Valid Thursday September 01, 2016 to Monday September 12, 2016
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT August 29 2016Synopsis
: At the beginning of the week-1
forecast period mid-level high pressure is expected across the Northern Plains
with mid-level low pressure across the Northeast and just off the Pacific
Northwest. Impacts from Tropical Depression 9 are the highlight of the week-1
hazards outlook. A surface low-pressure system is forecast to push south from
Canada into the Northern Plains late in week-1. During week-2 general
mid-level low pressure is anticipated across the west with mid-level high
pressure forecast for the east. Another potential tropical disturbance may
threaten the southeastern U.S. during the middle of week-2. Southern Alaska is
expected to be impacted by a series of surface low pressure systems during the
outlook period with mid-level low pressure forecast to build during week-2.
Hawaii faces potential tropical cyclone impacts from Hurricanes Madeline at the
outset of week-1, and Lester later in week-1. Hazards
Detailed Summary For Thursday
September 01 - Monday September 05:
- High winds across portions of the Southeast, Thu-Fri, Sep 1-Sep 2.
- Heavy rain across portions of the Southeast and the Mid-Atlantic, Thu-Fri,
Sep 1-Sep 2.
- Flooding possible across portions of Florida.
- Heavy rain across portions of the Central Plains, the Middle Mississippi
Valley, the Upper Mississippi Valley, and the Northern Plains, Sat-Sun, Sep
- Heavy rain across portions of the Middle Mississippi Valley, the Great
Lakes, and the Upper Mississippi Valley, Mon, Sep 5.
- Much above normal temperatures across portions of the Northern Plains and
the Northern Rockies, Thu-Fri, Sep 1-Sep 2.
- Flooding occurring or imminent across portions of the Middle Mississippi
Valley and the Lower Mississippi Valley.
- Slight risk of much above-normal temperatures for portions of the Great
Lakes, the Mid-Atlantic, the Northeast, and the Central Appalachians, Tue-Wed,
Sep 6-Sep 7.
- Slight risk of much below-normal temperatures for portions of the Northern
Intermountain Region and Northern Rockies, Thu-Sat, Sep 8-10.
- Severe Drought across the Central Plains, the Mid-Atlantic, the Lower
Mississippi Valley, the Central Great Basin, the Northern Plains, the Tennessee
Valley, the Great Lakes, the Southern Appalachians, Hawaii, the Northern
Rockies, the Northeast, California, the Northern Great Basin, the Southeast,
the Central Appalachians, the Southern Plains, and the Southwest.
During the course of week-1 anomalous
500-hPa ridging is favored to shift from the Northern Plains to the Northeast.
Anomalous 500-hPa troughing is forecast to build into the West over the course
of week-1 with this amplified pattern remaining through week-2. A cold front
ahead of this trough is forecast to push eastward across the northern tier
during the week. Tropical Depression 8 is expected to be off the eastern
seaboard at the beginning of the forecast period, with Tropical Depression 9
potentially coming ashore on the west coast of Florida early in week-1.
Heavy rainfall (greater than 1" in 24 hours) and high winds (exceeding 30
knots) are forecast across portions of the Southeast Thu-Fri, September 1 and 2
as Tropical Depression 9 is forecast to pass from the Gulf of Mexico across
Florida into the Atlantic. Dynamical model guidance currently supports this
system being a tropical storm both at the time of its landfall and upon
re-emerging into the Atlantic. ECMWF guidance is slightly more progressive and
further east with the forecast rainfall for this system relative to the GEFS.
Flooding is possible for portions along the west coast of Florida with this
system, while isolated inland flooding and severe weather are possible in
addition to the specified hazards on today's map. For up to date guidance on
this system please visit the National Hurricane Center (NHC) at
Much above-normal temperatures are forecast for portions of the Northern
Rockies and Northern Plains Thursday, September 1 and Friday, September 2 where
forecast high temperature anomalies could exceed 12-16 degrees F. Elsewhere,
marginally elevated fire weather conditions are not shown on the forecast map,
but expected across portions of eastern Idaho and southwestern Montana on
Thursday, September 1 due to the presence of low humidity, warm temperatures,
breezy conditions, and the presence of dry fuels.
Aforementioned warm conditions across the Northern Rockies and Northern
Plains are expected to wane with the passing of a cold front. This same
boundary is forecast to bring an eastward shifting heavy rain threat to
portions of the Northern and Central Plains and Upper and Middle Mississippi
Valley for Saturday-Monday, September 3-5.
Hawaii is expected to see potential impacts from a pair of tropical
cyclones during the week-1 period. Hurricane Madeline is forecast to pass
south the islands during the first and second of September, and expected to be
accompanied by heavy rains and high winds that predominantly influence the Big
Island. Later in week-1 Hurricane Lester is forecast to pass North of Hawaii
on September 3-4 and could bring a second round of high winds and rain. For
more information on these storms please refer to the NHC or Central Pacific
Hurricane Center at http://www.prh.noaa.gov/cphc/
A disturbance is expected for the Aleutians early in week-1 that is
forecast to push towards Southwestern mainland Alaska during the week. Heavy
rainfall is possible for the southern coastline of the state, however
discrepancies between GFS and ECMWF ensemble guidance limit a specific
geographic hazard depiction at this time. For Tuesday September 06 -
Monday September 12:
During week-2 an amplified pattern across the
northern U.S. is forecast with anomalous 500-hPa ridging in the east and
troughing for the west. Temperature-related hazards are anticipated with this
pattern, with a slight risk of much above-normal temperatures for parts of the
Northeast on September 6-7 and a slight risk of much below-normal temperatures
for portions of the Northern Intermountain Region and Northern Rockies
September 8-10. Both the GEFS and ECMWF ensemble guidance generally favor this
solution, with the biggest difference being ECMWF guidance extending positive
500-hPa height anomalies further south. Both aforementioned warm and cold
hazards are supported by the GEFS probabilistic extremes guidance for the 85th
and 15th percentiles of daily maximum and minimum temperatures respectively.
Also of concern during week-2 is the potential for tropical cyclone related
impacts to the southeastern U.S. around September 8-10 tied to a tropical wave
currently exiting the African coast. As of 2 PM EDT this system is currently
given a 50% chance of undergoing tropical cyclogenesis in the next 5 days by
NHC. The GEFS has been reasonably consistent with its forecasts the last two
days with this system in the vicinity of the southeastern coast during the
second half of week-2. The 00 UTC operational ECMWF features the system, but
has an interesting solution that out ahead of it spins up another tropical
cyclone with apparent frontal origins off South Carolina on the 7th and 8th of
September. Consideration was given to a heavy rainfall hazard forecast for the
aforementioned dates across the Southeast, but left off the map due to lack of
model consensus, the substantial forecast lead time, and the initial
disturbance not even entering the Atlantic as of yet. The forecast evolution
of this system will continue to be monitored closely over the course of the
week for any potential hazardous impacts to U.S. interests.
According to the U.S. Drought Monitor, the coverage of severe or greater
drought decreased slightly to 7.41 percent from 7.71 percent. Improvements were
realized across central Texas and the Tennessee Valley.
Click here to see a display of the GFS Ensemble Forecasts
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.