Quantitative Precipitation Forecast
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FOUS30 KWBC 190842
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
441 AM EDT Sat May 19 2018

Valid 12Z Sat May 19 2018 - 12Z Sun May 20 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NNW ITR 10 SE APA 15 WSW FNL 25 SSE BRX 20 ENE TOR
25 SSE AIA 15 WNW LBF 20 NNW BBW 15 W OFK 20 NW CIN 15 N OLZ MRJ
RFD 15 WSW GBG 20 SW MQB MWA 20 S HRO 25 WNW SEP 30 E MMPG
10 WSW MMPG 40 W DRT 10 S MAF 20 W LBB 30 SSE AMA 25 WNW PNC
30 SSE MHK 35 SSW BIE 20 SSE HDE 30 NNW GLD 25 NNW ITR.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
70 ESE MTH 30 SSE MTH 25 SSW APF 10 NNW SRQ 20 SSW OCF VVG
45 SSE BOW 30 WSW VRB 25 E TTS 95 E COF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 ENE SSI 35 W CHS 10 NE SSC 20 NW UDG AKH 10 SSW GRD 30 S 1A5
15 NNW RHP 15 S K8A3 20 SE GLW 35 SSW FFT 35 NNE LEX 15 NE SGH
20 W MNN 15 SSW CXPT 20 N HZY 10 E ERI 20 WNW IDI 20 SW CBE
30 SW OKV RMN DAA FME 20 NNW RDG 30 ESE BGM 30 NNW POU
15 WNW OXC 10 ENE HPN 15 NNE BLM 10 S SBY 15 SSW EDE 25 SW MRH
85 ESE SUT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 SW UIN 40 W SUS 35 ESE VIH 25 ESE TBN 40 SSW AIZ 55 N JLN
15 NE UKL 20 NNW TOP 25 SSW AFK 10 N CBF ADU 10 NW TNU
15 NNW AWG 45 SW UIN.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 E HXD CHS 30 SSW FLO 10 NNE SOP IGX 10 WNW RWI 10 SSW OAJ
30 SSE SUT 65 S SUT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WNW PVJ 35 WNW GLE 15 S RPH 20 WNW DYS 35 N SNK 25 SW CDS
20 NE CDS 20 WNW HBR 15 W CHK 20 WNW PVJ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NNE BLF 20 WNW LWB 20 SSW EKN 30 WNW SHD 25 S SHD 15 ESE ROA
15 E MWK 10 SSW SVH EHO 10 E GSP 20 NNW CEU 20 WSW AVL
20 NNW AVL 20 S TRI 15 S MKJ 10 NNE BLF.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 SE HST 15 SSW HST 25 WNW HWO 10 WSW SUA VRB 45 ENE FPR.


...OH Valley into the Mid Atlantic...

Will be another wet day across much of the east, although the
pattern will finally begin to progress today. The broad mid/upper
level trough will finally begin pushing off to the northeast,
which will push increased moisture into the northeast and push the
Mid Atlantic front north as well. Thus anticipate showers will
overspread the northeast with time, and generally become less
focused over the Mid Atlantic. Given weak to no instability, not
anticipating rainfall rates will be all that high today from the
northern Mid Atlantic into the Northeast, and thus a Marginal risk
should suffice from the eastern Mid Atlantic into southern NY to
account for the locally heavier amounts forecast.

The shortwave that has only slowly been progressing east across
the MS Valley into the OH valley over the last few days will pick
up a bit more speed off to the northeast today. Anticipate another
day of ample instability and moisture ahead of this wave and
trough axis for more scattered to widespread diurnally driven
convection. Main focus will be across the OH Valley into the
western Mid Atlantic. Mean flow is greater today, thus anticipate
storms will be more progressive than we have seen the past few
days. Thus in general would expect rainfall magnitudes to be
lower, although with continued high PWATs, briefly intense rates
are still likely. Normally this setup would probably not be too
much of a flash flood threat, however where recent rainfall is
saturating soils and lowering FFG, this rain may cause additional
flash flood concerns. Biggest threat appears to be across portions
of southeast WV south into northwest NC, where some signal this
convection today could briefly hang up and/or repeat near the
terrain resulting in localized heavier amounts. Given antecedent
rainfall here, and the possibility of intense rates with this
activity, additional flash flooding is possible...and will carry a
Slight risk here.

...Florida...

Another wet day across Florida as well. PWATs and 850 mb moisture
transport should both be higher today than previous days,
potentially resulting in a wetter overall day. Activity should
initially focus along the west coast sea breeze boundary, before
potentially shifting to the east coast overnight. Most of the 0z
high res guidance is quiet wet over eastern FL with this overnight
activity. The potential is certainly there for these heavier
totals given the increased southeasterly flow, strong convergence
signature and near climatological record PWATs. Appears like the
high res models are hinting at a subtle wave riding north,
interacting with these favorable parameters and producing a period
of south to north training. Tough to say for sure if this will
materialize, but certainly something to watch, as given wet
antecedent conditions, a greater flood threat could exist. With
the above environmental parameters in place, 0z HREF probabilities
of locally exceeding 5" in the moderate to high category, and wet
antecedent conditions, will go with a Slight risk across the
southeast Florida coast. Lower confidence with this risk area, but
the conditional risk appears high enough to warrant it at this
time and will monitor trends through the day.

...Central Plains into the Mid MS Valley...

Another active convective day expected across the area. By this
afternoon the surface setup should feature a cold front extending
from the Southern Plains into the Mid and Upper MS Valley, and a
dryline across western TX. The mid/upper levels will remain
broadly divergent and generally uncapped. Thus by afternoon will
see an uptick in convection along both these boundaries. PWAT
values will remain high enough to support heavy rains. Thus any
flash flood threat will come down to if and where convection is
able to train and or repeat for a period. The general consensus is
that the first area to convect will be along the front across
OK/KS this afternoon. This activity should move northeast along
the front for a period, but then should advect eastward into the
very unstable airmass forecast over MO. The orientation of
propagation vectors relative to the instability gradient does
support the potential for a period of west to east training of
convection across this area. Also, should see storms form further
northeast along the front from southeast NE into southern IA. Some
training along this front is also possible. Overall confidence is
low with exactly where the better convective training threat ends
up...with outflows from this mornings activity potentially playing
a role. Would lean towards the better threat probably being
somewhere over MO, given the placement of the stronger 850 mb
moisture transport, higher instability pool, and the potential for
this mornings convection establishing an effective boundary
further south. However southeast NE into southern IA is certainly
in play as well, likely being closer to the best mid/upper forcing
and having a slow moving cold front to potentially train along.
Thus opted to just go with a broader Slight risk to encompass both
potential areas.


...Southern Plains...

Higher confidence in what evolves over TX/OK...with widespread
development appearing likely along/east of the dryline. Would
appear like there is a window of potential training near the
intersection of the cold front and dryline from north central TX
into southern OK. This is depicted by a good amount of the 0z high
res guidance, and given the orientation of the fronts at play and
increasing 850 mb moisture transport, it seems plausible.
Eventually would anticipate any complex to become more progressive
off to the south into the instability pool. Will issue a Slight
risk to account for this flash flood potential. Further south
along the dryline it is less favorable for training. However could
see some backbuilding into the dryline for a period, which could
produce localized flash flood issues, and thus will go with a
Marginal risk there.

Chenard



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