Quantitative Precipitation Forecast
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668
FOUS30 KWBC 160101
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
900 PM EDT Tue May 15 2018

Valid 01Z Wed May 16 2018 - 12Z Wed May 16 2018


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 NNE LMT 35 S AAT 45 N BLU 35 NNE CIC 35 SE MHS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SE DUX 20 E PPA 15 NNW FSI MWL PWG 10 E GTU 20 NW HYI
10 W T82 35 NW JCT 10 SSE SWW 40 ESE LBB 35 E CVN 45 S DHT
15 SE DUX.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 WSW SPD 25 NNW LHX 10 E BKF 40 ESE GXY 25 W ITR 40 N EHA
20 SW EHA 25 WSW SPD.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S OXB 25 SSW NHK 25 SW LKU 15 ESE ROA 15 N UKF 25 S TRI
10 ENE DNN 10 W ANB EET 10 SE TCL 10 SSE MSL 45 ESE MKL 30 E OLV
10 ENE GWO 25 SE GLH 40 NNE GLH 15 N NQA 25 ENE DYR 30 SSW CKV
30 NE MQY 15 W EKQ 25 NNE SME LEX 20 WNW SDF 25 N HNB 10 SSW HUF
30 ENE HUF 10 E BAK 20 S LUK 35 W 3I2 15 S ZZV 10 WSW HLG
20 NNW 2G4 10 SW THV VAY 30 SSE JFK 40 E MJX 25 SE ACY 20 S OXB.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 W MIV 10 WSW WWD 10 NE SBY NHK 15 SSE CJR 20 SSW W99
30 NNE BKW 15 NE CRW 25 NW 48I 15 SSW 2G4 15 ENE MRB APG
20 W MIV.


0100 UTC Update...

Made extensive chances to the outlook areas, most notably with the
MRGL and SLGT risk areas across the eastern U.S. based on the
latest observational and mesoanalysis trends, along with the more
recent HRRR/experimental HRRR guidance. Have also incorporated the
latest (18Z) SSEO and HREF 40 im neighborhood probabilities of
QPF>FFG exceedance in delineating these risk areas, with the
higher probs favoring the shift in the SLGT risk area.

Hurley


...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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