Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
339 PM EDT Mon Apr 29 2019
Valid 12Z Thu May 02 2019 - 12Z Mon May 06 2019
...Flooding/Flash Flooding Threat in the Short Range Continues
into Thursday for the Southern Plains/Lower Mississippi Valley...
...16Z Update...
The overnight model guidance maintained a similar pattern as
described previously with the closed upper low in Canada and
troughing across the central U.S. Regarding the southern stream
upper low tracking through the eastern Pacific and into California
by early next week...the EC runs have been consistently slower
than the GFS runs for at least a couple of days. However, the last
couple of EC runs have been trending just a bit faster, and the
00Z GFS and mean trended slower, which made for much better model
agreement. Thus, was able to incorporate the 00Z GFS suite in this
forecast, along with the 00Z EC/EC mean, and the 00Z UKMET
(through day 5) and 00Z CMC, which all lined up well. The 06Z GFS
went against the trend, however, moving the low farther eastward
and beginning to phase it with the northern stream trough in the
West by day 7/Mon, so excluded that run from the forecast.
For additional information on sensible weather, please see the
previous discussion.
Tate
...Previous Discussion...
...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
Hazards:
- Heavy rain across portions of the Lower Mississippi Valley and
the Southern Plains, Thu-Sat, May 2-May 4.
- Heavy rain across portions of the Lower Mississippi Valley and
the Southern Plains, Mon, May 6.
- Flooding possible across portions of the Plains, the Mississippi
Valley,and the Great Lakes.
- Flooding occurring or imminent across portions of the
Mississippi Valley, the Northern Plains, the Great Lakes, the
Northern Great Basin, the Southern Plains, and the Ohio Valley.
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