderately intense storm (sub 996 hPa central pressure) located over
northeastern Labrador at 0000 UTC 8 Nov.
In effect,
discontinuous retrogression of the long-wave upper-level ridge
situated over the North Atlantic was in progress during this period.
The first ridge eruption occurred over northeastern Canada and the
northwestern Atlantic on 4-5 Oct in conjunction with the ET of Noel
as the storm approached the Davis Strait. The second ridge eruption
occurred in roughly the same location on 7-8 Oct in conjunction with
a trough passage across eastern North America. A related scientific
question is how the various transient synoptic-scale disturbances
interacted with one another and the larger scale ridge during the
discontinuous retrogression of the long wave ridge.
Part II of
Friday map discussion on the recent flooding rains in the Mexican
state of Tabasco will follow later.
----
Part II:
Hi
Folks,
The second part of Friday map discussion for 9 Nov'07
focused on the very heavy and destructive rains in the Mexican state
of Tabasco (adjacent to the southern end of the Bay of Campeche) at
the very end of October 2007. These rains triggered massive flooding
in many parts of Tabasco. Details on the flooding (in Spanish) can be
found at the following link:
http://smn.cna.gob.mx/
(click on link at left entitled: "Especial: Resena del frente
frio No 4")
The heavy rains followed a few days after the
passage of a strong cold front across Mexico on 23-24 Oct. The
NCEP/OPC surface maps (attached) for 1200 UTC 24, 26 and 29 Oct show
the cold front passing the Yucatan peninsular on the 24th, stalling
south of western Cuba on the 26th, and then retreating northwestward
into the southern Gulf of Mexico on the 29th. The heaviest rains in
Tabasco state fell on 28-29 Oct in the strong N/NE onshore flow that
developed to the west of the westward-retreating frontal boundary as
sea level pressures (SLPs) fell to the east and rose over the extreme
northwest Gulf of Mexico ahead of a second cool surge. Morning and
afternoon QuikScat images on 28 Oct and a morning QuikScat image on
29 Oct (link below) show the development of the strong northerly flow
overthe Bay of Campeche. Of interest, is that the strongest winds (>
15 m/s) develop west of southern Florida and then move SW toward the
northwest corner of the Yucatan peninsula. By the morning on 29 Oct
the winds in the southern Bay of Campeche reach 20 m/s (and are
locally higher) and spill into the Gulf of Tehunatepec as a part of a
strengthening Tehuantepecer.
Individual integrated
precipitable water (PW) mosaics (attached) for the
Gulf/Caribbean/Atlantic at 1200 UTC 27-29 Oct show that a corridor of
high PW values became established from Tabasco state NNE/NE to
northern Florida. The attached PW images were extracted from
individual loops at the following
link:
http://cimss.ssec.wisc.edu/tropic/real-time/tpw2/global/main.html
http://www.ssmi.com/qscat/scatterometer_data_daily.html
Select
the North Atlantic link and then click on the archive button below
the map to access older loops. The take home message from the PW
loops encompassing the 28-29 Oct period is the development of a
corridor of high PW values that move SSW/SW toward Tabasco state as
deep tropical moisture over the Caribbean associated with the
percolating Noel is transported westward and southward.
Supporting
evidence for the aforementioned high PW corridor and the westward
displacement of the frontal boundary by 29 Oct is found in the
attached 1200 UTC 26 and 28 soundings (from U-Wyoming; link below)
for 76644 (Merida, Mexico). Weak cold advection below 700 hPa on the
26th is replaced by weak warm advection below 700 hPa on the 28th as
the PW value increases from ~29 mm to ~47 mm. Backing winds above 450
hPa between the 26th and the 28th are indicative of trough
development over the northwestern Gulf of Mexico and ridge building
aloft to the east in conjunction with the development of TD/TS Noel
near Hispaniola. A visible image for 1745 UTC 28 Oct'07 (source:
GIBBS; link below) shows a solid band of cloudiness from Tabasco
state NNE/NE to northern FL in conjunction with the corridor of high
PW values. Coarse resolution satellite-derived rain-rain measurements
(mm per 3 h) obtained from the Navy/NRL (link below) show widespread
20-40 mm rainfall totals in the 3 h periods ending 0000 and 1200 UTC
29 Oct that coincide nicely with the aforementioned corridor of high
PW values that extends into Tabasco state. There is also evidence of
significant orographic rainfall enhancement in the mountains to the
south of Tabasco ending 0000 UTC 29 Oct. Rivers with headwaters in
these mountains empty into the Bay of Campeche and were a source of
the widespread
flooding.
