NATIONAL WEATHER SUMMARY

SEPTEMBER 2011

11st-10th…The low pressure system, Post Tropical Cyclone Lee, over the
Southeast, slowly moved northeast Tuesday and kept widespread
precipitation going from the Ohio and Tennessee valleys eastward
across the East Coast. Very heavy rains and flash flooding occurred
over the Appalachians, Mid-Atlantic and southern New England.
Moreover, severe thunderstorms developed over portions of the Mid-
Atlantic and Florida. A tornado was spotted in Glen Raven, North
Carolina and high winds knocked many trees and power lines. As ex-Lee
moved northeast, the Gulf States finally got a break from the recent
rain. Mostly sunny skies prevailed across the region, with
temperatures climbing back to the 80s and 90s in the afternoon. Out
West, sunny and dry weather occurred as high pressure held in place.
The only exceptions were the Four Corners, where monsoonal showers and
thunderstorms continued. In the Tropical Atlantic, Katia, south of
Bermuda, remained as a category 3 hurricane and continued to move
northwestward. No landfall threat was expected. Temperature wise, a
cool day prevailed across much of the East Coast Tuesday. Highs were
mainly in the 60s and lower 70s. Conversely, hot weather persisted
across the interior of the West and Southern Plains. Portions of the
Southwest saw temperatures soaring into the 100s in the afternoon.
Scattered storms persisted over the Ohio River Valley on Friday as the
remnants of Tropical Storm Lee lingered over the region. While the
system continued to lose its strength, it produced a few more
scattered rain showers over the Midwest, Ohio River Valley, and into
the Northeast. Heaviest rainfall was reported in Indiana, Pennsylvania
with a mid-day total of 1.20 inches of rain. Most of the area saw
around a half of an inch of rain. Flooding remained a major concern
for Pennsylvania and New York. To the west, a ridge of high pressure
covered the Rockies and stretched into the Plains. This brought warm
and mild conditions to most of the Central US. Highs remained in the
mid-80s across the Northern Plains and Upper Midwest. The South,
however, remained hot and dry, which created dangerous fire weather
conditions. Many evacuations remained in effect across eastern and
central Texas as multiple large fires threatened residences. Also in
the South, a stationary front lingered over the northeastern Gulf of
Mexico and produced more heavy rains and strong thunderstorms that
moved into eastern Florida throughout the day. Severe storms have not
yet developed and rainfall totals remained less than a half of an
inch. Out West, a trough of low pressure moved into northern
California and created scattered thunderstorms. The surface remained
dry and hot, due to a dominant ridge of high pressure that has hovered
over the West Coast for the past few days. These dry and windy
conditions at the surface, in combination with high chances of
lightning strikes, increased fire danger across northern California
and the Pacific Northwest.
The Upper Midwest and Great Lakes saw another chilly morning on
Friday, as a cold Canadian air poured in from the north. A ridge of
high pressure stretched over the Midwest and Mississippi River Valley,
into the Eastern US. The system pushed a cold air mass in from Canada,
which brought frost and freeze advisories to the Northern US.
Overnight lows dipped into the mid-20s in northern Minnesota and
northern Wisconsin, while upstate New York saw lows drop into the 30s.
The national low was 21 degrees reported in Hibbing, Minnesota.
Daytime highs were also affected by this cold system, with mid-day
highs in the 50s and 60s across the North. This chilly Fall weather is
still about 3 to 4 weeks ahead of schedule. Behind this system in the
Plains, a trough of low pressure advanced off the Rockies and into the
Plains. This triggered widespread scattered showers and thunderstorms
that stretched from Nebraska and Iowa to northern Texas. This brought
some drought relief to the Southern Plains, with a mid-day total of
1.65 inches of rain reported at Guadalupe Pass, Texas.
Also in the South, a stationary frontal boundary lingered over the
Southeastern US and produced some rain showers from the Carolinas to
Florida. Heaviest rainfall for the region was reported in Charleston,
South Carolina with a mid-day total of 1.60 inches. Severe storms have
not yet develop along this frontal boundary.

