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Area forecast discussion 
National Weather Service Des Moines Iowa
533 am CST Wednesday Jan 28 2015

Short term /today/...
issued at 355 am CST Wednesday Jan 28 2015

Complicated forecast today to say the least. Intense low east of
Maine continues to be holding back eastward translation of the upper
level ridge over the Midwest today...resulting in low stratus clouds
holding on over eastern Iowa yesterday afternoon. Fast forward to
current with low stratus and light fog expanding west a bit into
central Iowa along a weak frontal boundary extending west to east
over the forecast area at 08z. Mesoscale models doing a better job
with clouds than synoptic...hrrr captures the expansion and
generally begins to move the deck northeast during the day as the
plains low enters Iowa this afternoon. Over the north...moisture
will remain for much of the day so clouds and much cooler
temperatures this afternoon are likely across the north. A wide
range of temperatures is expected today with highs in the upper 30s
from Mason City to Waterloo to the middle 50s at Des Moines to near 60
over the far south. Will continue the near record high headline over
the southwest as once the clouds back off...temperatures should move
up rather quickly later this morning and early afternoon. By middle to
late afternoon clouds will begin to fill in again as the low begins
to increase lift across the region. By late afternoon partly sunny
conditions to cloudy skies will prevail. Winds will be south
southeast this afternoon with the stronger winds over southeast
sections. Despite the unseasonably warm temperatures aloft...6c
northeast to 14c southwest by midday cooling to 4c northeast to 10c
south...afternoon highs will be advection based rather than pure
mixing based. Toward sunset mostly cloudy conditions are expected.

Long term /tonight through Tuesday/...
issued at 355 am CST Wednesday Jan 28 2015

A very fast moving shortwave is still on track to impact dmx County Warning Area
Thursday morning. At 06z Wednesday...water vapor imagery easily picking up
this middle to upper low crossing over The Rockies. The models continue
to initialize well with placement of this middle to upper wave. Timing
has remained consistent...with the models placing this low directly
over central Iowa at 06z Thursday. Soundings once again show a sizable
dry air pocket from around 850mb to 600mb which will prevent cloud
thickness from exceeding 5 kft and...subsequently...keep this system
from producing anything beyond light precipitation. Kmcw to kest GFS
soundings support mainly dz/-ra...with a very narrow window of -ip
to -sn possible from around 09z to 12z. By 12z Thursday...this low will
be over northern Illinois and strong cold air advection along with very dry air in
the middle to upper levels will be brought into our County Warning Area. Though a fair
amount of sunshine is expected...daytime temperatures to only warm around 3
to 5 degrees from overnight mins due to cold air advection.

Thursday's winds remain Worth mentioning. Models showing 25 knots to
30 knots winds right off the deck...approaching 45 knots to the top of
the mixed layer. Surface pressure gradient of 3mb/100km to support
strong winds at the surface. With low over Great Lakes...winds will be
strongest across our northern County Warning Area. In all...Wind Advisory
beginning early Thursday am looking more and more likely with the next
update package.

While Friday should be sunny and quiet...it looks like quite a
different story is shaping up for the weekend...especially
Saturday night into Sunday morning. The Euro and the GFS are
beginning to come in line both temporally and spatially with
bringing our next chance for "impactful" snow accumulation to our
County Warning Area. Forecast soundings begin to saturate from top-down Saturday
afternoon. See little to no justifiable reason for precipitation during
the morning Saturday...so have lowered probability of precipitation accordingly. Saturday
evening...soundings begin to completely saturate across the County Warning Area
from SW to NE...becoming completely saturated between 00z sun and
06z sun. Both GFS and Euro have a low level jet transporting moisture into
this system from the Gulf of Mexico. The Euro is slightly further
north with this moisture...which is helping yield a comparatively
higher quantitative precipitation forecast. Highest snowfall amounts will thus be in our southern
County Warning Area. Cross sections clearly show lift through the dendritic growth
zone. Way too early for any headlines at this point...but Worth
noting that models may be keying in on a solution...which would
increase confidence.

Behind this system...Monday into the mid-week...it is a lock that
temperatures will be significantly cooler than they have been for
the past two weeks. The forecast challenge for now is how far the
bottom will fall out on temperatures. Ensemble runs are showing around -1
to -2 Standard dev on 850mb temperatures across our County Warning Area. Tonight's 00z GFS was
markedly colder than pvs runs. The GFS has 850mb temperatures down to
-19c across the NE portion of our County Warning Area...whereas the Euro has 850
mb temperatures down to only -10c. Since obvious lack of consistency from
GFS...will lean towards more consistent...less extreme...Euro. If
this 00z Wednesday GFS solution holds in subsequent runs...maximum and min temperatures
will need at least 5 degrees lopped off.

&&

Aviation...28/12z
issued at 533 am CST Wednesday Jan 28 2015

Stratus deck the main challenge early today with area of LIFR and
fog developing ahead of boundary now over central Iowa. Low
pressure in central South Dakota to move southeast. Hrrr model and
trends suggest that ceilings will improve over central/south after 15z
while northeast/north will remain in MVFR/IFR conditions for most
of the day. Br and now fog has developed over the north with kmcw
down to 3/4sm. Have brought in 1/2sm fzfg for brief period prior
to 14z with limited improvement toward 18z. After the passage of
the low tonight...winds become more northwest and increase
dramatically after 06-08z remaining strong through end of period.
Ceilings will lower again north after 03z with potential for -dz over
north after 00z. Ceilings slowly improve but remain IFR/MVFR over much
of area after 03z. /Rev

&&

Dmx watches/warnings/advisories...
none.
&&

$$

Short term...rev
long term...kotenberg
aviation...rev

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