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000
FXUS63 KPAH 211921
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
221 PM CDT Sun Apr 21 2024

.KEY MESSAGES...

- A Frost Advisory remains in effect until 8 AM CDT Monday with
  lows dropping into the mid 30s late tonight.

- The next chance of rain arrives late Tuesday into Tuesday
  night with light rainfall amounts. A few rumbles of thunder
  are possible. Additional chances of rain are possible late
  week.

- Above normal temperatures with highs in the 80s are likely
  Friday through the weekend. The pattern turns more active
  beginning Saturday with the potential for strong storms
  increasing through the weekend.

&&

.DISCUSSION...
Issued at 219 PM CDT Sun Apr 21 2024

A 1030 mb sfc high pressure is now located over Oklahoma this
afternoon as the pressure gradient has allowed for breezy conditions
with deep mixing above 850 mb. Scattered cu has also developed
across the FA, but skies quickly turn clear tonight with the loss of
diurnal heating as the high pressure builds southeast. The boundary
layer will also quickly decouple with sfc wind quickly turning calm.
These conditions are ideal for radiational cooling as the NBM 50th
percentile has minTs progged in the 34-37 degree range. There are a
few locations that could dip closer to freezing, especially across
the Ozark Hills. It is worth mentioning 300 ft AGL model soundings
indicate the temp will be 3-4 degrees warmer with a shallow
inversion. This means even a transient 3 mph wind could cause temps
to be a bit variable across the FA, but still pretty confident most
locations go calm to support frost. For this reason, a Frost
Advisory remains in effect until 8 AM CDT.

Anticyclonic flow on the backside of the high on Monday will allow
for southerly return flow and more seasonable conditions with maxTs
back in the mid to upper 60s. The warming trend continues into
Tuesday with maxTs rising into the low to mid 70s as a 500 mb
shortwave ejects southeast of the Dakotas. By 00z Wednesday, the
right entrance region of a 80 kt jet max at 500 mb will be located
over IN/IL, with enhanced 300 mb divergence. The better forcing
helps to squeeze out a bit more 700 mb moisture along the I-64
corridor as a cold front sags south of sfc low pressure over the
great lakes region. Model guidance is in decent agreement on timing
as light pcpn will move across the FA from northwest to southeast
late Tuesday into Tuesday night. The 12z NAM is a bit more robust
with pockets 300-600 J/kg of MUCAPE and 700-500 mb lapse rates
around 7.0 C/km, but this only results in general thunder. One
caveat to the forecast is a trend for higher QPF amounts as the EPS
is now showing between a tenth to a quarter of an inch, which also
has support from the deterministic GFS/NAM. Overall, the consensus
by the WPC is for QPF to range from a few hundreths to two tenths of
an inch up north as the GEFS is not quite as wet.

An upper level ridge axis builds across the central CONUS Wednesday
into Thursday as a 500 mb low moves onshore over California. The GFS
is still showing a subtle 700 mb impulse that could trigger a few
light rain showers in the afternoon, but most model guidance has
remained consistent in keeping the energy south of the FA. In fact,
the NBM keeps the PoPs silent as there is only a 10% probability for
measurable QPF. However, Thursday night into Friday may feature a
better risk for pcpn as a warm front provides some isentropic lift
combined with a shortwave ahead of the aformentioned 500 mb low.
Higher humidity and much warmer maxTs in the upper 70s to lower 80s
can be expected to end the week on Friday.

Model uncertainty increases Friday night as the GFS is more
amplified with the 500 mb low near the NE/SD border compared to the
ECMWF/CMC. If the GFS scenario were to be correct, a 850 mb jet
would cause an influx of theta-e and moisture transport with PWATs
rising to 1.5" across the FA. At the moment, this appears to be an
outlier as the GEFS only indicates a 10-20% probability for over an
inch of rainfall, but heavy rain would be a concern should this
scenario play out. Daily chances for convection then begin Saturday,
and become more likely next Sunday-Monday as a 500 mb longwave
trough digs across the Rockies. This remains a period when severe
weather probabilities will be elevated as the GEFS still shows a
high probability of SBCAPE exceeding 1000 J/kg. Meanwhile, the EPS
is still meager with instability while the GEPS is more of a
compromise. While the details are murky this far out, there is
confidence in a robust warm sector regime with dewpoints in the
upper 60s, theta-e around 340K, and maxTs in the 80s that will
support the potential for an active period of convection. At the
very least, it will feel a lot more like summer with humid
conditions.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1123 AM CDT Sun Apr 21 2024

Visible satellite imagery shows SCT cu development across the
region this morning. Brief BKN around 5 kft AGL cannot be ruled
out this afternoon; otherwise, skies quickly turn clear tonight
as high pressure builds in from the west. N-NW winds around 9-12
kts with gusts between 15-20 kts will quickly turn calm after
sunset. Mainly clear skies to start the day Monday with S-SW
winds around 5-7 kts.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Frost Advisory from midnight tonight to 8 AM CDT Monday for
     ILZ075>078-080>094.
MO...Frost Advisory from midnight tonight to 8 AM CDT Monday for
     MOZ076-086-087-100-107>112-114.
IN...Frost Advisory from midnight CDT /1 AM EDT/ tonight to 8 AM
     CDT /9 AM EDT/ Monday for INZ081-082-085>088.
KY...Frost Advisory from midnight tonight to 8 AM CDT Monday for
     KYZ001>022.

&&

$$

DISCUSSION...DW
AVIATION...DW