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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
452 PM CST Thursday Mar 5 2015

Synopsis...
issued at 300 PM CST Thursday Mar 5 2015

Arctic high pressure over the region today providing sunny skies
but cold temperatures. 2 PM readings ranged from 8 to 14 across
the dvn County Warning Area...and at some locations wind chills were still in the
single digits below zero.

&&

Short term...(this evening through friday)
issued at 300 PM CST Thursday Mar 5 2015

Forecast focus on the beginning of a welcome warming trend.

Tonight...warm air advection develops later tonight as winds turn
southerly on the back side of the departing high pressure ridge. A
band of middle level clouds should also move across the County Warning Area later
tonight in association with an upper level trough. Therefore...the
coldest readings...mainly in the single digits...should occur
this evening followed by slowly rising temperatures after midnight.

Friday...partly cloudy skies and south to southwest winds will bring
warmer temperatures into the County Warning Area. Afternoon highs should range from
around 30 from Dubuque to Freeport...to the lower 40s in our far
southwest counties. However...wind gusts in the 20 to 25 miles per hour range
are expected.

Long term...(friday night through thursday)
issued at 300 PM CST Thursday Mar 5 2015

Transition away from a middle winter Arctic regime to a more springlike
pattern is the primary focus in the long term. Models continue to
diverge into separate camps with regard to the amount of surface
warming early in the week and then even more so late in the week with
large differences in the southward penetration of a strong cold
front. In the medium range...a series of middle level shortwaves and at
least one clipper-type system in the northwest flow aloft will move through
over the weekend.

Friday night through Saturday...a clipper is prognosticated to move through
the Great Lakes early Saturday. Over the local area...with low level
moisture lacking...this is expected to result in little more than a
wind shift and period of middle level clouds. SW winds and increasing
clouds should hold mins in the middle to upper 20s overnight. Winds
shift to the northwest following the weak frontal passage Saturday with middle
level subsidence providing afternoon sunshine. Model blend highs
from the upper 30s NE to upper 40s in the far SW look reasonable.

Late Saturday night into Sunday...there remains poor model agreement
with the timing...strength and available moisture with the next middle
level shortwave. This results in large differences in quantitative precipitation forecast placement
and whether a weak wave of low pressure moves along an associated
weak surface front. The GFS and European model (ecmwf) are most bullish with light
quantitative precipitation forecast...while the NAM is essentially dry. With below average
confidence...weak forcing... and little moisture for the system to
work with on...will limit probability of precipitation to slight chances north of I-80. If
this occurs...it would most likely be light snow or flurries...then
possible light rain or snow showers in the afternoon mainly over northwest
Illinois. Temperatures should again reach at least middle 30s north...with
middle and possibly upper 40s in the south...where the current edge of
the snow cover will be retreating rapidly.

Beyond...the big question is how the low level thermal fields and
associated feedback from the melting snow and ice will respond to
the change to a more zonal middle level flow and low level S-SW warm
advection regime. There remain Stark differences in how models
depict this...falling mainly into two different camps. The GFS and
Canadian are consistently on the cold side...depicting a gradual
warming from highs in the 30s Monday to 40s and 50s by Wednesday. At the
same time...the European model (ecmwf) has 40s and 50s Monday...reaching widespread
60s by Wednesday. Our forecast follows a blended approach...resulting in
40s Monday...mainly 50s Tuesday and 50s to around 60 Wednesday with overnight
lows in the 20s early...then 30s by middle week. This is a reasonable
compromise for now...and hopefully trends over the next few days
will lend a better handle on how fast the snowmelt will occur and to
what extent the low levels will be able to tap into the low level
warming.

Thursday...the GFS drives a cold front through the forecast area
well into MO and Illinois...while the European model (ecmwf) has a passing surface low and
the frontal position holding up well to the north across Minnesota and WI.
Our current forecast maintains 50s...but it could also be either the
40s or potentially the 60s depending on the frontal position.

&&

Aviation...(for the 00z tafs through 00z Friday evening)
issued at 452 PM CST Thursday Mar 5 2015

VFR conds through this taf cycle. Arctic high pressure over the
region will shift off to our east overnight. West winds early this
evening will turn south later this evening and overnight...then southwest
on Friday. Wind speeds will be around 10 knots or less tonight then
occasional gusts to around 20 knots on Friday.

&&

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

$$

Synopsis...haase
short term...haase
long term...sheets
aviation...haase

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