Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 301124

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
624 AM CDT Thu Mar 30 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 334 AM CDT Thu Mar 30 2017

A slow-moving low pressure system will continue to influence the
region today and tonight. Due to the initially slow movement of
this system, parts of the LSX CWA will be in a favorable location
for severe thunderstorms today, especially across the eastern CWA
during the afternoon hours. The potential for severe
thunderstorms will shift eastward with time, and the eastern half
of the CWA (especially locations east of the Mississippi River)
will have a greater chance of experiencing severe weather through
the evening hours compared to the rest of the CWA.

Ongoing SHRA/TSRA early this morning will gradually move out of
the CWA, leaving several hours for air mass recovery before the
next round of convection develops ahead of an approaching cold
front associated with the aforementioned low pressure system.
Although there is some question about the amount of cloud cover
and resultant destabilization today, models still depict 500-1000
J/kg of CAPE across the eastern CWA in the presence of 40-50 kts
of 0-6km shear. This will be sufficient for severe thunderstorms.
The primary threats are hail and damaging winds. A few isolated
tornadoes aren`t entirely out of the question, especially if
enough clearing occurs and instability values are higher than
expected, but forecast 0-1km shear values of around 10-15kts are
fairly low. The potential for tornadoes is greater farther east
where 0-1km shear values are much more favorable.

Lingering precipitation behind the departing low pressure system
should exit the region overnight. Overnight lows will be around 10
degrees cooler than last night due to a cooler post-frontal air


.LONG TERM...  (Friday through Wednesday)
Issued at 334 AM CDT Thu Mar 30 2017

Another disturbance will move onshore near the CA/OR border on
Thursday and settle into the southwestern CONUS on Friday as a
closed low pressure system. This feature then makes slow eastward
progress over the weekend, eventually approaching MO/IL. As has
been the case for the last few nights, the GFS, ECMWF, and GEM now
offer different solutions for the evolution of this feature and
for the evolution of the next 2-3 upstream disturbances. The
general consensus is that an active weather pattern will persist
through the middle of next week. Expect around 1-2 days between
the increased precipitation chances associated with these periodic
low pressure systems.



.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 612 AM CDT Thu Mar 30 2017

Main TAF concerns will be low stratus today and convective timing
this morning into this afternoon. IFR cigs and IFR vsbys have
built into UIN/COU respectively this morning. Expect these
conditions to improve quickly at COU, but to persist at UIN
through much of this morning. VFR cigs/vsbys are present at the
St. Louis metro sites currently and will persist through the next
couple of hours, but approaching showers/storms late this morning
into early this afternoon will bring lowered cigs/vsbys. A few
showers will persist at all sites late this afternoon into this
evening behind a cold front pushing through. This front will also
bring more widespread MVFR cigs towards the end of the period.

A few showers/isolated storms will continue to push north into the
terminal this morning. These storms should become more widespread
late this morning into early this afternoon, bringing periods of
lowered cigs/vsbys in heavy rain. Otherwise, expect a cold front
to push through late this afternoon bringing a wind shift to the
west and MVFR cigs.



Saint Louis     68  45  54  41 /  60  50  10   0
Quincy          61  40  49  37 /  70  80   5   0
Columbia        59  42  54  40 /  50  60   5   0
Jefferson City  60  43  56  40 /  50  60   5   0
Salem           71  47  53  40 /  80  40  20   0
Farmington      66  46  58  40 /  70  40   5   0




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