000
FXUS63 KEAX 230519
AFDEAX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE KANSAS CITY/PLEASANT HILL MO
1119 PM CST WED FEB 22 2012

...UPDATED AVIATION...

.DISCUSSION...

Short term (Tonight - Friday)...

Thermal gradient ended up a bit further south than anticipated with
a weak trough passage earlier this afternoon. Coupled with periods
of mid clouds, readings ended up a bit cooler than anticipated, but
with lighter wind has averaged out to a really nice day.

The presence of a deep trough over the eastern US and a powerful jet
blasting into the Pacific Northwest will collectively enhance the
mid-upper level thermal gradient just north of the area with a
tendency toward more northwesterly upper flow through the next 36 to
48 hours. This will allow several shortwave impulses to rapidly
translate through the mean jet branch, the most significant of which
will deepen across the Dakotas tonight.

Model output seems to have diverged into two camps with the
intensity and placement of this shortwave, leading to significant
differences in the precipitation fields tomorrow and tomorrow night.
The SREF mean closely matches the 12Z NAM/OPGFS which takes the mid
level trough and surface low across Iowa, with a secondary sfc low
across northern Missouri. This is the preferred solution, and would
tend to dry-slot the CWA, keeping the bulk of precipitation across
Iowa into the Great Lakes region. Ahead of the wave, a narrow stripe
of light rain may clip north central/northeast Missouri later
tonight into Thursday, so have kept slight to low chance POPs here.
The bigger impact tomorrow will be the winds which will increase
sharply during the late morning owing to a strong post-frontal
pressure gradient. Could see gusts frequently in the 30 to 35 mph
range. The stronger cold advection will lag until later in the day
so temps will have a chance to again reach into the 50s except the
far northwest, but again with a bite to the air.

Only change made to the short term forecast was to lower
temperatures Friday. After bottoming out near 30 Friday morning,
moderate low level cold advection will persist within broad cyclonic
flow. This will also act to retain cloud cover, especially over the
northeast CWA, so do not expect much of an upward response, and this
is well justified with the 925 and 850mb temp forecasts as well as
1000-500mb thicknesses below 520dm. Surely we could (and should) be
much much colder than forecast for this time of year as the
adjustments made still only place temperatures just below normal.

Bookbinder
Medium Range (Saturday - Tuesday):

The main challenge in the extended continues to be the timing of a
system for early next week followed by a secondary wave in the
Tuesday timeframe. Models are in good agreement with the upper
pattern through Saturday, depicting transient shortwave ridging
across the Plains and Midwest. While this will moderate the
temperatures across the area, especially as the upper trough gets
shunted eastward, think that fairly large temperature gradient will
exist across the forecast area. Our northeastern zones will still be
under the influence of cold air aloft to tune of -4C to -8C at
850mb. While there is ample warm advection just don`t see that area
making it out of the upper 30s. On the contrary, our southwestern
zones may be able to climb into the upper 40s to near 50 degrees.

Guidance remains in reasonable agreement into Sunday with appears to
be a very strong system ejecting into the Central Plains and moving
into the Upper Midwest. Models have been consistent taking the upper
level wave to the north of the area so it appears as though we
should be in the warm sector of any system until it passes to the
northeast. Much of the impacts in our area will depend on how well
moisture is able to stream back northward from the Gulf as well as
timing of any frontal passage during peak heating. There is too much
uncertainty to nail anything down at this point in time but the
strength of the system suggest that if moisture can be lifted
northward then there is a chance for some strong storms in the
Central Plains into western Missouri. But moisture, at this time,
looks to be the limiting factor. Despite there being high pressure
in the southeastern CONUS helping shift the fetch of winds over the
Gulf to onshore the moisture would need to travel a great distance
to have much of an impact and at this time just have a hard time
seeing that happen. So a broken line of showers/rain seems more
likely as the front moves through.

That front is expected lay out/stall to our south leaving cold air
in place across the region. A secondary wave is then forecast to
move into the Plains and interact with this preexisting baroclinic
zone and quickly spin up another surface low that then tracks across
Missouri to our south. This would be a favorable scenario for snow
for us and think that mentioning a chance for rain/snow for Tuesday
and snow for Tuesday night is reasonable at this point in time. All
that said, next week looks to be active across the region with
highly variable weather. It must be late winter or early spring.

CDB

&&

.AVIATION...

For the 06Z TAFS...VFR conditions are expected for the overnight
hours as overcast mid level clouds around 9kft with SE winds around
5-10kts will be the rule. Wind this morning may become light and
variable for a period as a cold front approaches tomorrow morning.
Have removed LLWS from the previous TAF as 00Z models runs have
significantly back off on 2kft winds for tonight. The aforementioned
cold front is forecast to move through the terminals between 12Z and
14Z. Behind the front winds will veer to the WNW around 10-12kts
tomorrow morning. A strong pressure gradient behind the front will
cause surface winds to pick up to 15-20kts and become gusty with
gusts to 30kts. Models are also now suggesting that a reinforcing
surface trough behind the front may further increase wind to
20-25kts with gusts to 35kts later tomorrow afternoon and tomorrow
evening. Model soundings are also indicating a broken to overcast
deck around 3-4kft moving into the terminals for late tomorrow
afternoon and tomorrow night but cigs should remain just above MVFR
conditions.

73

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
KS...NONE.
&&

$$

WFO EAX

NWS EAX Office Area Forecast Discussion