Area Forecast Discussion
Issued by NWS Paducah, KY

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345
FXUS63 KPAH 200725
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
225 AM CDT Fri Apr 20 2018

.SHORT TERM...(Today through Sunday night)
Issued at 215 AM CDT Fri Apr 20 2018

Winds vary from 4-5 kts in places, to calm. Similarly, temps vary
from near 40, to some mid 30s already showing up. With these
trends, we`ll continue the headline freeze/frost thru expiration
(14Z) this morning.

The surface High over IA early this morning migrates eastward to
the Great Lakes during the day. Light easterlies keep dry/cool air
over the region, and soundings suggest mix down dew points in the
upper 20s-lower 30s this pm. That`ll make for low RH readings this
pm, particularly in the Ozarks, where mid 20s percentile is
possible, creating an elevated fire danger with drying fuels.

Models continue to track our late weekend weather maker south of
the area. The Canadian, which had the landfall best pegged 24
hours ago, is further south than the others operationally by its
evolution/formation in the southern Plains. This trending adds
confidence to the southern track, and as such, we are not prepared
to introduce any thunder with the rain chances, as most models
keep even elevated instability south of the FA.

Pcpn chances move in from the south/west Sat night, and
increase/spread across the area Sun-Sun night. Most of the
appreciable QPF is over by 12Z Monday, with nearly 1 inch of storm
total rainfall possible along our Arkansas and Tennessee border
areas, tapering to 3/4 inches from CGI-PAH-MAD, with 1/4 inch
amounts (or less) along/north of a MDH-OWB line.

Below normal temps continue thru the Quilt Weekend forecast. Temps
today and Sunday will make their way into the low end 60s, while
the warm day (Saturday) makes the best push closer to seasonal
norms with mid-upr 60s most locations, maybe 70F along the TN
border counties of southwest KY.

Lows tonight will be near 40F, with maybe a 37-38F possible in
sheltered, remote northern locales. Isolated patches of frost
could occur there, but headlines are not anticipated.

.LONG TERM...(Monday through Friday)
Issued at 215 AM CDT Thu Apr 19 2018

Now that the closed low in southern CA/NV/AZ is within a denser
observational network, there should be a little more consistency in
the resolution/timing of the system as it move in and around the WFO
PAH forecast area on Monday. The Canadian guidance has been fairly
consistent the past couple of days with the evolution of this
system, but the deterministic 00z Friday GFS seems to have taken
over as the preferred medium range guidance for this forecast
package. At this point, there is medium to high forecast confidence
(50-70%) with the rain chances Monday into Monday evening.

Forecast confidence for rain chances Tuesday through Thursday are
below average (generally below 40%) as there exists high model
variability in both the deterministic and ensemble guidance on the
timing, evolution, translation, and phasing of the northern
U.S./southern Canadian border shortwave developing next Monday.
Given the variability, will stick with the low PoP regionally
blended model guidance as a starting point. The antecedent eastern
Pacific and western Canada circulations serving as a genesis
point for the dominant shortwave on Monday are not even expected
to move over the northwest U.S. until Sunday at the earliest.
Utilized a blend of the regionally blended model initialization
with some influence of the current deterministic/MOS GFS guidance
and the spatially reduced NAM guidance.

All in all, it appears that next week will see below normal (5-10
degrees below) highs and lows and mainly showery precipitation
with the greatest coverage Monday, then again Wednesday and
Thursday. Temperatures may rebound to near normal next Friday with
dry conditions into next weekend.

&&

.AVIATION...
Issued at 215 AM CDT Fri Apr 20 2018

Despite near dry adiabatic lapse rates in the lower 4K FT AGL this
pm, condensation pressure deficits in excess of 100 mb should
preclude development of impact low VFR bases. Time/height cross
sections reveal very dry air in the 850-500 mb layer until late
tonight, when some nominal moisture increase down to about 600 mb
may portend scattered cirrus advection topping the H5 ridge during
the last few hours of the planning phase of the forecast.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Frost Advisory until 9 AM CDT this morning for ILZ080-081-
     084>094.

     Freeze Warning until 9 AM CDT this morning for ILZ075>078-082-
     083.

MO...Frost Advisory until 9 AM CDT this morning for MOZ076-086-087-
     100-107>112-114.

IN...Frost Advisory until 9 AM CDT this morning for INZ085>088.

     Freeze Warning until 9 AM CDT this morning for INZ081-082.

KY...Frost Advisory until 9 AM CDT this morning for KYZ001>022.

&&

$$



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