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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 2052Z Oct 24, 2020)
 
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Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
452 PM EDT Sat Oct 24 2020

Valid 12Z Tue Oct 27 2020 - 12Z Sat Oct 31 2020

...Record cold in the central US Tue before relenting...

...Heavy precipitation threat from the Southern Plains to the
southeastern third of the CONUS next week...


...Guidance Evaluation/Preferences...

In general, the longwave pattern is in agreement given the usual
spread in timing features and placement of precipitation.
Consensus favored a combination of the 00Z ECWMF/EC mean, 00/06
GFS and GEFS mean, and the 00Z UKMET/CMC. The ECWMF favored
precipitation further north and heavier across the Plains and
Midwest while the was a little lighter and south. The CMC was very
wet along the eastern Gulf Coast and later into the Southeast. A
combination of he above provided a middle of the road approach at
this time.

...Weather/Hazard Highlights...

An early season cold spell occurring over much of the West,
Rockies and Plains during the short range periods will linger into
Tuesday; the cold airmass is expected to moderate and move
eastward during extended period. Numerous daily low records, as
well as low maxes, will be possible Tuesday-- especially for
locations across the Southern/Central Plains were temperatures
will average 20 to upwards of 40 degrees cooler than normal for
late October. As the airmass moderates, daily values will still
hover around 5 to 15 degrees cooler than seasonal normal. Outside
of this cold airmass, temperatures will be roughly 5 to 10 degrees
warmer for parts of the Pacific Northwest, California and into the
Great Basin region.

Most of the active weather will be across the southern half of the
country. Warm, moist air will be transported north from the Gulf
ahead of a Tropical Depression #28.  Meanwhile, a series of waves
along a frontal boundary will lift/track east across the
Southern/Central High Plains early on and then progress toward the
Southeast and Mid-Atlantic regions. Within the warm sector,
scattered to widespread heavy rain will be possible Tuesday and
Wednesday primarily for parts Texas and Oklahoma, but also the
surrounding area. In the cold sector, snow along with sleet and/or
freezing rain near the transition zone is expected. As the system
moves across the Midwest/Mississippi Valley it will spread the
heavy rain/wintry precipitation along with it. Heavy precipitation
will be possible for the Southeast, Appalachians and the
Mid-Atlantic region this weekend as the front pushes across the
East Coast and a tropical storm weakens as it treks across the
Southeast.

Campbell

Additional 3-7 Day Hazards information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php


WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, winter weather outlook probabilities
and heat indices are at:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml