Air Resources Laboratory banner image
Air Resources Laboratory web site National Oceanic and Atmospheric Administration (NOAA)

ia discuss

Office: DMX

FXUS63 KDMX 141142

Area Forecast Discussion
National Weather Service Des Moines IA
542 AM CST Thu Dec 14 2017

.SHORT TERM.../Today through Tonight/
Issued at 325 AM CST Thu Dec 14 2017

Clouds still in place across much of the forecast area with some
clearing into the far northeast. For the most part some additional
clearing may come into the east/north this morning, but clouds will
then increase by late morning and remain in place this afternoon
into tonight. This is due to a shortwave trough currently dropping
through the western Dakotas/MT set to drop through IA by this
evening. Increasing low level moisture is expected, with thickening
low level clouds and potential for some very light snow flurries.
greater chances exist to the west of the forecast area, so have left
some slight chances pops just skirting the far west by late
afternoon/early evening. Otherwise went with scattered flurries for
the entire forecast area this evening into the overnight hours. Will
have some weak warm advection in place today, with another shot of
cold air expected tonight. However with the clouds in place, warming
will be limited with highs mainly in the upper 20s to mid 30s
expected. Tonight with the clouds in place, expect temps to drop
to around 20 to 25 across the forecast area.

.LONG TERM.../Friday through Wednesday/
Issued at 325 AM CST Thu Dec 14 2017

Bottom Line Up Front...
At this time, no hazardous weather conditions for the next
several days. After Friday, temperatures should be a solid 10 to
20 degrees above normal across Iowa, with the best widespread
precipitation chances occurring on Sunday.

Friday and Saturday...
An upper low will dip southeastward through the Great Lakes
region. As of now, it appears any (precipitation) impacts from
this low should remain east of Iowa. This low should bring an
elongated stratus deck with it, generally keeping Friday cloudy.
Winds will be slightly breezy Friday afternoon. But with a
pressure gradient of around 3mb/175 km, and given transport layer
winds, expecting wind values to top out in the 15 to 20 mph range,
with gusts to 25 mph.

For Saturday, 850mb temps make it into the +5 to +9C range across
Iowa. With the above-mentioned low pulling away to the northeastern
CONUS, am thinking a decent amount of sunshine can make it to the
ground during daytime heating hours. The record high for Saturday is
62 (1939)... which may be a little bit of a tall order to reach...
however, temperatures are trending upwards, so mid to possibly upper
50s seems very plausible.

Sunday Into Monday...
At this time, our best chances for widespread precipitation
appear to be on Sunday. For the past several days, models have
been showing an upper low pushing northeastward from west Texas
towards the Midwest and eventually the Ohio Valley region. The sfc
reflection for this low seems to be weak and becomes disorganized
as it makes it into the Midwest, with a MSLP of around 1015mb or
so. Our best precip shot comes from the baroclinic zone extending
off the NE quadrant of this low. For the past several runs, there
has been decent low-level frontogenetical forcing that has been
well-aligned with this baroclinic zone that has been positioned
more or less from the SW corner of Iowa through the NE corner of
Iowa at 12z Sun. A lack of low-level moisture is the biggest
mitigating factor...with the best moisture being relegated to SE
Iowa. Still some disagreement remains among the models, with the
GFS and now the NAM generally being faster and father east than
the ECMWF.

Ultimately, any impacts from wintry precipitation should effectively
be nil for central Iowa. Temperatures will be above freezing, and
with pavement temperatures likely warm from Saturday's highs in the
40s and 50s, any snow should melt upon contact.

Tuesday and Beyond...
Somewhat strangely, the 00z Thu run of the long-range models show
better agreement for Tuesday (12/19) and beyond timeframe than
the Friday (12/15) through Monday (12/18) time period. Worth
noting that run-to-run consistency remains somewhat low, though
has begun to improve over the past 36 hours.

