Quantitative Precipitation Forecast
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FOUS30 KWBC 220045
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
744 PM EST Wed Feb 21 2018

VALID 01Z Thu Feb 22 2018 - 12Z Thu Feb 22 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 S FLP FWC 30 E MIE 20 NW BJJ 20 W BVI 25 S HLG 15 SE 3I2
30 SSE JKL 25 N CHA 25 SW 3A1 15 NE JAN 30 W MCB 10 NW LFT
20 E KXIH KBBF 30 NW KOPM 10 NNW BKS 30 NNW HBV 25 WSW UVA
35 W ECU 30 S E29 10 E E29 30 NE JCT 35 NNE 6R9 15 E TKI
15 S FLP.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WNW KBQX 10 N VCT 25 NE LHB 15 NW 3T1 10 NE MWT 15 SSW BVX
30 ENE M30 25 SSW CVG 45 WNW HTS 25 SW HTS 20 SSW LOZ 35 W CSV
30 NNW HKS 45 SE ESF 15 N KVBS 15 WNW KGVX 15 WNW KBQX.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 ESE OLV 20 ESE GLH 20 WNW TVR ESF DRI 30 NW BPT 30 E UTS
20 E JSO 30 NW SHV 25 ESE M89 NQA 25 ESE OLV.


...Lower Mississippi Valley and Piney Woods...

Widespread ongoing rain / some heavy / will lead to multiple
flood-related hazards over generally the Lower Mississippi Valley
and adjacent areas. There is a risk of flash flooding in some
areas, especially the southern periphery of the precipitation
shield. Elsewhere continued long duration rainfall will pile on to
inundated areas, and although not specific to the Excessive
Rainfall Outlook, significant river flooding is likely and already
occurring in much of this region / see Significant River Flood
Outlook product.

At 01Z we maintained much the same configuration to the Slight and
Moderate Risk areas as was seen in the previously issued outlook.
Moderate risk straddles the areas of heavier new rainfall/lesser
antecedent rainfall (east TX to northern MS and southwest TN) and
areas of lesser rain rates but saturated ground (northern LA and
southern AR). We shortened up the back edge of the Marginal and
Slight Risk areas, reducing their coverage over south/southeast
Texas per the movement of a defined shortwave through that area.
This wave will lift quickly northeast overnight, taking the deep
layer ascent farther away from the source of unstable air over
Louisiana, and allowing for a lessening of low level inflow. Thus,
in the long term tonight we expect rain rates to lessen here, but
through at least 04-05Z there will be potential for hourly rain
rates exceeding 1.25 inches, and small scale training that could
boost totals even higher, resulting in new flash flooding even in
areas that had yet to receive much rain.


...Tennessee into the Ohio Valley...

As the synoptic shortwave trough over Texas lifts northeastward
along the surface frontal boundary, deep layer ascent will
increase the focus for organized precipitation along with some
convective enhancement overnight, from Tennessee into Kentucky,
with intensities tapering off farther north and east. MUCAPE
values may only reach one or two hundred J/KG this far north, but
could support brief heavier downpours along with widespread rain.
Given low flash flood guidance values in this region, we will
maintain Marginal and Slight Risk probabilities here overnight,
with one to two inches of steady rainfall, and locally higher
amounts expected. This is a longer duration style of inundation
event for many locations, but particularly susceptible basins,
especially closer to the instability axis in Tennessee, could see
flash flooding.

Burke
$$





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