Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
156 AM EST Mon Mar 08 2021
Valid 12Z Thu Mar 11 2021 - 12Z Mon Mar 15 2021
...Late week heavy rain threat from the south-central Plains to
the Mid-South...
...Heavy snow threat for the south-central Great
Basin/Rockies/High Plains...
...Weather/Threats Highlights and Guidance/Predictability
Assessment...
An amplified and southern stream upper trough/closed low will
settle over the West/Southwest later this week into the weekend in
a pattern with above normal forecast predictability. System track,
deformation and upslope will favor some enhanced rain and higher
elevation snow over the south-central CA/Great Basin/Rockies/High
Plains along with advent of below normal temperatures. Lead
energies forecast to eject from the trough will support a quite
wavy and slow-moving south-central to Mid-South front whose Gulf
moisture and instability pooling will fuel a focus for locally
enhanced rainfall and training convection. Ahead of this
evolution, upper ridging will support much above normal
temperatures for the East into later this week. A cold front will
dig through the East later week into the weekend in response to
amplified northern stream upper trough passage.
A composite blend of reasonably well clustered guidance from the
18/00 UTC GFS/GEFS mean, 12/00 UTC ECMWF/ECMWF ensemble mean and
the 01 UTC National Blend of Models seems to offer a good forecast
starting point and continuity days 3-5.
Forecast uncertainty increases by later weekend when the Southwest
feature seems slated to eject to the south-central U.S.. Height
falls and instability may re-invigorate moisture inflow and heavy
precipitation potential over and onward from the south-central
U.S.. This would include a wintry threat focus for the
south-central Rockies/High Plains that has potential to spread
across the central Plains and Mid-MS Valley/Midwest by early next
week on the cooled northern edge of the expanding precipitation
shield with system progression and wrapping flow.
For this day 6/7 period, the 12/18 UTC GFS/GEFS are progressive
compared to the 12 UTC ECMWF/ECMWF ensemble mean and to a lesser
extent the 12 UTC Canadian. Prefer a solution on the less
progressive side of the full envelope of guidance closest to the
ECMWF ensemble mean considering flow separation and closed
trough/low nature. The 00 UTC ECMWF trended closer to the ECMWF
ensemble mean. The 00 UTC GFS/Canadian/GEFS mean have trended
significantly slower and more in line, bolstering forecast
confidence, but forecast spread and continuity remain less than
ideal.
Schichtel
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook 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