Area Forecast Discussion
Issued by NWS St. Louis, MO

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811
FXUS63 KLSX 180305
AFDLSX

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
905 PM CST Fri Feb 17 2017

.UPDATE...
Issued at 905 PM CST Fri Feb 17 2017

Forecast appears to be on track with only minor adjustments made
into Saturday.

Upper level LOW is located over eastern OK this evening with an
area of rain on its downstream flank with the northern extent near
the intersection of MO-KS-OK. The LOW center is expected to track
E-NE thru far southeastern MO around midday Saturday and into the
OH Valley Saturday night.

Scattered WAA showers associated with this LOW are still expected
to move into southeast MO late tonight and continue past daybreak
with a transition at some point toward late morning to an attempt
at getting a deformation zone of stratiform pcpn going in nearly
this same area. It is at this point where a few tweaks to the
forecast were made--expanding the northern coverage a bit into
STL metro and most of the I-70 corridor for some sprinkles
possible late Saturday morning and into the afternoon.

Otherwise, temps left alone for most areas from previous forecast.

TES

&&

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 234 PM CST Fri Feb 17 2017

The main item of interest over the next 24-30 hours will be the
threat of any rainfall associated with the lifting upper low
currently located over the southern Plains.  Model consenus shows
the upper low lifting east-northeast tonight to the vicinity of the
NW AR/SW MO border by 12Z Saturday, and then into the TN Valley by
early Saturday evening. The increase in clouds with this system will
contribute to mild temperatures tonight with most locations only
experiencing lows in the 40s, and some record high mins will be
possible. The unseasonably warm temperatures (+20 to +25 degrees
above average) will continue on Saturday as well, however the
greater cloud cover should temper the max temp readings back a bit
from those experienced the last few days.

Rainfall is a little more iffy. Weak large scale ascent associated
with the upper low spreads into southeast MO and southern IL
overnight and persists to varying degrees on Saturday morning. The
low levels however are quite dry and moisture will be largely
confined to the mid-upper levels. I prefer the RAP depiction of this
and thus some scattered rain showers seem the most probable scenario
across parts of southeast MO and southern IL, with the probability
diminishing and shunting east in the afternoon with the progression
of the upper system.

Glass

.LONG TERM...  (Saturday Night through Next Friday)
Issued at 234 PM CST Fri Feb 17 2017

Upper ridge to build into region Saturday night, so will see dry and
above normal temperatures through the rest of weekend and into early
next week. Near record highs Sunday and Monday in the upper 60s to
mid 70s.

By Monday, upper ridge begins to move off to the east as next
weather system approaches. So will see low level moisture on the
increase as well as decent instability for our area. But still have
the issue with split flow aloft, models continue to lift the
northern stream wave out faster through the Great Lakes region,
while southern stream closed low tracks eastward slowly. However,
12z model runs are a bit more optimistic with two streams phasing
together, giving us better chances for rain early Monday morning
through Tuesday morning. Could see scattered/isolated thunderstorms
Monday afternoon/evening, mainly over central/northeast MO, as well
as west central IL, so added thunder mention there.

Weak boundary washes out over region for mid week with zonal flow
aloft, so will see slightly cooler highs in the mid 60s to low 70s.

Next system to approach area on Thursday with strong cold front
moving through Friday. This is when we will have our best chances of
showers and a few thunderstorms. Highs will dip down into the low
50s to mid 60s by Friday, but still above normal for this time of
year.

Byrd

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 545 PM CST Fri Feb 17 2017

VFR conditions and southwesterly surface winds will prevail at the
TAF sites thru the valid period. An upper level storm system will
pass to our south late tonight and Saturday morning, and should
result in some rain shower development, but this currently is
expected to remain to the south of the TAF sites, but if any one
area and time has a greater chance than the others, it is the STL
metro sites around 12z. Will monitor observations and the latest
model data for any adjustments and inclusion of rain mention in
the TAFs this evening.

TES

&&

.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: 72/2017  68/1971  71/1930  72/2016


&&

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

$$

WFO LSX



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