Scientific Forecaster Discussion
fxus63 kdmx 151142
Area forecast discussion
National Weather Service Des Moines Iowa
542 am CST sun Dec 15 2019
..updated aviation discussion...
Discussion.../today through Saturday/
issued at 341 am CST sun Dec 15 2019
Only concern wrt to precipitation this week is the incoming
shortwave to bring light snow to far southern Iowa today into this
evening. Otherwise, temperatures return mild by mid to late week
and conditions remain dry.
Light snow looks to continue to develop over portions of Nebraska
and spread east into western Iowa later this morning. Saturation
throughout the entire column looks questionable the further north
of Interstate 80 you go. Even though there is ice introduction
for several hours over portions of west to northwest cwa, there
remains a fairly deep dry layer below 850mb to the surface to
contend with for any snow to reach the surface. Plus the forcing
isn't great within the dendritic layer and certainly not enough to
overcome the dry layer. Thus, not expecting much accumulation
across the aforementioned location. However, potentially could
see a few snowflakes make it through the dry layer this morning
through the early afternoon and have a high pop/low quantitative precipitation forecast scenario
going for west-central to northern portions of the forecast area.
Further south, mainly along and south of Highway 34 to the
Missouri border, has better shot at receiving some snow
accumulation. For instance at Lamoni, the column becomes
completely saturated by mid-afternoon as the dry layer is
overcome by the snow due to a bit better forcing within the
dendritic layer and decent mid-level moisture advection. Have an
inch or two going along the far south to southeast portions of the
County Warning Area by tonight. By around 06z and after, the column begins to lose
ice introduction from west to east and with some linger forcing
and enough low level moisture, have mention of fzdz across the
south. Low confidence with any significant ice amounts as
shouldn't last long with the forcing moving east fairly quickly.
Monday through Saturday...large and slow moving surface high
pressure builds into the region Monday and gradually shifts east
through mid-week. Monday will remain cool before temperatures
rebound by Tuesday and Wednesday to above normal. Only system to
keep an eye on is a weak shortwave progged to move across the
state late Thursday into Friday. European model (ecmwf) and GFS are in decent
agreement with the timing and location of the surface low that
develops and the upper low. Plus, both agree this system is
significantly moisture starved, so likely only a wind shift and
slightly cooler temperatures Friday.
Aviation.../for the 12z tafs through 12z Monday morning/
issued at 533 am CST sun Dec 15 2019
MVFR to IFR ceilings later this afternoon and tonight to impact
dsm, otm, fod, and likely mcw and alo. The snow is looking to
cause some MVFR and possibly IFR visibility for a few hours at
otm and maybe at dsm. Lower confidence to mention the IFR ceilings
but confident to introduce MVFR visibility for the snow at dsm.
The MVFR stratus looks to stick around until Monday morning.