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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
1118 PM CST Wednesday Nov 26 2014

issued at 430 PM CST Wednesday Nov 26 2014

Updated grids to fine detail the mesoscale snow band the is still
intact in southeast Iowa from Newton through Burlington to Macomb
Illinois. This snow band has already peaked in intensity...but is
unlikely to move in the next few hours. A secondary peak of
intensity may begin to develop around Macomb by 00z...and that
will be watched. For now...this update reflects both 100 percent
probability of precipitation in the axis...and drys out the forecast farther northeast
including the quadrant cities and Clinton. As the upper trough over
Minnesota passes through this evening...there will likely be some
flurries or light snow over the remainder of the County Warning Area...but
measurable snow appears unlikely.


issued at 230 PM CST Wednesday Nov 26 2014

A nearly vertically stacked low pressure system was moving across
southern Iowa and northern MO this afternoon. A narrow band of
light to moderate snow has been rotating slowly to the north-northeast through
the day. This band of snow was likely producing 1 to 3 inches of
snow across far western zones. A spotty report of 4 inches is
possible with the heaviest band just south of iow.


Short term...(this evening through thursday)
issued at 325 PM CST Wednesday Nov 26 2014

Main forecast concern for the short term is the snow the rest of
today and into tonight. Snow is expected to push slowly to the
north and east and diminish as the day wanes on.

Guidance has been very poor at resolving the duration of the
heaviest snow band and any other precipitation. The hrrr
continually diminished the band until recent runs when it finally
brings it across the County Warning Area tonight as light snow. The condensation
pressure deficit appeared to be the best tool for discriminating
where the snow might end up. As a result most of the weather grids and
probability of precipitation were based off of forecaster experience and observations.
Believe the snow band will lift to the north and and become
parallel to an east west orientation. The band will then diminish
in intensity as the vortmax and surface low advect out of the
area. Residual snow associated with a south moving boundary is
possible. Confidence in snow from this boundary is low so only a
chance of snow was included for this. Overall totals for this
event appear to be 1 to 3 in the snow band and even a couple of
spotty 4 inch reports...especially from Sigourney to Montana pleasant.

Thanksgiving was a straightforward forecast with cold
temperatures and skies clearing across the area on Thursday. No
precipitation is expected at this time during the day.

Long term...(thursday night through wednesday)
issued at 325 PM CST Wednesday Nov 26 2014

Thursday night...lows (single digits and teens) likely to occur most
areas during the evening before warm advection commences with
increasing southeast winds and thicker clouds leading to steady or
rising temperatures overnight. Shortwave topping rockies ridge and sliding
southeast through upper Midwest combined with isentropic ascent likely to
generate band of snow... with isentropic lift and left exit region
(favored lift quadrant) of 110-120+ knots upper Midwest to Great Lakes
jet streak supportive of best measurable potential to our north from
Minnesota into WI. Nonetheless...will have to watch for some light precipitation
potential later Thursday night into early Friday am north of I-80. Bufr
soundings show some top down saturation with initial warm advection
but then most soundings depict loss of ice in cloud... with then
saturated low levels suggesting if any precipitation could be drizzle
or freezing drizzle possibly. Or could possibly envision
seeder feeder mechanism for flurries. Due to very low measurable
potential and given uncertainty with ptype in a likely trace event I
have opted to leave out any precipitation mention attim.

Friday and Friday night...warm advection processes migrate northeast
during the day on Friday along with bulk of opaque cloudiness allowing
for return of at least partial sunshine most areas especially southwest
1/3-1/2. With the solar insolation and southerly winds I have temperatures
warming into the 40s for highs across southern County Warning Area and coolest readings
in the lower 30s north where clouds to hang on longest. Friday night
may not see much drop off in temperatures with continued warm advection on
strengthening southerly winds most likely to result in steady to rising
temperatures once again.

Saturday-Saturday night...this period looks generally mild as region
basks in warm sector ahead of Arctic front which trends show some
slowing. Went near to just above warm side of guidance most areas
for highs Saturday with gusty southwest winds and little or no cover.
Overall with mixing through 925 mb to 850 mb (discounting NAM which is
likely hanging on to snow cover too long) supports highs in the range
of upper 40s to middle 50s. Have nudged up lows Saturday night with
slowing of front... and may need to adjust upward more if slowing trend
continues especially southeast 1/2 of County Warning Area. General range of lows is
upper 20s northwest to lower 40s southeast.

Sunday-Sunday night...with slowing trend of Arctic front nudged up
highs a couple degrees... a bit more southeast 1/2 of County Warning Area. Front looks
to come through dry with shallow low level moisture and dry middle
levels. Strong cold advection commences in wake of front with gusty
northwest winds for falling temperatures. Timing of front roughly by middle am
northwest to early afternoon southeast. Much colder temperatures Sunday night with lows in range
of 10-20 degrees and gusty northwest winds making for wind chills in
single digits with sub-zero readings possible northeast Iowa.

Monday through Wednesday...Arctic airmass to remain entrenched through
Monday with below normal temperatures. Beyond that through midweek there
is considerable uncertainty with pattern as European model (ecmwf) advertising northwest
flow shuttling reinforcing shot of colder air and thus continued below
normal temperatures. Meanwhile... GFS shows digging trough through Great Basin
with warm advection in advance leading to moderating temperatures and potential
for some precipitation by midweek as moisture increases in vicinity of stalled
boundary nearby. Consensus forecast closer to GFS scenario with some
agreement from UKMET... thus gradual moderation of temperatures through midweek
with introduction of some precipitation chances.


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1115 PM CST Wednesday Nov 26 2014

MVFR ceilings and 4 to 6 mile visibilities in very light snow and
light fog will end before 12z Thursday as dry air pours into the
region behind a cold front. Winds will be north around 12 to 15
kts...and will only weaken late Thursday afternoon as winds
decouple. After the early MVFR period...the rest of the period
will be VFR / clear.


Dvn watches/warnings/advisories...


short term...Gibbs
long term...05

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