Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
248 AM EDT Mon Apr 12 2021
Valid 12Z Thu Apr 15 2021 - 12Z Mon Apr 19 2021
...Central Rockies/High Plains Heavy Snow Threat...
...Guidance/Predictability Assessment...
The WPC medium range product suite was primarily derived from a
blend of well clustered guidance of the 18 UTC GFS/GEFS mean, 12
UTC ECMWF/ECMWF ensemble mean and the 01 UTC National Blend of
Models (NBM). Guidance is in better agreement than yesterday,
bolstering forecast confidence. Applied most blend weight to the
models days 3-5 (Thursday-Saturday). Shifted blend weights in
favor of the ensemble means and NBM days 6/7 (Sunday-next Monday)
amid growing forecast spread. This acts to maintain good WPC
continuity in an overall forecast scenario that seems in line with
latest 00 UTC guidance.
...Weather/Hazards Highlights...
A closed mean trough/low over the West and lead cold Canadian high
pressure (with temp anomalies ~10-20 degrees below normal) this
week should allow a potentially heavy upslope snow event over the
North-Central Rockies/High Plains linger into mid-late week. Some
deformation and terrain enhanced precipitation still remains
possible over parts of the Great Basin. Confidence is also
increasing on a moderate rain focus then gradually shifting into
the Plains Thursday-Friday.
Meanwhile, a wavy frontal boundary settles and lingers this period
into the northern Gulf of Mexico and vicinity to focus several
periods of moderate to heavy rains over Florida/Gulf Coast/Lower
Mississippi Valley/Southern Plains through the forecast period.
Timing and details remains uncertain with ejecting focus from
southern stream impulses, but the Central Gulf Coast states and
vicinity have had much above normal rainfall recently, so there
may be flooding concerns.
Farther north, recent guidance has trended stronger and less
progressive with a main upper trough/low over the Mid-Atlantic and
Northeast Thursday-Friday. Moderate to locally heavy rainfall can
be expected to accompany an associated front and surface low trek
across the region. There may also be some mountain snows over the
cooled Northeast. Ample coastal low genesis will also present some
maritime and coastal threats later week into the weekend.
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