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Area forecast discussion...updated aviation 
National Weather Service St Louis MO
628 am CST sun Nov 23 2014

Short term: (through late this afternoon)
issued at 331 am CST sun Nov 23 2014

Surface low to begin lifting northeastward towards forecast area
today. Will see showers on the increase this morning and spread
north across the region. Some instability today so there is a chance
of thunderstorms mainly along and south of I-70. As for
temperatures, will depend on cloud cover and rainfall. But feel that
temps will rise into the mid 50s to low 60s by this afternoon.

Byrd

Long term: (tonight through saturday)
issued at 331 am CST sun Nov 23 2014

(tonight-wednesday)

While specific precip trends are certainly tricky tonight and into
Monday, latest synoptic and hi-res guidance suggests the general
scenario will be that this afternoon's band of rain and embedded
thunderstorms will rotate east out of the area this evening, as
additional precip begins to form to our west as secondary shortwave
drops south in the wake of today's system. This secondary area of
precip should then wind down to spotty areas of light rain/light
snow during the day on Monday.

Yesterday's guidance as well as 00z model output is now suggesting
more precip lingering in the cold air late tonight and early Monday
than was indicated by earlier runs. I have not made any major
changes to the timing of the changeover from rain to snow over the
northwest half of the County Warning Area in the 06-12z time frame; this may be a
bit too fast, but didn't want to discount the intensity of the
cold air advection. In the far northwest counties, it appears that this strong cold air advection will
cause freezing levels to drop enough to support the rain changing
over to all snow for a few hours late tonight and into early
Monday morning, and based on this have added some minor accumulations
of under an inch in our extreme northwest counties.

Min/Max temps for tonight/Monday will be based on non-diurnal, 3
hourly temp trends during this time frame.

No major changes in going forecast trends heading into midweek, with
dry and chlly weather on Tuesday followed by a brief warmup and low
pops for the fast-moving, moisture-starved system on Wednesday.

(Thursday-saturday)

Medium range guidance has come into better agreement with a less
amplified solution for Thanksgiving day, suggesting a ribbon of
light precip over northern sections of the County Warning Area as shortwave
interacts with baroclinicity that is draped across the region.
Pattern suggests that there should be a strong temperature
gradient from north to south across the region, with highs in the
30s over the cold air in the north while approaching 50 in the
warmer air over southern sections of the County Warning Area.

This agreement jumps the tracks heading into the latter half of the
week, with Gem and European model (ecmwf) forecasting broad trofing over the central
Continental U.S. While the GFS maintains a more quasi-zonal look. Of course,
given the intensity of the baroclinic zone this somewhat subtle
difference will make a huge impact on sensible weather trends, and
especially on temperatures. This discrepency can be seen in the
surface prog forecasts for Friday morning; European model (ecmwf) and Gem have broad
and cold Canadian high over the plains and into the upper
Mississippi Valley with north/northeast winds over our fa, while GFS
as surface low over the northern plains and southerly winds over our
area. MOS guidance based on these solutions offer a more
quanitative and Stark measure of this discrepency...a whopping
20-25 degree difference on friday's highs between the colder
European model (ecmwf) and warmer GFS. For now have maintained earlier (colder)
trends, based on consensus of Gem and ecmef.

Truett
&&

Aviation: (for the 12z tafs through 12z Monday morning)
issued at 628 am CST sun Nov 23 2014

Next round of showers continuing to develop and slide northward
through forecast area and persist through most of forecast period.
Cigs to lower to MVFR by mid morning, then down to IFR. In the
meantime, winds to persist from the southeast to south today. As
surface low lifts through region, cold front associated with it to
slide through area tonight. Front to move through kcou by 03z
Monday, KUIN by 04z Monday and Metro area tafs by 07z Monday.
Winds to veer to the west behind from and become gusty at times.
Colder air will filter on back side of system with rain becoming
mixed with snow after midnight tonight.

Specifics for kstl:
next round of showers continuing to develop and slide northward
moving into the Metro area by 14z and persist through most of
forecast period. Cigs to lower to MVFR by 14z, then down to IFR by 20z.
In the meantime, winds to persist from the south today. As
surface low lifts through region, cold front associated with it to
slide Metro area by 07z Monday. Winds to veer to the west behind
from and become gusty at times. Colder air will filter on back
side of system with rain becoming mixed with snow after 13z
Monday.

Byrd
&&

Lsx watches/warnings/advisories:
MO...none.
Illinois...none.
&&

$$
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