Areal Flood Warning 2, NWS St. Louis, MO

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1202 PM CST Mon Feb 4 2019

.SHORT TERM...  (Through Late Tonight)
Issued at 232 AM CST Mon Feb 4 2019

Focus through the period will be precip chances, with an added
focus tonight on temperatures, which may result in potential for
FZRA.

A surface low has developed and is currently centered over
eastern KS, with a second centroid over northern IA, which will
become the primary low. As this low continues to develop, the
accompanying cold front will push southeast through the CWA today.
The front is expected to be just entering the far NW portions of
the CWA around 15z, along a KPPQ to KJEF line at 18z, K3LF to KCPS
to KTBN at 21z, and just SE of the CWA at 00z. There is good
model agreement with this timing of the cold front.

Clouds have spread across the region early this morning ahead of
the approaching cold front. These clouds, coupled with the strong
southerly flow, have helped to keep temps generally in the 50s. A
few locations that have decoupled have dropped into the lower 40s.
Expect breaks in the clouds to develop ahead of the front across
southern portions of the CWA. Some question remains just how much
clouds will clear up today. Regardless, with the strong WAA ahead
of the front, have trended aoa the warmer guidance for temps
today. If more clearing can occur, the going forecast may still be
too cool.

Models continue to suggest light precip possible along the front.
Confidence is still somewhat low, but models now show a brief
period of lift just ahead and along the front which should support
light showers. A few of these showers have developed over eastern
IA. Given the coverage should remain scattered, have kept PoPs
capped at 50 percent.

Rain should come to an end quickly behind the front. While temps
behind the front currently drop quickly to freezing behind the
front, this should be tempered somewhat today with what little
insolation does exist. As the surface low continues to pull east
into the NE U.S., the cold front should stall somewhere across
northern AR. This will help relax the pressure gradient across the
area and the CAA will subside somewhat. Still, expect temps to
drop below freezing across all but the southern third or so of the
CWA.

The NAM/GFS prog a weak s/w ejecting into the Plains tonight. This
coupled with WAA into southern portions of the CWA may support some
light rain and/or freezing rain across portions of SE MO and into
central MO by sunrise Tues. The GFS suggests a drier boundary layer
that would be less supportive of rain, while the NAM keeps deeper
clouds across this area. Have added slight chance PoPs for late
tonight. Will need to continue to monitor this for potential impacts
into Tues morning.

.LONG TERM...  (Tuesday through Sunday)
Issued at 232 AM CST Mon Feb 4 2019

The overall scenario for Tue through Thu remains unchanged:
ascent over a stalled frontal boundary will produce periods of
precipitation, most of which will fall as rain and some of which
will fall as a wintry mix of rain, freezing rain, sleet, and snow.
It still appears that the wintry mix will be confined to parts of
central and NE MO into west central IL.

BUFKIT soundings depict a deep (~200 hPa thick) and intense (near
+10 deg C) warm nose aloft and a much shallower cold air mass
near the surface for Tue/Tue night. This means that the
precipitation type at any given time will depend heavily on the
surface temperatures and will vary between rain and freezing rain
as the temperatures cross 0 deg C. Sleet and snow are both
expected during precipitation onset and ending, but the dominant
wintry precipitation type in central/NE MO and west-central IL
for the bulk of the event should be freezing rain. Elsewhere, only
rain (non-freezing) is currently anticipated. As the event is
winding down, deepening cold air will cause the rain to mix with
and then change over to snow across the area, but no accumulations
are expected.

The total ice accretion in central/NE MO and west central IL will
range from a trace to around two tenths of an inch (6am Tue
through 6pm Thu). However, the amount of ice on outdoor surfaces
will be less than the event total because there will be at least a
brief break in the precipitation on Wed and temperatures will
warm into the mid-40s. This means that ice accretion from the
first wave on Tue afternoon/night will likely melt before the
second wave begins on Wed afternoon/night.

Compared to 24 hrs ago, the models are slightly farther north with
the northernmost extent of the stalled frontal boundary as it
wavers across the region during the middle of the week. A
slightly more northward position doesn't seem entirely
unreasonable given that a new wave of low pressure will develop
in CO/KS along the western edge of the boundary, and the resulting
atmospheric response will tend to push the boundary northward as
a warm front. Once this final wave of low pressure lifts
northeastward into the Great Lakes, the trailing boundary will
pass through the region as a cold front, and a much colder air
mass will spread into MO/IL.

