Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Des Moines Iowa
645 PM CDT Friday Sep 4 2015

Discussion...
issued at 319 PM CDT Friday Sep 4 2015

Area continues beneath southerly flow in the lower levels and at the
surface as the state remains sandwiched between a large area of high
pressure over the Ohio Valley and a developing low pressure system
stretching from central ND southwestward into northwest Kansas. Weak pv
advection and Theta-E advection has been in place just to the west
of the County Warning Area throughout the day...which has resulted in a small area of
showers and thunderstorms across portions of eastern NE...southeast South Dakota and northwest
Iowa. The area of lift is expected to slowly translate across the
northern County Warning Area early this evening and will be reinforced late this
evening into the overnight hours as the low level jet picks up and is oriented
into NC Iowa and central Minnesota. Therefore precipitation that is creeping into the
northwest County Warning Area is expected to continue to push eastward. Expect some
diminishment within the area into the middle evening hours...but then
additional development/enhancement expected with the onset of the
low level jet with storms expected to remain sub-severe. Southerly flow
continues to increase into Saturday/Sunday as the upper trough over
the Pacific northwest pushes through the northern rockies and into southern
Saskatchewan/Manitoba by late Sunday. The associated area of low
pressure will remain will deepen and lift into the northern plains/Minnesota
through the weekend with the associated cold front to be pushing
into the northwestern County Warning Area by Sunday afternoon. Ahead of this front
expect the warm and humid weather to continue. A few weak impulses
shove out ahead of the main trough Saturday night into Sunday which
could bring some chances for storms ahead of the main frontal
passage warm air advection and weak baroclinic zone in place across the western
County Warning Area. Otherwise frontal boundary to drop through the County Warning Area Sunday night
with more widespread precipitation chances possible. Deep layer shear
increases to around 30-35 kts with decent instability...so some
severe storms possible. Frontal boundary stalls out across the
southern County Warning Area...so storm chances linger into Monday/Monday night as
weak energy continues to move through the region aloft. Additionally
activity possible into Tuesday/Tuesday night as a stronger wave pushes
through in the near zonal flow aloft. This will push the lingering
frontal boundary to the south of the state with high pressure
building in for Wednesday. Previous runs the past few days have held
this area of high pressure in firm control of the area...but both
the GFS/ec today have another shortwave trough digging into the back
of the main trough over the northern plains toward late week. This
may result in some showers/isolated storms Wednesday night and maybe
into Thursday. Timing is tough at this range with some
discrepancies. Temperatures trending cooler through the week still
on track with 850 mb temperatures dropping from the lower 20s celsius this
weekend into the the low teens to around 10c by the end of the
week.

&&

Aviation...04/18z
issued at 645 PM CDT Friday Sep 4 2015

Weak elevated convection should brush northern sites this evening but
remain VFR. There could be another brief period of radiation fog
near kmcw as well...possibly down to IFR for an hour or two.
Otherwise expect continued VFR conditions at kdsm/kotm with mainly
scattered/broken middle clouds.

&&

Dmx watches/warnings/advisories...none.

&&

$$

Discussion...beerends
aviation...small

National Weather Service Glossary of Abbreviations