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
000
FOUS30 KWBC 171451
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1050 AM EDT Thu May 17 2018

Valid 15Z Thu May 17 2018 - 12Z Fri May 18 2018


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 WNW CYQK 10 NE RRT 25 NNE TVF 15 SW CKN 20 ENE KBAC
45 NW ABR 50 SE MBG 30 NNW 9V9 10 NNW ONL 15 WNW BVN 25 NW GRI
LXN 10 SSW IML 20 NNE AKO 25 N BFF 25 NW CUT 30 SE 2WX 30 NW HEI
20 W K20U 50 W GDV 40 SSW JDN 35 ESE 3HT 30 N WYS 30 ESE SMN
55 NNW MYL 20 SSW SKA 30 SSE OMK 10 WSW CWUS 25 WNW CYQK.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 SSW EUL 35 SE MUO 25 N BYI 25 S BYI 30 NNE 9BB 35 N WMC
55 SW REO 35 NW REO 45 SSW EUL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 N CDS FDR RPH BWD 25 NNE SJT 30 NNW BPG 35 WSW LBB
40 WNW PVW 15 SSW DUX 10 SSW BGD 35 N CDS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
135 ENE FFA 130 ENE FFA 50 ESE SUT 55 E SSI 25 ENE COF
25 ESE KLNA 35 ENE MTH 40 ESE RSW 35 E RSW 15 E BKV 10 S GNV
20 NW LHW 10 WNW HQU MGE 20 NNE MXF 50 NNW GZH 35 NNW PIB
15 S GLH 20 SE LIT 25 SE SGF 20 WNW TBN 15 S CPS FOA 25 NNW FFT
35 NW JKL 20 ESE JKL 30 SW CRW 20 NE CRW MGW 20 S JST 10 ENE LNS
BLM 50 ESE MJX 135 ENE FFA.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SSW KHZE 10 N KHZE 25 ESE MOT 25 NE K5H4 30 NE K46D
10 SSW JMS 40 SW JMS 20 WSW K7L2 50 SW KY19 30 SSW KHZE.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NNW W99 MRB 10 WNW APG 15 SW ILG 20 SSE PHL 10 NE ACY
25 SE ACY 45 SE WWD 30 ESE OXB 20 NNW MFV 10 ESE RIC 20 ENE DAN
10 NNW INT 15 SSW HKY 15 ENE CEU 20 W CEU 1A5 30 NNE 1A5
40 SSW TRI 15 NW VJI 10 NW I16 25 WSW 48I W22 25 NNW W99.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NNE GLH 10 ESE SGT 15 SE SRC 15 WNW BVX 10 ESE FLP BPK
10 WSW UNO 15 ENE UNO 45 WNW POF 25 SSW FAM 25 SE FAM 20 N CGI
10 SW CIR DYR 20 SE KM04 20 NNW TUP CBM 40 WSW GTR 20 SE GLH
15 NNE GLH.


1500 UTC update

...Lower MS Valley...

A slight risk area was added over the Lower MS Valley for the
continued potential of slow moving convection this morning into
this afternoon in the vicinity of the upper vort over northeast
Arkansas.  The latest rap forecasts show little movement to this
vort for the remainder of the morning into this afternoon.  The
potential for slow moving cells to flare up in the vicinity of
this circulation will continue.  Rainfall rates of 1-2"+ per hour
possible in the slowest moving cells.  Please see the  WPC
mesoscale precipitation discussion #0157 valid until approximately
2000 utc for additional information across this area.

Elsewhere---no changes were made at the moment to the previous
risk areas.

Oravec


Day 1...


...Mid Atlantic, Southeast and FL...

Widespread showers and thunderstorms will again be common today
across much of the Southeast into the Mid Atlantic. Broad
troughing over the area with embedded shortwaves and broad upper
divergence will provide the synoptic support for convection. PWATs
will remain well above normal, with much of the area above the
climatological 90th percentile, and some near record values for
this time of year. The broad synoptic support, well above normal
moisture, and ample instability...will all set the stage for
another day of locally heavy rains.

