Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1126 PM CDT sun Mar 29 2015

issued at 320 PM CDT sun Mar 29 2015

Today has been a very changeable day. Warm advections rains earlier
broads between a few hundredths and a tenth of rain...some of which
briefly froze on elevated surfaces before melting...and evaporating.
This cold surface air is still linging in the northeastern County Warning Area as of
2 PM. Sunshine...and deeply mixed heating prefrontal has allowed for
a wedge of upper 50s to around 60 in our western 1/2 so far...with
hourly temperature rises around 8 to 10 degrees to achieve this from
the early day cold. Looking over central Iowa...cold advection is
already returning the state back to the lower 50s. All of this is
occuring in a windy well mixed airmass...with sustained winds of 15
to 25 miles per hour...gusting to 40 or slightly higher. We have been handling
this with Special Weather Statement well as highlighting a enhanced fire
spreading danger.


Short term...(this evening through monday)
issued at 320 PM CDT sun Mar 29 2015

Winds will remain strong until and inversion begins to set up around
sunset. The high pressure moving in should continue to bring
subsidence...and through the continued mixing...clouds should
rapidly decrease around sunset. A clear night is expected
overnight...but with the ridge going south of Iowa...we should
remain north of the a reasonably strong pressure gradient
through the night. This flattened ridge will counter act the
radiational cooling...allowing most sites to remain above freezing.
Lows in the lower to middle 30s are expected to be widespread....but
most of the night should be spent in the upper 30s to middle 40s.

Monday appears spectacular by sensible standards. Sunshine...west
winds of 10 to 15 miles per hour...and highs in the lower to upper 60s from
east to west are expected. Otehr than a potentially increased grass
fire danger...tomorrow will be easily the most pleasant day in a
long while.

Long term...(monday night through next sunday)
issued at 320 PM CDT sun Mar 29 2015

Monday night and Tuesday...will side with the middle of the Road 12z
GFS with respect to it/S handling of mass fields of the passing
clipper system north/northeast of the area Monday night. Elevated
moisture draw to produce any type of precipitation in the local area Monday
evening still seems problematic at this point and besides a small
area of slight chance probability of precipitation in the far northeastern County Warning Area...will maintain
a dry forecast into Tuesday morning. The County Warning Area will still look to be engulfed
in the system/S breezy warm sector for most of the evening...until
frontal passage late that night from the northwest. Overnight lows to occur
toward 11-12z Tuesday. Most 12z run solutions suggest Post-frontal deep
mixing-northwest winds and colder air lag to boost/allow temperatures to
warm to Monday values or even a degree or two warmer...but the
latest 12z run European model (ecmwf) suggests a quicker incoming cold air advection regime may make
it hard to get those mild of temperatures...more in the way of upper 50s to
middle 60s. Tuesday another elevated grass fire threat day.

Wednesday and Thursday...the latest run medium range solutions
continue to suggest passing upper ridge well as surface
anticyclone fro a mainly dry and really warming Wednesday. The warm draw
up across the County Warning Area advertised by most models would support widespread
70s across the local forecast area...with some possible upper 70s south of
i80. Do not buy the 12z GFS more aggressive moisture return during the
day in increasing south-to southeast low level flow pattern and breaking
out some spotty warm sector showers in the afternoon in the west and
south. As the main upper level low rolls out of the far northern
plains and across Manitoba/Ontario into Thursday...the GFS continues to be
much more progressive with incoming frontal passage and associated showers/
storms for Wednesday night and most of the convection exiting out of the
County Warning Area by 12z Thursday. Extent of forcing and thermodynamic profiles of the
GFS also would support a better chance at a strong to severe storms
Wednesday evening in or close to the dvn County Warning Area. Some locally heavy rain also
advertised by th 12z GFS. But this in contrast to the European model (ecmwf) which
suggests a slower/weaker frontal forcing regime as well as less
impressive thermodynamics for stronger storms. The Euro suggests a
mainly along and Post-frontal precipitation regime west of the MS river late
Wednesday night...with the showers and a few storms then pushing across the
rest of the County Warning Area Thursday morning before moving off to the east. Both the
solutions then suggest the front get get shunted well south of the
region into the Southern Plains and Tennessee Valley by Friday morning thanks
to strength of incoming northern plains into the middle MS river low level
ridge axis. Thursday night into Friday morning would be mainly dry if these
latest solutions verify.

Friday through next Sunday...the 12z European model (ecmwf) does not have much low level
cyclonic development on the southern front with more frontogenesis
occurring into the northeastern County Warning Area to Lee of main upper l/west trough
axis Friday. The 12z GFS does ripple a low along the boundary across the
Tennessee Valley and produces a secondary def zone of precipitation into the
southern third to half of the dvn County Warning Area on Friday...with north to
northeast flow cool advecting to possibly a rain-snow mix by
afternoon or even all wet snow parameters and some accumulation
possible on elevated surfaces in those areas. Again with ongoing
model behavior making for low confidence...will maintain chance probability of precipitation
for Friday in the south half for mainly a cool rain. But seems the
trends of the European model (ecmwf) are starting to take over and next Friday may be a
none weather day. Will keep Friday night dry and cooling with incoming ridge
axis settling across the Southern Plains and western Ohio River/Tennessee
valleys...the 12z Euro has a Great Lakes clipper Friday night. Little in the
way of organized probability of precipitation for the rest of the weekend with another
temperature moderation to the milder side possibly by next Sunday or
Monday. ..12..


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1122 PM CDT sun Mar 29 2015

VFR conditions the next 24 plus hours with clear or fair skies as high
pressure moves in. Northwest to west winds of 5 to 10 kts overnight
will become westerly and increase to 10 to 20 kts by middle morning and
then decrease after sunset to less than 10 kts out of the southwest.


Dvn watches/warnings/advisories...



short term...Ervin
long term...12

National Weather Service Glossary of Abbreviations