Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 080352
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
952 PM CST Sat Dec 7 2013
Issued at 944 PM CST Sat Dec 7 2013
Several narrow snow bands have developed this evening across
southwest Missouri in an area of strong mid level frontogenetical
forcing and low/mid level warm advection ahead of a short wave
moving through the southern plains. Snow is reaching the ground in
and there are areas that have a dusting. The latest RAP and HRRR
runs increase the forcing and shift it northeastward parallelling
I-44 during the overnight hours and into the St. Louis metro area.
This seems reasonable based on observed trends. The only question
is the coverage and whether a wider more solitary band will evolve
or whether it will remain with several narrow bands. At this time
I have increased the pops within this corridor but only mentioned
scattered snow showers due to the uncertainty in the coverage
evolution. Some areas could certainly pick up a dusting to half
inch beneath them. If the coverage expands I will probably need to
boost pops into the likely category before the evening is over.
.SHORT TERM: (Through Sunday Evening)
Issued at 301 PM CST Sat Dec 7 2013
Strong shortwave dipping into the base of the upper level trof
across the western CONUS will move across the Four Corners tonight
and emerge into the Plains on Sunday morning. Impressive warm
advection forecast to develop ahead of the shortwave with light qpf
noted on all model guidance to march northeast across the CWA from
late tonight through Sunday afternoon. Believe this is one of those
high PoP/low QPF events. Precipitation type is not clear cut...as
lack of ice crystal formation is noted on model soundings. I also
note that there is a steady stream of mid and high level clouds
streaming northeast from Texas. Wonder if the ice crystals from the
higher clouds will lead to a seeder/feeder situation, ultimately
allowing the precipitation to fall as more snow or snow grains
rather than freezing drizzle late tonight and tomorrow morning.
Tomorrow afternoon the best lift will be moving northeast and the
lower atmosphere will be warming so precipitation will likely turn
to areas of freezing drizzle that may continue into the evening.
Overall believe snowfall amounts will remain under an inch and any
freezing drizzle will only produce a light glaze. Will let the
evening and overnight shifts take a look at the 00Z model data to
determine the need, if any, for headlines on Sunday.
.LONG TERM: (Sunday Night through Next Saturday)
Issued at 301 PM CST Sat Dec 7 2013
Cold front will progress southeast across the CWA late Sunday
night, reinforcing the cold for the beginning of the work week.
Next shortwave moves into the Plains Monday night an CWA will be in
a favorable area of synoptic lift provided by the right entrance
region of the jet streak to our northeast. This may ultimately
provide another chance of light snow south of Interstate 70. Have
kept slight chance PoPs at this time.
Extended forecast remains dry and cold with cold front passages
Wednesday and Friday.
.AVIATION: (For the 00z TAFs through 00z Sunday Evening)
Issued at 541 PM CST Sat Dec 7 2013
Some minor changes in timing to the prev TAFs, but focus remains
the approaching precip. Latest guidance suggests precip will begin
as SN as it moves in from W to E thru the region. This event still
appears to be a high probability, low precip event. By late
morning into the afternoon Sun, the top of the cloud deck will
start to erode, removing ice crystals, changing the precip over
to FZDZ. A lot of uncertainty remains as to when this change will
occur and how long the FZDZ will linger into the afternoon. Cigs
shud remain in the low end MVFR cat thru much of the afternoon.
However, cigs shud drop quickly into IFR cat around sunset as the
Specifics for KSTL: Only some minor changes to timing of different
cloud deck arrivals. Did introduce FZDZ Sun afternoon with
increased confidence of occurrence. However, timing of onset of SN
and then change over to FZDZ remains uncertain. IFR cigs are
expected as or shortly after precip ends.