Lows on Thu night will range from the upper single digits to
around 20 degrees, which will seem quite cold in comparison to the
unusual warmth of the preceding days. Highs on Friday will be in
the 20s-30s. The 1045 hPa surface high which will be responsible
for driving the colder air mass into MO/IL then passes north of
the region, and therefore temperatures should begin to moderate
for Fri-Sun as the surface high shifts eastward and winds turn
southerly to southeasterly around the back side of the departing
high pressure center.

Another low pressure system will be organizing out west towards
the end of the week, but models disagree on the overall upper air
pattern as well as the number of PV anomalies and the placement of
troughs. Nevertheless, they are in broad agreement on an active
pattern which would support a chance of rain and snow from Sat
night through Sun night.

Kanofsky

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1140 AM CST Mon Feb 4 2019

A cold front stretching from near KAIZ to KPPQ will continue
moving southeast this afternoon. the front should be through east
central Missouri by 21Z, and into far southeast Missouri and
southeast Illinois by 00-01Z. South-southwest flow ahead of the
cold front will shift sharply to the northwest with gusts to
20-25kts. Some light rain showers will accompany the front as
well...possibly bringing visibility down to 3-5 miles. Lower
ceilings between 700-1500ft are also likely behind the front...but
much of the widespread IFR behind the front in western Missouri
appears to be lifting, so I'm not sure how widespread the IFR will
be the further the front moves east this afternoon. Flight
conditions are expected to improve this evening along and north of
the I-70 corridor, but MVFR ceilings will likely persist tonight
across southern Missouri. The front is expected to stall over
northern Arkansas tonight and then lift back to the north
Tuesday. Ceilings will likely lower across the area back to MVFR
levels Tuesday morning as this occurs. There may also be some very
light rain or drizzle in the cold air north of the front, but
model guidance is not in good agreement on this point at this
time.

SPECIFICS FOR KSTL:

Ceilings are expected to fall back to MVFR ahead of a cold front
this afternoon. The cold front is expected to move through the
terminal between 20-21Z this afternoon. There may be a few showers
along or ahead of the front, but the rain does not look like it
will be heavy enough to impact the visibility at the terminal.
MVFR ceilings will likely prevail behind the front...though a
short period of IFR is still possible. Ceilings are expected to
improve this evening...possibly increasing to VFR, but current
indications are that the VFR conditions would be a fairly short
duration. The cold front is expected to stall over northern
Arkansas and them move back to the north on Tuesday. This will
likely bring lower ceilings below 2,000 feet back to east central
Missouri, and possibly some afternoon rain showers as well.

Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

WFO LSX

Hazardous Weather Outlook
National Weather Service Saint Louis MO
353 AM CST Mon Feb 4 2019

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-051200-
Adams IL-Audrain MO-Bond IL-Boone MO-Brown IL-Calhoun IL-Callaway MO-
Clinton IL-Cole MO-Crawford MO-Fayette IL-Franklin MO-Gasconade MO-
Greene IL-Iron MO-Jefferson MO-Jersey IL-Knox MO-Lewis MO-Lincoln MO-
Macoupin IL-Madison IL-Madison MO-Marion IL-Marion MO-Moniteau MO-
Monroe IL-Monroe MO-Montgomery IL-Montgomery MO-Osage MO-Pike IL-
Pike MO-Ralls MO-Randolph IL-Reynolds MO-Saint Charles MO-
Saint Clair IL-Saint Francois MO-Saint Louis City MO-Saint Louis MO-
Sainte Genevieve MO-Shelby MO-Warren MO-Washington IL-Washington MO-
353 AM CST Mon Feb 4 2019

This Hazardous Weather Outlook is for portions of eastern and
central Missouri as well as west central and southwest Illinois.

.DAY ONE...Today and tonight.

There is a slight chance of freezing rain late tonight across portions
of southeast and into central Missouri. A light glaze is possible.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

A wintry mix of precipitation is likely Tuesday through Thursday
mainly across northeast Missouri and west central Illinois. Two
rounds of ice accumulation are expected with around a tenth of an
inch of ice possible each time.

There is a chance for thunderstorms mainly for areas south of
Interstate 70 for Tuesday afternoon through Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated through tonight.

Tilly