Chris's Corner - March Madness 2019

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
701 PM CDT Sun May 5 2019

.SHORT TERM... (Through Late Monday Night)
Issued at 310 PM CDT Sun May 5 2019

A broad-based upper TROF existed over the eastern two-thirds of the
CONUS this afternoon, resulting in a flat flow over our region.
Within this flat flow were several, generally weak, upper level
disturbances. At the surface, a cold front extended from central
Wisconsin through northern Iowa and into southern Nebraska.
Temperatures were in 70-75 range for most locations with thin cirrus
clouds moving overhead. The column is rather dry at the moment and
that, along with the lack of a surface boundary, is keeping things
precipitation free currently.

The surface cold front to our northwest will continue to push
southeastward tonight, reaching southeast IA by 12z/Wed and likely
too far away still to have much impact on rain chances in our
forecast area. However, increasing moisture in the column late
tonight and development of a low level jet should allow for isolated
to scattered shower/storm development edging into central/northeast
MO towards daybreak Monday that will carry into Monday morning for
most areas north and west of STL metro.

Precipitation will stagnate some later on Monday until the cold
front, by now pushing into northeast MO, can re-energize with the
heating of the day. Models are also focusing in on enhanced lift
and development over in northwest MO Monday afternoon with a complex
of storms that develops there then tracking E-SE into our forecast
area Monday night, mainly in central, east-central, southeast MO.
Scattered development late in the afternoon in central MO may become
strong-severe and continue with the leading edge of the complex that
emerges out of northwest MO in the evening. With a cold front
expected to sag to near the Interstate 70 corridor late Monday
night, some backbuilding is expected and could lead to an increasing
flood threat for overnight Monday night.

Max temps on Monday are expected to be a bit higher than
persistence, although persistent rain/clouds may keep things close
to persistence in areas north/west of STL metro: with readings
peaking in the 75 to 80 range. Min temps tonight should be in the
low-mid 50s, higher than persistence thanks to clouds, with upper
50s to low 60s most locations Monday night.

TES

.LONG TERM... (Tuesday through Next Sunday)
Issued at 310 PM CDT Sun May 5 2019

The overall scenario from Monday night of an active flat upper flow
pattern with regular passages of disturbances, a surface frontal
boundary lingering around, and a high precipitable water (PW)
content in the column, is expected to continue through Thursday,
with moderate to high PoPs for much of this period.

There is a strong model consensus on PWs through Thursday hovering
around 1.5" which is above the 90th percentile for early May values
and this, along with high warm cloud depths for much of this period,
will promote efficient rain processes with what falls. It is hard
to nail down exactly who will get the higher rainfall chances, and
therefore the deterministic QPF that we are going out with will tend
to be on the low-side.

Temperatures will tend to slip to below normal values with highs in
the 60s, possibly upper 50s, on the cool side of the front in
northern MO, but areas on the south side with any period of sunshine
will have little problem rising into the upper 70s or near 80. This
will be the forecast problem through Thursday on where exactly the
frontal boundary ends up each day.

This wet period will culminate in the ejection of a strong upper
level storm system that is currently expected to track west and
north of our region late Wednesday into Thursday, dragging the cold
front thorough for the final time. While there appears to be a good
setup for severe thunderstorms with this event, the timing will be
key, and it appears the more organized convection will be to our
west on Wednesday and may fire just to our east on Thursday.
Refinements and confidence increases on timing will occur as we
approach the event.

Otherwise, look for a pattern change after Thursday as a more
amplified upper TROF builds over our region from the north and will
promote a cooler, less thundery, situation for Friday and into next
weekend. In fact, some areas may dip into the upper 30s for lows
Friday and Saturday morning with the right amount of clearing.

TES