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000
FXUS63 KPAH 171033
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
533 AM CDT Tue May 17 2022

.SHORT TERM...(Today through Thursday night)
Issued at 304 AM CDT Tue May 17 2022

For today through this evening, the middle and upper ridge axis
will move over the WFO PAH forecast area with little more than
high level cirrus impacting the area. With modest southerly flow
rose temperatures into the lower 80s. This may be slightly
underdone, depending on the mixing, so would not be surprised in
seeing some middle 80s across the area as well.

From after midnight tonight through noon on Wednesday, mainly
elevated convection associated with the passage of a minor mid-
level mesoscale shortwave will pass across mainly the northern
third of the WFO PAH forecast area. The highest PoPs will be
focused along the northern third of the area during the morning
daytime hours.

From Wednesday afternoon through Wednesday night, the
aforementioned shortwave shears out, leaving some channeled
vorticity across the area. The combination of weak low/middle
level convergence and instability, oriented in a roughly a west to
east zone from southern Illinois, eastward to southwest Indiana
and northwest Kentucky may lead to more focused thunderstorm
activity during the late evening Wednesday. QPF amounts during
this time do not appear to be impressive, given the weak flow and
steering currents.

However, given the positive NAEFS/ECMWF ensemble 1.5 to 2.5
standard deviations of precipitable water and integrated water
vapor over the aforementioned area, would not be surprised to see
a few pockets of excessive rain. This is in line with the marginal
area of excessive rainfall indicated by WPC.

Although the WFO PAH forecast area is outlooked in an SPC
Marginal Risk of of Severe Storms late tonight (in the northwest
part of the forecast area) and across the entire area Wednesday
and Wednesday night, do not have a high confidence of organized
severe convective activity. Cannot rule out isolated strong or
severe thunderstorms with the passage of the shortwave and in the
lingering channeled zone of vorticity and instability on
Wednesday and Wednesday evening.

For Thursday and Thursday night, heights/thicknesses rise from
the south as a capped warm sector builds in advance of sub-
synoptic scale shortwave working in the northwest U.S. and
northern Plains area, shifting the mean baroclinic zone back to
the central Plains and upper Midwest. Should see a marked increase
in temperatures in excess of 10-12 degrees above normal on
Thursday.

From a model perspective, blended the Canadian/European/NAM
guidance with the NBM initialization for the broader sub-synoptic
scale features (including PoPs and QPF), with the
HREF/NAMNest/HRRR guidance associated with storm-scale
PoP/QPF/Wind fields.

.LONG TERM...(Friday through Monday)
Issued at 304 AM CDT Tue May 17 2022

A strong cold front will make its way through the Quad State at some
point Friday night into Saturday. Aloft, a large positively-tilted
upper trough will extend from the Rockies northeast toward Hudson
Bay Friday. The tail end of this trough will drag its heels eastward
and eventually push the cold front through our region.

Ahead of the cold front, strong south winds will likely require a
Lake Wind Advisory for Friday with sustained winds 15 to 20 mph and
gusts 25 to 30 mph. It will be hot, as well, with highs pushing 90
degrees over much of the region. The 00Z GFS indicates 700mb
temperatures near 12C, while 700mb to 500mb lapse rates are around
9C/km, which is nearly dry adiabatic. Despite plenty of SBCAPE,
without a boundary or upper forcing to break the cap, storms are
unlikely to develop.

As the cold front approaches and the upper trough impinges on the
region, showers and thunderstorms will become more likely later
Friday night and Saturday. It should be rather unstable south of the
front Saturday which could support a few strong to severe
thunderstorms, but the 00Z GFS and ECMWF both indicate that the
stronger winds aloft will lag behind the front, which should keep
overall storm organization/intensity in check.

The 00Z GEFS and 18Z ECENS struggle to generate high probabilities
of just a half an inch of QPF, let alone an inch or more, so heavy
rainfall and flooding are not a great concern at this time, even
with the boundary being oriented nearly parallel to the upper flow.

Surface high pressure will settle over the region Sunday as the flow
aloft become nearly zonal. Forecast confidence decreases heading
into next week, as the 00Z GFS generates a significant upper trough
over the Four Corners Monday, while the ECMWF, and to a certain
extent the CMC, have a flatter, nearly zonal flow continuing through
next Tuesday. Cluster analysis on the 12Z Ensembles showed
considerable spread in the pattern by next Monday, which adds to the
uncertainty. Due mainly to the GFS, the NBM has chance PoPs
returning Monday night into next Tuesday. Would prefer to have a dry
forecast until the GFS gets some better support from the other
guidance.

Temperatures will start out well above normal Friday and then drop
down to near normal Saturday depending on frontal/convective timing.
Sunday will see highs generally around 70 or nearly 10 degrees below
normal. From highs around 90 to highs around 70 in just 2 days is
impressive. Temperatures will climb back to near normal levels by
next Tuesday.

&&

.AVIATION...
Issued at 533 AM CDT Tue May 17 2022

Either clear skies or high level cirrus clouds expected through
the early evening across the WFO PAH TAF sites. Some lower VFR
cloud decks are expected closer to 06Z Wednesday as the remnants
of a decaying MCS move closer to KMVN and KCGI.

Some lingering climatologically favored fog will lift within the
first 1-2 hours at KCGI and KMVN this morning, with VFR
visibilities expected for most of the forecast period for each of
the WFO PAH TAF site.

&&

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

$$

SHORT TERM...Smith
LONG TERM...DRS
AVIATION...Smith