Valid Thursday September 26, 2019 to Wednesday October 02, 2019
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT September 18 2019Synopsis
: Mid-level high pressure is
favored for the eastern half of the lower 48 states and Alaska. Mid-level low
pressure is predicted for the western half of the contiguous U.S., potentially
bringing anomalously cool temperatures to the area. A strong storm is predicted
to form over the Bering Sea at the beginning of Week-2, which may impact the
west coast of mainland Alaska. Hazards
- Slight risk of
much below normal temperatures across parts of the western half of the CONUS,
Fri-Mon, Sep 27-30.
- Slight risk of heavy precipitation for portions of the West Coast states,
Thu-Sat, Sep 26-28.
- Slight risk of heavy precipitation across parts of the Central Plains and
Upper and Middle Mississippi Valley, Thu-Mon, Sep 26-30.
- Slight risk of high winds across parts of the Great Plains, Thu-Sat, Sep
- Slight risk of high winds across parts of the Central and Southern Plains
Plains, Sat-Mon, Sep 28-30.
- Slight risk of high winds for coastal parts of western mainland Alaska,
Wed-Fri, Sep 25-27.
September 21 - Wednesday September 25: WPC Days 3-7 U.S.
Hazards For Thursday September 26 -
Wednesday October 02:
There are significant differences between the 6Z
GEFS and 0Z ECMWF, especially during the beginning half of the period. The 6z
GEFS indicates mid-level ridging building across the eastern third of the CONUS
at the beginning of Week-2, whereas the 0Z ECMWF ensemble shows amplified
troughing. Due to consistency in the model solutions over the past several
days, the forecast favors and reflects the 0Z ECMWF ensemble solution. A slight
risk of heavy precipitation is introduced today for parts of the West Coast
states, Sep 26 to 28, where the ECMWF reforecast tool indicates a 20 percent
chance or greater of 3-day rainfall totals reaching or exceeding the upper 85th
percentile and one inch. Amplified troughing across the West in combination
with the potential of moisture surges associated with Tropical Storms Mario and
Lorena in the Eastern Pacific Ocean may support localized heavy rainfall across
parts of the Southwest at the beginning of Week-2. Given the high model
uncertainty regarding the evolution of the mid-level trough and whether these
tropical storms will track northward enough to support a moisture surge, a
related heavy precipitation hazard is not highlighted at this time but will be
monitored in the upcoming days.
The aforementioned mid-level amplified troughing across the West is
anticipated to continue throughout much of Week-2. This pattern is expected to
support a slight risk of much below normal temperatures across parts of the
western half of the CONUS, Sep 27 to 30. The ECMWF reforecast tool indicates a
20 percent chance or greater of some areas falling to the lowest 15th
percentile and freezing. This could be the first freeze event of the fall for
some areas in the West.
There is a potential for mid-level ridging to build across parts of the
eastern CONUS at the beginning of Week-2. Both the ECMWF and GEFS reforecast
tools show a 20 percent chance or greater for areas across the Eastern
Seaboard, Southeast, and Southern Plains reaching the uppper 85th percentile.
However, since the expected temperatures do not reach the NWS heat advisory
criteria, additional excessive heat risk areas are not designated at this time.
Surface low pressure is anticipated to form across the Rockies and shift
eastward during Week-2. The 0Z ECMWF indicates significantly stronger and
widespread low pressure across the central CONUS associated the with the
mid-level trough, compared to the 6Z GEFS. Despite the model disagreement,
there has been good day to day model consistency in both the GEFS and ECMWF
indicating increased chances for heavy preicpitation across the Mid-West during
the Week-2 period. A slight risk of heavy precipitation (3-day rainfall totals
reaching or exceeding the upper 85th percentile and one inch) is highlighted
across parts of the Central Plains and Upper and Middle Mississippi Valley for
Sep 26 to 30. The expected heavy rainfall may exacerbate or prolong flood
conditions in the Missouri River basin. Parts of the Missouri River basin is
already at 200 percent or greater of their normal rainfall for the last 30 days
according to gauge amounts.
In addition to the forecast heavy rainfall across parts of the Mid-West,
surface low pressure over the Rockies and Great Plains supports a slight risk
of high winds across parts of the Great Plains, Sep 26 to 28. The slight risk
of high winds is isolated to the Central and Southern Plains Sep 28 to 30.
Sustained wind speeds in the highlighted areas may reach the upper 85th
percentile and 20 mph.
There is good model agreement indicating the possible formation of a strong
storm system in the Bering Sea and tracking eastward, approachnig the west
coast of mainland Alaska by the beginning of Week-2. A slight risk area is
highlighted across the west coast of mainland Alaska, Sep 25 to 27. The 6Z
deterministic GFS shows the potential for some areas to experience sustained
wind speeds of 35 mph or greater. This storm may also support strong southerly
onshore flow to parts of the South Coast of Alaska, leading to localized heavy
precipitation. However, due to the high model uncertainty regarding associated
precipitation impacts, a heavy precipitation risk is not designated for Alaska
at this time.
Forecaster: Melissa Ou
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.
Week-2 Probabilistic Extremes Tool
GFS Ensemble Forecasts