Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FOUS30 KWBC 160105
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
804 PM EST Thu Feb 15 2018

VALID 01Z Fri Feb 16 2018 - 12Z Fri Feb 16 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NW AOH 20 ESE CGF 20 SSW BFD 20 WNW SEG 15 NW RDG 10 SE LNS
15 W THV 20 ENE CBE 20 SW W99 20 NW HSP 30 SSW 48I CRW 20 NE HTS
30 WNW HTS 55 ENE LEX 15 NE FFT 10 W HNB 10 NNW CUL 15 ENE SLO
10 SE PRG 20 NW AOH.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 N CRW 30 W 3I2 25 SE LUK 35 SSE BAK 15 ENE BAK 30 SSE MIE
25 WNW DAY 25 NNE SGH 10 S MFD CAK BVI 20 NW IDI 25 SSW FIG
10 NNE AOO 10 NNE CBE 15 W W99 25 SSW EKN 48I 30 N CRW.


0000 UTC update

Only made slight tweaks to the going marginal and slight risk
areas. Complex system evolution this evening across the Ohio
Valley into portions of PA. Continue to see some west to east
training of showers and embedded thunderstorms north of the warm
front from eastern OH into southwest PA. Meanwhile convection
continues to form further west across portions of southeast IL
into central IN. This appears to be developing on the leading edge
of the better mid/upper level forcing moving in from the west, as
evidenced by the light rain and virga moving across KS/MO earlier
this afternoon...and just ahead of a strengthening cold front.

As we head through the evening hours and the better forcing
continues to move into the area...will see a more pronounced
surface cold front develop and move more steadily off to the
southeast. However over the next several hours will continue to
see some training of rainfall over portions of OH and PA, with
generally 1-3" amounts expected. Across portions of IL/IN/OH
should see some southwest to northeast training of convection over
the next several hours as the developing convection only slowly
moves eastward. After about 04z the cold front will become more
well defined and progressive off to the southeast, which will help
limit total rainfall amounts. But in the meantime would expect
1-2" (isolated 2-3") amounts from far southeast IL into central IN
and portions of southwest OH.

Overall this activity will be right around the magnitude where
flooding/flash flooding could become a concern. The slight risk
area was maintained where FFG is a bit lower and some of the
embedded higher rates have a better chance of locally exceeding
it. One area to pay attention to is the axis from east central OH
into southwest PA, where the earlier warm frontal convection
dropped 1-2" of rain. Quite possible that the convection with the
cold front could move across these same areas overnight, and while
this activity will be progressive by that time, a quick additional
1" is possible, which could exacerbate any ongoing flooding issues.

Chenard

Previous discussion

...Ohio Valley eastward into the central and northern
Appalachians, the Laurel Highlands, and central Pennsylvania...

The broad mid-upper level WSW flow, with subtropical origins ahead
of the upper trough southwest of Baja, will allow for an
elongated, robust warm conveyor belt/moisture plume ("atmospheric
river" per the ARDT integrated water vapor transport anomalies)
into the central and eastern CONUS during the day 1 period prior
to the cold frontal passage. The 00Z guidance continues to denote
a heavy rainfall signal across the OH valley into the
central-northern Appalachians, Laurel Highlands, and into central
PA in light of the abnormally rich deep-layer moisture/theta-e
profile along with a vigorous upper jet streak (170 kts at 250 mb)
that will provide a relatively prolonged period of robust,
deep-layer ascent via the approaching left-exit region initially
and (by overnight Thursday into early Friday) associated more from
right-entrance region upper jet forcing and strengthening
low-level frontogenesis ahead of the front. PW anomalies during
the event will peak around 3.5 standard deviations above normal
per the SREF and GEFS, which along with the 850 MB west-southwest
inflow of 50-55+ kts and moisture flux anomalies between 4-5
standard deviations above normal, will make for nearly optimal
rainfall efficiency/short-term rates for mid February considering
the lack of instability (mucapes < 400 j/kg).

In terms of the QPF, the majority of the high-res CAM guidance
with recent events characterized by strong dynamical forcing,
impressive moisture profiles, and minimal instability (i.e.
Largely stratiform) were generally underdone in terms of the
breadth of moderate-heavy rainfall area when compared to the
global guidance. With this in mind, the WPCQPF was essentially a
blend of the 00Z ECMWF, GFS, and in-house bias corrected ensemble
mean, which matches up favorably with the RGEM as well as a blend
of the WRF-ARW and ARW2. The 00Z NAM meanwhile was a northern
outlier with respect to the max axis of 1.5+ inch totals.

Given the stratiform component, the high-res guidance does not
show much deviation above the mean QPF -- i.e. max totals are
expected to be in the 2.5-3.0" range. However, given the
antecedent soil conditions and relatively low 3 and 6 hourly FFGs,
the probabilities of exceeding 1.0-1.5" within 3 hours and
especially 1.5-2.0" within 6 hours across the SLIGHT risk area are
decidedly elevated per the latest HREF.

Hurley
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.