The Weather Prediction Center

College Park, MD

Quantitative Precipitation Forecast Discussion

[Abbreviations and acronyms used in this product]
Geographic boundaries:    Map 1- [Color] [B/W Print Version]      Map 2 - [Color] [B/W Print Version]

Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
615 PM EDT Sat Mar 24 2018

Final Day 1, Day 2 and Day 3 QPF Discussion
Valid Mar 25/0000 UTC thru Mar 28/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr

Day 1

...21Z Update...

Few changes needed to the existing day 1 forecast based on trends
seen in the afternoon radar and satellite imagery. 

...Southeast/southern Appalachians into South/southern Plains...

The vigorous, compact upper disturbance over the mid MS valley and
western OH valley this afternoon will slide south and east toward
the southern Appalachians, through the Southeast and off the
Southeast coast over the next 24 hrs. However, a short wave diving
through the nern quad of the country will sharpen the upper-level
confluence and overall weaken the dynamic short wave. Thus still
anticipate a healthy precip shield with decent rates to push
through eastern KY/TN into swrn VA/western NC and nern GA before
zipping through the Southeast. The guidance captures this scenario
quite well and provided confidence in carrying 1-2 inch areal avg
qpf amounts with locally higher values over the southern
Appalachians, due to favorable orographics. Meanwhile, the
associated surface cold front will eventually stall and become
quasi-stationary across the South into the southern Plains Sun
afternoon. This could trigger isolated showers/storms across the
region, especially across northern TX into OK as lower upper
heights from the west begin to reach the southern tier of the
country. Overall WPC followed a model blend for QPF, which
included global models and hi-res guidance.

...West into Upper Midwest...

A couple of different upper-level systems will keep the West
unsettled Sat evening through Sun. One upper-level short wave
across the northern Rockies and inter-mountain West will lift
north and east into central Canada and clip the northern Plains
and parts of the Upper Midwest. Overall qpf amounts should be
relatively light with this feature, though global models and
hi-res guidance capture a streak of elevated moisture and an
active low level jet for enhanced qpf amounts of likely rain mixed
with snow across eastern ND. Meanwhile upstream, a closed mid to
upper low over the eastern Pacific will move through northern CA
and OR to reach the inter-mountain West/Great Basin. Marginal Pac
moisture transport is expected with this system but expect the
favored terrain and especially the northern CA coast into the
northern Sierra with enhanced onshore flow and qpf amounts.
Overall WPC stayed very close to the operational GFS and ECMWF on
mass fields and qpf amounts.

Day 2

Plains---Mid to lower MO Valley---Mid to Upper MS Valley

The elongated upper trof centered from the northern Rockies into
the Great Basin and into the Southwest at the end of the day 1
time period will be pushing steadily eastward day 2 and begin to
separate into two distinct streams.  The southern stream is
expected to amplify into a closed low over the southwest Monday
afternoon---while the northern stream height falls are more
progressive pushing out of the northern Rockies into the northern
high plains.  Precipitation should begin to become more organized
downstream of both branches of this elongated trof day 2 as pw
values rise to 1 to 2 standard deviations above the mean through
most of the Great Plains---lower MO Valley and Mid to Upper MS
Valley in a region of fairly difluent upper flow with embedded
shortwaves.  Overall--it appears the precipitation areas should be
fairly progressive day 2---limiting the heavy precipitation
potential.  Model consensus is for .25-.50"+ amounts across these
areas.  Accumulating snowfall potential will be confined to the
northern portion of this broad precipitation area from the
northern Rockies of north central WY---east northeastward into the
northern high plains of northeast WY/far southeast MT---western SD
and then farther to the northeast from eastern SD into central to
northern MN.  See the latest QPFHSD for additional winter weather

Southeast into northern Florida

A well defined frontal boundary will be dropping southward from
the southeast into northern Florida day 2.  PW values expected to
pool to 1 to 1.5 standard deviations above the mean in the
vicinity of this front---supporting widespread shower activity
Sunday evening from southern GA into north FL.  The low level flow
is then expected to veer to a more easterly direction Monday along
the east central to northeast FL coast with scattered showers
possible in this onshore flow.

Day 3

Southern Plains---lower MO Valley---Mid MS Valley into the OH
Valley and Great Lakes

The broad upper trof will remain split into two distinct streams
day 3.  There are timing differences with the slower moving
southern stream with the GFS faster in lower heights into the
Southern Plains while also being somewhat weaker with the southern
stream closed low.  This does have ramifications with the
precipitation development day 3 from the Southern
Plains---northeastward into the lower MO Valley and OH Valley. 
WPC is favoring the majority model solutions of being slower than
the GFS with the height falls into the Southern Plains and
subsequently slower to push the potentially heavy precip
southeastward.  Despite the mass field differences---there is
consensus for developing widespread heavy precipitation this
period across these areas which will remain in an axis of much
above average pw values---2 to 3+ standard deviations above the
mean---strengthening southerly to southwesterly low level flow
into the frontal zone stretched southwest to northeast across
these areas and in an overall favorable right entrance jet region.
 No significant changes planned to the day 3 excessive rainfall
potential outlook with a a broad marginal and slight risk area
stretching from north central TX into central to eastern
OK---southeast KS---northwest AR---southern to central MO into
southern IL.  Areal average 1-2"+ precipitation amounts possible
across these areas---with training of cells possible in a
southwest to northeasterly direction parallel to the above
mentioned front---supporting locally heavier to excessive amounts.
 The northern stream energy moving from the northern Plains into
the Great Lakes will continue to be very progressive.  This should
keep precip totals on the moderate side .25-.50" through the Great
Lakes day 3. 

Lee of the central to southern Rockies

A separate precip max possible day 3 in the lee of the central to
southern Rockies where the combination of post frontal upslope
flow to the northwest of the southwest to northeast oriented front
emanating from the southern Plains and large scale lift to the
northeast of the southern stream closed low will support moderate
to heavy snowfall totals across central to eastern CO into central
to north central NM.

Pacific Northwest Days 2 & 3

The westerly onshore flow off the northeast Pacific into the
Pacific Northwest will be strengthening early Monday and remain
strong through Tuesday.  With pw values in this strengthening
onshore flow expected to rise to 2+ standard deviations above the
mean---moderate to heavy precip totals likely through the
Washington/northern Oregon Cascades---west to the  central to
northern Oregon coast range into the Olympic range both day 2 and


Graphics available at

Last Updated: 615 PM EDT SAT MAR 24 2018