Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EST Sat Nov 13 2021

Valid 12Z Sat Nov 13 2021 - 12Z Mon Nov 15 2021

...Low pressure formation tonight over New England will likely bring a
round of enhanced rain/wet snow and gusty winds across the region...

...A lull in the active weather today over the Pacific Northwest before
the next wave of heavy rain arrives on Sunday....

...An Alberta clipper will deliver another around of snow and gusty winds
across the northern tier states through the weekend...

Even as the large cyclonic circulation over the Great Lakes weakens and
retreats into Canada, one last piece of upper-level energy rotating around
the back side of the system is interacting with a secondary cold front to
produce an organized band of rain moving toward the Appalachians this
Saturday morning.  The rain is accompanied by temperatures falling into
the 30s together with wind directions shifting to the west as a large cool
air mass over the mid-section of the country moves into behind the cold
front.  By tonight, a low pressure center is forecast to form and
intensify rather quickly over New England as the cold front begins to exit
the East Coast.  Some thunderstorms could form later today over southern
New England as the low develops, and they could become strong.  In
addition, a burst of precipitation is forecast for interior New England
tonight following the passage of the low center.  The higher elevation
could see a burst of wet snow together with gusty winds right behind this
intensifying compact storm.

Shifting focus out west, onshore moisture flow from yesterday's
atmospheric river will continue to wind down this afternoon, however, the
potential for high rainfall rates of 0.5-0.75 inches per hour and flooding
associated with these heavy downpours will persist, especially across
steep terrain and burn scarred areas. As such, the Weather Prediction
Center has issued a Marginal Risk of Excessive Rainfall for portions of
the Pacific Northwest. A brief reprieve from the rain will occur early
Saturday before a second, stronger atmospheric river reaches the coastline
Saturday night, this time delivering 3-5 inches of rain in 24 hours to the
region. Given the already saturated soils from the previous days' rain and
the concern for more widespread rapid run-off and urban flooding, the
Weather Prediction Center has upgraded to a Slight Risk of Excessive
Rainfall for portions of extreme northwest Washington beginning Sunday
morning.

Further inland, a new low pressure center will organize over Alberta,
Canada tonight as the energy from the dissipating atmospheric river
progresses east. Reinforced by a shortwave trough aloft, this system will
deepen overnight as it moves southeast into the Northern Plains. Trailing
to the south of the low an associated warm front is expected to serve a
dual purpose: allow temperatures throughout the west and Great Plains to
rise 10 to 15 degrees above normal and provide instability for another
round of snow across the Northern Tier. Widespread snowfall totals of 2-4
inches are expected from eastern North Dakota to Michigan, while a
precipitation transition zone further west will allow for the development
of freezing rain and light ice accumulations from northeast Montana to
western Minnesota.

Elsewhere in the Central/Southern Plains, dry and breezy conditions
coinciding with low values of relative humidity has prompted the issuance
of an Elevated Risk of fire weather by the Storm Prediction Center through
Saturday morning, as these conditions could allow any fires that ignite to
spread rapidly.

Kong/Zavadoff


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