Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
406 PM EDT Sun Oct 24 2021

Valid 00Z Mon Oct 25 2021 - 00Z Wed Oct 27 2021

...There is a High Risk of excessive rainfall over the Sierra Nevada
Mountains and a Moderate Risk of excessive rainfall over the Middle
Mississippi and Ohio Valleys through Monday morning...

...Heavy snow for the Sierra Nevada Mountains...

...There is an Enhanced Risk of severe thunderstorms over parts of the
Middle/Lower Mississippi and Ohio Valleys through Monday morning...

A strong storm just west of the Pacific Northwest Coast will impact the
West Coast over the next several days.  Strong onshore flow will stream
moisture into Northern/Central California, producing heavy rain and snow
over parts of California. Therefore, the WPC has issued a High Risk of
excessive rainfall over the Sierra Nevada Mountains through Monday
morning.  Significant and potentially life-threatening flash flooding
flash is expected with the storm. Some areas that normally do not
experience flash flooding will flood. Heavy snow is also forecast for the
Sierra Nevada Mountains through late Monday afternoon.  The excessive
rainfall threat lessens to a Slight Risk over parts of the Sierra Nevada
Mountains with a Marginal Risk over other parts of the Sierra Nevada
Mountains and parts of the Southern California Coast from Monday into
Tuesday morning.  The excessive rainfall threat ends on Tuesday for
California.

Moreover, rain and highest elevation snow will develop over parts of the
Pacific Northwest into the Northern Intermountain Region and continue into
Monday. On Monday, after the front passes, the snow levels will lower over
the Northwest portion of the country.  On Tuesday, rain and higher
elevation snow move into the Rockies, with rain developing over parts of
the Northern/Central High Plains by Tuesday evening.

Meanwhile, an area of low pressure over the Central Plains and associated
front will interact with moisture flowing northward over the
Plains/Mississippi Valley to produce showers and thunderstorms over the
region through Monday afternoon, with some storms becoming severe. 
Therefore, the SPC has issued an Enhanced Risk of severe thunderstorms
over parts of the Middle/Lower Mississippi and Ohio Valleys through Monday
morning. The hazards associated with these thunderstorms are frequent
lightning, severe thunderstorm wind gusts, hail, and a few tornadoes.
Furthermore, there is a 10% or greater probability of EF2-EF5 tornadoes
over parts of the region and a 10% or greater probability of wind gust of
65 knots or greater.  Additionally, there is a 10% or greater probability
of two-inch or great hail over parts of northeastern Missouri through
Monday morning. However, the severe thunderstorm threat is not the only
threat over the Midwest.  Heavy rain will develop along the front,
therefore, the WPC has issued a Moderate Risk of excessive rainfall with
the rain and thunderstorms over parts of the Ohio Valley through Monday
Morning. The associated heavy rain will create numerous areas of flash
flooding. Furthermore, many streams may flood, potentially affecting
larger rivers.

As the system moves eastward, the risk of severe thunderstorms weakens
slightly to a Slight Risk over parts of the Mid-Atlantic and the
Central/Southern Appalachians on Monday.  Also, rain will develop over
parts of the Great Lakes Sunday evening into Monday. The rain moves into
parts of the Northeast early on Monday.  On Tuesday morning, the area of
low pressure moves to the northern Mid-Atlantic Coast and off the New
England Coast by Tuesday evening. Overnight Monday into Tuesday, the low
aids in streaming moisture into the Northeast, producing heavy rain.
Therefore, the WPC has issued a Slight Risk of excessive rainfall with the
rain.  The associated heavy rain will create mainly localized areas of
flash flooding, with urban areas, roads, and small streams the most
vulnerable starting on Tuesday and going through Tuesday night.

Lastly, the front associated with the Pacific Northwest system moves out
of the Rockies and onto the Plains by Tuesday evening. The system will
produce rain and thunderstorms over the Plains on Tuesday evening.

Ziegenfelder

Graphics are available at
https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php