Quantitative Precipitation Forecast
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FOUS30 KWBC 211852
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
252 PM EDT Sat Apr 21 2018

VALID 21Z Sat Apr 21 2018 - 12Z Sun Apr 22 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 E KGVX KGVX 20 SSE BYY 30 NW 5R5 20 ESE 3T5 62H 15 ENE TPL
10 W JWY 20 N LUD 15 ESE SPS FDR 10 S HBR 15 SE CSM 30 S JWG PWA
10 N SNL 20 E SNL 20 NNE MLC 15 W RKR 25 SW RUE 15 S RUE
15 SW SRC 15 SE SGT 10 ESE MLU ACP 20 SSE KVBS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 ESE KLNA 40 W PBI 15 N GIF LEE 20 NE VVG 40 NNE TTS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
HQZ 35 N PRX 20 S MWT 10 SSW HOT 30 SSW LIT 10 WNW PBF
15 NNW LLQ 30 E ELD 25 ESE BAD 35 NNW UTS 40 NNE LHB HQZ.


1900 UTC update

...East Central Florida...

There is a multi-hi res model signal for locally very heavy
rainfall amounts across east central Florida tonight into early
Sunday.  The frontal boundary lying west to east across central FL
this afternoon is expected to move little during the upcoming day
1 period.  Low level southeasterly to southerly flow into this
boundary----along with pw values rising to 1.5 to 2 standard
deviations above the mean---will set the stage for locally very
heavy amounts.  Still a lot of uncertainties with some of the
details in the hi res guidance---especially some of the very high
totals such as the 10"+ in the arw...nssl wrf and nam conest and
the 14" amounts in the hrrr experimental.  While these models all
have very heavy totals over portions of east central Florida---the
placement differs from between 60 and 80 nm.  This and the very
small scale of the maxima is leading to the low confidence.
Still---with the multi-model signal for potentially  heavy rain
amounts---a marginal risk area was introduced in the update to the
day 1 excessive rainfall potential outlook over the east central
coast of FL for localized runoff issues especially over urbanized
areas.


...OK / TX / AR / LA...

There is a Slight Risk of excessive rainfall over the ARKLATEX
region, extending a short distance into southeast Oklahoma, and
extending farther down into the Piney Woods of east Texas. All in
all, there are some limiting factors today, including high Flash
Flood Guidance values and a narrow axis of marginally strong
instability. Still, there will be some wetting rain early in the
period during warm advection, followed by a diurnal maximum of
rainfall coverage and intensity this afternoon/evening. It is
during the early onset of the afternoon convection, in particular,
that cell mergers and local bouts of training may contribute to
rain rates nosing toward FFG values.

A Marginal Risk area is drawn back up the Red River to about
Wichita Falls and including southern OK / north TX. There may be a
period of relatively slow cell movement during the morning during
the approach of a jet streak rounding the base of the upper
trough, and this could be followed by other heavy showers in the
afternoon dependent upon destabilization beneath increasingly cold
upper level temperatures. Isolated flash flooding is possible
today.

Burke/Oravec
$$





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