Valid Sunday April 23, 2017 to Thursday May 04, 2017
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT April 20 2017Synopsis
: A surface low pressure system is
forecast to move eastward across the southeastern quarter of the CONUS at the
beginning of the period, exiting the Southeast coast by Apr 25. Meanwhile, a
storm system is anticipated to form over the Northern Plains by April 24 and
track across the northern tier, exiting the Great Lakes by Apr 26. An area of
upper-level low pressure is expected to develop over the western U.S. early
next week and persist through at least the early part of Week-2. Multiple
surface low pressure systems are forecast to move across the Gulf of Alaska
during the next two weeks. Hazards
Summary For Sunday April 23 - Thursday April 27:
- Heavy precipitation
across portions of the Pacific Northwest, Mon-Wed, Apr 24-Apr 26.
- Heavy precipitation across portions of the Central Rockies and the Central
Plains, Wed, Apr 26.
- Heavy rain across portions of the Southeast and the Mid-Atlantic, Sun, Apr
- High winds across portions of the Central Rockies, the Central Plains, and
the Northern Plains, Mon-Tue, Apr 24-Apr 25.
- Much above normal temperatures across portions of the desert Southwest,
Sun, Apr 23.
- Much above normal temperatures across portions of the Southern Plains,
Tue-Wed, Apr 25-Apr 26.
- Heavy rain across portions of the Great Plains and Mississippi Valley,
Fri-Sat, Apr 28-Apr 29.
- Slight risk of much below normal temperatures across parts of the western
half of the CONUS, Fri-Sun, Apr 28-Apr 30.
- Slight risk of much above normal temperatures for portions of the Southern
Plains, Fri-Sat, Apr 28-Apr 29.
- Moderate risk of much above normal temperatures for portions of the
Southern Plains, Fri-Sat, Apr 28-Apr 29.
- Slight risk of much below normal temperatures for portions of the North
Slope of Alaska and the Northwest coast of Alaska, Fri-Sun, Apr 28-Apr 30.
- Slight risk of much above normal temperatures for portions of the Southeast
and the Mid-Atlantic, Fri-Sun, Apr 28-Apr 30.
- Severe Drought across the Lower Mississippi Valley, the Tennessee Valley,
Hawaii, the Northeast, California, the Southeast, the Southern Appalachians,
the Southern Plains, and the Southwest.
- Flooding possible across portions of the Central Plains, the Lower
Mississippi Valley, the Southern Plains, the Middle Mississippi Valley, the
Upper Mississippi Valley, and the Great Lakes.
- Flooding occurring or imminent across portions of the Middle Mississippi
Valley, the Northern Plains, and the Northern Great Basin.
- Severe Drought across parts of Arizona, California, the southern Great
Plains, Ozarks, the eastern U.S, and Hawaii.
A shortwave trough is forecast to advance east across the southeastern
quarter of the CONUS this weekend into early next week. This feature may bring
heavy rain (2 inches of rainfall or greater in a 24-hour period) to parts of
the Southeast and the Mid-Atlantic on April 23.
An upper-level trough is likely to develop across the western U.S. next
week. A relatively wet pattern can be expected next week throughout the Pacific
Northwest, northern Great Basin, and north-central Rockies due to the trough
aloft. An area across the Pacific Northwest is highlighted for potential for
heavy rain and snow at the highest elevations for April 24 to 26. Localized
areas may receive 2 inches or greater of liquid equivalent in a 24-hour period.
The amplifying upper-level trough and the development of multiple surface
lows across the high Plains are forecast to result in periods of high winds
(gusts above 40mph) for parts of the western U.S. and high Plains, April 24 to
Deterministic model runs continue to indicate a shortwave trough ejecting
onto the Great Plains by April 26, with lee side cyclogenesis. Locally heavy
rain and high elevation snow (one inch or greater of liquid equivalent in
24-hours) is expected to develop across the Central Rockies and the Central
Plains on April 26 as a low pressure system interacts with increasing low-level
moisture from the Gulf of Mexico. The longwave pattern favors a multi-day
outbreak of severe weather across the central U.S. next week. However, the
Storm Prediction Center states that confidence is too low to define a specific
area at this time.
Amplified mid-level troughing is forecast to build across the majority of
the western half of the CONUS at the beginning of the period. This pattern
supports increased chances for much above normal temperatures across portions
of the desert Southwest on April 23. Maximum temperatures near or above 100
degrees F can be expected in the outlined area and these maximum temperatures
are 10 to 15 degrees above-normal for late April. Much above-normal
temperatures are expected to shift east to the southern Great Plains on April
25 and 26 as downslope flow results in maximum temperatures warming into the
low to mid 90s (degrees F). For Friday April 28 - Thursday
Model guidance remains consistent with its forecast of an
upper-level trough centered over the west-central U.S. at the beginning of
Week-2. The position and amplitude of this upper-level trough coupled with
enhanced moisture return from the Gulf of Mexico signal an increasing risk of
heavy rainfall (1 to 2 inches, locally more) and the potential for severe
thunderstorms across the central U.S. on April 28 and 29. The outlined hazard
area for heavy rainfall is based on 48-hour precipitation amounts from the
deterministic 0/6Z GFS and 0Z ECMWF models and their ensemble means which are
in good agreement for days 8 and 9 as well as the GEFS Reforecast Tool. The
GEFS Reforecast Tool indicates increased chances for potential heavy rain
across the Lower Mississippi valley for the rest of week-2 as the mid-level
trough shifts eastward. Models show the trough becoming less amplified toward
the middle of week-2. This region will be monitored in the upcoming days. This
trough also supports a slight risk of much below normal temperatures across
parts of the western half of the CONUS April 28 to 30. The highlighted area
indicates at least a 20 percent of freezing temperatures which could have an
impact to sensitive vegetation.
Downstream of the amplified mid-level trough, amplified mid-level ridging
is expected to build across the eastern half of the CONUS. This pattern
supports a slight to moderate chance of much above normal temperatures across
the Southern Plains April 28 to 29 and across the Southeast and Mid-Atlantic
April 28 to 30. These areas may experience maximum temperatures reaching the
85th percentile and temperatures reaching 90 Deg F or greater.
Surface high pressure is predicted to develop across northern mainland
Alaska from the beginning of week-2 until at least the middle of week-2. This
supports a slight chance of much below normal temperatures across the North
Slope of Alaska and the Northwest coast of Alaska April 28 to 30. The GEFS
Reforecast Tool indicates the potential for this area experiencing minimum
temperatures reaching the lowest 15th percentile and less than zero degrees F.
According to the U.S. Drought Monitor released on April 20th (using data
through 8am Eastern time, April 18th), coverage of severe, or greater
intensity, drought throughout the CONUS remains the same as last week (1.44
percent). This remains the lowest coverage of D2-D4 drought over the CONUS
since Aug 2010.
Forecaster: Melissa Ou
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.