Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
246 AM EDT Tue May 03 2022
Valid 12Z Fri May 06 2022 - 12Z Tue May 10 2022
...Enhanced rainfall threat with closed low track into
Friday/Saturday from the Ohio Valley to the
Appalachians/Mid-Atlantic...
...Heavy snow threat from the Northwest to the North-Central Great
Basin/Rockies Friday into next week...
...Active pattern set to transition to Omega-style blocky pattern
by early next week...
...Pattern Overview and Guidance Evaluation...
Guidance remains varied with the progression of a closed upper low
tracking from the central to eastern U.S. this period, with the
GFS/GEFS mean still on the fast side compared to the better
clustered and slower recent ECMWF/UKMET/Canadian and ECMWF
ensemble mean solutions. The WPC forecast continues to lean
towards the slower side of the forecast envelope, given
continuity, but also the general nature of a separated southern
stream flow with an embedded closed system. The 12 UTC ECMWF/ECMWF
ensemble mean seemed to offer a decent representation of the
slower guidance cluster, but the latest 00 UTC ECMWF offers new
uncertainty with a more northward track trend.
This less progressive 12 UTC ECMWF/ECMWF ensemble mean consensus
seemed to work well for the rest of the country and maintains good
WPC product continuity, though with more emphasis on the ECMWF
ensemble mean into day 6/7 amid growing forecast spread. There
remains a general theme of leading main upper troughing reaching
the coast Thursday, with a growing signal to develop and reinforce
an amplified mean upper trough over the West Friday into early
next week as part of a developing Omega style block over the lower
48 to also include downstream development of an amplified and
warming east-central U.S. upper ridge and stormy western Atlantic
closed low/trough.
...Weather/Threat Highlights...
A closed upper trough and well organized surface low/frontal
system is expected to track from the south-central Plains/lower
Mississippi Valley Friday to the Ohio Valley then
Appalachians/Mid-Atlantic over the weekend. The Storm Prediction
Center shows a threat for severe weather into Friday across
portions of the Lower Mississippi and Tennessee valleys. Strong
storms are also possible into the weekend with slow/steady
downstream track of the system. Upper diffluence, ample moisture
inflow, and instability will also offer a threat for enhanced
comma head and wavy lead/trailing frontal rainfall focus from the
mid-lower Mississippi and Ohio valleys to the
Appalachians/Mid-Atlantic.
Robust digging of a series of dynamic upper systems will lead to a
dramactic change over much of the West this period as an amplified
mean upper trough and wavy/well defined frontal systems become
established over the region Friday into next week. This will
support significant cooling and bring a widespread precipitation
focus from the Northwest through the north-central Great
Basin/Rockies to include a substantial and lingering threat for
heavy terrain focusing snows. These troughs will support
temperatures as much as 10-20 degrees below normal across a large
portion of the West. Upper dynamics and slow wavy frontal
translation should also support an emerging convection/rainfall
pattern with local runoff concerns across the north-central U.S.
by later weekend/early next week, albeit with less certain system
details at these longer time frames. This could lead to runoff
issues as the region has experienced quite a bit of rain in April.
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, experimental excessive rainfall
outlook, 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/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml