Scientific Forecaster Discussion
fxus63 kdmx 171733
Area forecast discussion
National Weather Service Des Moines Iowa
1233 PM CDT Tue Oct 17 2017
Short term.../today through tonight/
issued at 341 am CDT Tue Oct 17 2017
The primary concern through the period will be high temps today with
high confidence in fair and mild weather continuing. A weak short
wave/pv anomaly shows up well across far eastern NE in water vapor
imagery and objective model analysis early this morning. This has
produced weak thermodynamic and kinematic forcing, now into Kansas and
MO, but resulted in little more than patchy high cloudiness due to
an extreme lack of moisture.
Boosted highs today above even the warmest MOS guidance to near the
warmest raw model output. Examination of 00z oax and dvn raobs vs
Mon highs suggests we should again be able to mix to near h85,
beyond expectation of late October model forecast soundings, and
current temps are generally 10 to 15 degrees warmer than this time
Skies look to remain mostly clear into the night. After a lull
today, warm/Theta-E advection will increase into the night to our
west in response to a very fast moving wave currently off the
Pacific northwest coast reaching ND/Manitoba by 12z Wed. There will be a
noted lobe of deep forcing just ahead to our north and west, but
moisture will remain scare.
Long term.../Wednesday through Monday/
issued at 341 am CDT Tue Oct 17 2017
We remain in a very quiet period weather wise through Friday. Precip
chances are almost nil and the main concern will be temps. On
Wednesday a shortwave passes through the region which may bring a
few clouds across mainly northern Iowa and temps similar to today
versus a little warmer. Otherwise with a large ridge overhead we
will see a gradual warming trend through the week with much above
normal highs in the mid to upper 70s and lows in the 40s and 50s.
The weekend will bring with it our next chance for rain...and
thunderstorms though models are not in particularly good agreement.
All models start out Friday night with a deep trough over The
Rockies advancing into the plains for Saturday. The GFS is more
bullish on the warm advection ahead of a surface low pressure system
and cold front and breaks out precip across the western half by 06z
while the other models are more overnight Friday night. The cold
front advances across Iowa during the day Saturday and tonights
models show a bit more instability and shear across the state along
the boundary. Certainly sufficient for thunderstorms however, it is
too far out to determine any severe threat although if the shear
continues to show 40+ kts deep layer, and the front does indeed
come across during the day, a few strong to severe storms cannot
be ruled out. The Euro is a little slower moving the upper trough
through and as such, keeps precip over the area longer however the
Euro appears to be the least consistent of the models, as it
developed a closed low in the trough over the Southern Plains last
run and this run it's back to a trough. There will also be at
least some potential for heavy rainfall though the best chances
appear to be south and east of the forecast area. At any rate, we
will be in for a wet first half to the weekend.
After the passage of the cold front...which will merely knock temps
back to only slightly above normal for this time of year, a second
deep trough passes through the state on Monday and this will bring a
pretty strong shot of cold air to the region with highs on Tuesday
only in the 50s and some light rain across northern portions.
This may be a pattern changer for US as we stay in northwest flow
with several shortwaves coming through keeping US in cooler
Aviation.../for the 18z tafs through 18z Wednesday afternoon/
issued at 1233 PM CDT Tue Oct 17 2017
VFR conditions expected throughout the taf forecast period.
Winds could become a bit gusty out of the southwest Wednesday.