Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 191735

Area Forecast Discussion
National Weather Service Paducah KY
1235 PM CDT Sat Aug 19 2017

Issued at 1235 PM CDT Sat Aug 19 2017

The AVIATION section has been updated for the 18Z TAF issuance.


.SHORT TERM...(Today through Monday night)
Issued at 420 AM CDT Sat Aug 19 2017

Delayed discussion this morning while addressing near term and
eclipse-related forecast concerns. A more detailed eclipse weather
discussion will follow.

Weak surface convergence/trough evident in LAPS mass and pressure
fields this morning. Current convection over southwest Indiana
being reflected near this boundary. Canadian and GFS Ensemble
suggest sharpening/deepening of the trough over southern Illinois
through 7 am CDT with sharpening lapse rates enough to redevelop
convection along the surface trough. The Canadian/NAM-
WRF/ECMWF/ESRL HRRR guidance have a general handle on the timing
and location of this convective activity this morning as it moves
across southeast Illinois, Southwest Indiana, and the Pennyrile
region of west Kentucky. This activity should diminish quickly
from the west into the afternoon as the mid/upper level trough
axis moves to the east.

The northern limb of a weak and low amplitude ridge will build in
from the southwest during the afternoon and evening hours,
suppressing convection. Minor shortwave impulses ejected from the
offshore closed upper low near southern California will work to
dampen the ridge over the area overnight, bringing a small chance
for rain to southeast Missouri early Sunday morning. The ridge
will build back in during the day on Sunday and Sunday night,
limiting any potential for convection overnight.

This ridge will help delay the onset of convection from the upper
Midwest/Upper and Middle Mississippi Valley on Monday and Monday

The capping effect of the ridge will also minimize mixing of low
level dewpoints during the latter part of the weekend. Heat Index
values could reach into 95 to 100 degree range on Sunday. Due to
the potential for a significant influx of persons into the area,
may issue and special weather statement highlighting the heat
index values for Sunday and Monday.

...Saturday morning forecast discussion on solar eclipse weather
for the Quad State region...

This discussion will highlight the expected weather and concerns
associated with the solar eclipse. The coverage area includes
southeast Missouri, southern Illinois, southwest Indiana, and west

Opaque cloud cover through the main solar eclipse period, 17z-19z
(noon through 3 pm CDT) should remain below 30% (mostly sunny)
over all, but parts of southeast Missouri and southwest Illinois.

Suspect the increased coverage of cloud over southeast Missouri
will likely be due to debris clouds drawn downstream from remnant
MCS (Mesoscale Convective System, aka thunderstorms clusters) over
MO/KS overnight and during the morning hours on Monday. The upper
level flow should deflect most of the cloud cover to the east-
northeast. The ridging aloft and moisture trajectory near the
surface should slow the progression of the linear MCS further to
the north through the evening hours on Monday. The upper level
flow from these storms should keep most of the clouds north and
east of the area for the most part during the eclipse period. Even
if there is a cirrus deck in place, it should be thin enough to
see the eclipse.

The eclipse itself should reduce the impact of heat index values
along the core path, but heat index values between 95-102 degrees
will be likely over the delta region of southeast Missouri and
extreme southwest Kentucky and Illinois between 1 pm and 5 pm.

Thunderstorms will move in mainly during the afternoon and
nighttime hours on Tuesday and could pose a concern for travelers
leaving late in the day.

.LONG TERM...(Tuesday through Friday)
Issued at 420 AM CDT Sat Aug 19 2017

Tuesday into early Wednesday, a mid/upper upper level trough will
drop southeast into the MS/OH River Valleys with an associated
cold front. Should be plenty of moisture to work with too, with
surface dew points in the muggy 70s. Tuesday afternoon and evening
now look to bring the highest thunderstorm chances to the
forecast area. Given instability and shear expected, would not be
surprised to see a few strong to severe storms around the region.
Once the surface front passes on Wednesday, a major change in air
mass should take place as high pressure drops southeast from
Canada into the Midwest and western Great Lakes. High late in the
week will only be near near 80 in most locations with lows in the
mid 50s to near 60.


Issued at 1235 PM CDT Sat Aug 19 2017

An isolated shower or storm will be possible this afternoon over
west Kentucky mainly near the TN border. No impacts expected for
the TAF sites. Winds today will be under 10kts mainly from the
west, but the direction may vary a bit with strong mixing

Clear and calm conditions for most of the night may result in some
fog development, but it should be of the shallow and patchy
variety. Have inserted MVFR fog at a few locations, but lower
conditions are possible. There is some indication that some lower
VFR clouds may increase late tonight which could hamper

Any convection Sunday will be very isolated and therefore is not
likely to impact the TAF sites. South winds will pick up with
mixing mid-morning.




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