Download Alaskan Autumn Storm of 22

Alaskan Autumn Storm of 22-24 November 2010
By
Richard Grumm
National Weather Service State College, PA 16803
and
Rick Thoman and James A. Nelson
National Weather Service Alaska Region
1. INTRODUCTION
A surge of tropical moisture (Figure 1) over
the western flank of an anomalously strong
and poleward shifted subtropical ridge (Fig.
2) produce rain over portions of Alaska on
22-24 November 2010. Liquid rainfall over
inland regions of Alaska is rare during the
cold season. Thus rainfall amounts
approached record levels in many locations.
Temperatures were much above normal, as
much as 25F above normal. Barrow went
above freezing. The cold ground caused
freezing rain. In Fairbanks, the rain froze on
the roads and exposed ground until the
ground temperatures rose above freezing.
During the event portions of central AK
received relatively rare liquid rain which
approached record values. Barrow's
maximum temperatures on the 22 and 23 of
November were about 25 degrees above
normal. Anchorage and Fairbanks suffered
from an extended period of freezing rain on
the “deeply frozen ground”. The freezing
rain continued until the surface ground
temperatures warmed above freezing.
Higher elevations received heavy snow from
the weather system.
Rain and freezing rain in interior Alaska are
unique events. Fairbanks had over 0.60
inches of rainfall, one of the largest winter
season rainfall events on record. The record
event occurred on 20 January 1937 when
0.99 inches of rain fell on the city. Several
other locations set daily precipitation
records (Need table of amounts and previous
records for Barrow etc). True freezing rain,
with ice on trees and power lines is also a
relatively rare event. The last true freezing
rain events in Anchorage were observed in
1995 and 1980 (exact dates would be
useful).
The value of anomalies in identifying
potential high impact weather events
(HIWE) has been demonstrated by Hart and
Grumm (2001), Grumm and Hart (2001),
and Graham and Grumm (2010). The first
two studies focused on the eastern United
States and the latter on the western United
States. Junker et al. (2008) showed the value
of precipitable water anomalies to identify
atmospheric rivers (AR: Ralph et al 2008)
and to characterize the potential for heavy
rainfall along the West Coast of the United
States. These concepts were applied to the
NCEP GEFS and it was shown that forecasts
of anomalies may aid forecasters in better
anticipating heavy rainfall events (Junker et
al 2009. It will be shown that the Alaskan
event of the 22-24 November 2010 was
associated with a strong signal when
examined using standardized anomalies.
This paper will document the rare Alaskan
warm rain event of 22-24 November 2010.
The focus is on the anomalous pattern that
produced the unique conditions and NCEP
GEFS forecasts of the event.
2. METHODS
The overall pattern was reconstructed using
the 1.25x1.25 degree Japanese Re-analysis
data (JRA25:Onagi 2007). The anomalies
were derived using the JRA25 and
comparing it to the 30-year mean and
standard deviations computed from the
NCEP/NCAR re-analysis data (Kalany et. al
1996). All anomalies herein are shown as
standardized anomalies (Hart and Grumm
2001).
i. large scale pattern
In addition to the warm air, the subtropical
anticyclone pushed abnormally warm air at
925 hPa (Fig. 6) and 850 hPa (not shown).
The deep warm air produced conditions
warm enough for rain. The arctic
anticyclone was associated with cold air
with -12 to -30C air over southeastern
Alaska and northwestern Canada. This
retreating cold air mass left the cold ground
over central Alaska which produced the
freezing rain at the ground during the event.
The the precipitable water pattern and the
500 hPa pattern in 24-hour increments are
shown in Figures 1 & 2 respectively. These
data show a evolution of a sharp subtropical
ridge over Alaska with 3 to 4 σ 500 hPa
height anomalies by 18/0000 UTC with a
closed 5760 m contour over southern Alaska
at 19/0000 UTC. There was a surge of high
PW air into the region with PW anomalies
peaking over 6σ above normal at 23/0000
UTC.
