Quantitative Precipitation Forecast
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FOUS30 KWBC 151449
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1049 AM EDT Tue May 15 2018

Valid 15Z Tue May 15 2018 - 12Z Wed May 16 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 N LHX 30 ENE COS BKF 30 SE GXY 15 SSW AKO 25 NW ITR 20 S ITR
40 NE LAA 25 N LAA 40 N LHX.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NW NFW 10 NE JCT 10 SW SJT F05 25 NW GAG 30 WSW PTT 35 E P28
15 WNW TUL 25 NNW HRO 25 WNW BVX 25 ENE DEQ 15 SSW PRX 10 NW NFW.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
85 E KIPN CEW LSF 10 NE RYY 25 SW RHP 40 ENE TYS 10 E BCB
10 SW MTV 15 WSW IPJ 25 WSW CAE 20 NNE SAV 15 ESE SSI 30 NW DAB
10 NW VVG 10 NNW CTY 75 SW CTY 160 W SRQ 85 E KIPN.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SE MHS 20 S MHS 20 W RDD 35 SW RBL 45 ESE O87 35 W O54
35 NE ACV 20 ESE CEC 20 SSW SXT 25 N MFR 45 ENE RBG 55 WSW RDM
50 SW RDM 20 NE LMT 25 WNW AAT 45 S AAT 55 ENE CIC 25 NE CIC
35 SE MHS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SW FTK 10 NE HSB 10 SW FAM 30 SSW SUS STL 25 SW TAZ
10 NNW MTO 20 SW AID 15 ENE CMH 15 N ZZV BTP 15 ESE FIG
25 NNW DUJ 25 ENE GKJ 10 ENE JHW 20 ENE PEO 25 SSE UCA
10 WNW DDH CON 15 S PSM 10 NW OWD 15 E IJD 15 SE HFD 15 E HPN
25 E BLM 30 SSE MJX 30 E WWD 10 W GED KW66 20 WNW SHD 25 WNW 6V3
10 SSE 1A6 EKQ 20 SW FTK.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
RJD 25 NE W99 25 NW LWB 40 WSW HTS 30 NNE LEX 25 SSW CVG
10 SSW KI68 25 SSW LHQ AGC 30 ESE AOO 15 WNW CXY 25 N RDG
15 NW 12N TEB BLM 10 ENE ACY 15 NNE WWD RJD.


1500 UTC update

No changes made to the previous Excessive Rainfall Outlook.

Oravec


...Northeast/Mid-Atlantic/Central Appalachians/Ohio Valley...

A mid-level shortwave associated with ongoing convection across
the Great Lakes is expected to become embedded within the base of
a broad upper trough centered over the Great Lakes/Northeast and
move progressively across the Northeast.  This is expected to spur
a convective complex that is forecast to move across northern
Pennsylvania and southern New York into New England during the
late morning and afternoon hours.  This may produce some locally
heavy totals, but given the anticipated progressive nature of
this system, widespread heavy amounts along the leading edge of
this system are not expected.  However, the tail end the
convection is expected to hang up across southern Pennsylvania,
northern Maryland into New Jersey as it merges with a
quasi-stationary boundary extending across the region.  Convection
will continue to train across the region into the evening hours as
a deepening moisture pool coinciding with the boundary interacts
with energy emanating from the south and west.  Meanwhile,
additional convection development initiating near a weak wave over
the Ohio valley Tue afternoon/evening is expected to move east --
resulting in an axis of moderate to heavy accumulations extending
from the northern Mid Atlantic coast back into the Ohio valley.  A
Slight risk was drawn from southern Ohio and northeastern Kentucky
to New Jersey and northern Delaware.  HREF neighborhood
probabilities for accumulations of 2-inches or more reach
significant values across a large extent of this region during the
period.  These amounts would likely cause runoff concerns,
particularly across portions of the southwestern Pennsylvania,
northern West Virginia and western Maryland -- where 3-hr flash
flood guidance values are 1.5 inches or less.

...Southeast to the southern Appalachians...

A closed low will continue to drift north over the northeast Gulf
of Mexico this period.  Southerly winds east of the center will
continue to channel deep moisture along the Florida peninsula into
southern Georgia, supporting the potential for moderate to heavy
rains across the region.  Upslope flow and pooling moisture along
an inverted trough extending to the north is expected to extend
the threat for moderate to heavy rains further to the north into
the southern Appalachians.

...Southern Plains to the lower Mississippi valley...

Several areas of thunderstorms are expected to develop as the
atmosphere becomes moderately to strongly unstable later today.
Models are showing the typical spread with respect to the finer
details, but there is some consensus that a MCV may support some
organized heavier amounts as it moves from eastern Oklahoma into
Arkansas during the afternoon.

Meanwhile, additional storms are expected to develop along the
Texas dryline and within an upslope flow regime further to the
north over high plains and into the foothills eastern Colorado.
Slightly anomalous moisture, supported by weak southerly flow will
support the potential for locally heavy amounts with these storms.

...Pacific Northwest and northern California...

Southerly inflow ahead of an approaching upper trough will support
and increase in moisture, raising the potential for shower and
thunderstorm development across the region later today.  There may
be enough available moisture (PW anomalies increase to around 2
standard deviations above normal) to support some locally heavy
totals along the favored terrain of southwest Oregon into northern
California.

Pereira
$$





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