The most pronounced wave is across south GA as of 06z...and will
slowly track north northeast into the Mid Atlantic. In the lower
levels a west to east boundary is forecast to drift slightly
southward and set up across central VA into the Delmarva.
Anticipate the heaviest rainfall totals during the day 1 period
will end up focused near this boundary. As the aforementioned wave
approaches from the south, should see gradually increasing 850 mb
moisture transport into the front. The greatest instability should
also focus along/south of this front. Thus the expectation is that
the highest rates will generally be along/south of the front...and
the front should act as a focus mechanism for some backbuilding
and west to east training. Overall, the high res guidance was in
good agreement on this evolution...although some latitudinal
differences with the front, and thus max QPF axis, were noted. WPC
generally went for a middle ground solution, accounting for all
the 0z HREF members and the 0z Experimental HRRR. Ended up with a
swath of 3"+ near the front across central VA into the Delmarva.
The 0z HREF depicts moderate to high probabilities of 5"+
amounts...suggestive that localized amounts of this magnitude are
certainly a possibility. The 06z Experimental HRRR has an
impressive rainfall swath over this area as well, and while it is
most likely overdone, it does hint at the potential of the setup.
Given that FFG is higher across this area, and lingering
uncertainty on the exact axis and area extent of higher amounts,
opted to just keep a Slight risk for now. However, will need to
closely monitor trends through the day, and some chance a Moderate
risk may need to be considered at some point today along this
front.

The Slight risk was extended south and west of the front as well
into portions of WV, southwest VA and western NC. Generally expect
convection to be less organized here, however intense rates are
still probable, and given lower FFG, flash flooding will be
possible. The Slight was also extended into northern VA and MD, to
account both for lower FFG, and some uncertainty on the
aforementioned axis of more significant frontal convection (some
chance it ends up north of our current forecast).

...Lower/Mid MS Valley, OH/TN Valley into the Central Gulf coastal
region...

Main forcing here will be the presence of a mid/upper level shear
axis and embedded shortwaves. The presence of these features,
combined with moderate instability, should result in scattered to
widespread convective development. Weak shear will limit the
organization of storms, and most storms should thus be short
lived. However, will likely see some cell mergers given the
expected widespread nature of activity, along with some localized
organization along outflows. Also, weak mean storm layer winds
along the shear axis will also support slow moving cells. PWATs,
while not as anomalously high as further east, will remain above
average. All of this suggests, that while an organized widespread
flash flood threat is unlikely, isolated flash flooding will again
be probable today across this region. WPC did increase our QPF
amounts quite a bit from our previous forecast over this
area...and is generally in line with the 0z HREF guidance and a
Marginal risk was issued.


...Central and Northern Plains...

Moderate to high instability will develop along/ahead of a
boundary over the western Plains today. The approach of a
mid/upper level trough from the west will result in increased
upper level divergence over this boundary, and increasing 850 mb
moisture transport. These factors will combine to produce a
favorable environment for convective development by this
afternoon. The increased southerly flow will also result in
increasing PWATS, with values into the well above normal range by
thus evening. The combination of high cape/moisture suggest the
likelihood of intense storms capable of producing heavy rainfall
rates. In general think storms will be moving quick enough off to
the east to prevent any extreme rainfall totals. However does
appear like there may be two areas to watch for the potential for
locally heavier amounts. One across ND, where a stationary west to
east boundary could act as a focus mechanism for training for a
period this afternoon/evening. Will maintain a Slight risk here,
generally in the overlap of higher HREF 3" probabilities and the
heavier QPF axis in the 06z Experimental HRRR. The other area is
across NE, closer to the core of 850 mb moisture transport. The
increasing low level jet and moisture transport corridor this
evening may allow for some backbuilding of convection for a period
over NE. Although the corridor of moisture transport appears to
progress enough to the east with time to suggest that long
duration training/backbuilding is less likely. Given this and the
fact that a majority of this will be occurring over the higher FFG
Sand Hills, will just leave a Marginal risk here.


...Great Basin, Northern Rockies, MT...

Troughing over the area will continue to support widespread shower
activity into Thursday. Multiple shortwaves embedded within the
trough will help focus convective activity. PWAT values near these
shortwaves will be in the well above normal range. Thus locally
heavy rains will be possible with each wave, with at least weak
instability forecast as well. Thus anticipate locally heavy totals
across northern NV into southern ID, eastern WA into northern ID,
and much of MT. Anticipate mainly pulse convection given low
shear...although slow storm motions and some localized
organization along outflows will still allow for pockets of heavy
rains and some flash flood threat. A Marginal risk was issued to
cover this threat.


...Southern Plains...

Isolated to scattered convection is likely today ahead of the dry
line over TX, possibly aided some by the approach of the
subtropical upper jet. PWAT values above normal will support some
locally heavy rains. Not thinking we will see much in the way of
organization, but as usual, anticipate some brief repeat cell
activity will be possible resulting in some localized heavier
rains. Given this potential will go with a Marginal risk here.

Chenard

$$





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