Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Fri Oct 18 2019
Valid 12Z Mon Oct 21 2019 - 12Z Fri Oct 25 2019
...Upper Midwest/Great Lakes Storm...
...Potential Tropical Cyclone Sixteen to threaten the Northeast...
...Heavy rain and mountain snow from the Cascades to the
North-Central Rockies...
...Guidance/Uncertainty Assessment and Weather
Highlights/Threats...
An amplified and generally progressive flow pattern will support
several significant weather systems over the lower 48 states next
week. The WPC medium range product suite was primarily derived
from a composite blend of reasonably well clustered guidance from
the GFS/ECMWF/UKMET/Canadian Monday and Tuesday in a pattern with
above normal forecast predictability, albeit with uncertainty with
track/interaction of Potential Tropical Cyclone Sixteen as per
NHC. Switched to quite compatable GEFS/ECMWF ensemble mean
guidance later next week in a period of gradually increasing
forecast spread, but with a pattern evolution offering at least
average predictability given decent guidance continuity and system
organizations.
A closed upper low/trough will lift from the Plains through
eastern North America early to mid next week. Deep surface
cyclogenesis into the Upper Midwest/Great Lakes will act to ramp
up winds and unsettled weather/wrap-back snow while also forcing a
lead frontal system and Gulf of Mexico moisture return to combine
with upper support to fuel a widespread swath of heavy
rain/convection across the east-central states. Activity over the
Northeast may be also significantly enhanced by
interaction/merging with a Mid-Atlantic to New England
extratropical coastal low and deepened moisture associated with
current Potential Tropical Cyclone Sixteen.
The pattern meanwhile reloads upstream as upper impulses/jet
energies/height falls work progressively inland over the
Northwestern U.S. early-mid next week that carve out another
amplified central U.S. upper trough mid-later next week. A series
of systems/frontal passages offer a risk of heavy rain and
mountain snow from the Cascades to North-Central Rockies. Below
normal temperatures will sweep down through the interior
West/Rockies then Central U.S. Temperatures will become 10-15
degress below normal over the n-central states as the post-frontal
high surges southward. Lead Gulf of Mexico moisture return into
the central Gulf Coast and lower MS/TN Valleys may fuel enhanced
rain/convection, with modest precipitation inland over the
east-central states including some threat of wrapping snows for a
cooling Upper Midwest.
Schichtel
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