Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Thu Jan 12 2023

Valid 12Z Thu Jan 12 2023 - 12Z Sat Jan 14 2023

...Atmospheric river expected to impact areas from northern California to
coastal Pacific Northwest through early Saturday...

...Threat of severe weather increasing across the interior Southeast later
today...

...Heavy snow possible across northern New England early Friday along with
a period of freezing rain/sleet...

The relentless parade of cyclones that have been targeting California in
the past week is forecast to shift focus and impact areas farther to the
north.  A large cyclone well off the West Coast will direct the
atmospheric river in a more northerly course further up and parallel to
the West Coast during the next couple of days.  This will orient the
threat of heavy precipitation from northern California northward along
coastal Pacific Northwest through early Saturday, with northwestern
California having the highest chance of receiving excessive rainfall. 
This shift in the course of the atmospheric river is related to a change
in the weather pattern across the U.S., allowing a ridge of high pressure
to build over the western U.S. while a rather strong low pressure system
moves swiftly through the eastern half of the country.  While the
strengthening ridge over the western U.S. will help keep the moisture from
moving much farther inland, it will also keep the heaviest precipitation
locked in place across northern California to coastal Pacific Northwest. 
By Friday night, this somewhat stagnant pattern will show signs of
breaking down, allowing the next Pacific cyclone to direct yet another
surge of atmospheric river toward California by Saturday morning.

Meanwhile, a low pressure system developing over the mid-section of the
country is expected to intensify and track northeastward across the Ohio
Valley today, and then across New England on Friday.  Thunderstorms
currently erupting over the mid-Mississippi Valley are forecast to shift
east-southeastward and reach the interior Southeast later today where an
enhanced threat of severe weather is forecast into this evening.  The
hazards associated with these thunderstorms are frequent lightning, severe
thunderstorm wind gusts, a few tornadoes, and a minimal threat of hail. 
Showers and embedded heavy rain and thunderstorms will then expand up the
East Coast tonight ahead of a strong cold front.  Meanwhile, colder air to
the north of the system will support snow across interior/northern New
England from tonight to Friday morning.  The snow could become heavy as
the low pressure center approaches, along with a period of freezing rain
and/or sleet.  The wintry precipitation could change to plain rain during
the day on Friday.  Colder air wrapping around the low center will then 
change the rain back to snow as the system departs into Canada later on 
Friday.  Colder air surging in behind the storm will also initiate 
lake-effect snow mainly downwind from the lower Great Lakes by early on 
Saturday.  Blustery winds developing behind the system across the Great 
Lakes and down into the Ohio Valley will be accompanied with mixed rain 
and snow wrapping southward across these areas toward the spine of the 
Appalachians.  Farther south into Florida, showers and thunderstorms will 
accompany the passage of the cold front on Friday before colder air arrives 
from the northwest Friday night.

Kong


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