Valid Monday April 23, 2018 to Friday May 04, 2018
US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM
EDT April 20 2018
Synopsis: The 3-7 day period is likely to begin
with mid-level low pressure over the Southeast, supporting a strong storm
system which is forecast to impact the East Coast. The temperature patterns in
Week-2 are expected to become more moderate compared to past few weeks. Mid
-level high pressure is likely over much of the CONUS, minimizing chances for
high impact events. Two surface low pressure systems are expected to impact the
Aleutians and southern coast of Alaska, leading to a fairly active 3-7 day
period for the region. Mid-level low pressure is forecast to weaken over Alaska
Flooding possible across portions of
the Northern Plains.
Flooding occurring or imminent across portions of the Lower Mississippi
Valley and the Northern Plains.
Flooding likely across portions of the Upper Mississippi Valley and the
High winds across portions of the Southeast and the Mid-Atlantic, Mon-Tue,
Apr 23-Apr 24.
Heavy precipitation across portions of the Alaska Panhandle and mainland
Alaska, Mon-Tue, Apr 23-Apr 24.
High winds across portions of the Alaska Panhandle and mainland Alaska,
Mon, Apr 23.
High winds across portions of mainland Alaska and the Aleutians, Mon-Wed,
Apr 23-Apr 25.
High significant wave heights for coastal portions of mainland Alaska and
the Aleutians, Mon-Wed, Apr 23-Apr 25.
Severe Drought across the Central Plains, the Central Rockies, the Central
Great Basin, the Northern Plains, the Southern Rockies, California, the
Southeast, the Southern Plains, and the Southwest.
For Monday April 23 - Friday April 27:
At the beginning of this period, a strong low pressure system will be
moving northward out of the Southeast along the East Coast, after impacting the
lower Mississippi Valley prior to this period. Heavy rain (greater than 1.5
inch in 24 hours) is forecast along the Southeast and into the Mid-Atlantic for
Apr 23-24, with the southern Appalachians most likely to receive up to 4
inches. Model guidance shows this system tracking along the coast longer than
previously expected, so the affected area reaches further north than in prior
forecasts. Coastal regions are also forecast to experience high winds (greater
than 30 knots), Apr 23-24. A second storm system is expected to move
southeastward out of the Great Lakes region immediately after, possibly
bringing more rain to the Mid-Atlantic; however, rainfall totals for that
system are likely to remain below 1 inch.
The rest of the period looks relatively quiet for the majority of the lower
48. A frontal system is likely to move over the central U.S. during the
beginning of the period, though all impacts from the system are forecast to
remain below hazardous criteria at this time. Surface high pressure moving
southward from Canada is expected result in a drier pattern for much of the
central and eastern CONUS.
Mid-level troughing is forecast to move over Alaska during the 3-7 day
period, likely supporting an unsettled pattern for the region. At the beginning
of the period, surface low pressure in the Gulf of Alaska is forecast to bring
heavy precipitation (greater than 2 inches per 24 hours) on Apr 23-24 to the
southeastern Alaska coast and parts of the Panhandle. Most of this
precipitation is expected to fall as rain, though snow is possible for areas at
higher elevations. High winds are expected to accompany the heavy precipitation
along the coast for Apr 23. The other strong surface low pressure system (976
hPa) in the Bering Sea is forecast to move eastward across the Aleutians and
parts of mainland Alaska. The Aleutians are likely to experience high winds and
significant wave heights (exceeding 20 feet) as the system moves through, Apr
For Saturday April 28 - Friday May 04: Mid-level ridging and a more zonal
pattern limit the risk of in high impact events for the lower 48 in Week-2.
Model guidance does show agreement in a closed low pressure system moving
inland from the western coast toward the middle of Week-2, which could cause
some unsettled patterns for the western half of the US. However, spread in
ensemble members between the GFS and ECMWF shows uncertainty of the placement
of this system as it tracks across the CONUS, precluding a forecast for any
associated hazards at this time.
The mid-level pattern is expected to deamplify for Week-2 over Alaska,
leading to less storminess for the region. No hazards are currently posted for
Week-2 in Alaska.
The US Drought Monitor, valid on April 17, shows a 1 class improvement in
drought coverage over the Northern Plains. There was degradation in drought
conditions over parts of the Four Corners Region. Overall, the severe drought
coverage during the past week has slightly decreased to 16.33% from 16.69% last
Forecaster: Christina Finan
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.