Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 270132
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
832 PM CDT Wed Jul 26 2017

.UPDATE...
Issued at 831 PM CDT Wed Jul 26 2017

Just sent an expiration notice with the Heat Advisory that ended
at 8 pm CDT. Once the temperature/dewpoint limits during maximum
heating on Thursday are ironed out by the midnight forecast crew,
an special weather statement may or may not be needed to
highlight up to 105 degree values over southeast Missouri on
Thursday. Otherwise, increased coverage of convective activity
overnight and Thursday should mitigate any further heat advisories
for the remainder of the week.

&&

.SHORT TERM...(Tonight through Friday night)
Issued at 234 PM CDT Wed Jul 26 2017

The main forecast issue is convection associated with a strong
cold front that will cross our region Thursday night/Friday
morning. The timing and location of storms will be influenced by
mesoscale features that even the high-res models are not in
agreement on.

In the near term, isolated storms have developed in a very moist
and unstable environment this afternoon across southern IL, sw
Indiana, and nw Kentucky. Heat indices in the 105 to 110 range
have been widespread this afternoon, and the Heat Advisory will
continue into this evening.

The isolated activity this evening may then give way to a more
widespread period of thunderstorms overnight, mainly along and
north of a kmdh-kowb line. A 500 mb shortwave over Iowa at this
time will move eastward into Indiana overnight. This shortwave may
provide enough upper-level support to induce new convection along
outflow boundaries generated by the ongoing storms over southern
IL or the morning mcs that is decaying over Missouri. The 12z nam
is one of several high-res models that follow this idea.
Therefore, pops will be in the likely category overnight along
I-64. Heavy rain appears to be the primary hazard due to the
excessive moisture content of the atmosphere.

On Thursday, the timing and coverage of storms becomes very
muddled. While the models all generate qpf, the placement and
amounts are very random. One possibility is that the potential
overnight mcs will lay out a boundary across western KY and se
Missouri. This boundary would then become active during the
afternoon. The forecast basically follows this thinking, with
highs temps ranging from the lower 80s along the White River of
Indiana to the lower 90s along the Arkansas border. Heat indices
could again be a concern along and south of a kcgi-kpah-khop line,
but there is too much model variability to warrant any headlines.

Thursday night, the cold front will move southeast into the Lower
Ohio Valley. The gfs remains quite a bit slower than most other
guidance. The official forecast follows a faster consensus blend,
but in reality mesoscale outflow boundaries will likely make the
front difficult to locate. Showers and storms will be likely Thurs
night as a strong 500 mb shortwave drops southeast across the
Great Lakes region. Again, heavy rainfall will be a concern due to
high precip water values. Severe weather potential may be limited
by poor air mass recovery in the wake of outflow boundaries from
multiple rounds of storms. The convection should wind down
Friday as the front exits our region in the morning.

The cooler and drier air will be slow to filter southward on
Friday, however the difference should become noticeable Friday
night as dew points fall through the 60s.

.LONG TERM...(Saturday through Wednesday)
Issued at 234 PM CDT Wed Jul 26 2017

Above average confidence in the extended period with a welcome
pattern change to cooler, less humid conditions. Little, if any,
precipitation is expected through mid next week.

At 12z Saturday, surface high pressure will be centered over the
Great Lakes Region, helping to usher in a drier and cooler airmass
on northeast winds. Very little movement in this high pressure is
expected into early next week. As far as the overall upper level
synoptic pattern goes, ridging will be centered over the western
U.S. with troughing over the east. Our area will be dominated by
northwest flow aloft.

Dry conditions will be in place this weekend into Monday. Some
guidance is hinting at some diurnal convection as early as Tuesday
afternoon, but the confidence in this is too low to have mentionable
PoPs. By Wednesday, chances appear a bit better regarding diurnal
activity, and thus have some slight PoPs for this period.

Temperatures will be below normal this weekend, gradually rising
closer to normal by Tuesday and Wednesday as upper level heights
rise slightly. With highs in the low to mid 80s along with lower
humidity levels, it will be a very pleasant late July weekend.
Dewpoints are forecast to drop at least into the upper 50s to lower
60s area wide, and quite possibly into the mid 50s in some locales.
These values will be near or below the 5th percentile as far as
typical late July dewpoints go. Morning low temperatures will drop
into the upper 50s to lower 60s for a couple nights, providing an
almost early Fall-like feel to the air. A gradual rise in humidity
levels is expected next week, but it appears we should keep
dewpoints below 70 through Tuesday, and possibly into Wednesday for
much of the region. Overall, we can`t ask for much better weather to
close out July!

&&

.AVIATION...
Issued at 831 PM CDT Wed Jul 26 2017

Delayed discussion for the 00z Thursday WFO PAH TAF issuance.

Somewhat of a challenge to depict best convective activity times
with the approach of pre- frontal trough later tonight, ahead of
main cold front over southern IA, southeast NE, and central KS at
8 pm CDT. Diffuse warm front boundary still remains poised near
southeast Illinois, southwest Indiana, and northwest Kentucky at 8
pm CDT. This boundary will become more defined as impacts from
convective outflows from earlier thunderstorms this afternoon
smooth out with time.

There appears to be a pre-frontal boundary stretching from central
Missouri to near the St. Louis Metropolitan area. Attempted to
utilize the high resolution guidance, as well as the NAM-WRF
guidance to introduce rain chances overnight into each of the WFO
PAH TAF sites ahead of the pre-frontal trough. Attempted to focus
convection across the WFO PAH TAF sites in the 08z-14z time frame,
then again in the 20z-24z time frame. The second round of
convective will likely occur ahead of the main frontal passage.

Kept ceilings in VFR category for a majority of the time, with
some intrusion into MVFR visibilities for the KEVV and KOWB TAF
locations.

&&

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

$$

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



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