Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 PM EDT Wed Apr 27 2022
Valid 12Z Sat Apr 30 2022 - 12Z Wed May 04 2022
...Overview...
Latest guidance continues an active pattern with a series of
Pacific systems entering and progressing across the lower 48. The
first system will be a closed upper low and associated surface low
pressure that should lift slowly northeastward from the
north-central Plains, passing through the Northeast in weakened
form by next Monday-Tuesday. This will spread rain across much of
the central U.S. with some chance of wintry weather spreading into
the northern High Plains on the backside of the low. Lighter
rainfall will extend farther east. The next system should be
somewhat weaker, progressing from the West Coast to near the East
Coast during the period. Then a stronger system is likely to track
from the West Coast into the Rockies/Plains during
Monday-Wednesday. The latter two systems will bring rain and high
elevation snow to the Northwest and then areas of enhanced
precipitation to parts of the central and eastern U.S. depending
on system/frontal details.
...Model Guidance Evaluation...
Within what has been a fairly agreeable pattern from the multi-day
mean perspective, some challenges are ongoing for specifics of
individual systems. Solutions have converged fairly well for the
leading system tracking out of the Plains during the weekend but
still diverge a bit by day 5 Monday with the 06Z GFS and now the
12Z UKMET straying somewhat to the faster/northward side of the
spread. Meanwhile there are still meaningful detail and track
issues with the shortwave reaching the West during the weekend,
with the new 12Z ECMWF at least adjusting somewhat north of its
00Z run whose upper low center was on the southern side of the
envelope. Once this feature ejects from the West, model runs over
recent days have differed greatly over specifics (including the
surface reflection). However in a positive trend today's 00Z
through 12Z runs seem to be clustering a little better toward
maintaining enough definition of the shortwave to support a
surface wave over or just east of the Mid Mississippi Valley by
early Tuesday and near the East Coast Wednesday. There is still a
significant question of stream interaction over eastern North
America that complicates the forecast after early Tuesday. The
final system in the series continues to provide a difficult
forecast though. GFS runs remain on the faster side of the spread,
bringing it well into the Plains by midweek. The 00Z ECMWF jumped
back close to the persistently slow CMC (which itself changed to
an intermediate timing in the new 12Z run) while the new 12Z ECMWF
is close to its 00Z run. The 06Z GEFS mean hedged back to a
compromise, close to the 00Z CMC mean and a bit ahead of the ECMWF
mean, before gravitating closer to the operational run again in
the 12Z cycle. The array and variability of latest runs favored a
compromise approach between the GFS and 00Z ECMWF aloft, slower
than continuity but offering some flexibility pending future
trends.
Based on the guidance available through the 06Z cycle, the updated
forecast used a composite of 00Z/06Z models early to tone down the
more extreme aspects of one or more solutions, followed by adding
some input from the 06Z GEFS/00Z ECMWF means along with the models
to yield the desired intermediate solution late. Admittedly the
favored model/mean blend ended up producing a surface evolution a
tad slower than ultimately desired by day 7 Wednesday though.
...Sensible Weather/Threats...
The first surface low pressure system affecting the lower 48 over
the weekend will spread precipitation across much of the central
and eastern U.S., with some wintry weather possible in the Dakotas
and the best chances in the higher elevations of the Black Hills.
In portions of the Dakotas, precipitation may begin as rain and
transition to mixed precipitation or snow, though details of these
threats remain somewhat uncertain. Additionally, rain could become
heavy to locally excessive from parts of the Plains into the
Mississippi/Ohio Valleys on Saturday. Then as the low pressure
system shifts eastward early next week, precipitation chances
should spread eastward with heavier activity tending to become
more localized. The trailing front will likely stall over the
southern Plains as another system approaches from the West and
current forecasts show potential for heavy rainfall on Sunday
across this region. There is enough uncertainty with details of
this incoming system to suggest potential for future shifts in the
expected axis of heaviest rainfall. With another potential
early-mid week wave plus a trailing one reaching the Plains by
around Wednesday, rain/showers and thunderstorms will likely
persist from the Plains eastward through much of next week. Some
areas over the central U.S. will need to monitor forecasts of the
midweek system given its potential to produce significant weather
and sensitivity to additional rainfall. The latter two upper
shortwaves/surface systems will bring rounds of mostly light to
moderate precipitation (snow in the higher elevations and rain in
the lower elevations) across the Northwest, mainly in the
Saturday-Monday period and perhaps lingering over parts of the
Rockies after then.
Temperature-wise, the general trend over the lower 48 will be for
cooler than average weather in the northern tier and warmer than
average in the southern tier. The core of the coldest air should
be across the northern High Plains to Midwest, where highs will be
around 10-20F below average due to being in the cold sector of
initial low pressure affecting the region followed by influence
from the southern periphery of Canadian high pressure and moisture
arriving with another system toward midweek. Lows should stay
closer to normal though. Meanwhile, slightly above normal
temperatures should stretch across much of the southern tier, with
mainly warmer than average lows also spreading into the
Ohio/Tennessee Valleys during the weekend and more of the East
next week. Best potential for some plus 10-15F anomalies for
highs will be over the southern High Plains early next week while
similar anomalies for morning lows may be a little more common on
some days.
Rausch/Tate
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