The 850 hPa winds and wind anomalies are
shown in Figure 7. These data show a
narrow region of above normal 850 hPa
winds which moved over western Alaska at
22/0000 UTC moving into interior sections
by 22/1200 UTC. A second surge of
modestly above normal winds moved into
southwestern Alaska on from 22/1800
through 24/0000 UTC. The high terrain may
have limited the deep penetration of these
winds into interior sections.
The NCEP GEFS was used to show
forecasts of the event. Standardized
anomalies were computed using the
ensemble mean and the NCEP/NCAR reanalysis data. Precipitation forecasts are
shown in milli-meter and in probabilistic
categories of occurrence.
3. RESULTS
As the subtropical ridge developed, the 250
hPa jet over the ridge (Fig. 3) increased in
strength. The total wind anomalies in this
features were 2 to 4σ above normal and
peaked at 5σ above at 19/0000 UTC. As this
enhance jet shifted eastward, a strong jet
entrance circulation move over much of
central and southern Alaska (Fig. 3g-i).
ii. Regional pattern
The mean sea-level pressure (MSLP), PW,
and 925 hPa temperatures over the region
are shown in Figures 4-6 respectively. Two
surface anticyclones were present, a cold
arctic anticyclone was present over
northwestern Canada (Fig. 4a-d) and a large
northward displaced subtropical anticyclone
was present over the north Pacific basin
(Figs. 4-i). The flow about the latter feature
was associated with the surge of high PW air
into Alaska. These data show several
periods of PW anomalies in excess of 6σ
above (Fig.5b,c, and e) with many periods of
3 to 5σ above PW values.
iii. GEFS forecasts
For brevity 9 GEFS forecasts for each
variable are shown. Only the ensemble mean
and standardized anomalies are presented.
More appropriate ensemble probability
displays are limited to a few fields.
Figure 8 shows the GEFS mean PW field
and standardized anomalies from 9 runs all
valid at 24/0000 UTC. These data show the
surge of high PW air into AK at 24/0000
UTC. The consistent PW forecasts showed
a surge of 10 to 20 mm PW values with a
large area of 3 to 5σ anomalies over central
AK with some areas of 6σ anomalies in
some of these forecasts. These large
anomalies imply low spread amongst
ensemble members.
The 500 hPa and 250 hPa heights and winds
(Figs. 9-10) showed a consistent pattern
over AK as did the 850 hPa temperatures
(Fig. 11) which showed the surge of
abnormally warm air into the region. These
forecasts, with large anomalies imply low
spread and convergent forecasts.
Based on the pattern and the low-level
temperatures in the GEFS, not surprisingly,
the GEFS predicted a wide swath of 16 to 32
mm (0.70 to about 1.5 inches) of liquid
equivalent precipitation for the period
ending at 1200 UTC 24 November 2010
(Fig. 12).
Plume diagrams from the 22/0000 UTC
GEFS for Anchorage and Fairbanks are
shown in Figure 13. These data show the
initial onset of freezing rain in Anchorage
followed quickly by rain for the 23r and 24th
of November. The GEFS showed around 1
inch (25mm) of rain in Anchorage with a
range of 0.39 to 1.59 inches. Fairbanks
showed a similar evolution with a higher
mean rainfall (1.26 inches) and a higher
maximum rainfall. The plumes, showing
rain as the primary precipitation type in
Fairbanks suggest very warm profiles which
are shown in Figure 14. These data show the
above freezing 2m and 850 hPa
temperatures during the initial surge of
precipitation.
iv. impacts and significance
During winter, defined at November
through March, liquid precipitation is a
rare event in Fairbanks (65N/148W),
Alaska. Amounts in excess of 0.10
inches are considered to be extremely
rare events. Climatologically, in the past
50 years there have been just 10 winter
rain events with 0.10 inches or more of
liquid precipitation. These events
typically occur early and late in the
season with 3 of 1 of all events observed
during the first half of November.
The total liquid rainfall of 0.95 inches on
22-24 November 2010 was the second
greatest winter rain event at Fairbanks
since 1904. The record rainfall, of 0.99
inches was set on 20 January 1937.
Since hourly observation began in
March 1941 the 39 hours of rainfall on
22-24 November 2010 is a new record.
There was a rainfall event of similar
duration from 2-3 November 1935.
