Area Forecast Discussion
Issued by NWS Des Moines, IA
FXUS63 KDMX 180453
AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1153 PM CDT Mon Oct 17 2016
.SHORT TERM.../This evening through Tuesday/
Issued at 315 PM CDT Mon Oct 17 2016
Precip trends associated with the current frontal system and its
passage will be the primary concerns into tonight. A strong jet
currently extending from CA into MN will push into the Great Lakes
by 12z driving an associated surface low from the Missouri River to
Lake Superior by that time. A short wave/PV anomaly moving from CO
into the Dakotas has spread a good deal of thermodynamic and
mechanical forcing through Iowa but it is starved for deep moisture
with little hope of elevated convection. Uncapped 1000-2000 J/kg
MLCapes have developed in a zone of strong 0-2km moisture
convergence from just north of the IA/MN border into WI however
where shallow near surface based convection has recently formed. A
few showers or storms may just brush far northern IA into the
evening ahead of the advancing forcing and triple point, noted
between Sioux City and Tekamah at 19z, before it reaches southeast
WI. Otherwise the frontal passage should be dry with diminishing
forcing aloft and little to no potential for surface based
development farther south due to strong inhibition.
Des Moines has at least tied its record high by 3pm /86F/ but the
cold front should be nearly through the entire forecast area by 06z.
This will drop temperatures, and more so reduce humidities, but
Tuesday morning lows will still be closer to normal highs than
.LONG TERM.../Tuesday night through Monday/
Issued at 315 PM CDT Mon Oct 17 2016
Not much change in the overall forecast this issuance. Still
expecting the cold front to be through the area by Tuesday morning
but with a Southwest flow aloft...only looking at moderately cooler
air working in for Tuesday into Wednesday. Soundings show a lot of
dry air so not looking for much in the way of precip or cloud cover.
We will mainly see a wind shift and temps about 10 to 15 degrees
cooler than today...which will still be in the 65 to 75 range and
that is still above normal for this time of year.
The main forecast problem remains the upper trough passing through
in the Wednesday/Thursday time frame. This feature will bring
colder temps to the state with 50`s expected for highs on Thursday.
However...at least weak warm advection returns Friday across the
Southwest so highs moderate some into the weekend. Highs Friday
should be between the mid 50`s Northeast to the mid 60`s Southwest.
The coldest night will be Thursday night with lows in the 30`s. The
problem remains one of whether we see precip with the passing
trough. Models all paint precip to varying degrees across at least
part of the forecast area Wednesday afternoon and evening. Forcing
though is not that impressive and mainly focused across the far
West. Forecast soundings show a pretty dry atmosphere and it`s
doubtful whether we realize enough forcing to develop precip. The
best opportunity for that would be Wednesday afternoon and in
keeping with collaboration with neighbors I have left a small
window across the Northwest Wednesday afternoon for some sprinkles.
Not really seeing more than that.
For the remainder of the long term forecast...a ridge builds over
the West and gradually nudges into the Upper Midwest. Warmer and
still dry weather is what`s in store for central Iowa. Models
differ on a shortwave riding down the flow in the Friday/Friday
night. The Euro is pretty bullish on this while the GFS has this
feature over Illinois and the Great Lakes. In either event it would
be another sprinkle event for the Northeast/East at best and
confidence is not near high enough to include in any forecast at
.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1153 PM CDT Mon Oct 17 2016
Cold front to continue to push across the state and may have some
IFR cigs with it especially at the northern taf sites. Winds then
to go northwesterly behind the front through the day Tuesday.