Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262020
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
320 PM CDT MON SEP 26 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 315 PM CDT Mon Sep 26 2016

Clear, dry and much cooler conditions for tonight as a strong
surface ridge continues to build into our area from the Plains with
northwesterly upper level flow due to the deep upper level low just
north of the Great Lakes region.  The 850 mb temperatures late
tonight will range from around 8 to 11 degrees C across our forecast
area.  There will be good radiational cooling due to a crystal clear
sky, surface dew points only in the lower to middle 40s, and
diminishing surface winds this evening.  Although it will feel much
cooler than the past several nights, lows tonight will only be
around 5 degrees below normal for late September.  There will be
some steam fog in the river valleys late tonight and early Tuesday
morning due to the cool air over the warm river water, but this
should be mainly confined to these areas due to the dry
surface/boundary layer conditions.

GKS

.LONG TERM...  (Tuesday through Next Monday)
Issued at 315 PM CDT Mon Sep 26 2016

The synoptic pattern at the start of the long term period will
feature a strong upper-level low over the northern Great Lakes, with
ridging across the western CONUS.  This low will meander to the
southeast through the period, becoming cut off from the upper-level
flow over the Ohio Valley by this weekend.  This regime will keep
seasonably cool and dry conditions in the forecast through the
period.

Tuesday will be fairly similar to today, although it will likely be
a couple of degrees warmer ahead of a cold front slated to move
through on Wednesday.  Mixing to around 850mb will once again yield
fairly breezy conditions across northern MO/western IL given around
25 knots of flow in this layer.  Look for sustained winds of 15-20
mph with a few gusts around 25 mph.

A rather strong PV anomaly will dig southeast around the upper-level
low on Wednesday.  This will help drive a cold front through the
region Wednesday morning.  The strong mid-level ascent associated
with the impulse will likely bring some enhanced cloudiness to the
region Wednesday afternoon, but forecast soundings are just too dry
to squeeze out any measurable precipitation. Behind the front and
with at least some cloudiness (especially in IL), Wednesday`s
temperatures will be the coolest of the period (and of this young
fall season), with highs only expected in the upper 60s/low 70s.

Canadian high pressure will then remain in control for the remainder
of the week into the upcoming weekend.  This will keep dry
conditions in the forecast but temperatures will slowly climb
through the 70s each day Thursday through Monday of next week.

KD

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1135 AM CDT Mon Sep 26 2016

Northwest surface winds will back around to a westerly direction
by late this afternoon or early this evening as the surface ridge
centered over the southern Plains shifts slowly southward. A
surface low just north of the Great Lakes region will also drift
slowly southward. The surface wind will become west-southwesterly
by late tonight, albeit quite light. The wind will increase again
Tuesday morning from a westerly direction. A clear sky can be
expected through the forecast period. There may be some steam fog
in the river valleys late tonight and early Tuesday morning due to
the cool air over the warm river water which could impact SUS and
CPS, although the surface/boundary layer will be quite dry.

SPECIFICS FOR KSTL: Northwest surface winds will back around to a
westerly direction by late this afternoon or early this evening
as the surface ridge centered over the southern Plains shifts
slowly southward. A surface low just north of the Great Lakes
region will also drift slowly southward. The surface wind will
become west-southwesterly by late tonight, albeit quite light. The
wind will strengthen again Tuesday morning from a westerly
direction. A clear sky can be expected through the forecast
period.

GKS

&&

.FIRE WEATHER...
Issued at 317 PM CDT Mon Sep 26 2016

Winds around 15 mph and minimum relative humidity between 25 and
30 percent will combine with dry fuels to produce an elevated
fire danger across parts of northeast Missouri and west central
Illinois again on Tuesday afternoon. Increasing relative
humidities and lower wind speeds should mitigate the fire danger
across the rest of the area.

KD


&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     53  77  55  70 /   0   0   0   5
Quincy          48  74  51  67 /   0   0   5   5
Columbia        50  74  52  69 /   0   0   0   0
Jefferson City  50  77  53  70 /   0   0   0   0
Salem           49  75  52  69 /   0   0   0   5
Farmington      47  77  53  70 /   0   0   0   0

&&

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

$$

WFO LSX



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