Area Forecast Discussion
Issued by NWS Paducah, KY

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894
FXUS63 KPAH 261935
AFDPAH

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

.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 1241 PM CDT Wed Jul 26 2017

Isolated showers and storms were just starting to pop up at noon
today. Most of the activity this afternoon is forecast to occur
near a weak front that extends from the kowb area northwest across
kevv. The mention of vcts was continued in the kevv/kowb tafs for
this afternoon. Otherwise, expect mainly scattered cumulus clouds
based around 4 to 5k feet.

The cumulus clouds will dissipate around sunset. Southwest winds
will remain strong enough to inhibit fog tonight. VFR conditions
will persist through Thursday morning.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until 8 PM CDT this evening for ILZ075-080>082-
     084>094.

MO...Heat Advisory until 8 PM CDT this evening for MOZ076-086-087-100-
     107>112-114.

IN...None.
KY...Heat Advisory until 8 PM CDT this evening for KYZ001>013.

&&

$$

SHORT TERM...MY
LONG TERM...SP
AVIATION...MY



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