Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 121655

1155 AM CDT MON OCT 12 2015

Issued at 1155 AM CDT MON OCT 12 2015

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

UPDATE Issued at 1058 AM CDT MON OCT 12 2015

Updated the forecast to increase PoPs late this afternoon up to
40-50%. Most convection-resolving guidance this morning and the
12Z NAM are generating better coverage of convection along or
just ahead of the cold front around 21Z. This is occurring farther
to the northwest than accounted for in the early morning forecast.
It will still primarily be a west Kentucky event, but initial
development may be near KPAH and KEVV around 21Z. It still looks
like a short window in time with most of the activity weakening
and to the southeast of the area by 00Z.

NAM soundings over west Kentucky reveal a very deep well-mixed
boundary layer, and just enough moisture to get convection going.
Wind fields have enough helicity in the 0-3km layer to support
supercell structures, but the instability may not be great enough
to sustain individual cells long enough for the storms to get
organized. Given the steep low-level lapse rates, a few strong
wind gusts are still the primary concern.


.SHORT TERM...(Today through Wednesday night)
Issued at 300 AM CDT Mon Oct 12 2015

The main forecast issue for today is precip potential with a
southeastward moving cold front. The cold front was over northwest
Missouri early this morning. The RUC/NAM/HRRR and a couple of cam
models are all in strong agreement the front will extend from the
Lower Ohio Valley to the Missouri Bootheel at 21z. All models show
dry conditions until that time. Starting around 21z, most guidance
generates qpf along the front as it crosses western Kentucky.
Taking a look at model soundings, there is an elevated warm layer
around 850 mb that acts as a cap until that time. A narrow axis of
surface-based capes up to around 1000 j/kg develops and becomes
the focus for convection late this afternoon. The window of
opportunity is fairly short, since stabilization begins around
00z. Will maintain a 20 to 30 percent chance of showers/storms
this afternoon and early this evening, mainly across west
Kentucky. The limiting factors for higher pops are marginal low
level moisture and weak frontal convergence.

As for highs today, the main concern is the large amount of
moisture indicated by NAM/RUC/GFS model soundings in the 800/700
mb layer. If this translates into extensive cloudiness today,
highs would have trouble reaching 80. This does not appear likely
enough to lower forecast temps, so will keep lower to mid 80s in
the forecast.

The forecast becomes as dry as a bone after any lingering precip
exits western Kentucky this evening. Guidance indicates very dry
air through the entire column late tonight through Wednesday. Will
forecast clear skies and zero pops. As we have seen in recent very
dry air masses, diurnal temp ranges tend to be greater than the
models indicate. Will forecast lows below guidance, especially
Tuesday night, when winds will become nearly calm. Some river and
lake fog is likely on Tuesday night/early Wed morning, much like
early Sunday morning.

.LONG TERM...(Thursday through Sunday)
Issued at 300 AM CDT Mon Oct 12 2015

Main weather system is Thursday night. Models agree on fropa
Thursday night, with a band of decreasing moisture just behind the
front moving through from NW to SE. ECMWF continues to paint scant
QPF, while the GFS and GEM are dry. There has been back and forth on
the minimal model QPF, or lack thereof. Really don`t like flip
flopping on slight chance PoPs. But for now we prefer to leave the
minimal mention of showers out until there is a clearer run to run
signal and greater consensus. Other offices per coord have backed
off the slights as well, that were collaborated prior (yesterday
afternoon). Otherwise breezy and warm Thursday ahead of the front,
then cooler and dry rest of Friday through the weekend as all the
models move high pressure SE from the Upper Midwest Saturday to the
Mid Atlantic by Sunday evening. Temps will be a blend of ensemble
MOS, and our existing numbers.


Issued at 1155 AM CDT MON OCT 12 2015

Gusty southwest winds will veer to due west as a cold front
approaches this afternoon. The latest guidance indicates that
scattered showers and thunderstorms will develop near the cold
front beginning around 21Z in the vicinity of KEVV and KPAH. The
convection will move quickly eastward and will have the greatest
chance to impact KOWB. Any convection should be southeast of the
terminals by 00Z. West winds and dry advection should prevent any
fog overnight, so the forecast is VFR outside of TS. Northwest
winds will pick up with mixing Tuesday morning.




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