Previous Day 1 Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
357 AM EDT Fri May 11 2018

Valid 12Z Fri May 11 2018 - 12Z Sat May 12 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
RWL 35 SE BIT 25 NNW VEL 20 SW CMS 35 SSW BVR BVR 40 NW RIW
25 ESE WRL 15 WSW DHS BFU 20 ENE DGW 15 NNE BRX 30 E ARL RWL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SSW BUU 15 SW JVL 15 SE MRJ 20 NE LNR 20 NW UNU 20 E ETB
15 ENE UGN 25 SSW BUU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 NNE UNV FKL 15 W HZY 15 NE ERI 10 SE CWPC 20 WSW ROC
15 ESE PEO 20 SSE BGM 10 N AVP 20 E IPT 35 NNE UNV.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SE OEB 15 SW BEH 15 W BIV 20 WNW MKG 20 SSE LDM 15 E MOP
25 E CFS CYZR CYQG DUH 10 SE OEB.


...Upper Mississippi Valley/Great Lakes/Northeast...

Broad warm advection ahead of an amplifying trough in the West
will continue to support moderate to locally heavy rains to the
north of a wavy slow-moving boundary extending across the mid
Mississippi and Ohio valleys.  Heaviest amounts are expected to
occur in association with a shortwave trough moving from the upper
Mississippi valley across the southern Great Lakes region late Fri
into early Sat.  Limited instability north of the boundary is
expected to hamper rainfall rates.   However, given the wet
antecedent soil conditions, rainfall totals may pose runoff
concerns across portions of the region from southern Wisconsin and
lower Michigan to western New York and northern Pennsylvania. 
Therefore, continued to highlight these areas with a 'marginal'
risk for excessive rainfall.

...Northern Rockies/High Plains...

The previously noted trough in the West will continue to amplify
this period, with a closed low dropping south from the Northwest
into the Great Basin.  Some of the heaviest amounts of the period
are expected to center across Wyoming -- where anomalous moisture
and sufficient instability, supported by low level easterly
inflow, is expected to interact with larger scale forcing along
the left-exit region of the upper jet.  Heavy snows are expected
for portions of the Big Horns and western Wyoming ranges, with
moderate to locally heavy rainfall totals across the lower
elevations.  These heavier rainfall amounts may pose runoff
concerns and therefore continued to highlight portions of central
to eastern Wyoming with a 'marginal' risk for excessive rainfall.

Pereira