Scientific Forecaster Discussion
fxus63 klsx 231138
Area forecast discussion...updated aviation
National Weather Service Saint Louis MO
638 am CDT Mon Oct 23 2017
Short term... (through late tonight)
issued at 343 am CDT Mon Oct 23 2017
Closed midlevel low is currently near the MO/Arkansas border as of 0800
UTC and is continuing to move very slowly eastward. Most of the
precipitation last evening and overnight last night fell just ahead
of the 850-hpa frontal boundary where there was strong moisture
advection. That area has by and large pushed off to the east, though
parts of south-central Illinois will likely still get clipped by
some additional light rain this morning. Further to the
west/southwest, am expecting deformation zone to try and fill in
with light rain as the low continues to deepen. Increased pops
substantially for the morning hours, mainly across portions of
southeast Missouri and southwest Illinois. The threat of rain with
this feature will push off to the east of the area by early
afternoon as the system gets kicked out quickly into the Ohio Valley
as an upstream shortwave trough amplifies across the upper Midwest.
Because of the increased sky cover and chances of rain, decreased
high temperatures several degrees across parts of southwest Illinois.
Meanwhile, a secondary cold front will move through the region late
this afternoon ahead of the shortwave trough moving across the upper
Midwest. Scattered rain showers are possible behind this frontal
boundary predominantly across northeast Missouri and west-central
Illinois tonight. Tight pressure gradient will lead to some fairly
gusty west-northwest winds late this afternoon into at least the evening hours
as well, on the order of 20-30 mph. As for temperatures tonight, it
will be nearly 10 degrees cooler behind the front tonight compared
to this morning, with lows in the low to mid 40s expected areawide.
Long term... (tuesday through sunday)
issued at 343 am CDT Mon Oct 23 2017
The synoptic pattern at the start of the long term period will
feature a large trough over the Midwest and Great Lakes region. This
will keep north/northwesterly upper-level flow over the region until
Thursday. Yet another trough will slide out of Canada into the
eastern Continental U.S. Towards the end of the period bringing the coolest air
of the season to the area this weekend.
Tuesday will be a raw, cool, and damp fall day across the area. The
strong/deep upper-level low will be meandering across the Great
Lakes region, sending vort lobes into our area around its periphery.
One such vort Max should help Foster the development of showers on
Tuesday mainly across Illinois and eastern MO. With the rain chances,
widespread cloud cover, and brisk west/northwest winds (sustained
around 20 mph with gusts upwards of 30 mph) it will be a cool day.
Temperatures will struggle to get out of the 40s in many areas, and
may not get out of the mid 40s in portions of Illinois.
Heights will rise on Wednesday and especially into Thursday as 850mb
warm air advection commences. Temperatures should warm as a result,
into the 60s on Wednesday and near 70 on Thursday.
By Thursday night, a surface cold front will push through the region
ahead of another strong pv anomaly diving southeastward out of
Canada. While there could be a few showers near this boundary
Friday, it mostly appears to be a mainly dry fropa. This front will
certainly pack a punch though, as the coolest temperatures of the
season will spill in behind it. Low temperatures are expected in the
upper 20s and low 30s by Saturday and Sunday mornings. Given the
agreement seen in the ensemble and operational guidance on this cold
air intrusion, confidence is increasing that this weekend will bring
our first freeze to at least parts of the area, effectively ending
the growing season. With the cool/dry air in place, rain chances
look slim through the upcoming weekend.
Aviation... (for the 12z tafs through 12z Tuesday morning)
issued at 624 am CDT Mon Oct 23 2017
Scattered showers may affect the Metro terminals this morning but
should move off to the east by noon. Cold front will move through
the region this afternoon with northwest winds picking up in
speed. Expect sustained winds of 10-15 knots and gusts in the
20-25 knot range through tonight at kcou and KUIN. Strongest wind
gusts likely at KUIN very late this afternoon through the early
overnight hours. Scattered showers may also affect KUIN tonight.
Specifics for kstl:
Expect scattered showers to redevelop early this morning. Not
expecting widespread coverage so just mentioned a vcsh group for
now. Threat for showers should move off to the east by noon.
Another cold front moves through by mid afternoon. Winds will pick
up in speed early Tuesday morning with sustained winds of 10-15
knots and gusts of 20-25 knots.