Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
300 AM EDT Sat Apr 30 2022
Valid 12Z Tue May 03 2022 - 12Z Sat May 07 2022
...Overview...
A series of Pacific systems (each supported by an upper trough
that may contain a closed low for a period of time) progressing
across the lower 48 will produce active weather during the period.
These systems will spread rain and high elevation snow across the
Pacific Northwest and north-central Rockies/High Plains, and then
mostly rain over a large part of the central/eastern U.S. There
will be two primary systems of interest, one tracking from the
south-central High Plains through the Great Lakes early in the
week and the second entering the West by Monday and reaching near
the Midwest by Friday. Some thunderstorms could be strong with SPC
indicating a threat of severe weather over the southern Plains and
vicinity into Tuesday with the first system and then again a
couple days later ahead of the next one. Heavy rain will also be a
threat with each system. WPC has now issued an experimental medium
range "Slight Risk" for excessive rainfall next midweek over/near
the eastern southern Plains, with runoff issues affected by
additional short range rainfall. The midweek threat signal is
stronger than normal as a closed upper system/lead upper
diffluence combine with increasing inflow into a wavy front. Late
in the period the guidance suggests an evolution toward larger
scale features with mean troughing aloft reaching the eastern
Pacific/West Coast while ridging builds over central Canada and a
trough reaches eastern Canada/Northeast U.S. The pattern during
the period will likely leave the southern half or third of the
West, the northern Plains near the Canadian border, and the Gulf
Coast as the relatively drier areas during next week.
...Model Guidance Evaluation...
Latest 18/00 UTC GFS and 12/00 UTC ECMWF/UKMET mass field and QPF
solutions seem best clustered days 3-5 (Tue-Thu) and have good
ensemble and continuity support in a period with seemingly above
normal predictability. WPC product continuity is well maintained,
bolstering forecast confidence.
Forecast spread increases dramatically into days 6/7 as guidance
struggles both with Pacific system track issues inland into the
West and with closed system progression out from the Plains.
Recent GFS runs curiously show much more robust height
falls/system digging across the West Coast to the Southwest while
in contrast the Canadian and especially the ECMWF instead focus
into the Northwest. A favored GEFS mean and double weighted ECMWF
ensemble mean blend shows only moderate system digging into the
West along with downstream system progressions out from the
central U.S. on the slower side of the full envelope of guidance
solutions. This best takes into account the nature of patterns
with closed lows/troughs in a split southern stream.
...Sensible Weather/Threats...
Over the West, another system will spread moisture from the
Pacific Northwest through the Rockies into early and middle part
of next week. Depending on exact system details, this could
produce some enhanced totals, including accumulating snows into
the north-central Rockies and adjacent High Plains. Subsequently,
an amplified upper trough and surface frontal system forecast to
reach the West Coast next Thursday-Saturday should bring a renewed
precipitation focus into the Pacific Northwest and then farther
inland. However, the southern extent of precipitation will depend
on the upper trough's precise amplitude becomes increasingly and
wildly uncertain by next Friday.
Over the central/eastern U.S., the Northeast may see lingering
light precipitation on Monday with a weakening front. The trailing
cold front will likely stall over the southern Plains while the
next system emerges from the West, with this system currently
expected to track through the Plains/Midwest early next week.
There is decent potential for areas of moderate to heavy rainfall
from portions of the central/southern Plains northeastward,
including a Slight Risk area of excessive rainfall during Monday
into early Tuesday over the south-central U.S. Some severe weather
is also possible, with the Storm Prediction Center currently
indicating the best potential for severe thunderstorms across the
southern Plains in that same time frame. A localized area of snow
may be possible over the north-central High Plains. The guidance
signal is also growing that the next system in the series tracking
out of the West may produce yet another area of significant
rainfall over and east from the central U.S. mid-late next week.
Confidence is slowly improving for this system's details at least
through Thursday, with progression in the slower portion of prior
spread adding somewhat to the heavy rainfall potential over some
locations. Prior rainfall could make some areas sensitive to
additional rainfall from this latter system. Fortunately the
guidance continues to produce most if not all precipitation to the
south of the far northern Plains where soil conditions are the
wettest.
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