Area Forecast Discussion
Issued by NWS Kansas City/Pleasant Hill, MO

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357
FXUS63 KEAX 262315
AFDEAX

AREA FORECAST DISCUSSION
National Weather Service Kansas City/Pleasant Hill MO
615 PM CDT Wed Apr 26 2017

.Discussion...
Issued at 302 PM CDT WED APR 26 2017

Large upper-level trough continues to work through the central
U.S. this afternoon with lingering light shwr activity currently
impacting the southern 2/3rds of the forecast area. All
appreciable instability now resides well east of the fcst region,
thus we can expect lingering shwrs for a few more hours this
evening before all activity eventually shifts eastward. Main
issue with this afternoon`s package revolves around possible frost
development early Thursday morning as high pressure gradually
builds into the region. Biggest questions involve whether skies
will clear enough for the current temp forecast to materialize,
and also whether winds will weaken enough for frost development.
Despite these uncertainties, enough evidence is there to support
partial clearing after midnight which facilitated the issuance of
a frost advisory for the far northwestern zones after midnight.

Previously mentioned high pressure should result in dry
conditions on Thursday before shwrs redevelop over the region
Thursday night into Friday as an 850 low approaches from the west.
Isentropic ascent should increase across the region beginning
tomorrow night as a strengthening low-level jet interacts with an
inverted trough and midlevel front which both should begin
working across our area tomorrow evening. Shwr activity should
gradually come to an end by Friday afternoon as the lagging sfc
low eventually tracks over the area. Rainfall amounts with this
system should remain less than a half inch as instability should
be limited thus preventing heavier rainfall rates.

Bigger concerns make their initial appearance early Saturday with
the threat for moderate and potentially locally heavy rainfall
continuing through much of the upcoming weekend. Main culprit
continues to be a stalled surface front which today`s model runs
suggest will be quite a bit south of our area, mainly south of the
I-44 corridor before feature begins to lift north as a warm front
by early Sunday morning. South of the front, fcst models continue
to show impressive moisture advection out ahead of a deep longwave
trough approaching from the Four Corners region. With PWAT values
on the order of 3 to 4 standard deviations above normal with an
even stronger low-level jet, the ingredients appear to be in place
for a widespread heavy rain event across the Ozarks and mid-
Mississippi Vly. From today`s model viewpoint, much of our region
appears to be spared the heaviest rains, which makes sense based
on the expected frontal position for latest guidance trends.
Despite this, long duration rainfall looks increasingly likely
this afternoon, which over time, will certainly add up. Latest
event total QPF fcst calls for over 3 inches south of the Route 50
corridor, with totals as high as an inch and a half up along the
Iowa border. This rainfall will certainly lead to a response on
area rivers and streams, but best potential for any convective
rainfall rates will remain south of our area thanks to the
southward position of the front. In fact, much of the upcoming
event looks to be thunder free, expect for areas along and south
of Route 50 where some elevated instability may be able to sneak
north enough to lead to some embedded storms.

Rain shwrs eventually come to an end late Sunday night as main
sfc low tracks away from the region. Strong cold advection on the
backside of this system will lead to a chilly start to next week
with temperatures gradually increasing by midweek as warm air
advection increases ahead of the next system that should begin
impacting the area Tues ngt/early Wed.

&&

.Aviation...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 615 PM CDT WED APR 26 2017

Ceilings should linger in the high MVFR or low VFR range through
the evening and into the overnight hours, perhaps thinning out
around sunrise tomorrow. Winds will remain from the northwest
through the overnight hours and then back to the southwest
tomorrow afternoon. Once wind speeds decrease this evening, they
should remain below 10kts through the rest of the forecast.

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
KS...Frost Advisory from 1 AM to 8 AM CDT Thursday for KSZ025-102.

MO...Frost Advisory from 1 AM to 8 AM CDT Thursday for MOZ001>004-011-
     012-020.

&&

$$

Discussion...32
Aviation...CDB



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