Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
255 AM EDT Tue Apr 03 2018


Prelim Day 1 QPF Discussion
Valid Apr 03/1200 UTC thru Apr 04/1200 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


Day 1

...OH Valley into the central Appalachians...

Low level southwesterly flow is expected to remain strong through
Tuesday morning into a strengthening west to east oriented frontal
zone across the OH Valley region.  This will support the continued
threat of organized overrunning convection along and north of this
boundary in a region where pw values will be rising to 1.5 to 2+
standard deviations above the mean.  The day 1 qpf leaned toward
the hi res guidance of the arw...nmmb...nssl wrf and latest hrrr
which all showed heavy rain potential in the vicinity of south
central IN...southern OH...northern WV into far southwest PA.  In
these regions runoff risks will continue through most of Tuesday
morning when training of cells in a west to easterly direction is
possible.  Uncertainties are with the axis of the heaviest
precip...with the hi res guidance showing run to run and model to
model differences.  In areas of training---hourly rainfall totals
of .50-1"+ and totals of  2-4" in a few hours are possible.  A
west to east oriented marginal and slight risk area will be
maintained this period in the area of training potential.

...Upper MS Valley--Great Lakes into the northeast...

There is fairly good model agreement with the deepening surface
low pushing northeastward from the mid MS Valley into the Great
Lakes this period.  A well defined comma head/deformation
precipitation band will be expanding east northeastward from the
Upper MS Valley into the Great Lakes Tuesday and into southeast
portions of Ontario/southwest QB Tuesday night-Wednesday morning. 
 At the same time---strong isentropic lift to the northeast of the
northeastward moving warm front will support expanding
precipitation into the northeast from the northern
Mid-Atlantic---across much of NY state and into New England. 
Early spring heavy snows likely in the comma head/deformation
precipitation band from southern MN/northern IA---central WI---the
northern L.P. of MI and into portions of southeast Ontario and
southwest QB.  Accumulating snows also likely on the northern edge
of the warm advection precipitation across northern Maine.  See
the latest QPFHSD for additional winter weather information across
these areas.

...Northeast TX---lower to mid MS Valley---lower OH Valley---TN
Valley into the southern Appalachians...

Late Tuesday afternoon frontal to pre-frontal convection should
blossom along the trailing cold front from the above mentioned
deepening low moving into the lower Great Lakes region in an
increasingly unstable axis from eastern TX---the lower to mid MS
Valley---lower TN Valley and lower OH Valley region.  MUCAPE
values of 1000-2000+ j/kg expected along with pw values rising to
1.5 to 2+ standard deviations above the mean along and ahead of
this front during the 1800 UTC Tuesday to 0600 UTC Wednesday
period. This frontal boundary is expected to be fairly progressive
to the southeast---but widespread heavy rains possible late
afternoon into early evening from northeast TX into portions of
the lower MS Valley---lower TN Valley.  1"+ precip total possible
across these areas---with lesser totals to the east and southeast
toward the central Gulf Coast---mid to upper TN Valley where
activity should be decreasing Tuesday night into early Wednesday
morning.  During the convective peak period late afternoon into
evening---there will be some potential for runoff issues---with a
marginal risk area depicted on the Excessive Rainfall Outlook for
this period from northeast TX into portions of the lower MS
Valley---lower TN Valley. 

...Pacific Northwest/northern Rockies...

A warm frontal boundary will be pressing slowly east northeastward
toward the Pacific Northwest day 1.  Increasingly moist west
southwest low level flow with this boundary will support
increasing showers late Tuesday afternoon into Tuesday night/early
Wednesday from coastal Oregon/coastal Washington---inland to the
Washington-Oregon Cascades.  Model consensus is for light totals
in the .10-.25" range across these areas.  Light precip totals
also likely inland across the northern Rockies from northwest WY
into western MT and northern ID.

Oravec