Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
259 AM EDT Mon May 09 2022
Valid 12Z Thu May 12 2022 - 12Z Mon May 16 2022
...Blocky pattern through late week to support record heat over
the Southern Plains/Lower Mississippi Valley into the Midwest
along with episodes of central U.S. convection and an emerging
onshore rainfall focus to the Carolinas...
...Overview...
The start of the period will feature a mean trough aloft over the
West, ridging that extends from the southern Plains through Great
Lakes/Northeast, and an upper low off the Southeast coast.
Temperatures will likely challenge daily records under and near
the upper ridge axis late this week while parts of the West will
see chilly weather with rain and higher elevation snow. Between
these regimes, a storm system emerging over the northern Plains
may produce some areas of heavy rainfall where wet ground
conditions already exist. Then during the weekend and early next
week most guidance shows the pattern transitioning toward a
western ridge/east-central U.S. trough configuration. This
evolution should finally push the rainfall focus to the east of
the Plains. The initial upper low tracking into the Southeast
around Friday due to a retrograding Atlantic ridge should quickly
lift northward and open up during the weekend, with associated
rainfall spreading into and north from the Carolinas. The ridge
building over the West will lead to increasing coverage of very
warm to hot temperatures over the southern half of the West during
Saturday-Monday.
...Guidance Evaluation/Preferences...
Based on guidance available through the 12Z/18Z cycles, the 18Z
GFS and 12Z ECMWF/CMC provided the most compatible and consistent
cluster for the overall forecast through the period along with
reasonable support from the ensemble means. The starting blend
used those three operational runs for about the first half of the
period and added in a moderate weight of 18Z GEFS/12Z ECMWF means
thereafter.
GFS/ECMWF continuity and trends of other guidance still seem to be
pointing more toward some variation of a GFS/ECMWF scenario for
the vigorous system expected to emerge from the West and track
over the northern Plains into southern Canada late this week.
Aside from some detail variability, GFS/ECMWF runs converged
fairly well over the past day or so while the previously fast CMC
has been gravitating in their direction. UKMET runs had been the
most extreme with a southern track of the western upper low/trough
but the new 00Z run is finally trending in a favorable direction.
Behind this system, models and ensembles still show a moderate
amount of spread for the character of trailing energy that
consensus shows flowing through the Northwest and then sharpening
over the Plains and east-central U.S. while ridging builds into
the West. The favored model cluster mentioned above fit well
within the ensemble mean template but the new 00Z cycle has
introduced more spread in opposing directions, as the GFS has
trended flatter with the trough (due to stronger depiction of
shortwave energy reaching the West by Monday) while the CMC forms
a closed low farther south than other guidance.
Finally, latest trends for the upper low reaching the Southeast
coast around early Friday have been toward faster northward
progression after that time along with opening of the low by late
Saturday.
...Weather/Threat Highlights...
The strong upper ridge extending from the southern Plains through
the Great Lakes/Northeast as of Thursday will promote much above
normal temperatures from much of the Plains and Mississippi Valley
through the Great Lakes and Northeast late this week.
Highs/morning lows will be at least 10-20F above normal with some
embedded plus 20-25F anomalies possible from the central Plains
into Great Lakes, and locations across a fairly broad area may
challenge daily records. After Friday expect the above normal
temperatures to be more confined to the Great Lakes/Northeast and
the far southern Plains/western Gulf Coast region. There will be
a lingering potential for daily records over the Northeast into
Saturday and over eastern Texas and vicinity through the end of
the period.
The frontal system and upper dynamics crossing the Northwest late
this week will produce a brief period of enhanced rain and high
elevation snow as well as highs 5-15F below normal. Meanwhile the
southern part of the West should moderate to slightly above normal
by Friday. Then arrival of the upper ridge will extend the
warming trend over the West through the weekend. Highs of 10-20F
above normal should expand from California eastward from Saturday
onward and some locations could reach record highs by
Sunday-Monday. Northern areas of the West should be closer to
normal and one or more fronts may produce periods of light to
moderate precipitation over the Pacific Northwest.
Late this week the system emerging from the West and developing
over the northern Plains before tracking into southern Canada,
along with associated fronts, may produce areas of heavy rainfall
over parts of the far northern tier where some areas are quite
sensitive to added rain due to very wet ground conditions. The
experimental Day 4 (Thursday-Thursday night) Excessive Rainfall
Outlook has introduced a Slight Risk area over parts of northern
North Dakota and Minnesota where there is the best overlap of
guidance signals for significant rain and instability, along with
high soil moisture. Depending on system evolution, areas farther
west back to the northern High Plains could also see significant
rainfall. Some locally moderate to heavy showers and
thunderstorms will be possible farther south along the wavy
trailing front (which may hang up for about a day as western
energy catches up to it) but so far with less agreement for
specifics. The Storm Prediction Center is also monitoring the
potential for severe weather, so check the latest outlooks for
updated information. Rainfall and the focusing front should
become more progressive from Saturday onward, leading to a drier
trend over the Plains. Retrogression of the western Atlantic
upper low into the Southeast toward the end of the week should
spread rain into the Carolinas and vicinity by around Friday with
some of this moisture spreading northward thereafter. Highest
totals should be over or near the eastern Carolinas. Amounts
farther north should trend lighter due to decreasing focus of
moisture as the upper low opens up while it lifts northward.
Rausch
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