Area Forecast Discussion
Issued by NWS St. Louis, MO

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431
FXUS63 KLSX 260419
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1119 PM CDT WED MAY 25 2016

.UPDATE...
Issued at 908 PM CDT Wed May 25 2016

The evening has been quiet so far as forcing has been weak over
the area. Have lowered PoPs the rest of the evening into the
overnight hours. It still looks like there may be some showers and
thunderstorms move into northeast Missouri and west central
Illinois after midnight. This development will be in response to
the RAP showing some low level moisture convergence underneath a
weak mid level vort max moving across the area. The experimental
HRRR runs have been very consistent with depicting this
development, so will maintain high chance PoPs over the northern
CWA late tonight into early Thursday morning. Otherwise, the rest
of the forecast still looks good.

Britt

&&

.SHORT TERM...  (Through Late Tonight)
Issued at 248 PM CDT Wed May 25 2016

Convection across parts of southeast MO and southwest IL should
shift east-southeast of our forecast area by early this evening.
With shortwave energy shifting east-northeast of the region it
appears that most of the forecast area should be dry this evening.
Still a lot of uncertainty as to where convection will initiate
later tonight, but it appears that there may be convection
developing and moving into parts of northeast MO and west central
IL late tonight on the nose of a southwesterly low level jet. With
continued southerly surface winds and relatively high surface dew
points, lows tonight will be at least 10 degrees above normal for
late May and a little warmer than the previous night.

GKS

.LONG TERM...  (Thursday through Next Wednesday)
Issued at 248 PM CDT Wed May 25 2016

Low confidence forecast continues with regards to the location,
timing and coverage of convection expected with weak southwest
flow shortwaves continuing to move through the area coupled with
a warm, moist and unstable southerly low level flow. May be mainly
scattered diurnal convection during the afternoon and early
evening on Thursday with slightly warmer temperatures. Should see
an increase in cloud cover along with coverage of showers/storms
by Friday as an upper level trough/low over southwest US
approaches from the Plains. Will increase pops into the likely
category on Friday over the entire forecast area, along with
cooler high temperatures due to the increased cloud cover and
precipitation coverage/duration expected. This upper level trough
should shift northeast of our area by Saturday night with a lull
in the convective activity expected from Saturday night through
at least Sunday night. The warm and humid weather pattern should
continue for Memorial Day into the next work week with weak
southwest upper level flow and weak surface winds. Mainly
scattered diurnal convection is expected during the afternoons and
early evening hours. The ECMWF model does have an upper level
trough moving eastward through the northern Plains which sends a
cold front southeastward through our forecast area on Wednesday
which would be a focus for convection, but the GFS model does not
have these features, so for now will just have chance pops for
the end of the extended forecast period.

GKS

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1119 PM CDT Wed May 25 2016

Showers and thunderstorms could still occur at anytime during the
TAF period in this warm and unstable airmass. Chances are not high
enough to include at any terminals before 12Z except KUIN when
scattered showers and thunderstorms currently enter northwest MO
may affect that terminal. Some MVFR/possible IFR ceilings and
visibilities may occur with the heavier downpours during this
time. Otherwise expect dry and VFR conditions until after 00Z when
showers and thunderstorms are expected to move into the area from
the west. Winds will be southerly except when otherwise
influenced by outflow from thunderstorms.

Specifics for KSTL: Mainly dry and VFR conditions are expected
the next 30 hours. There is some potential for thunderstorms
during the period, with the main chance occurring after 12Z on
Thursday. Any thunderstorms would have the potential to bring
MVFR or possible IFR ceilings and visibilities with the heavier
downpours.

Britt

&&

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

$$

WFO LSX



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