Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 291759
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
1159 AM CST Thu Jan 29 2015
Issued at 1157 AM CST Thu Jan 29 2015
Updated grids and products have been sent to reflect increased
cloud cover and minor tweaks to the wind speeds through this
.SHORT TERM: (Through Late This Afternoon)
Issued at 343 AM CST Thu Jan 29 2015
Observational data at 08z indicated a low pressure area over
northwest IL with a cold front extending to the southwest of it thru
UIN and COU. A warm front extended from near UIN southeastward thru
southern IL. Temps have stayed up or risen into the 50s in the warm
sector of this system, and then have plunged into the 30s quickly
behind the cold front in IA and far northwest MO. Satellite data
shows low clouds move in shortly after cold frontal passage with
plenty more where they came from over the Upper Midwest and northern
Plains. Radar data shows generally echo-free mosaics over our
region but some obs at ground level have indicated spotty sprinkles
or drizzle underneath the low cloud shield that moves in.
Otherwise, an upper level disturbance was over northern MO early
this morning with another further upstream over eastern SD--all part
of the northwest flow aloft that is in place.
The cold front will push thru the forecast area by 15z with low
clouds to then inundate and persist for the remainder of the day.
Some clearing is then expected in central MO late, possibly
spreading eastward into tonight. High temperatures for the day,
technically, will all be hit early this morning. But for daytime
purposes, we should see near steady temps after the initial fall
shortly after frontal passage. This favors at or below the coolest
MOS for most locales, except near the front after daybreak for areas
south and east of STL metro, where the warmer MAV MOS will probably
work out better given the gradient.
Pcpn will be a tough call today since there is not much to latch on
to and radar is having a tough time picking it up. Added some
scattered sprinkles or flurries for northern MO and central IL thru
this morning where it looks like there will be some better upper
level support and lift as well as low level convergence. These
should all be significantly reduced by 18z and have kept the
.LONG TERM: (Tonight through Wednesday)
Issued at 343 AM CST Thu Jan 29 2015
Surface ridge to build into the region tonight with northwest winds
gradually diminishing. Colder air to filter in with lows in the low
to mid 20s.
On Friday, mostly sunny skies to prevail but temperatures will only
rise into the low 30s east to low 40s west.
Surface ridge to move off to the east late Friday night allowing
southerly winds to return once again ahead of next weather system.
However, lows will still be in the 20s Friday night.
As for next weather system, models still have differences with
placement and timing of frontal boundary. NAM is the slowest and
warmest initially while the GFS and ECMWF are a bit faster and
colder. Will side more with GFS/ECMWF solutions, with precipitation
beginning during the day Saturday and spreading east. It will begin
as a mix of rain and snow, transition to mostly rain briefly during
the afternoon hours with highs in the low 40s. Then as colder air
filters in rather quickly, precipitation to change to all snow
everywhere just after 00z Sunday. As for precipitation amounts, both
the GFS and ECMWF 00z Thursday runs are showing highest values along
the I-70 corridor. However, since there continues to be plenty of
model differences with this storm, it is difficult to determine
snowfall amounts and where the maximum axis of snow will occur. For
now it still does appear that at least a portion of our forecast
area will see accumulating snow Saturday night and Sunday.
Beyond that, the precipitation will come to an end Sunday night with
colder air filtering in and temperatures at or below normal for the
rest of the forecast period. Extended models do indicate a clipper
system will slide through Tuesday night and Wednesday with most of
the energy to the north of the forecast area, so kept slight chance
pops through the period.
.AVIATION: (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1121 AM CST Thu Jan 29 2015
MVFR clouds stretch nearly to the Canadian border and winds at
cloud level are out of the northwest. This should keep MVFR clouds
(generally 1500-3000 ft) in place for the rest of the day and
overnight. Clouds are expected to diminish tomorrow morning after
a low pressure system has moved farther away from the region and
drier air starts to erode the western edge of the cloud shield.
Gusty northwest winds will diminish and become more northerly