Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
402 PM EDT Mon Oct 21 2019
Valid 12Z Thu Oct 24 2019 - 12Z Mon Oct 28 2019
...Guidance/Uncertainty Assessment and Weather
Highlights/Threats...
Guidance agrees that the active flow pattern will reload over the
cooling/unsettled West Wed/Thu as digging upper impulse/jet
energies support some enhanced Rockies snows. Height falls should
then act to carve out an amplified central U.S. upper trough later
week. Pattern evolution uncertainty grows quickly thereafter,
resulting in low forecast confidence for the southern and eastern
U.S. Guidance continues to indicate two possible scenarios by
this weekend: (1) A more amplified upper trough draws in deep
moisture from the Gulf and results in a low pressure system that
spreads heavy rainfall well inland, as represented by ECMWF/UKMET
and CMC solutions; or (2) less flow separation between the
northern and southern streams will keep a cold front moving
steadily across the southern and eastern U.S., as represented by
recent GFS runs. Overall, the most recent operation models that
indicate scenario 1 show a trend toward a slower eastward ejection
of the amplified upper trough. On the other hand, the UKMET is
hinting at a tropical low center lingering off the Texas coast as
the upper trough approaches. The GEFS/EC/CMC ensembles are mixed,
with ECMWF ensemble members showing scenario 1 but with highly
variable forward motion of the associated upper-level shortwave.
With the consideration of the amplitude of the upstream upper
ridge, the next main upper trough should bring renewed cooling
with enhanced precipitation/mountain snows through the Northwest
then Rockies until next weekend. So, wavelength spacing with the
downstream system seems sufficient to allow for at least some
southern stream separation. WPC progs modestly lean the forecast
to show such potential. However, with the ensemble means continue
to support a less prominent system due to the high degree of
uncertainty, the new WPC prognostic charts now show a less
prominent frontal wave moving across the Southeast during the
weekend compared with previous progs.
Schichtel/Kong
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
- Heavy rain across portions of the Southeast, the Lower
Mississippi Valley, the Southern Plains,
and the Tennessee Valley, Thu-Fri, Oct 24-Oct 25.
- Heavy rain across portions of the Lower Mississippi Valley, the
Tennessee Valley, the Middle
Mississippi Valley, the Southern Appalachians, the Southeast, and
the Ohio Valley, Sat, Oct 26.
- Flooding likely across portions of the Pacific Northwest and the
Northern Great Basin.
- Much below normal temperatures across portions of the western
High Plains and the
Northern/Central Rockies, Mon, Oct 28.
- Enhanced wildfire risk across portions of southern California,
Thu, Oct 24.
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