11th-17th…In the southern Plains, rain barely dented the historic,
year-long drought. Topsoil moisture improvements in the south-central
U.S. but provided only limited relief to drought-ravaged pastures and
rangeland. Beneficial rain also fell across the Four Corners States
and from the central Plains into the middle Mississippi Valley.
Although the moisture in the nation’s mid-section arrived too late for
summer crops, soaking rains (locally in excess of 2 inches)
replenished soil moisture. Farther north, an early freeze occurred
across the upper Midwest. The freeze, which occurred on September 15—
roughly 2 to 3 weeks earlier than normal—halted the growth of late-
developing summer crops in much of Minnesota, North Dakota, eastern
South Dakota, northern Iowa, and northern Wisconsin. Later, toward
week’s end, scattered frost was reported from the lower Great Lakes
region into the Northeast. Midwestern weekly temperatures generally
averaged 4 to 8°F below normal. Elsewhere, mostly dry weather aided
fieldwork operations in much of the Northwest and Southeast, although
a few heavy showers dotted the middle and southern Atlantic coastal
plain. Early in the week, record-setting, late-season heat persisted
in the Northwest. Seattle, WA, set a monthly record with 9 consecutive
days (September 3-11) of 80 degree warmth. The previous record of 8
days in a row had been set from September 7-14, 1989. Elsewhere in
Washington, Yakima (95, 97, 98, 99, 98, 98, and 95°F) posted daily-
record highs on 7 consecutive days from September 7-13. Meanwhile,
heat returned to the drought-ravaged south-central U.S. Lufkin, TX
(105°F on September 13), set a record for its latest reading of 105°F
or greater (previously, 110F on September 4, 2000). Elsewhere on
September 13, the hottest weather on record so late in the year also
affected locations
such as Shreveport, LA (107F); Longview, TX (107F); Texarkana, AR
(106F); and Houston, TX (102F). Houston (99, 101, 102, and 100F) also
tallied four consecutive daily-record highs from September 11-14.
Wichita Falls, TX, having long since broken its 1980 annual record of
79 days with 100-degree heat, tallied a daily record high of 105F on
September 13 for its 100th triple-digit day of 2011. However, the
second half of the week featured much cooler weather from the Plains
eastward. International
Falls, MN (27, 19, and 23F), notched a trio of daily-record lows from
September 14-16. Other daily records for September 15 included 26°F in
Mason City, IA; 29F in Eau Claire, WI; and 30F in Sisseton, SD. Later
in the day, the high temperature climbed to just 45F in Kearney, NE,
where it was the coldest September day since September 24, 2000 (40F).
Chilly weather lingered across the Great Lakes region through
September 16, when daily-record lows dipped to 27F in Rhinelander, WI,
and 29F in Gaylord, MI. Patches of light snow accompanied the chilly
weather in the Great Lakes region. On September 14, Duluth, MN, noted
a trace of snow, while Rhinelander recorded its earliest trace of snow
(previously, September 15, 1916). Uncharacteristically heavy showers
dotted the Four Corners
States and occasionally expanded to cover much of the West. On
September 12, daily-record rainfall totals included 0.10 inch in Yuma,
AZ, and 0.07 inch in Redding, CA. The following day, rainfall records
for September 13 reached 1.10 inches in Kingman, AZ, and 0.99 inch in
Needles, CA. For
Kingman, it was the wettest day since February 19, when 1.50 inches
fell. For Needles, it was the wettest day since December 22, 2010,
when 1.01 inches fell. In Colorado Springs, CO, a 4.50-inch total on
September 14 represented not only the wettest September day on record,
but also the wettest day for any month. In both instances, Colorado
Springs’ previous record had been 4.29 inches on September 11, 2008.
On September 15, Tucson, AZ, was pelted by 2.84 inches of rain,
marking its wettest day since October 1, 1983 (2.96 inches). Tucson
also set a September record with 5.57 inches of rain, eclipsing its
1964 standard of 5.11 inches.
Showers lingered through week’s end in the West; daily record amounts
for September 16 included 1.03 inches in Ely, NV, and 0.20 inch in
Idaho Falls, ID. By September 17, heavy showers erupted across the Mid-
South, where daily record amounts reached 3.02 inches in Joplin, MO,
and 1.98 inches in Harrison, AR. Pockets of heavy rain also developed
along the Mid-Atlantic Coast, where Cape Hatteras, NC (6.96 inches),
collected a daily-record total for September 17. Mild weather
prevailed across the Alaskan mainland, while showery conditions
persisted in the southeastern part of the state. Daily record highs
were established on September 12
in locations such as Skagway (75F) and Sitka (74F). The following day,
highs reached daily-record levels in Northway and Eagle (both 74F).
Meanwhile, weekly rainfall reached 4.26 inches in Port Alexander,
aided by a total of 3.12 inches on September 14. Similarly, Kodiak’s
5.95-inch weekly sum was boosted by a daily-record amount of 3.46
inches on September 12. Farther south, a mostly dry weather pattern
led to large daily temperature fluctuations in Hawaii. Kahului, Maui
(61F), posted a daily record low on September 11. However, a few
heavier showers developed after mid-week in windward locations. On the
Big Island, for example, Hilo (1.54 inches on September 15)
experienced its wettest day since May 6, when 1.71 inches fell.
Elsewhere on the Big Island, Mountain View netted 4.57 inches in a 24-
hour period on September 15-16.

