Area forecast discussion 
National Weather Service Denver/Boulder Colorado 
310 PM MDT Sat may 18 2013 


Short term...deep upper trough will continue its slow eastward 
progress across the Rocky Mountain region next 24 hours. A spoke of 
middle-level energy/lift now rounding the southeast side of this 
trough is prognosticated to swing northeast over the forecast area by 
this evening. Convection associated with this shortwave becoming 
more widespread upstream over south central Colorado. Closer to 
home...dry line is presently snaking southward through extreme 
northeast Weld...western central Morgan and southwest Washington 
counties and down across Kit Carson County. 50s/lower 60s dewpoints 
on its east side and 30s dewpoints to its west. Surface based convective available potential energy in 
the higher dewpt air in the 1000 to 3000 j/kg range. Storm Prediction Center has most 
of this area under a Tornado Watch. Beginning to see strong storms 
firing along this dry line. Models show the dry line remaining 
nearly stationary through about 00z when the shortwave trough 
passes overhead. Should then see drier air up along the Front 
Range spreading east across the plains through the evening. 
Believe that/S when T-storms will become more numerous across the 
far northeast corner of the state with the dry line pushing across 
the area. Model are forecasting the best bouyancy near the Nebraska 
border with convective available potential energy near 4000 j/kg early this evening. Vertical 
shear profile not all that favorable for tornadic super 
cells...although could a few spin ups along outflow boundaries. 
Main severe weather will be hail up to 2.5 inches in diameter and 
damaging straight line winds to around 60 miles per hour. Storm motions in 
excess of 25kts should keep rainfall amounts low and any chance 
for flooding even lower. 


Elsewhere...atmosphere will be drier and less unstable. This will 
limit T-storm intensity...but not there numbers. Expect to see 
scattered showers and T-storms in the high country and isolated to 
scattered T-storms on the plains adjacent to the Front Range. Low 
dewpoints along the base of the foothills should result in the 
precipitation chance for the County warning forecast area. However gusty winds and small hail still 
a possibility in these areas. 


Overnight...upper trough continues to shift over the region. Should 
see storms winding down most areas by midnight...although storm may 
linger till morning in the far northeast. Isolated showers also a 
possibility throughout the night in the high country with the snow 
level lowering to around 10500 feet by sunrise. 


On Sunday...upper trough rotates across the state on Sunday with 
winds shifting to the northwest on the back side of the trough 
during the day. Should see scattered showers and afternoon T-storms 
with lingering large scale lift and cold advection. However precipitation 
amounts will be on the low side. Temperatures on Sunday some 8-12 
degree f cooler than today. Highest elevations in line to see a mix of 
rain and snow...with light accumulations possible on the highest 
peaks. 


Long term...closed upper level low will be centered near the 
Nebraska pan handle Sunday evening. One short wave trough will be 
over western Kansas and another will be near the Grand Canyon. Since 
northeast Colorado will be between short waves...just expecting 
isolated convection. 


The short wave trough over the Grand Canyon will move into New 
Mexico on Monday. At the surface...a cold front will push south 
across Colorado bringing northerly winds. Increased moisture behind 
the front combined with low and middle level lift will bring a good 
chance for showers. A few thunderstorms will also be possible due to 
daytime heating making the airmass slightly unstable. Convective available potential energy will be 
less than 500 j/kg...so no threat of severe weather. Because of the 
cooler airmass and cloudy skies...high temperatures will be Monday 
will be around 60 degrees. 


Northwest flow aloft will prevail Monday night and Tuesday as the 
main low continues to move east. Showers will decrease Monday night 
as the airmass stabilizes and lift decreases. For Tuesday...chances 
for precipitation will be limited to the higher terrain and eastern 
plains. 


Expect Wednesday to be dry as an upper level ridge moves across the 
state. Temperatures will start to rebound Wednesday with highs 
climbing above 70 degrees. 


The warming trend will continue into the later half of the week and 
the weekend as a southwest flow aloft prevails. Models indicate low 
level moisture will increase on Thursday and Friday. Because of 
this...will have a slight chance of thunderstorms in the forecast. 
For Saturday...will not mention any chance of thunderstorms because 
of dry air that is forecasted to move into the area be the European model (ecmwf). 
Because of the drier air...highs may be able to climb into the 80s. 




&& 


Aviation...isolated thunderstorms in the Denver area through 03z 
this evening will have the potential to produce hail up to a half 
inch in diameter and wind gusts to around 40 kts. Moderate 
rainfall with these northeastward moving storms could briefly 
reduce visibilities to 4-5 miles. Winds in the Denver area will be 
highly variable with the passing convection. After 03z...most of 
this storm activity should move north and east of the Denver 
metropolitan area. Surface winds are then expected to gradually transition 
to a south-southwest wind of 7-14kts. On Sunday...the Denver area 
could see a stray light rain shower in the area during the 
morning...then scattered showers and isolated T-storms in the 
afternoon. Storms not expected to be as intense with the cooler 
airmass moving over the region. 


&& 


Hydrology...no concerns at this time. Although showers and 
thunderstorms through this evening could cause minor rises on 
small creeks and streams in and near the mountains. 


&& 


Bou watches/warnings/advisories... 
none. 
&& 


$$ 


Short term...Baker 
long term....meier 
aviation...Baker