Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Sun May 01 2022
Valid 12Z Wed May 04 2022 - 12Z Sun May 08 2022
...Model Guidance Evaluation...
Guidance remains varied with the progresion of a closed upper/low
tracking out of the West into the Plains and eastward, with the
GFS/GEFS mean still on the fast side compared to the best
clustered and slower 12/00 UTC solutions of the
ECMWF/UKMET/Canadian and ECMWF ensemble mean. Have leaned on the
slower side of the forecast envelope given nature of a separated
southern stream flow with embedded closed systems. This guidance
combination also seems to work well for much of the rest of the
lower 48 over medium range time scales. With the mean trough
settling near the West Coast, there is a general theme of a
leading shortwave reaching the coast Thursday and then another
feature arriving around Saturday. While recent models/ensembles
have varied wildly for later week/weekend amplitude, latest
guidance is converging on a more commom scenario.
...Pattern Overview and Weather/Threat Highlights...
An active spring pattern continues across much of the lower 48
states this week. A lead moderate rainfall focus will be with a
system working into the Northeast Wednesday, with cooling
post-frontal Canadian high pressure settling in the wake of the
main low. Meanwhile, a closed upper low/trough low forecast to
track through the central Rockies midweek and associated surface
system development will spread rain and higher elevation snow
across the northern-central Rockies and High Plains. This system
could produce some locally terrain enhanced totals. This system
will then emerge over the Plains and present potentially heavy
rainfall, with the WPC experimental Excessive Rainfall Outlook
still showing a Slight Risk over/near parts of the south-central
Plains Wednesday into Thursday. The threat signal is stronger than
average as the southern stream closed upper system and upper
diffluence/instability combine with increasing inflow of Gulf
moisture into a wavy front. The Storm Prediction Center is also
monitoring severe threats for this area Wednesday-Thursday.
Organized rain should translate generally eastward through the
rest of the week with low/frontal system progression that will
focus some widespread moderate to heavy amounts. The most likely
axis of highest rainfall totals extends from the mid-lower MS and
OH Valleys through the central Appalachians and Mid-Atlantic given
expected upper low/trough and surface system track and trailing
cold front.
Upstream, a moderately amplified upper trough and surface frontal
system forecast to reach the West Coast and progress inland next
Thursday into next weekend should bring a renewed precipitation
focus into the Pacific Northwest and then farther eastward. The
southern extent of precipitation will depend on the upper trough's
precise amplitude which has been quite uncertain recently in
guidance, but latest trends suggest that most moisture should be
confined to the northern half of the West. The upper
dynamics/surface front could reach far enough east to start
producing at least scattered rainfall over the northern High
Plains by next weekend. Expect renewed potential again by next
weekend to progress into and across the West with another frontal
surge as unsettling upper trough energies earnestly dig into the
region.
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