http://weather.uwyo.edu/upperair/sounding.html
http://www.ncdc.noaa.gov/oa/rsad/gibbs/gibbs.html
http://www.nrlmry.navy.mil/sat-bin/rain.cgi
Selected
maps of potential temperature and winds on the DT with layer-averaged
925-850 hPa relative vorticity, and 850/300 hPa streamfunction and
nondivergent winds for selected times between 23-29 Oct round out the
attached images. All of these images were obtained from the
McTaggart-Cowan GFS animation builder (link below). At 0000 UTC 23-24
Oct the NNE-SSW oriented band of 925-850 hPa layer mean relative
vorticity that marks the initial cold front can be seen advancing
eastward across the Gulf of Mexico. An E-W oriented PV tail from a
trough over the central Atlantic is evident from north of Nicaragua
eastward to Puerto Rico and beyond. TD/TS Noel would eventually form
under remnants of this PV tail a few days later. Weak disturbances
(PV anomalies) that fractured from the western end of the PV tail and
continued moving westward helped to maintain deep tropical moisture
over the western Caribbean. One of these weak fractured PV anomalies
is evident near the eastern side of the Yucatan peninsular at 0000
UTC 24 Oct. By 0000 UTC 27 Oct, remnant patches of 925-850 hPa
layer-mean frontal relative vorticity are evident from just west of
Florida southward to the east of Yucatan. Comparison with the
attached NCEP/OPC surface frontal analysis for 1200 UTC 26 Oct
suggests that these vorticity patches lie near and to the west of the
analyzed surface frontal position.
At 0000 UTC 28 Oct a
concentrated area of 925-850 hPa layer-mean relative vorticity is
centered near 25 N and 87 W. This concentrated cyclonic vorticity
maximum developed between 0000 and 0600 UTC 27 Oct in the patchy
frontal vorticity region noted previously to the west of Florida.
This cyclonic relative vorticity maximum can also be seen at 850 hPa
to the northwest of western Cuba at 0000 UTC 28 Oct. Over the next 24
h this cyclonic vorticity maximum moves southwestward to the Bay of
Campeche (seen also in the 925-850 hPa layer-mean relative vorticity)
and is accompanied by a northerly surge into Tabasco state in
conjunction with rapidly increasing PW values and the onset of warm
advection. To the east, a broad 850 hPa cyclonic circulation
strengthens by the 29th as TD/TS Noel begins to percolate. At 300
hPa, a trough over the northwestern Gulf of Mexico at 0000 UTC 28 Oct
is associated with confluent flow over the western Gulf and the
Yucatan peninsula. Broadly speaking, the corridor of high PW values
that develops from northern Florida to the Bay of Campeche and
Tabasco state on 28-29 Oct is associated with weak warm-air advection
near (but not under) the right-front entrance region of a modest 300
hPa jet that resides over the northwest Gulf of
Mexico.
http://www.atmos.albany.edu/facstaff/rmctc/DTmaps/animSelect.php
Loops
of: 1) 1000-500 hPa thickness, 700 hPa vorticity and winds, 2)
925/300 hPa streamfunction and nondivergent winds, and 3) 925/300 hPa
velocity potential and divergent winds for this case can be found at
the below links constructed and maintained by UAlbany Ph. D. student
Heather Archambault. In conjunction with the attached images for
specific times, these loops make it evident that the low-level
cyclonic vorticity maximum that developed west of Florida on the 27
Oct and reached the southern Bay of Campeche and Tabasco state on 29
Oct was the main player in focusing the excessive rainfall that led
to the widespread and destructive flooding in the low-lying areas of
Tabasco state.
·
1000-500-hPa
thickness, SLP, 700-hPa absolute vorticity, 700-hPa wind
·
500-200-hPa
thickness, SLP, 300-hPa absolute vorticity, 300-hPa wind
·
Streamfunction,
nondivergent wind, full wind vorticity: 925
hPa 300
hPa
·
Velocity
potential, irrotational wind, full wind divergence: 925
hPa 300
hPa
·
700-hPa
geopotential height, temperature, wind, upward motion
·
700-hPa
geopotential height, wind, total column precipitable water
·
1000-500-hPa
thickness, SLP, 24-h SLP change
The
events that conspired to enable the widespread and destructive
flooding in Tabasco state strike me as relatively rare (one or two
sigma events?). Most cold fronts that reach the Gulf of Tehuantepec
are fast-moving and are usually devoid of significant deep moisture
and associated heavy precipitation. Such cold fronts are driven by a
strong polar anticyclone (usually 1030+ hPa) that surges equatorward
along the eastern slopes of the Rockies. As the anticyclone moves
equatorward east of the Rockies it often splits into two separate
cells. One cell, terrain-tied, tracks equatorward through eastern
Mexico while the second cell, dynamically driven, typically tracks
eastward along the Gulf coast (polar anticyclones don't like warm
water) and then up along the Atlantic coast.
The initial cold
front passage across the western Gulf of Mexico on 23-24 Oct mostly
followed the classic Tehuantepecer "script" whereas the
second event on 28-29 Oct did not. Instead, the second Tehuantepecer
event was driven by an increasing SLP gradient across the Gulf of
Mexico that was as much a product of weak SLP pressure falls over the
eastern Gulf of Mexico and western Caribbean as it was by weak SLP
rises over the northwestern Gulf of Mexico. The weak SLP falls to the
east occurred in the western envelope of the cyclonic circulation
associated with the percolating TD/TS Noel. Low-level warm-air
advection in easterly flow centered along a corridor located near ~20
N from the Gulf of Mexico to near Cuba/Hispaniola appeared to play an
important role in the observed SLP falls over the eastern Gulf of
Mexico and the western Caribbean. The dynamical role of the W-E
oriented PV tail described above in facilitating SLP falls associated
with the westward-moving frontal boundary and, in effect, inducing a
Tehuantepecer and heavy rains beneath a corridor of SSW/SW-moving
deep tropical moisture in Tabasco state needs to be ascertained.
Ditto for the organization of low-level vorticity maxima near and
close to the frontal boundary in the eastern Gulf of
Mexico.
-----
Part III:
Hi Folks,
Appended
below is a post from Jim Steenburgh I received earlier this evening
about a short-lived intense storm in the Black
Sea yesterday
(Sat) that sunk a number of ships and drowned an as yet unknown
number of sailors. Included is my response and Jim's response to me.
The bottom line is that the same arctic PV anomaly that contributed
to the rapid intensification of European storm #1 to ~975 hPa over NW
Europe likely played a similar role in European storm #2 (I included
a brief synopsis in my response to Jim appended below). There is also
the suggestion that the arctic PV anomaly received a small
reinforcement of arctic air from the NNW in the 12 h ending
00Z/10.
Attached are selected images of SLP/1000-500 hPa
thickness/250 hPa isotachs, and DT pressure/850 hPa-DT shear/925-850
layer-mean relative vorticity at 12 h intervals for 9-11 Nov'07
(all images were obtained from the McTaggart-Cowan GFS animation
builder).
The salient points are as follows:
1. The arctic
PV anomaly that helped to intensify European storm #1 outran this
storm as it dived SE toward the Alps while the storm itself moved ESE
and filled.
2. Cold air moving SE in the wake of European
storm #1 was clearly blocked by the Alps as evidenced by the 1000-500
hPa thickness packing on the north/east side of the Alps at
12Z/9.
3. Because the Alps have a finite east-west width, the
advancing cold air surged around the eastern end of the barrier and
cascaded SE across Italy and the Adriatic Sea.
4. After the
arctic PV anomaly crossed the Alps and encountered the strengthening
baroclinic zone from the Adriatic Sea eastward to the Ionian Sea it
triggered new cyclogenesis (note the closed 1004 hPa isobar over the
southern Adriatic Sea at 00Z/10).
5. Rapid deepening occurred
in two stages: 1004 to <992 hPa in the 12 h ending 12Z/10 and <992
hPa to <980 hPa in the 12 h ending 06Z/18 when the storm was over
the Black Sea. Little change in central SLP is indicated in the GFS
initialization between 12Z/10 and 18Z/18 while the storm was over
land.
6. As Jim rightfully pointed out, European storm #2
could have been considerably more intense than shown on the mesoscale
over the Black Sea in response to significant surface heat and
moisture fluxes.
7. Between 00Z/10 and 12Z/10 the coupling
index (CI; not shown; defined as theta on the DT minus theta-e at 850
hPa) was < -5, indicative of tropospheric-deep instability over
the southern Aegean and Ionian Seas where European storm #2 first
intensified rapidly.
The storm's transit across the Black Sea
during the second phase of rapid deepening was accompanied by CI
values <0.
Interesting series of storms overall.....
Date:
Sun, 11 Nov 2007 18:10:59 -0700
From: Jim Steenburgh
<Jim.Steenburgh@utah.edu>
To:
meteo-inscc@lists.utah.edu, adam.varble@utah.edu,
Jon
Zawislak <jon.zawislak@utah.edu>,
Lance
Bosart <bosart@atmos.albany.edu>
Subject:
Loss of ships on the Black and Azov Sea
Folks:
If you
don't believe that shipwrecks still happen, check out the book
"Extreme Waves" by Craig B. Smith, or this latest posting
on CNN about the disaster on the Black and Azov
seas:
http://www.cnn.com/2007/WORLD/europe/11/11/russia.spill/index.html.
What
happened over the Black Sea? GFS analyses
(http://www.met.utah.edu/cgi-bin/jimsteen/gfs/displayGFS.cgi?region=SY_EU&fileHour=anal07111118F000)
show that the incipient cyclogenesis occurs in classic fashion to the
lee of the Alps as an upper-level shortwave trough impinges on that
barrier in large-scale northwesterly flow. The cyclone then drifts
SEward to the boot-heel of Italy before swinging eastward and then
NEward across the Black Sea.
It's relatively unremarkable case
of cyclogenesis until the low moves over the Black Sea. At around
10/18Z the analyzed central pressure is only about 988 mb, but after
this time the cyclone undergoes incredible mesoscale intensification,
dropping about 12 mb in 12 h (in the analyses, which undoubtably do
not resolve the subsynoptic scale structure of this event). An
incredible pressure gradient develops in
the wake of the storm
over the Black sea. The analyzed cyclone fills rapidly as soon as it
moves over mainland Russia.
This suggests that this event may
be similar to an "arctic hurricane". Rapid mesoscale
development occurs as nearly vertically stacked surface low and
upper-trough move over the warm waters of the Black Sea. Similar
mid-latitude events have been documented over the
Mediterranean by
Dick Reed and others. It would be interesting to know if SSTs
over the Black Sea are unusually high and if this may
have
contributed to the extreme nature of this event. I'd
also like to know if this has been an unusually warm fall in this
part of Eurasia.
Jim
Hi Jim,
The arctic PV
anomaly that got involved with the rapid deepening phase of the NW
Europe storm (European Storm #1) of 8-9 Oct that was the subject of
my part I Friday map discussion post from 9 Oct was also responsible
for triggering new cyclogenesis to the lee of the Alps (reminds me of
the Bleck and Mattochs and Mattochs and Bleck papers from the
mid-1980s). This arctic PV anomaly outran its original progeny but
then latched on to the surface baroclinic zone on the east side of
the Alps (it looks to me that the cold air in the wake of European
storm #1 was initially blocked by the Alps but then did ye olde
end-around to the east of the mountains. From there, the cold air
raced down the Adiratic Sea and then established a relatively strong
baroclinic zone from the Ionian Sea eastward to the Aegean Sea. With
the arrival of the arctic PV anomaly it was then Katie bar the door
time and European Storm #2 was born.
Go ahead and send a post
to
map?
Lance
..........................................................
Date:
Sun, 11 Nov 2007 19:24:32 -0700
From: Jim Steenburgh
<Jim.Steenburgh@utah.edu>
To:
Lance Bosart <bosart@atmos.albany.edu>
Subject:
Re: Loss of ships on the Black and Azov Sea
Lance:
Yes,
go ahead and sent to Map. The cyclogenesis in the lee of the Alps is
of the Uberstromungs type (Pichler and Steinacker 1987), which I note
only because I like the name. Based only on a quick and dirty
analysis based on the GFS, it reminded me a lot of the case described
in the classic paper by Buzzi and Tibaldi 1978. I wonder how good the
forecasts were. You can't get the mesoscale right if you can't get
the large scale right. A small error in the track of the PV anomaly
and low center would have probably yielded nothing like was observed.
Perhaps this contributed to so many ships being caught off
guard.
Jim