Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 010859
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
359 AM CDT Wed Apr 1 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 354 AM CDT Wed Apr 1 2015

An upper ridge axis will pass overhead today. At the surface, a
boundary which was located near the MO/AR border last night will
be drawn northeastward as a warm front during the day in response
to a developing low pressure system over the northern plains. The
thermal ridge axis will be over central MO and good mixing
conditions are forecast. Based on these factors, people in MO/IL
can expect another day of unseasonably warm temperatures with
afternoon highs reaching the mid to upper 70s. Attention then
turns to fire wx. Although winds will be rather breezy at times
due to the tightening pressure gradient, increasing dew points
throughout the day will probably keep RH values too high to meet
Red Flag Warning criteria but low enough to meet criteria for
Heightened Fire Danger. This will be mentioned in the Fire Weather
Forecast (FWF) and Hazardous Weather Outlook (HWO) products.

Kanofsky

.LONG TERM:  (Tonight through Tuesday)
Issued at 354 AM CDT Wed Apr 1 2015

One area of convection is possible late this afternoon and early
tonight near the eastern Ozarks where instability will be a bit
higher compared to farther north. Another area of convection is
expected to develop tonight near a cold front which will stretch
from KS through NEB into IA. As decaying upstream convection moves
southeastward, precipitation chances across the LSX CWA will
increase overnight, especially after midnight and especially
across northeast MO/west central IL. PW values are forecast to be
around 0.8-1" tonight, which is near the 75th percentile for April
in this part of the country.

The cold front will sag southward on Thu, eventually becoming
oriented W-E. Ahead of the front, PW values rise to around 1.3" by
18z, which is at +2SD for April. Despite the cloud cover which
will inhibit diurnal destabilization, an increasingly moist air
mass will be spreading northeastward ahead of the cold front. Any
breaks in the clouds will add to the instability. Another round of
thunderstorms is expected to develop on Thursday afternoon,
especially south of I-70. Some of the storms could be strong to
severe based on forecasts of 40-60 kts of 0-6km bulk shear. The
shear vectors are forecast to be oriented nearly parallel to the
approaching cold front.

The cold front`s southward progress on Thu night may be delayed
by a new surface low which develops on the tail end of the front
in KS in response to an approaching shortwave. The surface low
then rides along the boundary on Thu night and Fri, and the cold
front finally sinks south of the area late Thu night or early Fri
morning.

Compared to the late spring warmth of the last few days, Fri`s highs
in the 50s and Fri night`s lows in the mid-30s will seem like a
blast of winter. Temperatures will begin to rebound slightly over
the weekend after a surface high pressure center shifts southeast
of the area and low-level flow becomes southwesterly around the
back side of the high. The area remains beneath northwest flow
aloft this weekend. Another low pressure system could bring
precipitation to parts of MO/IL early next week.

Kanofsky

&&

.AVIATION:  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1044 PM CDT Tue Mar 31 2015

Little if any cloud cover expected this forecast period. There
may be a few cirrus clouds, and also a few diurnal cumulus clouds
Wednesday afternoon and early evening. Light surface winds in
surface ridge axis will become s-sely late tonight. The wind will
strengthen and become gusty during the day on Wednesday as the
surface ridge shifts east of the region and a cold front moves
southeastward through the northern Plains causing the surface
pressure gradient to tighten over our area.

Specifics for KSTL: Little if any clouds for much of the period.
There may be a few cirrus clouds, and also a few diurnal cumulus
clouds Wednesday afternoon into the early evening. The light
surface wind will veer around to a sely direction late tonight.
The wind will strengthen and become gusty during the day on
Wednesday. Mid-high level cloudiness will increase late Wednesday
night due to an upper level disturbance and the approaching cold
front.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX





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