Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 252010 CCA
AFDPAH

Area Forecast Discussion...CORRECTED
National Weather Service Paducah KY
310 PM CDT Fri May 25 2018

.SHORT TERM...(Tonight through Sunday night)
Issued at 253 PM CDT Fri May 25 2018

A cluster of convection that developed at midday over the Purchase
Area has quickly dissipated and sent an out a nearly circular
outflow that has scoured the airmass over a good portion of
southern Illinois, west Kentucky and even into adjacent portions
of southeast Missouri. There will continue to be some isolated to
scattered convective development on the outflow, except to the
east and northeast where drier air already resides.

Two broken lines of convection over southeast Missouri will
continue to move eastward until they have gobbled up all of the
remaining unstable surface airmass. These storms will also come
down quickly once they encounter the worked over air spreading
west out of west Kentucky and southern Illinois. Most of this
activity should be done by 22Z.

The latest HRRR data tries to bring another area of convection
eastward into southeast Missouri late this evening or overnight,
but even it tends to dissipate as it moves into our region. Will
keep a slight chance of showers and storms through tonight and
into Saturday morning, but it should be dry in most locations. If
winds go calm and skies can scatter or clear for any significant
period of time tonight, patchy dense fog will be a possibility,
especially over the western half of the region.

The weak mid/upper-level trough that is helping to support this
afternoon`s convection will get hung up over our region through
the weekend. This is largely due to the approaching tropical
system in the Gulf of Mexico. It will keep mainly diurnal chances
of convection over mainly west Kentucky Saturday and Sunday. Weak
flow will continue, so our primary concerns will continue to be
localized heavy rainfall and flooding along with frequent
lightning and a few very isolated downbursts.

It will remain hot and humid outside of thunderstorm outflows
through the weekend. Afternoon heat indices may reach triple
digits in a few locations Sunday.

.LONG TERM...(Monday through Friday)
Issued at 253 PM CDT Fri May 25 2018

Correction added for discussion on Monday precipitation chances in
second paragraph.

This extended forecast discussion will be focused on two weather
items. The first will be the strength of a southwest to northeast
oriented, vertically stacked, high pressure ridge to suppress
convective activity on Monday (Memorial Day), and secondly, the
impacts of the subtropical named circulation Alberto on parts of the
WFO PAH forecast area between Tuesday and Thursday of next week.

For Monday and Monday night(Memorial Day), subsidence associated
with the ridge should suppress any convection (showers and
thunderstorms during the morning and evening hours. A few storms
may develop during the heating of the day in the afternoon, so a
small chance of storms was added during this time period.
Heat index values will likely reaching into the 90 to 95 degree
range during the afternoon outside of any rain areas. The 12z
ECMWF is a little more robust about developing afternoon
convection over the WFO PAH forecast area on Monday, but kept the
WFO PAH forecast area dry to reflect the collaborative input from
surrounding offices and to keep within the regional model guidance
initialization.

For Tuesday through Friday, given the range of forecast
possibilities associated with the current subtropical storm
Alberto, plan to keep the local forecast close aligned to the
Tropical Prediction Center/National Hurricane Center (TPC/NHC) and
the Weather Prediction Center (WPC) forecasts. Those with specific
interests associated with this circulation should refer to these
NOAA/NWS websites for more information.

A this time, the TPC/NHC forecast most closely aligns with the 00z
ECMWF guidance with the position and general intensity of the
expected remnants of Alberto, as it is forecast to move through
eastern Mississippi, western Tennessee, and near the Pennyrile
region of West Kentucky. The latest 12z Friday model run of the
ECMWF places the center of the circulation near the Todd/Muhlenberg
County KY by 7 pm Wednesday. At this point, frictional effects of
the circulation over land, the diurnal expansion and contraction of
the dynamic precipitation core with the circulation, and the
interaction with the surrounding ridge may play havoc with the
timing, location, and intensity of the circulation and attendant
precipitation.

From a QPF (rainfall amount) perspective, a majority of the rainfall
associated with the circulation is expected to fall during the
afternoon/evening hours on Tuesday, Wednesday, and Thursday. With
this forecast package (subject to many changes the next several
days), rainfall amounts are forecast to range from 0.6" to 1.00"
across the Pennyrile region of West Kentucky and into southwest
Indiana. WPC`s seven day forecast of QPF, suggests 1.5" to 2.00"
over the same area, but this includes any and all forecast rain from
today (Friday) through next Friday, June 1st. This would suggest
that at least half of the rainfall next week may likely be
associated with the remnants of Alberto, assuming it maintains a
similar track. Again, there will be some uncertainty as to the
eventual track and impact of Alberto for our area.

Temperatures next week will remain coolest (lower 80s) in the
vicinity of the greatest rainfall and cloud cover expected with
subtropical storm Alberto. However, after the passage of this
system, temperatures will be on the rise with subsidence behind the
circulation. This will likely generate heat index values in the
upper 90s on May 31st, with some locations see heat index values
around 100 during the afternoon on June 1st.

&&

.AVIATION...
Issued at 1239 PM CDT Fri May 25 2018

The TAFs are basically a convective forecast today. KPAH and KCGI
have a good chance of experiencing a TSRA this afternoon, while
KEVV and KOWB may stay just east of the activity today. The
convection should die off by sunset, and then we will be watching
for new development mainly in the east late Saturday morning. KEVV
and KOWB will be the most likely to see a TSRA Saturday. If a site
gets significant rainfall this afternoon, some fog potential will
exist late tonight if skies can clear out sufficiently. Too much
uncertainty to add to the forecast at this time.


&&

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

$$

SHORT TERM...DRS
LONG TERM...Smith
AVIATION...DRS


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