18th-24th…Rain ended early in the week across the southern Plains,
followed by a return of warm, dry weather. Meanwhile, significant rain
with weekly totals of 2 inches or more shifted into the mid-South,
Ohio Valley, and Southeast. A few totals in excess of 4 inches were
reported, mostly in the southern Appalachians. Heavy rain of at least
2 inches fell in parts of the mid-Atlantic coastal plain and southern
New England, triggering a new round of flooding. Farther west, cool,
damp weather occurred in the Midwest. Some of the heaviest rain of
locally 2 inches or more fell across the southern and eastern Plains.
The slow-moving storm responsible for the rain held temperatures more
than 5F below normal in parts of the Midwest. In the wake of the
September 15 upper Midwestern freeze, chilly weather lingered across
the north-central U.S. In particular, widespread frost was noted
across the northern Plains and far upper Midwest from September 21-23.
The northern Plains also received some heavy rain, with locally heavy
amounts reported in North Dakota. Elsewhere, mostly dry, unusually
warm weather (more than 5F above normal in some areas prevailed west
of the Rockies. Early in the week, locally heavy showers lingered on
the southern Plains. Before the rain ended, Waco, TX received 2.13
inches on September 18, experienced its wettest calendar day since
January 9, when 2.44 inches fell. Elsewhere on September 18, daily
record amounts included 2.20 inches in Daytona Beach, FL; 1.39 inches
in Batesville, AR; and 1.07 inches in Longview, TX. Heavy showers
continued for several days in the Southeast, where daily-record
amounts reached 3.49 inches (on September 20) in Birmingham, AL, and
2.88 inches (on September 21) in Greenville-Spartanburg (GSP), SC.
GSP’s 3-day period rainfall totaled 5.84 inches. Meanwhile, a slow-
moving storm arrived in North Dakota, resulting in daily-record totals
for September 20 in Minot received 1.17 inches and Grand Forks
recorded 1.13 inches. High winds accompanied the storm across the
north-central U.S. For example, Helena, MT (55 mph on September 19),
clocked its highest September gust since September 25, 1999. On
September 20, a gust to 62 mph was recorded in Hettinger, ND. Farther
west, Bishop, CA, noted its highest September wind gust on record,
with 59 mph on September 20. Late in the week, heavy rain returned to
the waterlogged mid-Atlantic and Northeastern States. Daily-record
amounts for September 23 included 3.19 inches in Baltimore, MD; 3.06
inches in Mt. Pocono, PA; and 2.97 inches in Greensboro,
NC. In Harrisburg, PA, where 1.76 inches fell on September 23, both
the annual (59.90 inches) and September totals (16.51 inches) set
records. Harrisburg’s previous marks had been set in 1972 (59.27
inches) and September 1975 (14.97 inches), respectively. Periods of
heat continued to affect the south-central U.S., helping to negate the
beneficial effects of any rainfall. On September 18 in Texas, McAllen
and Harlingen (both 100F) tied daily-record highs. Warmth also
overspread the Pacific Coast States, where Oakland, CA (88 and 91°F),
opened the week with consecutive daily-record highs on September
18-19. Elsewhere in California, Sacramento (100°F on September 21)
also notched a daily-record high. Farther inland, Reno, NV (90 and
94F), posted consecutive daily-record highs on September 21-22. Later,
heat returned to Texas and expanded across the northern High Plains.
In Montana, daily record highs on
September 23 included 93°F in Havre and 91°F in Billings. By
September 24, daily-record highs in Texas reached 99F in both
Abilene and Austin (Camp Mabry). Late-week heat also covered the
Northwest, where Lewiston, ID (10°F on September 24), registered its
latest 100-degree reading on record. Previously, Lewiston’s latest
triple-digit reading had occurred on September 21, 1967. In contrast,
several daily record lows were set across the north-central U.S. In
Nebraska, both Alliance (26F) and Chadron (28F) tied daily record
highs for September 22. The following day, Sioux City, IA (29F),
tallied a record low for September 23.

25th-30th…More scattered showers popped up across the Great Lakes and
Northeast on Friday, as a low pressure system lingered over the
region. The system started to slowly advance eastward and continued to
push a cold front through the region. The system kicked up scattered
showers, but rainfall totals were significantly less than the past few
days. However, due to the already soaked soils, flooding remained of
concern across the Northeast and Lower Great Lakes from Ohio to New
York. Heaviest rainfall was reported at Mt. Washington, New Hampshire,
which saw a mid-day total of 0.93 inches of rain. As this system
passed, a ridge of high pressure over the Rocky Mountains advanced
eastward over the Plains and into the Central US. The ridge brought
another seasonably warm day to the Rockies, with highs in the upper
70s to lower 80s. In between these two systems, strong winds developed
over the Upper Great Lakes as the pressure rapidly changed from lower
to higher. This produced strong winds from the north that also brought
in some cool Canadian air. Frost advisories have been issued for the
Upper Midwest. Out West, a low pressure system off the West Coast
produced a cold front that slowly moved onshore. This has not yet
produced rain showers, but has pushed patchy clouds onshore.