Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 272339

Area Forecast Discussion
National Weather Service Des Moines IA
539 PM CST Mon Feb 27 2017

...Updated Aviation Discussion...

.SHORT TERM.../Tonight through Tuesday/
Issued at 320 PM CST Mon Feb 27 2017

Confidence:  Medium.

Main challenges will be fog and convection. Clouds beginning to fill
in south with isentropic lift and warm air advection increasing
ahead of the short to our southwest.  A second and slightly stronger
wave will move across the region tomorrow with better forcing over
the east. Showers will be on the increase between 00 and 06z over
the area with potential for thunder increasing late evening as well.
Hires models again split on fog potential...but guidance continues
to hit the north with areas of fog overnight.  Increasing low level
moisture and snowpack north will likely result in fog tonight.  Will
not go with headlines for now...but will need to monitor for
potential later tonight.  As the upper level system moves across the
southeast Tuesday...instability will peak from the morning through
afternoon hours.  GFS and Euro differ on translation of system with
the Euro being a bit slower. Despite this...GFS and NAM bufr
soundings show favorable shear and instability southeast for
potential strong storms for a short window between 2 and 5 pm
tomorrow afternoon.  Overnight lows tonight will be quite mild with
readings in the mid 30s northwest to the mid to upper 40s southeast.
South of the warm front Tuesday...expect highs to reach the upper
50s to mid 60s. Over the northwest lower 40s are expected with lower
50s from southwest to northeast Iowa. Fog will remain a problem
early tomorrow morning north with patchy fog holding on through at
least mid morning over the remainder of the region...dissipating
fastest in the south where temperatures will warm the quickest.

.LONG TERM.../Tuesday night through Monday/
Issued at 320 PM CST Mon Feb 27 2017

Surface low will be exiting the state at the beginning of the
period although the upper trof will still be approaching from the
west. Strong cold advection will be underway on the backside of
the surface system. Aloft, strong Q-convergence and forcing will
support lift into Tuesday night, however moisture will become
problematic as bulk of moisture transport will occur south and
east of the state. However, some light precipitation is still
expected with best threat across the east. In addition, as the
cold advection persist, a transition from any light rain/sprinkles
to light snow/flurries is expected during the night from NW to SE.
There may be some lingering pcpn first thing on Wednesday morning,
however strong subsidence will push into the state with drying
throughout the atmospheric column.

Temperatures will be closer to normal on Wednesday into Thursday
with Canadian airmass in place. However, warm advection begins
again by early Friday and persist into the weekend as larger
scale upper ridging slides into the central United States. There
will be a series of shortwave during the later half of the week
into the weekend that graze northern Iowa and bring low chances of
precipitation to the state at times through the later half of the
week, although none will produce much in the way of significant
precipitation. Temperatures will once again rise well above normal
by the end of the weekend with thermal ridging approaching and
south to southwest surface flow.


.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 527 PM CST Mon Feb 27 2017

Scattered showers are likely tonight into tomorrow morning with
periodic visibility restrictions from the rain. High confidence in
the LIFR/IFR ceilings moving into the state late tonight into
Tuesday but lower confidence in mentioning the visibility
restrictions due to uncertainty of timing of precip. Fog still
looks possible over northern Iowa impacting FOD, MCW, and ALO but
left out LIFR mention attm with the rain/drizzle potential.
Conditions begin to improve late Tuesday morning.





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