River Flood Warning 62, NWS Paducah, KY

Area Forecast Discussion
National Weather Service Paducah KY
709 PM CDT Tue Jun 26 2018

.UPDATE...
Issued at 709 PM CDT Tue Jun 26 2018

Updated Aviation Discussion for 00z TAFs.

&&

.SHORT TERM...(Tonight through Thursday night)
Issued at 509 PM CDT Tue Jun 26 2018

Much delayed this discussion this afternoon due to convective
watches, warnings, and potential for other headlines during the
next few days.

In coordination with SPC, extended Severe Thunderstorm Watch
Number 224 east-southeast to southern Illinois as atmosphere has
recovered sufficiently for severe potential into that area.

High Resolution, Convection Allowing Models (CAM), such as the
ESRL HRRR and RAP guidance are having some spatial issues dealing
with the detection of cold pool expansion and upshear thunderstorm
development along and behind the series of MCS (Mesoscale
Convective Systems) moving through the WFO PAH forecast area. The
trend is to develop convection (showers and thunderstorms) and
resultant higher QPF (rainfall amounts) much further south than
has been actually occurring. This seems to be the bias the last
couple of days. Adjusted forecast PoP grids northward to reflect
the better rainfall potential for the remainder of this afternoon
and this evening.

Once the small MCS (currently over southern IL and southeast
Missouri) moves east, the expectation is for a third MCS to move
through overnight and into Wednesday morning. There continues to
be some uncertainty on coverage of severe weather further to the
south and east this evening and overnight, so will have to monitor
and adapt, as needed.

With the frontal boundary moving south on Wednesday, kept a
prolonged period of chance PoPs matching closely to the stalling
boundary through the area and reflecting the instability along
and south of the front (as highlighted by the SPC Day 2 Severe
Weather Outlook).

Most of the convection should be capped to the west going into
Thursday from the west, but there may be enough insolation and
weak shear for a slight chance/chance of thunderstorms during the
afternoon on Thursday.

Have been strongly considering an excessive heat watch or heat
advisory from Thursday afternoon through Saturday afternoon (and
possibly into Sunday). The likelihood for issuing a heat advisory
or better headline continues to be greater than 70 percent.
However, due to the potential for convective activity near the
start time of an advisory on Thursday, combined with procedural
implications of issuing an advisory at or beyond 48 hours, will
just continue a mention of elevated heat index values in a
hazardous weather outlook and a strongly worded special weather
special statement. Regardless, it will be quite warm for the
latter part of this week.

.LONG TERM...(Friday through Tuesday)
Issued at 509 PM CDT Tue Jun 26 2018

Hot and humid conditions will be the primary weather story in the
long term. The main forecast challenge is convective coverage and
resulting impacts on heat indices.

The models have slowed the arrival of the 500 mb high by a day.
Therefore, Friday now appears to be the hottest day as the 594 dm
high center passes over the lower Ohio Valley. A few isolated storms
are possible. Afternoon heat indices will peak above 105 degrees,
which is well advertised in the HWO and social media messaging.

The 500 mb high will move northeastward over the weekend, which
means our region will be under the southwest periphery of the
anticyclonic circulation. The main challenge is how much convection
will occur around the high center. Highs will be in the lower to mid
90s with heat indices topping 100 each day. Isolated convection
could provide some local relief both Sat and Sun afternoon.

Early next week, a broad weak 500 mb ridge will extend from the
Plains to the Northeast. Most of the model guidance shows a weakness
in the ridge over our region, permitting some convective development
Monday and Tuesday. Although it will remain hot and humid, the
convection could limit heat indices to mainly sub-advisory
thresholds.

&&

.AVIATION...
Issued at 709 PM CDT Tue Jun 26 2018

Multiple lines of thunderstorms with trailing stratiform rain
moving through the area this evening. The complex of thunderstorms
moving in from southeast Missouri should rapidly spread eastward
and be ending from west to east by 03-05z timeframe. Some gusty
winds expected, perhaps severe up to around 50kts in some places,
as the main line moves through this evening. Should be a gradual
lull in activity by late evening/midnight. Some short term models
tending to redevelop some convection later in the overnight period
lasting into the morning hours. Went with vicinity mention for
now as unsure of the placement and overall coverage. Breezy WSW
winds expected tmrw with some gusts up around 20 kts. Overall VFR
cigs and vsbys should dominate the period, but may be some
temporary reductions with the stronger storms down to mainly MVFR.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

UPDATE...SP
SHORT TERM...Smith
LONG TERM...MY
AVIATION...SP

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