Quantitative Precipitation Forecast Discussion
NWS Weather Prediction Center College Park MD
301 PM EDT Fri Jun 01 2018


Prelim Day 1 QPF Discussion
Valid Jun 02/0000 UTC thru Jun 03/0000 UTC
Reference AWIPS Graphics under...Precip Accum - 24hr


...Central-Northern Plains and Upper Midwest...

There remains a good model signal for two distinct areas of
moderate to heavy rainfall developing this afternoon and evening
across the northern and central Plains into the Mississippi valley
as strong upper dynamics, deep moisture and instability converge
across the region.  The low level jet is expected to amplify over
the central and northern Plains this afternoon-evening as a
negatively-tilted upper trough translates east across the northern
and central Rockies.  Guidance shows PWs increasing in excess of
1.5 inches along a 40-50+ kt low level jet centered across
Nebraska and the Dakotas.  This moisture interacting with ample
instability and the aforementioned trough is forecast to support
developing storms, producing heavy rains across the Dakotas later
this afternoon.  As noted in the overnight discussion, with the
strengthening low level jet, the hi-res models continue to show a
period of slower eastward progression/cell training - raising the
potential for heavy amounts flash-flooding across this region. 
During the overnight hours, the general model consensus showed
convection moving more progressively eastward across eastern North
Dakota into Minnesota with a general downward trend in rainfall
rates as a developing convective complex to the south begins the
interrupt the inflow of deeper moisture. WPC QPF largely utilized
the HREF Mean as starting point across this region.

Further to the south, there remains a strong signal for a
convective complex developing and tracking southeast from central
Nebraska toward the mid Mississippi and lower Missouri valleys
overnight.  Recent runs of the RAP show PWs increasing to around 2
inches on the nose of 50 kt southerly inflow.  Upon organizing,
this system should become fairly progressive, however strong
southwesterly inflow may promote a period of backbuilding/training
convection, further raising the threat for heavy amounts across
portions of central Nebraska to northeast Kansas and northern
Missouri.  Convection is expected to wane as the complex continues
further southeast toward the lower Ohio and Tennessee valleys
during the morning hours on Saturday.  However models show
convection redeveloping later in the day along and ahead of cold
front pushing from the Plains into the Mississippi valley.  During
the Fri evening into the overnight hours, WPC QPF reflects a
northward shift in heavier amounts, similar to the HREF Mean. 
However, did not go as far north as the HRW-ARW and NSSL-WRF runs,
but instead gave more weight to the more southerly HRW-NMMB and
NAM CONEST solutions across Nebraska into Kansas and Missouri
overnight. 

...Eastern U.S....

Slow-moving, positively-tilted upper trough will nudge eastward
toward the Atlantic coast by Saturday. Until then, a broad area of
modest dynamical forcing east of the trough axis and surface front
will favor scattered-widespread convection once again today,
especially during the peak heating hours from late-afternoon into
early evening.  This may raise additional flash flooding concerns,
particularly across portions of the central Appalachian into the
Mid-Atlantic region where flash flood guidance values are quite
low given the recent heavy rains impacting the region. 

Then on Saturday models show energy over the Great Lakes dropping
southeast into the Mid-Atlantic, supporting surface low
development along the Delarmva coast.  Deep moisture pooling near
the center will fuel an increasing threat for developing moderate
to heavy rains across the Mid-Atlantic region during the afternoon
into the evening hours.

Pereira