Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
228 AM EDT Mon Apr 29 2019
Valid 12Z Thu May 02 2019 - 12Z Mon May 06 2019
...Southern Plains to Lower Mississippi/Ohio Valleys Severe Storm,
Heavy Rain and Flash Flood/Flood Threat into Thursday...
...Overview and Assessment of Model/Ensemble Guidance and
Predictability...
It remains the case that a large closed upper circulation settles
over western Canada this week as a series of northern stream
troughs with height falls and swaths of precipitation dig into the
Northwest and eastward over the wintry Rockies then U.S. northern
tier. There remains potential for some degree of phasing with a
southern stream flow of impulses/height falls working underneath
during this period from the Pacific inland over the U.S. southern
tier. The GFS/GEFS/FV3 have tended to be on the progressive side
of the full envelope of solutions while recent ECMWF runs and to a
lesser extent ECMWF ensembles and UKMET have been on the slower
side of the forecast envelope. The WPC medium range product suite
was mainly derived from a composite of the ECMWF/ECMWF ensemble
mean. This considers blocky upstream flow and inherent slow nature
of initially closed lows.
...Weather Highlights/Threats...
Dynamic troughing crossing the n-central U.S. and cooled
temperatures favors some early May Upper Midwest/Great Lakes
snows. A lead and wavy frontal system will progress late week
across the central then eastern U.S. Deepening inflow/moisture
from the Gulf of Mexico will feed into convectively active warm
sector meso-boundaries as well as a stark baroclinic zone overtop.
Strong to severe thunderstorms with some heavy rain and flash
flooding/flooding potential will threaten the Southern Plains and
Lower Mississippi/Ohio Valleys Thursday. Flooding remains possible
as particularly the Mississippi Valley has had flooding concerns
for weeks, and with the convective nature of the precipitation
flash flooding is possible as well. Less defined activity presses
over the East and South into Friday/Saturday. The front shifts and
stalls mainly offshore from the weekend into early next week in a
drier post-frontal pattern as new upstream trough energies with
more limited precipitation work back into the West in a continued
split flow regime.
Schichtel
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
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