Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
1208 PM EDT Sun Oct 20 2019
Valid 12Z Wed Oct 23 2019 - 12Z Sun Oct 27 2019
...Guidance/Uncertainty Assessment and Weather
Highlights/Threats...
An energetic pattern supports several significant lower 48 weather
systems this week.
A lead upper trough will lift through the Northeast midweek as a
main deepened surface low works into Canada. Lingering
rains/runoff issues over the Northeast may be enhanced by
interaction of a developing frontal wave from the Mid-Atlantic,
which will likely merge with the extratropical remnants of
Tropical Storm Nestor from off the East Coast.
Guidance also agrees that the flow pattern will meanwhile
reamplify well upstream as upper impulses/jet energies dig
progressively inland over the rapidly cooling West to support some
heavier snows into the north and central Rockies Wed/Thu.
Height falls should then act to carve out an amplified central
U.S. upper trough later this week. Pattern evolution uncertainty
grows quickly thereafter, resulting in low forecast confidence for
the eastern half of the country. Latest guidance continues to
indicate two possible scenarios by this weekend: (1) A more
amplified upper trough draws in tropical moisture from the Gulf
and results in a low pressure system that spreads heavy rainfall
well inland, as indicated by the ECMWF and CMC solutions; or (2)
less flow separation between the northern and southern streams
will keep a cold front moving steadily across the eastern U.S., as
indicated by the GFS. All of the ensemble means (GEFS, EC mean,
CMC mean) so far are more in line with the second scenario,
however.
The WPC morning grids were derived from a blend of yesterday's 12Z
ECMWF, 00Z EC mean, the 06Z GFS and 06Z GEFS together with WPC
continuity for Days 6 and 7. But for Days 3 to 5, the 00Z ECMWF
was used in instead of yesterday's 12Z ECMWF.
Kong/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