Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
248 PM EDT Fri Aug 16 2019
Valid 12Z Mon Aug 19 2019 - 12Z Fri Aug 23 2019
...Weather Pattern Overview...
A zonal upper level flow pattern is expected across the
north-central U.S. with a broad upper level ridge over the
southern tier states to start the work week. By mid-week, the
pattern is expected to become more amplified as a powerful low
pressure system develops off southeast Alaska, driving an upper
level ridge to develop up the Rockies and into the Canadian
Prairies and shunting low pressure toward eastern Canada. By the
end of the week, a cold front associated with the eastern Canadian
trough/low is expected to have crossed much of the eastern U.S.
with the upper level trough axis situated over the northeast U.S.
...Guidance/Predictability Assessment...
There is good overall deterministic model and ensemble agreement
with the overall synoptic scale pattern through the period with
details to the main two lows (one moving into southeast AK Tuesday
and the other crossing eastern Canada middle to late in the week)
differing particularly with magnitude of the parent low and timing
of amplifying shortwave troughs around these lows. The GFS remains
the deepest with the eastern low as it crosses northern Ontario
from the 20th to the 21st which slows its progression toward
Labrador and makes for less troughing in the northeast U.S. for
Days 6/7. The 00Z ECMWF deterministic continues to eject the
trough across the Canadian Rockies on the 22nd/Day 6 faster than
the 00Z ECENS mean which is east of the 00Z/06Z GFS/GEFS trough
axis. To address these differences, the medium range forecast was
based mainly on a deterministic model blend with slightly greater
weighting towards the ECMWF through Day 5, and then heavily toward
the GEFS and EC means for Days 6 and 7.
...Sensible Weather...
Temperatures are expected to remain above average across a large
portion of the nation into Wednesday with cooler than average
temperatures expected to spread east from the Plains to the
northeast downstream of the developing ridge over the Rockies and
warmer than normal conditions upstream. The heat is expected to be
most pronounced across the southern High Plains Monday with highs
of 10 to 15 degrees above normal. This will equate to widespread
triple digit heat for those areas. Cooler and less humid
conditions will likely be in place across much of the
north-central U.S. and extending to the East Coast to close out
the week after the passage of the cold front while the west
remains several degrees above normal.
Heavy rainfall is expected to be quite limited across the central
and eastern U.S. given a progressive cold front, though there are
indications the western end of the front may be slower over the
southern Plains where enhanced heat and humidity could cause local
issues due to heavy rain Wednesday into Friday.
Jackson
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
Hazards:
- Heavy rain across portions of the Central Plains and the Middle
Mississippi Valley, Wed-Fri, Aug
21-Aug 23.
- Severe weather across portions of the Upper Mississippi Valley
and the Northern Plains, Mon, Aug
19.
- Flooding occurring or imminent across portions of the Southeast
and the Northern Plains.
- Excessive heat across portions of California and the Southwest,
Wed-Fri, Aug 21-Aug 23.
- Excessive heat across portions of the Central Plains, the Lower
Mississippi Valley, the Tennessee
Valley, the Middle Mississippi Valley, the Southeast, the Southern
Plains, and the Ohio Valley,
Mon-Wed, Aug 19-Aug 21.
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