Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 141758

Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
1258 PM CDT Mon May 14 2018

Issued at 1235 PM CDT Mon May 14 2018

Appears a remnant MCV may just be beginning to help initiate
convection near the KC metro area. Line of agitated cumulus
extends to the ENE roughly along the Missouri River. Expectation
is for convection to continue to develop within an environment
characterized by 2000-2500 J/kg of MLCAPE and effective bulk shear
of around 20-30 knots. Convection should develop into
multicellular clusters as cold pools amalgamate and move ESE.
Still some uncertainty as to how quickly convection upstream
organizes and the track of the corridor of more organized
activity. Best guess is across portions of central and
northeastern Missouri late this afternoon moving toward the St.
Louis metro area by early evening. Some gradual weakening of
activity is depicted by many CAMs by the early evening hours,
likely in response to a slightly less sheared and unstable
environment. Main threats with convection late this afternoon will
be large hail and damaging wind gusts, with a transition to more
of a wind threat compared to large hail by early evening hours as
a more organized cold pool develops.



.SHORT TERM...  (Through Late Tonight)
Issued at 402 AM CDT Mon May 14 2018

The exact convective scenario for today/tonight remains unclear,
which is primarily a reflection of how many different ways there are
for SHRA/TSRA to develop and move across the area. In general,
precipitation chances will increase after 18z due to diurnal
instability as well as slight cooling aloft which will act to erode
an inversion near H7. Precipitation chances will increase further
after 00z after a southwesterly LLJ increases and focuses H85
moisture convergence across parts of the area. In addition to these
factors, the stalled frontal boundary located across northern MO and
southern IA (which has served as a focus for convection for the last
couple of nights) will also be sinking southward. Taken together,
this suggests that isolated to scattered SHRA/TSRA could develop
during the afternoon and one or more thunderstorm complexes should
develop tonight. The highest PoPs were focused across the northern
half of the CWA based on the position of the H85 LLJ and the
expected position of the frontal boundary. Given the instability and
the limited but nonzero shear, the primary severe weather threats
for this afternoon and tonight appear to be hail and damaging wind

Temperatures will be unseasonably warm again today with highs in the
mid/upper 80s to around 90 degrees. Similar to the last couple of
days, convective cloud debris will influence high temperatures for
today. Lows should be similar to or a few degrees cooler than last


.LONG TERM...  (Tuesday through Sunday)
Issued at 402 AM CDT Mon May 14 2018

Upper RIDGE that had dominated our region over this past weekend and
into today should have its dismemberment well underway by Tuesday as
the beginnings of several upper level disturbances begin to roll
across our region from a storm system over western CONUS.  The
western CONUS storm system will undergo cycling phases thru
dissolution and development as part of a larger Rex-Block as it gets
reinforced over the next week by additional storms coming onshore
from the Pacific.  The western CONUS Rex-Block pattern will remain
intact until late week.  At the surface, the synoptic cold front, or
rather what could be the heavily convective influenced effective
cold front, will make its main push thru our region on Tuesday and
Tuesday night with the front then stalling somewhere to our south
from Wednesday thru Friday.  The main result from all of this will
be moderately high rain chances initially being over much of the
forecast area at the start of the period with these rain probs
getting shunted more to the south over time, eventually with what
could yield a dry period from late Wednesday night thru early
Saturday.  Temperatures look to be above average thru Friday, but
not as anomalous as what we have seen this past weekend with
either clouds/rain or the frontal boundary being to the south
contributing to greater moderation towards climatological normals.

The dissolution of the western CONUS Rex-Block should lead to an
attempt at the development of an upper RIDGE back into our region
again for late Friday into Saturday.  The old surface front to our
south will also begin to buckle back to the north at this time and
the combo should yield to temperatures pushing even higher above
average along with a return of rain chances heading into Saturday
night.  Finally, a cold front looks set to push thru on Sunday and
continue the moderately high rain chances for much of the forecast



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1235 PM CDT Mon May 14 2018

Expectation is for an area of thunderstorms to develop across
portions of northwest Missouri and head ESE through parts of the
area. Some uncertainty as to the track of the more organized
storms, but KUIN at this juncture seems to have the highest
probability so added a TEMPO this afternoon. Kept VCTS mention at
all other terminals for now, but if confidence increases, will
need to ammend. Stronger storms will be capable of producing heavy
rainfall/reduced visibilities in addition to gusty winds and
potentially hail. Appears there will be a lull in thunderstorm
activity late this evening before additional storms develop later
on tonight. Cold front will slowly move through the area tonight
into Tuesday with winds veering to the west/northwest behind it
with lessening chances of showers/storms as well.


Maintained VCTS mention for early this evening for now as
monitoring developing thunderstorms across portions of northwest
Missouri. If confidence increases that terminal will be affected
by aforementioned storms, will need to ammend. Stronger storms
will be capable of producing heavy downpours/reduced visibility in
addition to gusty winds and hail. Should be a lull in activity
late evening/early overnight hours before additional storms try to
move toward the terminal later on tonight. Winds will shift to the
west/northwest by early Monday afternoon with a cold frontal




Record highs and record warm lows for St. Louis:
May 14th: 93 (2013), 73 (1915)
May 15th: 94 (1944), 72 (2013)

Record highs and record warm lows for Columbia:
May 14th: 90 (1987), 67 (1941)
May 15th: 90 (1944), 71 (1941)

Record highs and record warm lows for Quincy:
May 14th: 94 (1915), 66 (1932)
May 15th: 93 (1944), 69 (1962)




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