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Area forecast discussion...updated 
National Weather Service quadrant cities Iowa Illinois
1139 am CST Monday Dec 22 2014

Update...
issued at 1138 am CST Monday Dec 22 2014

At 1130 am CST...current radar depicts most of the County Warning Area
experiencing -ra with some moderate rain approaching Bureau and
Putnam counties. As a result had to up probability of precipitation across those counties
to account for current trends. Also had a report of some -rapl in
Freeport. Looking at model soundings decided to add a few hours of
the mix for Stephenson County until the warmer air gets there.
Otherwise no other tweaks to the forecast.

&&

Synopsis...
issued at 330 am CST Monday Dec 22 2014

Our complicated storm system is developing to the west tonight in
the plains...as surface low pressure is centered both in the central
Dakotas...and in western Oklahoma. The development near OK is
important to our forecast as it is a reflection of the forcing that
will impact our County Warning Area. Low levels are moist...while middle level moisture
is on the increase early today. The result has been almost
continuous bands of sprinkles since middle evening last night. Thus
far...only trace amounts of rain have been reported in eastern Iowa
with Rockford Illinois reporting 0.01. This supports our low pop forecast
the next several hours before deeper saturation arrives later this
morning.

&&

Short term...(today and tonight)
issued at 330 am CST Monday Dec 22 2014

Todays main challenges will be timing in two separate rounds of
rain. In a broad sense...the first shot of widespread rain will
sweep up from Missouri by middle morning...lasting through early to middle
afternoon...before entering into a lull for several hours. Another
much more strongly forced period of rain is expected this evening
and overnight...as the main upper level lows forcing will affect
our County Warning Area. In addition...mesoscale models are picking up on the
Oklahoma surface low...and bringing that up over our County Warning Area late
tonight. That should help increase convergence of moisture tonight
in our region...and higher quantitative precipitation forecast totals now appear more likely than
earlier indicated. Thankfully...we are warm enough already for all
rain to be taking place...and we should continue to warm through the
day aloft...and not cold advect at all at low levels until toward
Tuesday morning. Thus...I expect all precipitation to be in the form
of rain or possibly intermittent drizzle between periods of rain.
Since drizzle is possible between the rain periods today...I will
leave probability of precipitation high once the initial rain band moves in today.

Temperatures are already quite mild today...with middle to upper 30s
holding of most of the County Warning Area as of 2 am. Southeast winds becoming
east...will only draw in more mild air through the day...and highs
appear destined for the upper 30s north to middle 40s far south under
the damp cloudy conditions.

Tonight...with the low working overhead....and rainfall likely
continuing until late when the dry slot will finally lift through
the region...we will remain quite mild...and may hold in the 40s
much of the night. Fog will be possible...but given the rainfall
taking place...and the dry slots late arrival...I have chosen not to
include it in the grids. If it does occur...the west and southwest
would be most likely to see fog. Rainfall amounts during the day
should largely be 0.05 to 0... tonights robust diffluent
forcing with low level moist convergence supports an additional 0.25
to 0.50. Thus...widespread rain amounts with this system could end
in the 0.30 to 0.60 range easily.
Ervin

Long term...(tuesday through next sunday)
issued at 330 am CST Monday Dec 22 2014

Tuesday...00z run models in general agreement of suggesting
occluded...nearly vertically stacked low to roll just north of the
dvn County Warning Area by midday. In-wrapping dry slot from the south/southwest to
really eat away at any lingering light rain or drizzle in the area...
and freshly drawn up mild airmass to make for the mildest high temperatures
of the early week period with many areas in the low to middle 40s. Will
not add it to the grids for now...but will have to watch for the
potential of low level cyclonic convergent flow inducing some temporary
dense fog Tuesday morning especially north of i80 before the low complex
gyrates further to the north. Vertical profiles of accepted forecast
sounding models/the European model (ecmwf)/ do not top down cool to rain-snow mix until
early evening in the northwestern County Warning Area. In-wrapping lighter precipitation
shield from the northwest to have trouble not getting eroded by
drier subsidence slot jutting from the southeastern plains to the
southwestern Great Lakes...but eventually expect at least some flurries
or very light snow to make it across portions of the County Warning Area later Tuesday
night. Surface lows still not all that cold by Wednesday morning in the upper
20s to lower 30s...even milder to the east.

Wednesday and Thursday...assessing the 00z run medium range solutions
and upper jet balances pulsing through the most likely upper air
pattern/trough phasing...it still appears the County Warning Area to be mainly dry on
Wednesday into Wednesday night...as whatever cyclogenesis and phasing takes
place across the western Gulf states and cyclone propagation up the Tennessee
to eastern Ohio River valleys. Thus the xmas storm to likely take place
across the Tennessee Valley into the central and eastern Great Lakes. The 00z
GFS again a further west outlier and would produce 2-3+ inch snowfall
across the eastern i80 corridor portion of the dvn County Warning Area by Wednesday evening.
Think even the latest 00z run European model (ecmwf) a bit too far west and the older
runs appear more representative of what will happen looking at it/S
upper jet structure and l/west phasing process. For now will keep low
chance probability of precipitation going across the southeastern half of the forecast area for light
snow...but still see this day being not much of a deal. High temperatures
may even get into the middle to upper 30s across much of the area
especially with some thin spots in the overcast and day stays mainly
precip-free. Ridging to build in behind the eastern Ohio River valley/Great
Lakes late Wednesday night and Thursday morning...but progresses east enough for
return flow boosting temperatures to around 40 by late Christmas afternoon.
The new Euro MOS has highs in the middle 40s for much of the area on
Thursday.

Friday through next Sunday...again prefer the more consistent European model (ecmwf)
late week into the early weekend...with phasing and handling of the
next lingering piece of southern stream wave energy ejecting out
far enough to the west that the County Warning Area gets warm sectored on the 26th.
Increasing south/southwesterly boundary layer flow and temperature
advection if the Euro is right could lead to some temperatures in the
lower 50s in the south with no snow cover to take into account....
much of the County Warning Area to be in the middle to upper 40s anyway. Low level cold
conveyor interacting with what ever def zone precipitation manages to
swipe down and clip the County Warning Area could lead to rain changing over to
light snow Friday evening and overnight in the northwestern County Warning Area...
otherwise mainly dry conditions again into Sat. Chill down back to
normal fro Sat and Sunday as southwesterlies adjust further to the
south and any additional wave ejecting out along with it/S
associated def zone precipitation swath stays mainly south/southeast of the
County Warning Area. But will still have to watch for the southeastern County Warning Area to
possible get clipped by a southern stream system over the weekend
or early next week. ..12..

&&

Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1138 am CST Monday Dec 22 2014

With the current system moving through the area...main aviation
concerns will be due to visibility and ceiling issues. As the -ra makes
its way in here sites are going to ife and even LIFR sooner than
previously forecast. Expect the sites to stay down...especially if
there is precipitation at them. Precipitation is expected to wane this afternoon
providing a brief improvement in visibilities and even some ceilings. At
this time did not include that in the forecast as timing and
certainty of improvements is unknown and low. No freezing precipitation
is expected through the taf period.

&&

Dvn watches/warnings/advisories...
Iowa...none.
Illinois...none.
MO...none.
&&

$$

Update...Gibbs
synopsis...Ervin
short term...Ervin
long term...12
aviation...Gibbs

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