Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
634 PM CST Tuesday Jan 27 2015

issued at 300 PM CST Tuesday Jan 27 2015

Much of the dvn County Warning Area socked in with low stratus except our far SW
counties. This is due to a strong inversion about 850 mb with
little mixing and a light northeast wind. The clearing line to
our west was edging very slowly eastward. In northeast Illinois skies
were also clearing. Due to the stratus this was keeping temperatures
this afternoon only in the upper 20s to lower 30s at most locations.
However...readings were in the lower 40s in our far SW.

Elsewhere...warm temperatures were found in the plains with readings
in the 70s to lower 80s.


Short term...(this evening through wednesday)
issued at 300 PM CST Tuesday Jan 27 2015

Forecast focus on clouds and temperatures.

Tonight...challenging cloud forecast with low stratus expected to
remain across most of the County Warning Area. However...will need to keep an eye
on the edges as clearing pushes slowly eastward from central Iowa
and northern MO. Also clearing was occurring in northeast Illinois but
is expected to stay to our east. East winds this evening will
become southeast overnight. Minimum temperatures to range from the
upper teens far northwest Illinois to the middle 20s SW.

Wednesday...strong warm air advection develops which will allow
better mixing to bring down the drier air aloft. 850 mb winds
increase to 40-45 knots so surface winds should gust to 25 to 30 miles per hour.
The stratus should dissipate or clear from south to north with the
strengthening southeast to south winds. In the meantime...mid/high
level clouds will increase during the day. Nice warming as 850 mb
temperatures rise to 10 to 12c in our far southern County Warning Area to +4c in
northwest Illinois. Maximum temperatures will range from the middle 30s in far northwest
Illinois to the lower 50s in our far SW counties.

Long term...(wednesday night through tuesday)
issued at 300 PM CST Tuesday Jan 27 2015

Main forecast concern for the extended is the chance for
accumulating snow this weekend. The likelihood of precipitation is
increasing with this latest package. At this time it looks like we
may have a long duration accumulating snow event.

At the beginning of the period...a series of shortwaves will be
transversing the flow. A change from yesterday...the models are now
warmer throughout the layer...suggesting drizzle and rain...instead
of fzdz. Looking at models...the European model (ecmwf) is further south with the
first wave and probability of precipitation quantitative precipitation forecast across our area with frontal passage. The rest of the
models keep it north and US dry. A look at model soundings shows
that the cloud layer is very shallow and more indicative of drizzle
with some rain mixed in. Think that with 850 mb warm air advection...good cva and
moisture advection...rain cannot be ruled out Wednesday night into
Thursday morning across the area. As cold air surges in...a
transition will occur in the north. Before the cold air becomes
completely entrenched the chance for probability of precipitation will move out of the
area. No accumulation from snow is expected.

This overrunning...long duration event still looks
possible. Southwest flow will help to bring moisture north.
Models are in good agreement that precipitation will last 24 hours and
even longer. Precipitation looks to be light at this time with less than
0.40 of an inch liquid quantitative precipitation forecast being forecast today. The GFS spins up a
low to our east on Sunday where...the Gem and European model (ecmwf) keeps the
surface low to our south. This event will need to be paid attention
to in upcoming forecasts.

Once this system moves out...another clipper is forecast at the end
of the period. This system will likely bring snow to the area as cold
air will be in place as northwest flow dominates after this weekend.


Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 628 PM CST Tuesday Jan 27 2015

Low confidence in model handling of stratus shield in place at all
taf sites early this evening. Thus...have gone a bit more
pessimistic in clearing out the MVFR ceilings. Have delayed clearing
at kdbq/kcid/kmli until 18z Wednesday...14z at kbrl. Some light MVFR
fog most favored at kcid overnight.


Dvn watches/warnings/advisories...


short term...haase
long term...Gibbs
aviation...rp Kinney

National Weather Service Glossary of Abbreviations