In addition to the rainfall record, the
temperature remained near 35F and
remained above freezing for 49
consecutive hours. The low of 33F was
a record high low and tied for the record
high low for the month of November.
Since the commencement of hourly
observations this was the longest period
of above freezing temperatures recorded
at Fairbanks. It should be noted that
from 6-9 December 1934 there was a
period of 60 hours of above freezing
temperatures. There may have been a
long period of above freezing
temperatures during the 2-3 November
1935 rain event.
On 22 November 2010 the snow mixed
with rain and ice pellets at Barrow,
Alaska (71N/157W) then briefly
changed to rain. While not
unprecedented, rain this far north is an
extremely rare in winter.
At Nome, Alaska, (64N/165W), 1.27
inches of precipitation fell on the 20-21
November, nearly all of which fell as
rain. This set the greatest rainfall amount
record at Nome for November.
At McGrath (63N/156W) 1.20 inches of
precipitation on 22 November was the
greatest calendar day precipitation in
November, though it was not a 24 hour
precipitation record.
The 23/0000 UTC rawinsonde at
Fairbanks recorded 0.74 inches
precipitable water (PW), the second
highest PW value on record since 1957
second only to exceeded 0.75" set on 2
November 2003.
In Anchorage, there was 0.75 inches of
precipitation during the event of which
0.06 inches fell as freezing rain. Due to
the cold ground this caused serious
problems to transportation despite
temperatures near 34F during the event.
There were over 30 vehicle accidents
with 90 vehicles impacted. Icy roads
kept schools closed for 3 days and cause
the cancelation of many flights out of the
Anchorage airport.
Anchorage received 75% of its monthly
precipitation during the 3 day event and
set a daily precipitation record on 23
November 2010.
In the Anchorage area this storm was
comparable in impact to the event of 2021 January 2008 (Fig. 15) when rain also
fell in Anchorage. The PW values of 15
mm penetrated the region with PW
anomalies on the order of +3 to +4σ
above normal. The rawinsonde value of
0.81 inches on 23 November 2010 was a
99th percentile value for the month.
4. CONCLUSIONS
A surge of anomalously high PW air
penetrated the State of Alaska on 22-24
November 2010. This surge of high PW was
accompanied by above normal temperatures
and an unseasonably strong subtropical
ridge. The 500 hPa heights in southern
Alaska exceed 5760 m in the early stages of
the event. This warm moist air brought a
rare cold season rain event to the State.
This rare cold season rain event was
relatively well predicted by the NCEP GEFS
(Fig 12). The GEFS showed the potential for
a significant QPF event and conditions
warm enough to support the potential for
rainfall in lower elevations (Fig. 11).
Overall, 9 different GEFS forecasts showed
a high potential for the surge of above
normal moisture, temperatures, and the
strong 250 hPa jet over the massive
subtropical ridge. These relatively consistent
forecasts implied the potential for a
significant cold season event to include rain
over the region.
The PW pattern and strong anomalies
suggest and AR (Raph et al 2006) impacted
Alaska. With a source of the air from the
central Pacific, the air was warm and moist,
each contributing factors to the high impact
weather event (HIWE) in central Alaska.
The strong subtropical ridge and anomalies
500 hPa heights with this system played a
key role in the ability to transport the warm
moist air into Alaska.
The surge of high PW air and rain in
November 2010 occurred with an MEI value
of -1.606 for the Nov-Dec time period. The
event of January 2008 also during the cold
phase of ENSO with an MEI of -0.965.
During November 2003, another rain event,
the MEI as 0.361, a warm episode. The
November 2003 event had PW anomalies
over 5σ above normal (Fig.16).
The large anomalies in both the JRA25 data
and GEFS forecasts show that like many
HIWE’s, standardized anomalies were of
value in anticipating this event. Graham and
Grumm (2010) and Hart and Grumm (2001)
showed the value of standardized anomalies
in identifying significant weather events.
Clearly, a similar study could be conducted
for Alaska. A study of this type might aid in
identifying HIWE from the past to improve
forecasting of similar events in the future.
5. Acknowlegements
The AK Region of data and information on
the event. PSU for data access in real-time.
