Short Range Forecast Discussion
NWS Weather Prediction Center College Park MD
412 PM EDT Fri Oct 15 2021

Valid 00Z Sat Oct 16 2021 - 00Z Mon Oct 18 2021

...Severe weather and Excessive Rainfall on tap from the Mid-South to the
Great Lakes today; severe storms possible in the Northeast on Saturday...

...Fresh injection of cooler than normal temperatures overtaking the
Rockies and Heartland arrives in the Tennessee and Ohio Valleys on
Saturday; abnormally warm along the East Coast...

...Elevated fire weather conditions in Southern California; wet pattern
returns to the Pacific Northwest

The primary weather maker to close out the week is an elongated frontal
boundary stretching from Southeast Canada to the Southwest with embedded
waves of low pressure along the front. Scattered showers and thunderstorms
are beginning to spring up along the front, with increasing storm coverage
expected through today. The Storm Prediction Center continues to monitor
severe potential with these developing thunderstorms, particularly within
the Slight Risk (level 2/4) area from northern Arkansas and through the
Ohio Valley into the eastern Great Lakes today. Isolated severe wind
gusts, hail, and isolated tornadoes are possible, and a Severe
Thunderstorm Watch remains in effect until tonight across parts of the
Mid-South. There is also a Marginal Risk for Excessive Rainfall (level
1/4) over much of the same area, where isolated flash flooding is possible
given the moist pre-frontal airmass in place. As an upper trough tracking
through the Midwest amplifies Friday night, one particular area of low
pressure will rapidly deepen as it tracks from the eastern Great Lakes
Friday evening into southeast Canada on Saturday. The storm system's cold
front will swing through the Northeast and Mid-Atlantic and focus showers
and thunderstorms on approach. Some storms could be severe in the
Northeast, which has led SPC to issue a Marginal Risk for parts of the
region. The front races into the northwest Atlantic Saturday night and a
dome of high pressure builds in behind it, leading to the arrival of a
drier and seasonally cooler temperatures on Sunday.

Farther west, a chilly and dry air-mass lies in wake of this elongated
cold front tracking through the eastern half of the Lower 48. Today, much
below normal temperatures are engulfing the Intermountain West and the
Heartland. Chilly, sub-freezing overnight temperatures are possible over
portions of the Plains states which may impact sensitive vegetation and
crops in this region. Accordingly, Freeze Warnings, Freeze Watches, and
Frost Advisories extend from the Dakota/Minnesota International Border all
the way to the Southern Plains. Fortunately, a warm up arrives after
tonight over much of the Central U.S. as warm downslope flow beginning on
Saturday moderates the cool airmass in place to yield slightly above
average temperatures. In contrast to the cool weather in the Plains, the
airmass east of the front remains unseasonably warm; numerous daily record
warm minimum temperatures are likely to be challenged tomorrow morning
over the Mid-Atlantic and Northeast. The passage of the front on Sunday
will put an end to any record warmth chances in the East.

Elsewhere, a strengthening upper level ridge allows for drier and milder
temperatures to set up shop over the western third of the CONUS. Santa Ana
winds in Southern California combined with low relative humidity levels
have led to the issuance of Red Flag warnings and an Elevated Risk for
fire weather conditions. Ridging over the Intermountain West will keep
Santa Ana winds in the forecast into Saturday, prolonging the favorable
fire weather conditions in place there. Farther north, the coastal areas
of the Pacific Northwest begin to feel the affects of a deepening upper
trough in the Northeast Pacific as it siphons a ribbon of subtropical
moisture into western Washington. The Olympics and northern Cascades are
likely to contend with periods of rain just before an approaching frontal
system brings additional rainfall to western Washington and Oregon on
Sunday.

Asherman/Mullinax


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