Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1202 PM EDT Fri Sep 27 2019
Valid 12Z Mon Sep 30 2019 - 12Z Fri Oct 04 2019
...Heavy rainfall potential from the southern High Plains into
Great Lakes early to middle of next week...
...Anomalous warmth to persist over the central to eastern U.S.,
while very chilly conditions remain across the northern and
northwestern states ...
...Pattern Overview and Guidance/Uncertainty Assessment...
Through the extended period a highly amplified mean trough will be
positioned over the West with a broad ridge over the South and
Southeast. This pattern will largely remain unchanged over the
next 7 days; which will keep a much cooler airmass over the
Pacific Northwest and Intermountain Regions and a warmer one over
the central and eastern states. A wavy front is forecast to
gradually move across the central and eastern U.S. providing a
focus for precipitation from the Southern Rockies/High Plains,
through Midwest and Great Lakes regions to the Northeast.
Ensemble consensus remains quite good and the latest runs of the
deterministic guidance continues to be faster with ejecting energy
from the western trough eastward across the north-central U.S.
toward the Northeast. The Canadian model is persistent with
focusing more energy with the trough over Canada/Northeast U.S.
than others, but still usable in small quantities. The forecast
comprised of a blend of the 00Z ECWMF, 00Z/06Z GFS with lesser
weighting of the 00Z UKMET/CMC and the ensemble means.
...Weather Highlights/Threats...
The Heavy snow/rain over the Northern Rockies will taper off by
Monday as the the surface low pressure system moves further into
the Northern Plains. The trailing front will become more zonal
thanks to the ridge over the Southeast. Flow around the western
periphery of the Ridge will draw tropical moisture from the
eastern Pacific Ocean northward along the boundary, aiding in the
development of scattered to widespread precipitation spanning from
New Mexico to Maine. Multiple days of precipitation, potentially
heavy at times, over nearly the same locations may increase the
threat for flash flooding. This is especially the case for
portions of the Central Plains and Great Lakes.
Deep-layer easterly flow, associated will the decaying Tropical
Storm Karen, will promote an increase in rain/showers over
Florida. Please monitor NHC forecasts for the latest information
regarding Karen.
The western U.S. into Northern Plains are expected to have daily
temperatures averaging 10-25F below normal with localized areas in
Montana seeing highs at least 30F below normal. Daily records for
cold highs are most likely on Sunday but some are possible in the
days to follow. Many locations from the Gulf Coast to New England
will be averaging 10-20F warmer and numerous daily records may be
broken. As the pattern aloft begins to trend less amplified,
expect a gradual moderation of chilly western U.S./northern Plains
temperatures. However, record highs/warm lows remain a distinct
possibility over the southeastern U.S. through late next week.
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