6. References
Doty, B. E., and J. L. Kinter III, 1995:
Geophysical data and
visualization using GrADS.
Visualization Techniques Space
and Atmospheric Sciences, E. P.
Szuszczewicz and Bredekamp,
Eds., NASA, 209–219.
Graham, Randall A., Richard H. Grumm,
2010: Utilizing Normalized
Anomalies to Assess
Synoptic-Scale Weather
Events in the Western United
States. Wea. Forecasting, 25,
428-445
Grumm, R.H. and R. Hart. 2001:
Standardized Anomalies
Applied to Significant Cold
Season Weather Events:
Preliminary Findings. Wea.
and Fore., 16,736–754.
Hart, R. E., and R. H. Grumm, 2001:
Using normalized
climatological anomalies to
rank synoptic scale events
objectively. Mon. Wea.
Rev., 129, 2426–2442.
Kalnay, E., and Coauthors, 1996: The
NCEP/NCAR 40- Year Reanalysis Project.
Bull. Amer. Meteor. Soc., 77,437–471.
Onogi, K., J. Tsutsui, H. Koide, M. Sakamoto,
S. Kobayashi, H. Hatsushika, T.
Matsumoto, N. Yamazaki, H.
Kamahori, K. Takahashi, S.
Kadokura, K. Wada, K. Kato, R.
Oyama, T. Ose, N. Mannoji and R.
Taira (2007) : The JRA-25
Reanalysis. J. Meteor. Soc. Japan,
85, 369- 432.
Ralph, F. M., G. A. Wick, S. I. Gutman, M. D.
Dettinger, C. R. Cayan, and A. B.
White, 2006: Flooding on
California’s Russian River: The role
of atmospheric rivers. Geophys.Res.
Lett., 33, L13801,
doi:10.1029/2006GL026689.
Appendix-I AK-Region FTR excerpts.
•
A
WIDESPREAD
WINTER
WEATHER
EVENT CONTINUES TO BRING MIXED
Junker, N.W, M.J.Brennan, F.
Pereira,M.J.Bodner,and R.H.
Grumm, 2009:Assessing the
Potential for Rare
Precipitation Events with
Standardized Anomalies and
Ensemble Guidance at the
Hydrometeorological
Prediction Center. Bulletin of
the American Meteorological
Society,4 Article: pp. 445–
453
Junker, N. W., R. H. Grumm, R. Hart, L.
F. Bosart, K. M. Bell, and F. J.
Pereira, 2008: Use of
standardized anomaly fields to
anticipate extreme rainfall in the
mountains of northern California.
Wea. Forecasting,23, 336–356.
PRECIPITATION AND TRANSPORTATION
ISSUES
•
TO
MUCH
INTERIOR,
OF
NORTHERN AND SOUTHCENTRAL
ALASKA
BEGINNING MONDAY MORNING, MUCH
OF THE PRECIPITATION FELL AS EITHER
FREEZING RAIN OR RAIN THAT FROZE ON
“DEEPLY
FROZEN,”
ROADWAYS.
SNOW-PACKED
WHILE UP TO
18
INCHES
OF SNOW WAS REPORTED NEAR THE
SOUTHERN SLOPES OF THE
ALASKA
RANGE – THE RAIN/FREEZING RAIN IS OF
GREATEST IMPACT WITH ICE COVERING
NEARLY ALL OF ALASKA’S ROAD SYSTEM.
•
SUCH
A WIDESPREAD EVENT OF THIS
MAGNITUDE IS EXTREMELY UNUSUAL.
o FAIRBANKS HAS
OVER 0.60”OF
RECORDED
RAIN SINCE
MIDNIGHT.
