Quantitative Precipitation Forecast
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FOUS30 KWBC 190841
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
340 AM EST Mon Feb 19 2018

VALID 12Z Mon Feb 19 2018 - 12Z Tue Feb 20 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SW OSC 20 NW CWGD 25 N CYXU 25 SSE CWSN 25 WNW HZY 10 N AKR
MFD 10 ESE MIE HUF 10 ESE BLV 40 W FAM VIH 20 NNW SET 15 NW IJX
10 N FSW 15 WNW AWG 15 WSW MXO 10 NE MRJ 10 SE SBM 15 SW OSC.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 N SFY 10 SE ETB 10 ESE UGN 15 NNW SQI 30 N SFY.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 SW PRG 30 NNW SLO 30 SW TAZ 15 NE IKK 10 N EKM 10 NW JYM
10 WNW DUH 10 SSW TDZ 20 W FDY 25 SSE FWA 20 SW PRG.


Mid-Upper MS Valley / Great Lakes / Upper Ohio Valley,

Continued amplification of the longwave trough west of the Divide
and resultant downstream ridging across the eastern CONUS will
lead to a highly -PNA toward the end of day 1 (12Z Tuesday), with
500 MB height anomalies around 2.5 standard deviations below/above
normal over the west/east respectively. As the pattern aloft
becomes highly meridional, the surface front draped SW-NE from the
southern-central Plains northeast into the upper Midwest-upper
Great Lakes will exhibit little eastward progression, with the
northern extension of this front (especially over the upper
Midwest-upper Great Lakes) becoming bolstered by the strengthening
upper jet to the north and thus increasing right entrance region
dynamical forcing. Meanwhile, moisture parameters will too become
highly anomalous during the day 1 period, with PW values rising
above 4 standard deviations above normal per the SREF and GEFS and
850 MB moisture flux anomalies peaking over +5 standard deviations
in light of the 50-60 kt moist southwesterly inflow into the
frontal zone. According to the atmospheric river detection from
the ESRL site, a clearly defined Atmospheric River is noted from
the Caribbean and western Gulf, with integrated water vapor
transport values exceeding 750 kg/m/s.

From a dynamical and thermodynamical standpoint, precipitation
efficiency is about as high as it gets for mid February,
especially along/north of 40N, in the absence of robust deep layer
instability. While the latter will be a limitation to short term
rainfall rates, the robust degree of forcing and moisture
transport into the quasi-stationary front will support a rather
broad marginal risk for excessive rainfall during day 1 across
much of the Midwest into the Great Lakes and upper OH Valley
region, with 2 focused areas of a more enhanced ("slight") threat.
WPC did maintain the slight risk straddling the WI/IL border from
yesterday`s day 2 ERO, in light of the antecedent conditions/lower
FFG s, while introducing another slight risk axis from central IL
northeast through central-northern IN and far northwest OH given
the growing high-res model consensus of spotty 24 hour totals AOA
3 inches. Over this region, there remains a multi-model signal for
heavy rainfall along the axis of maximum PW values and 850-700 MB
moisture transport into the frontal zone, so despite the initially
high FFG  values, believe by Monday night more areas will become
susceptible to flash flooding with the additional rounds of heavy
rain.

Hurley
$$




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