Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 260916
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
316 AM CST THU NOV 26 2015
.SHORT TERM: (Through Late This Afternoon)
Issued at 316 AM CST Thu Nov 26 2015
Focus continues to be precip chances thru the afternoon.
Expect strong sly winds to continue thru today. A strong swly LLJ is
expected to continue over the region today as well. Mdls continue to
depict broad areas of moisture convergence across the area today.
This is expected to result in light SHRA off and on thru much of the
day. The better chances appear to continue to be across nrn portions
of the CWA. Believe will continue with higher PoPs across this area,
tho expect little accumulation with these SHRA.
That said, the area of more stratiform and somewhat heavier RA shud
be moving into the nwrn portions of the CWA late this afternoon into
the evening hrs.
Another forecast problem for today is temps. While expect extensive
cloud cover across the area, the strong sly flow shud help push
temps warmer. Have trended slightly above the cooler guidance for
.LONG TERM: (Thursday through Next Wednesday)
Issued at 340 PM CST Wed Nov 25 2015
(Thanksgiving Day - Saturday Night)
A strong wound-up storm system over the Great Basin region of the
western CONUS is expected to move little during this period,
maintaining an active southwest flow aloft over our region, and
shooting out pieces of energy or distrbances our way as well.
The first of these disturbances is expected to arrive late Thursday
afternoon, with essentially a near continuous train thru late
Saturday after that. This will be further augmented by a slow
moving cold front and rich moisture from the Gulf of Mexico. The
cold front will begin moving thru late Thursday afternoon in
northeast MO and will take all of Friday and much of Friday night
to move thru the remainder of the forecast area.
Despite much cooler air ushering in behind the cold front,
temperatures are expected to stay above freezing for most areas thru
this entire period and will keep pcpn-types as all rain.
The one exception could be in parts of northeast MO and west-central
IL late Friday night and early Saturday morning, where temps will be
around the freezing mark. Fortunately, much of the pcpn by that
time should be to the south with only light spotty pcpn currently
Otherwise, the main concern will be the prolonged period of heavy
rainfall--especially for parts of southeast MO and far southern IL--
where rainfall totals may top 4 inches by Saturday morning. A Flood
Watch has already been issued and considering that the rainfall
forecast has changed little since then, if not the heavy QPF axis
sliding a bit further south, no change was needed to the current
area. The only adjustment seriously considered was an extension in
time into Saturday for southeast MO and far southern IL, but wanted
to take another look or two at that to see if the southern trend
Temps will be quite mild for late November ahead of the front, but
will rapidly drop to below average for daytime maxes behind it, with
readings in some areas not getting out of the 30s. Fortunately,
plenty of warm air aloft should keep the pcpn as rain unless surface
temps can slip below 32F.
(Sunday - Next Wednesday)
Model solutions continue to vary quite a bit out in this period but
the general theme continues to be the storm out west gets nudged
into the main flow and tracks generally east, passing mainly to our
north by Tuesday sliding a surface TROF thru on Monday. Looks like
another round of primarily rain on Monday with this TROF. Temps
look to be around average for this time of year, with clear absence
of any significant cold air surges from the north, but also absent
any strong influence from either the moist Gulf of Mexico or the
much milder air to the south.
.AVIATION: (For the 06z TAFs through 06z Thursday Night)
Issued at 1140 PM CST Wed Nov 25 2015
Ceilings across the FA have increased throughout the evening as
some lower level dry air as worked north across the region.
However, both RAP and NAM low level RH progs are forecasting
renewed saturation during the predawn hours. Since SREF MVFR cig
probabilities are also coming up from southwest MO into west
central IL during the morning hours on Thursday, have introduced a
TEMPO for MVFR ceilings (1500-2000 ft) during the morning at both
KCOU and KUIN. Some lowering of ceilings are also expected in the
STL Metro area, but believe here the bases will remain above 3kft.
Strong southerly low level flow also persists, so will maintain
LLWS in the forecast until gusts come up early Thanksgiving
Precip is going to remain a hit and miss proposition. Spotty
showers currently extending from mid MO to central IL will likely
persist for several hours, and it`s certainly possible that
additional spotty, light, WAA-driven showers will reform over the
northwest half of the CWA throughout the predawn and morning hours
on Thursday. However, it certainly appears that the main rain
threat will be entering the area tomorrow evening, and
especially after 06z, as cold front finally pushes into western
sections of the CWA. Not only will the rainfall become heavier
and widespread, but ceilings and visbilibites will likely take a
nose dive with FROPA at both KCOU and KUIN after 06z.
Specifics for KSTL: VFR ceilings aoa 4kft are expected overnight
and into most of Thanksgiving Day. Strong low level jet will
maintain LLWS threat until mixing commences and transfers some of
the higher winds to the surface..in the 12-15z time frame.
.PRELIMINARY POINT TEMPS/POPS:
Saint Louis 67 52 56 39 / 30 100 100 80
Quincy 66 39 41 32 / 70 100 60 30
Columbia 67 40 42 34 / 70 100 80 60
Jefferson City 68 42 45 35 / 70 100 90 70
Salem 65 56 58 42 / 20 100 100 90
Farmington 64 54 57 39 / 30 100 100 90
MO...Flood Watch from this evening through Saturday morning FOR Boone
MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
Iron MO-Jefferson MO-Madison MO-Moniteau MO-Montgomery MO-
Osage MO-Reynolds MO-St. Charles MO-St. Francois MO-St.
Louis City MO-St. Louis MO-Ste. Genevieve MO-Warren MO-
IL...Flood Watch from this evening through Saturday morning FOR
Clinton IL-Madison IL-Monroe IL-Randolph IL-St. Clair IL-