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NATIONAL WEATHER SERVICE LINCOLN IL
1201 AM CST Thu Nov 27 2014

.UPDATE...
ISSUED AT 815 PM CST WED NOV 26 2014

Updated the forecast to better reflect the current conditions with
the snow in central and southeast IL this evening. A weakening
clipper type low was just south of St. Louis at 01z, with an
associated upper level trough/vort max in west central IL. Bands
of snow, fairly narrow but potent, were pivoting around a shear
axis which was positioned between Springfield and Lincoln early
this evening. With the upper level energy continuing to slowly
shift to the east-southeast, this main band finally started
translating more southward the past hour or so. Reports have
indicated around 2 inches of snow with this band from Astoria
through Petersburg to Springfield - although based on radar
estimates, there are probably a few areas with around 3 inches
near the Sangamon River from west of Petersburg toward Schuyler
County. 

Another snow band was rotating northeastward, ahead of the
shortwave trough, into southeast IL. Most areas with this band can
expect to get 1-2 inches of snow late this evening, with isolated
totals up to 3 inches. 

Overnight, there could be a little lingering light snow from the
upstream deformation zone currently across eastern Iowa. However,
this is weakening and the surface pressure pattern should become
less cyclonic with time, so any snow that does occur will be quite
light and short lived.

&&

.SHORT TERM...(Tonight)
ISSUED AT 310 PM CST WED NOV 26 2014

Vigorous Clipper system continues to dive southeast, with the center 
northwest of St. Louis at mid afternoon. Light snow struggled to 
move in initially with the drier air in place, but has made some 
good progress this afternoon, and had reached Decatur and Effingham 
by 3 pm. Visibility in the snow area has consistently been in the 1 
to 2 mile range. Recent grid updates have limited the rain/snow  
mix potential to only areas south of I-70 over the next couple 
hours, and latest observations would suggest that perhaps only 
Lawrenceville area would have this concern as temperatures there 
have reached near 40. 

Short-range models in good agreement with moving the system 
southeast along the Mississippi River through this evening. Areas 
north of I-74 still likely to see little of the action beyond some 
flurries, as the northeast flow will be establishing itself with the 
passage of the low. Have continued the light snow over most of the 
remainder of the CWA into mid evening, quickly diminishing to 
flurries from northwest to southeast late. Overall amounts still 
looking on the light side, around an inch or so from near Rushville 
southeast through Springfield toward Vandalia.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 310 PM CST WED NOV 26 2014

Weakening clipper system should be well off to our southeast by
Thursday morning with our area under the influence of low level
cold advection thru most of the day. Forecast soundings continue
to hold on to the low level moisture into at least the early 
afternoon hours before high pressure settles in from the northwest
by late in the day. This should result in a decrease in cloud cover
from northwest to southeast during the afternoon with temperatures
struggling through the 20s. Look for a fairly quick drop off in temps
tomorrow evening as the high shifts across the area with return flow
setting up over western IL after midnight, which should put a halt
to the temp fall across the west. A gusty south wind should help
bring warmer air back into the area on Friday with afternoon
temperatures in the 40 to 45 degree range. Forecast 850 temps by
Saturday afternoon in the +12 to +14 degree C range which should
translate to 50s for afternoon highs. With a slower trend continuing
in models for our next frontal passage on Sunday, most of our area
will enjoy mild temperatures with low 60s possible over southeast
Illinois Sunday afternoon.

Main forecast concern will be later Sunday and especially Sunday
night as models suggest some low chance POPs across at least our
east and far southeast as the front and low level cold air tracks
southeast. Not a lot of Gulf moisture will be available in our area
ahead of the front thru Sunday evening but as the boundary shifts
south of the area late Sunday night/Monday morning, we will have
to watch for the development of some light rain or drizzle with
overnight lows expected to drop into the low to mid 30s. For now, 
will hold on to slight chance to chance POPs over central thru 
southeast IL on Sunday ahead of the boundary with precip chances
getting shunted south with the front late Sunday night into Monday
morning. Most of the forecast soundings not showing much if any
ice crystals in the upper portion of the clouds Sunday night so
drizzle or even freezing drizzle along the northern edge of the
precip shield may need to be added in future forecasts for Sunday
night into early Monday morning. 

After another setback with temps on Monday in the wake of the
upper wave and attendant cold front that slips to our southeast,
warmer temperatures will return on Tuesday and hold thru the
remainder of the extended period as the upper flow transitions
more into a zonal flow thru much of next week. Significant model
spread really shows up after Tuesday with respect to shortwave
energy that had been parked out near the California coast over the
the weekend, which is forecast to eject across the Rockies and into
the Plains on Wednesday. The GFS is at least a day and a half faster
than the ECMWF with the wave as most of the guidance starts to show
POPs as early as late Tuesday night into Wednesday over the forecast
area, whereas the ECMWF speed would indicate rain chances holding
off until later Thursday into Friday. With more of a zonal flow
forecast across the lower 48 thru most of next week, would think the
quicker solution would be the way to go midweek and beyond. Will
indicate chance POPs starting on Wednesday with temperatures averaging
out close to or above normal after Monday. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1147 PM CST WED NOV 26 2014

VFR CONDITIONS ARE STARTING OFF THE TAF PERIOD AT ALL SITES AS
RIDGING CLEARS OUT THE CLOUDS TEMPORARILY. CURRENTLY NOT EXPECTING
THE CLEARING TO LAST ALL NIGHT SINCE SOUNDINGS AND SATELLITE STILL
INDICATE LOW CLOUD COVER WILL MOVE BACK INTO THE TAF SITES
OVERNIGHT...RESULTING IN MVFR CONDITIONS. WINDS WILL SHIFT MORE TO
THE NORTH NORTHWEST OVERNIGHT AS THE LOW PRESSURE CLIPPER SYSTEM
CONTINUES TO MOVE EASTWARD. MVFR CIGS COULD LAST INTO THE EARLY
AFTERNOON TOMORROW...WITH LOW CIGS BECOMING SCATTERED AROUND 19Z.
VFR CONDITIONS SHOULD PREVAIL THROUGH THE END OF THE TAF PERIOD.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Miller
SHORT TERM...Geelhart
LONG TERM...Smith
AVIATION...ALW




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