Basically, a "poor man's" omega block, elevated latitudinally, is
suggested to set up by Tuesday into Wednesday. At this time, it
looks like Iowa will be in the warm and dry side, with a 1030mb
sfc high located near the center of the country. 850mb temps seem
to peak around the +3C to +7C range- slightly cooler than is
slated for this upcoming Saturday. Thus, think sfc temps in the
mid 40s to low 50s could be plausible if this setup holds. Also,
if this omega block does take shape, long-range models would be
too fast in kicking in colder air by the end of next
week...meaning "persistence" could play into next weekend.


.AVIATION.../For the 12Z TAFS through 12Z Friday morning/
Issued at 542 AM CST Thu Dec 14 2017

Some clearing into the eastern TAF sites this morning possible,
and could push into KOTM as well. Otherwise low VFR to MVFR clouds
to remain entrenched across much of the state today and spread
across the state tonight. Low level moisture to increase across
the area tonight, with some low MVFR CIGS possible. Some flurries
possible this evening into the overnight hours. However have left
out of the TAF for now given uncertainty in narrowing down the
timing. Northerly winds to become more northwesterly to westerly
through the forecast period.





SHORT TERM...Beerends
LONG TERM...Kotenberg

Office: DVN FXUS63 KDVN 141123 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 523 AM CST Thu Dec 14 2017 ...AVIATION UPDATE... .SYNOPSIS... Issued at 252 AM CST Thu Dec 14 2017 06Z surface data has the cold front running from northwest Ohio, into southeast Iowa, and then to the eastern Dakotas. Dew points in the frontal zone were in the 20s with teens and single digits across the Great Lakes and upper Midwest. && .SHORT TERM...(Today and Tonight) ISSUED AT 252 AM CST Thu Dec 14 2017 Through sunrise, quiet but cold conditions will be seen across the area with more breaks developing in the clouds. For Thursday, quiet, dry and colder than normal conditions will be seen across the area. Clouds will be on the increase during the afternoon. Tonight, a weak upper level disturbance will move through the area. Moisture is very limited so only some passing flurries are expected. The flurries will end from west to east after midnight. .LONG TERM...(Friday through Wednesday) ISSUED AT 252 AM CST Thu Dec 14 2017 Chance of a light mixed precipitation event this weekend...then favorable regime flow for snow around Christmas. Long Term Forecast Confidence Assessment...fair or average. Main issue is light rain and possibly mixed precipitation event this weekend with any amounts light and flow pattern not supportive of significant snow/ice issues. Lingering second as confirmed past several days is highs most days up to 3 plus degrees too cool and lows with clear skies and lighter winds probably too mild by 2 to 3 plus degrees. Friday through Saturday...only minor changes, generally partly cloudy to mostly clear. Highs mostly in the 32 to 42 range on Friday, rising to the 42 to 52 on Saturday. Lows 15 to 25 on friday AM, rising into the 20s for mins on Saturday AM. Sunday...mostly cloudy with light precipitation in the form of light rain and possibly starting initially as snow/sleet before becoming all rain due to widespread warm air advection. Little winter impacts expected as temperatures rise mostly into the 40s and possibly lower 50s south. Clearing Sunday night with lows 25 to 33. Monday through Thursday ...northwest flow with fair skies and highs mostly in the 40s with mins mainly in the 20s. This is slightly above normal. && .AVIATION...(For the 12Z TAFS through 12Z Friday Morning) ISSUED AT 519 AM CST Thu Dec 14 2017 VFR conditions have developed across eastern Iowa and northern Illinois with a large pocket of MVFR conditions along the Mississippi river into western Illinois. The pocket of MVFR cigs is expected to slowly shrink in size through 18z/14. After 18z/14 VFR conditions are expected through sunrise Friday. A passing weak upper level disturbance after sunset will bring the risk of flurries and possibly more MVFR cigs. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && $$ SYNOPSIS...08 SHORT TERM...08 LONG TERM...Nichols AVIATION...08