Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 171129
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
529 AM CST Fri Feb 17 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 451 AM CST Fri Feb 17 2017

A disturbance which was located over TX early this morning will
slowly lift northeastward today and tonight. Despite the approaching
upper disturbance, little rain is expected due to the lack of
moisture through the column. The best opportunity for light
sprinkles would be across the southern one-quarter of the CWA after
midnight tonight when a modest increase in moisture aloft coincides
with increasing large-scale ascent. Even so, the most likely outcome
is an increase in mid/high clouds with perhaps a few isolated
sprinkles.

To call today`s forecast highs "a bit warm" is an
understatement...or perhaps an exercise in dry humor. The
combination of low dew points, a warm start to the day, good mixing,
and abundant insolation will push afternoon highs into the 70s,
which is 20-30 degrees above average for this time of year. BUFKIT
soundings depict mixing to slightly above 900 hPa where temperatures
of ~12 deg C would yield expected highs in the upper 60s. However,
mostly clear skies, favorable southwest winds, mixing to slightly
higher than 900 hPa, and recent MOS cold biases all support
increasing highs by several degrees.

There is an elevated fire danger across parts of the area today due
to the combination of low RH values, low fuel moisture values, and
breezy winds. Please refer to the fire weather forecast for details
(http://forecast.weather.gov/product.php?issuedby=LSX&product=FWF&sit
e=lsx).

Kanofsky

.LONG TERM...  (Saturday through Thursday)
Issued at 451 AM CST Fri Feb 17 2017

Much above normal temps with highs in the 60s to mid 70s and lows in
the 40s and 50s thru the entire fcst prd. These lows are aoa the
normal highs...and these temps are fcst each and every day thru the
prd. Very anomalous pattern to maintain that degree of warmth for
such an extended prd.

Sat

Vort max will pass across nthrn AR and into KY/TN. Models are
spitting out some spotty very light QPF. Think this may be more of a
sprinkle event with maybe a site or two that actually measures.
Right now going with very limited slight chance PoPs with no mention
of sprinkles...yet. Fire weather AFD will be updated by 5 AM.MOS
has had a cold bias recently and has been undercutting actual
highs by several degrees. Having said that... plenty of clouds
will keep temps from getting out of control Sat and generally went
with a blend of MOS

Sat night - Sun night

Weak SFC high builds into the region in tandem with an upper level
ridge. SFC ridge axis passes Sat night allowing return flow to
become established by Sun mrng. The sthrly winds coupled with rising
heights aloft and 850 temps in the lower double digits sets the
stage for a very warm day with highs fcst to be in the upper 60s to
mid 70s.

Mon - Tue night

The next system approaches the region on Mon. It is a split flow
system with an open wave nthrn stream short wave with a closed low
sthrn stream system. As a result...the nthrn stream short wave is
more progressive than the sthrn stream feature which will
effectively cause the system to become quite sheared by Tue. Due to
the strength of the upstream ridge...the system is slow to move E
Mon/Mon night. QPF and precip coverage decrease on Tue as the actual
nthrn stream trof move thru the area. Have slight chance and chance
PoPs to account for this precip threat. Any precip should move E Tue
evng. The closed low tracks across TX and into the nthrn Gulf of
Mexico and will not be a concern to our region. Clouds and precip
should keep temps mainly in the 60s on Tue but Mon will be another
very warm day with deep sthrly flow in advance of the approaching
system with highs once again in the upper 60s to mid 70s.

Wed - Wed night

Flow becomes more zonal for the middle of the week. No cold front is
assoc with the Tue short wave therefore winds remain sthrly and the
well above normal temps will continue. A short wave tracking along
the US/Canadian border will attempt to drag an assoc cold front into
the region Wed aftn/evng but it is fcst to stall across the nthrn
CWA or just off the the N/NW. Heights are not quite as high as
earlier in the week and 850 temps are not quite as warm so even
though temps are expected to be well above normal...they should be
a touch cooler than Mon highs.

Thu - Thu night
Fire weather AFD will be updated by 5 AM.
The Wed aftn/evng cold front stalls in response to the approach of
the next storm system. Another significant storm is fcst to move
onshore along the W Cost Tue/Wed and it is this energy that will
affect the cntrl CONUS for the end of the week. The stalled cold
front will transition into a warm from from late Wed night into Thu
mrng as a significant SFC low dvlps across the cntrl Plains. The
warm front is expected to remain nearly stnry along the IA/MO border
thru Thu before beginning to move N Thu night. WAA precip is
possible Thu night into Fri mrng. This system will continue to
affect the region thru Fri. Eventual position of the warm front will
be key to the temp fcst across the nthrn CWA for Thu. Regardless of
the frontal position though...temps will remain well above normal
thru the end of the week.

2%

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 522 AM CST Fri Feb 17 2017

VFR through the period with increasing mid/high clouds after
18/06z. LLWS conditions will diminish by mid-morning after diurnal
mixing increases, which will also lead to wind gusts near 20 kts
during the day. Winds will remain SW to S through the pd.

Kanofsky

&&

.FIRE WEATHER...
Issued at 451 AM CST Fri Feb 17 2017

Warm temps in the low/middle 70s with dew points in the middle
30s will produce minimum RH values near 20 percent. The
combination of the low minimum RH with winds of 12-15 mph and aftn
minimum 10 hr fuel moisture well down in the single digits will
produce a heightened fire danger across cntrl...NE and E cntrl MO
and W cntrl IL.

2%

&&

.CLIMATE...
Record Highs

 2/17  2/18  2/19    2/20
STL: 77/1911  74/1971  77/2016  78/2016
COU: 74/2011  71/1930  76/1930  76/2016
UIN: 70/2011  68/1971  71/1930  72/2016


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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