RAIN
WITH ADDITIONAL
FORECAST, FAIRBANKS
WILL COME NEAR OR BREAK
JANUARY 20, 1937
RECORD OF 0.99” FOR
THE
HIGHEST
DAILY
RAINFALL
DURING THE WINTER SEASON.
o SEVERAL
OTHER
LOCATIONS
SET DAILY HIGH TEMPERATURE
AND PRECIPITATION RECORDS
THROUGHOUT THE STATE
-
INCLUDING
BARROW, ALASKA
(WHERE
SNOW
BRIEFLY
TURNED TO RAIN MONDAY).
o ANCHORAGE LAST SAW A
“TRUE” FREEZING RAIN EVENT
IN 1995, PRECEDED BY 1980.
o IN FAIRBANKS, THIS EVENT IS
SAID TO HAVE BROUGHT THE
CITY “TO A HALT”
LOCATION: WIDESPREAD. FROM THE GULF
OF ALASKA TO BARROW AND NOME TO THE
CANADIAN BORDER. GENERALLY SPEAKING, AN
AREA THE SIZE OF TEXAS, NEW MEXICO AND
OKLAHOMA COMBINED
• WFO FAIRBANKS ISSUED A WINTER
STORM WARNING FOR FREEZING RAIN
(A PROVISION IN ALASKA REGION’S
SUPPLEMENTS FOR RAINFALL ON COLDSOAKED ROADS VS AN ICE STORM
WHICH
ALSO
IMPACTS
POWER LINES).
ISSUED
SUNDAY
THIS
TREES
AND
WARNING WAS
AFTERNOON
WITH
APPROXIMATELY 14 HOURS LEAD TIME.
Figure 1. JRA precipitable water (mm) and precipitable water anomalies in 24 hour increments from a) 0000 UTC 16 November
2010 through i) 0000 UTC 24 November 2010. ANomlies in standard deviations from normal. Return to text.
•
Figure 2. As in Figure 1 except for 500 hPa heights (m) and 500 hPa height anomalies in standard deviations from normal.
Return to text.
Figure 3. As in Figure 1 except for 250 hPa winds (ms-1) and total wind anomalies. Return to text.
Figure 4. As in Figure 1 except for JRA MSLP (hPa) and MSLP anomalies in 6-hour increments from a) 0000 UTC 22 November through i) 0000
UTC 24 November 2010. Return to text.
Figure 5. As in Figure 4 except for precipitable water (mm) and precipitable water anomalies. Return to text.
Figure 6. As in Figure 4 except for 925 hPa temperatures (C ) and temperature anomalies. Return to text.
Figure 7. As in Figure 4 except for 850 hPa winds and wind anomalies. Return to text.
Figure 8. GEFS ensemble mean forecasts of precipitable water and precipitable water anomalies valid at 0000 UTC 24 November 2010 from GEFS
forecasts initialized at a) 0000 UTC 21 November, b) 1200 UTC 21 November, c) 0000 UTC 22 November, d) 0600 UTC 22 November, e) 1200 UTC
22 November, f) 1800 UTC 22 November, g) 0000 UTC 23 November, h) 0600 UTC 23 November and i) 1200 UTC 23 November 2010. Return to
text.
Figure 9. As in Figure 8 except for GEFS 500 hPa heights and height anomalies. Return to text.
Figure 10. As in Figure 8 except for GEFS ensemble mean 250 hPa winds (ms-1) and wind anomalies. Return to text.
Figure 11. As in Figure 8 except GEFS 850 hPa temperatures ( C) and temperature anomalies. Return to text.
Figure 12. As in Figure 8 except for GEFS ensemble mean accumulated QPF (mm) valid for the period ending at 1200 UTC 24 November 2010.
Return to text.
Figure 13. GEFS forecasts initialized at 0000 UTC 22 November 2010 showing precipitation
by type at a point near Fairbanks and Anchorage, Alaska. Color coded data show the
precipitation by type. The gray lines show the instantaneous 6-hour QPF for each member. .
Return to text.
Figure 14. As in Figure 13 except for GEFS 2m temperatures, 850 hPa temperatures, and 700 hPa temperatures. Temperatures degrees C
except for 2m temperatures degrees F. Return to text.
Figure 15. JRA25 precipitable water (mm) and standardized anomalies in 6-hour increments from a) 1200 UTC 19 January 2008 through i) 1200
UTC 21 January 2008. . Return to text.
Figure 16. As in Figure 15 except for the period of a) 0000 UTC 01 November 2003 through i) 0000 UTC 03 November 2003. Return to text.