Weather

440 
fxus63 kdvn 060858 
afddvn 


Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois 
257 am CST Tuesday Jan 6 2009 


Synopsis... 
full latitude trough is pushing east from rockies into the plains 
early this morning. Energy is split with northern stream 
shortwave sliding east along the US/Canadian border. Much 
stronger shortwave noted upstream diving east/southeast into western 
Alberta province on strong 300 mb jet core of 150-165 kts which dives 
into intermountain west. Meanwhile... southern stream shortwave 
was seen digging across southern rockies. Several impulses 
ejecting out ahead and rippling northeast within strong 300 mb jet core 
of 150-165 kts that extends from old Mexico through the 
middle Mississippi Valley and middle Atlantic. Bulk of precipitation this morning 
confined to southern stream where deeper moisture being entrained. 
Middle clouds increasing rapidly S/east sections of County Warning Area early this morning 
with surge of elevated warm advection and Theta-E advection. 
Low levels quite dry per 00z dvn and ilx radiosonde observations... so no precipitation is 
reaching ground with middle level returns lifting into central Illinois. 
Some patchy freezing drizzle though was being reported near the 
St. Louis metropolitan area just ahead of h925-850 mb warm front. ..05.. 


&& 


Short term...today and tonight... 
northern and southern stream shortwave troughs are set to undergo 
better phasing by late tonight into Wednesday as they shift across the 
midsection of Continental U.S.. the County Warning Area will be caught in between these 
two systems and forcing mechanisms for much of the next 24 hours 
with moisture fairly shallow eliminating column saturation 
and any threat for measurable precipitation. Despite this... precipitation potential 
not none. H925-850 mb warm front to lift across the southeast County Warning Area 
this morning into early afternoon and will be accompanied by low clouds 
mainly S/east of brl-vys line and can/T rule out some -dz or -fzdz. 
Better potential though looks to reside just south of County Warning Area as flow 
veers to southwesterly... therefore left out mention but will 
continue to monitor trends in satellite and observation. Next potential for precipitation 
will be late tonight as northern stream shortwave digs S/east with the 
area coming under increasing upper diffluence. Moisture again is 
quite shallow and NAM/bufr soundings suggest no ice introduction 
leading to mainly -fzdz... with possibly few flurries far north 
but low confidence and also being late 2nd period have left out 
mention. As for maxes today... sided toward guidance blend and went 
on cool side south/east where more clouds to persist for good portion 
of day. Only minor tweaks to mins tonight from previous forecast. Surface 
winds veer to west then northwest after 06z with colder air oozing into 
northwest with potential to be few degrees colder northwest 1/3rd based on 
verification early this morning. ..05.. 


Long term...Wednesday through next Monday... 
respectable vorticity maximum prognosticated to move across the area on Wednesday. 
Moisture layer is quite shallow which makes precipitation 
questionable. However...low level lapse rates do become fairly steep 
which may be enough to offset everything. Even so...expect any snow 
amounts to be on the light side. Some respectable vorticity 
advection occurs Wednesday evening. Lapse rates are initially steep 
but stabilize as the evening progresses. So...there may be some 
lingering flurries Wednesday evening. High pressure quickly moves 
through the area on Thursday bringing a brief period of quiet weather. 


Late Thursday night/Friday another clipper system will move through 
the region. Made no changes to the forecast as there should be some -sn 
or a rain/snow mix on Friday which should bring some very minor 
accumulations. Quiet and chilly weather should be seen for the weekend as 
Arctic high pressure settles across the Midwest. 


Beyond next weekend...an active northwest flow pattern will remain 
established across the Continental U.S.. another clipper system will move 
through the Midwest around Monday. Global models suggest additional 
clipper systems about every 48 hours or so next week. ..08.. 


&& 


Aviation... 
VFR conditions expected for most if not all of the period. Low clouds 
with MVFR ceilings over MO will lift east/NE across southeast Iowa and west 
central Illinois... staying mainly S/east of kbrl and kmli taf sites 
as h925 winds veer to the southwest. Upper level system to dive into 
Minnesota tonight with cold front passing across taf sites with winds 
gradually veering to west and then northwest between 03z and 09z. 
Potential for some MVFR stratus to work across taf sites in wake of 
cold front... especially northern sites of kdbq/kcid being closer to 
upper level shortwave. ..05.. 


&& 


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


&& 


$$ 


05/08