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Area forecast discussion
National Weather Service Saint Louis MO
312 am CDT Tue Oct 16 2018

Short term... (through late tonight)
issued at 309 am CDT Tue Oct 16 2018

A ridge of high pressure centered over the eastern Great Plains is
currently bringing the mid Mississippi Valley the coldest
temperatures so far this fall. Latest temperatures in the low to
mid 30s are supportive of the frost/freeze headlines we currently
have in place. Of concern though is the high cloud cover streaming
up in upper level southwest flow east of a large upper low centered
over Arizona. These clouds are likely putting a damper on the
proper radiational cooling conditions which would produce widespread
frost across parts of east central and southeast Missouri in our
frost advisory area. Normally, I would cancel some parts of the
advisory at this point, but just to complicate matters GOES-16
channels 7 and 14 are showing holes in the clouds moving over parts
of southeast and east central Missouri into southwest Illinois.
There are many spots that look like the same temperature as the
ground in clear portions of the forecast area. Since I cannot
totally rule out frost, and the products are already in effect, I
will let the headlines ride as is for the time being.

Remainder of the day should be quiet as the surface ridge axis
shifts southeast into the Tennessee Valley and another relatively
weak cold front drops into the mid Mississippi Valley. I did bump
wind/wind gusts up slightly to 15-25 mph as the pressure gradient
tightens ahead of the front this afternoon across parts of
northern Missouri and west central Illinois. Otherwise relatively
light 5-10 mph westerly wind along with a decent amount of
insolation should allow temperatures to rise into the 50s across
the area. The aforementioned cold front loses some of its punch
overnight as its parent low up in southern Canada continues moving
east and the pressure gradient relaxes over the Mississippi
Valley. It doesn't look like the temperature advection behind the
wind shift will be particularly strong, but 5 to 10 mph west-
northwest winds won't be the best for radiational cooling.
Temperatures tonight will likely be a few degrees warmer than this
morning's readings in the upper 30s to low 40s.


Long term... (wednesday through monday)
issued at 309 am CDT Tue Oct 16 2018

Surface ridge will build into the region on Wednesday with sunny
skies and north winds. Despite the clear skies, temperatures will
only warm up into the mid 50s to low 60s, about 10 degrees below
normal for this time of year.

Below normal temperatures and clear skies will persist through
Thursday before next system moves in Thursday night. As surface
ridge slides off to the east, southerly flow will return to the
region with increasing low level moisture as well as a decent
shortwave sliding northeast towards forecast area. Warm air
advection shower activity will develop over southwestern Missouri
and track to the east into forecast area after 06z Friday. In the
meantime GFS and European model (ecmwf) indicate a pattern change with upper level
ridge building in the west and trof over the eastern U.S., So will
have northwest flow aloft over region with the first in a series of
cold fronts sliding southeast into the forecast area by late Friday
afternoon. This boundary will push the shower activity out of region
by 00z Saturday. Not a lot of cold air advection on backside of
system, but temperatures will remain below normal for this time of
year through the weekend and into early next week. Another cold
front will approach region on Monday, but extended models keep
majority of energy and moisture across the Great Lakes region closer
to main surface low.


Aviation... (for the 06z tafs through 06z Tuesday night)
issued at 1039 PM CDT Mon Oct 15 2018

Surface ridge extending from the Texas Panhandle northeast through
northwestern MO will shift slowly southward. Light west-
northwest surface wind will back around to a southwest direction
as it strengthens late Tuesday morning. Just high level
cloudiness mainly over the St Louis Metro area. Steam fog in the
river valleys late tonight/early Tuesday morning due to cold air
over the Warm River water may impact sus and cps.

Specifics for kstl: surface ridge extending from the Texas Panhandle
northeast through northwestern MO will shift slowly southward.
Light northwest surface wind will back around to a west-
southwest direction late Tuesday morning as it strengthens. Just
high level cloudiness this forecast period.


Preliminary point temps/pops...
Saint Louis 58 44 59 38 / 0 0 0 0
Quincy 57 39 55 34 / 0 0 0 0
Columbia 57 40 59 35 / 0 0 0 0
Jefferson City 58 38 60 36 / 0 0 0 0
Salem 56 41 58 35 / 0 0 0 0
Farmington 57 43 59 36 / 0 0 0 0


Lsx watches/warnings/advisories...
MO...frost advisory until 9 am CDT this morning for Crawford MO-
Franklin MO-Gasconade MO-Jefferson MO-Saint Charles MO-
Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte
Genevieve MO-Warren MO-Washington MO.

Freeze warning until 9 am CDT this morning for Audrain MO-Boone
MO-Callaway MO-Cole MO-Knox MO-Lewis MO-Lincoln MO-Marion
MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike MO-
Ralls MO-Shelby MO.

Illinois...frost advisory until 9 am CDT this morning for Bond Illinois-Clinton
Illinois-Fayette Illinois-Madison Illinois-Marion Illinois-Monroe Illinois-Randolph Illinois-
Saint Clair Illinois-Washington Illinois.

Freeze warning until 9 am CDT this morning for Adams Illinois-Brown Illinois-
Calhoun Illinois-Greene Illinois-Jersey Illinois-Macoupin Illinois-Montgomery Illinois-
Pike Illinois.

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