US Day 3-7 Hazards Outlook
NWS Weather Prediction Center College Park MD
403 PM EDT Fri May 07 2021
Valid Monday May 10 2021 - Friday May 14 2021
- Heavy rain across portions of the Southeast, the Lower Mississippi Valley, and the Southern
Plains, Mon-Wed, May 10-May 12.
- Heavy rain across portions of the Southeast, Wed, May 12.
- Heavy rain across portions of the Mid-Atlantic, Thu, May 13.
- Heavy rain across portions of the New England, Fri, May 14.
- Flooding occurring or imminent across portions of the Ohio Valley.
The primary concern through the medium-range forecast period (Monday, May 10th through Friday, May
14th) will be for multiple areas of heavy rain over central and eastern portions of the U.S. A low
pressure center will be located over the Mid-Atlantic Monday morning with a trailing cold front
through the Southeast to the Southern Plains. The cold front will push to the southeast on Tuesday
before stalling north of the Gulf Coast and remain quasi-stationary. Multiple waves of low pressure
will move eastward along this boundary across the Southern Plains and into the Southeast through
Thursday. Widespread heavy rain is expected across the Southern Plains and Southeast Monday through
Wednesday as these disturbances move eastward and rich Gulf moisture is advected inland,
overrunning the quasi-stationary boundary. Opted for one large area for simplicity and to account
for uncertainty in where the heaviest rainfall may fall each day as the disturbances transverse the
boundary. The heavy rain will extend further eastward to include eastern portions of Georgia and
South Carolina on Wednesday as the waves progress to the east and one area of low pressure begins
to better organize off the coast of South Carolina. Previous heavy rain across much of the Southern
Plains and Southeast has contributed to high soil moisture, leaving many of these areas susceptible
to flooding from the additional heavy rainfall through the period. The low pressure center off the
Southeast coast will begin to lift to the north along the Atlantic Seaboard Thursday into Friday,
passing east of the New England Coast by the end of the period. Heavy rain is likely across eastern
portions of the Mid-Atlantic Thursday and into Southern New England and the southwest coast of
Maine on Friday as the low passes just offshore.
Elsewhere, cool, moist upslope flow behind the front draped across the South along with a trough of
low pressure moving southeastward over the Northern and Central Rockies will lead to the chance for
rain across the Central High Plains on Monday. Snow is also forecast for portions of the Central
Rockies and it is likely some of the precipitation over the Plains will mix with snow. Due to the
mixed nature of the precipitation and expected light nature of any snow accumulations, neither a
heavy rain nor snow outlook was included. Higher snow accumulations are possible in southeast
Wyoming and into the Colorado Front Range, but should remain below a hazardous threshold and
isolated to the higher mountain peaks.
For Alaska, a Pacific storm system will move into the Bering Sea by Thursday, with associated
frontal boundaries moving east across the Aleutian Islands and the Gulf of Alaska into Friday.
There is an indication that heavy rain is possible with this system from the Aleutian Islands east
across the Alaskan Peninsula and into southern mainland Alaska. However, significant differences
between the models with respect to both the timing and placement of the heavy rainfall preclude an
outlook area at this time.
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